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Welding of Aluminum Alloys to Steels: An Overview

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Since the need for the joining of dissimilar materials is increasing, the wide range of requirements of the numerous industries would lead to the development of new welding techniques or at least to improvement of the existing technologies capable of joining the components from the miniature assemblies to extremely large earth-moving vehicles. Among the different materials, iron-based alloys and aluminum-based alloys are the most significant materials that are finding applications in the various industries to offer more viable and sustainable products. However, welding of these metals has been always a kind of dilemma for the engineers. There are a certain number of methods to join these dissimilar metals but no one could establish a reliable or a sort of credible welding method for the industrial applications while quality, cost, human resources and facilities are taken into the main considerations. This paper reviews the recent works on the joining of different aluminum alloys to different steels. The effect of the joining conditions on the formation of intermetallics and microstructural development, mechanical properties and applications of the joints are discussed.
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J. Manuf. Sci. Prod. 2014; 14(2): 59–78
M. Mazar Atabaki, M. Nikodinovski, P. Chenier, J. Ma, M. Harooni and R. Kovacevic*
Welding of Aluminum Alloys to Steels: An Overview
Abstract: Since the need for the joining of dissimilar mate-
rials is increasing, the wide range of requirements of the
numerous industries would lead to the development of
new welding techniques or at least to improvement of the
existing technologies capable of joining the components
from the miniature assemblies to extremely large earth-
moving vehicles. Among the different materials, iron-
based alloys and aluminum-based alloys are the most
significant materials that are finding applications in the
various industries to offer more viable and sustainable
products. However, welding of these metals has been
always a kind of dilemma for the engineers. There are a
certain number of methods to join these dissimilar metals
but no one could establish a reliable or a sort of credible
welding method for the industrial applications while
quality, cost, human resources and facilities are taken into
the main considerations. This paper reviews the recent
works on the joining of different aluminum alloys to dif-
ferent steels. The effect of the joining conditions on the
formation of intermetallics and microstructural develop-
ment, mechanical properties and applications of the
joints are discussed.
Keywords: welding, steel, aluminum, intermetallics
PACS® (2010). 81.20.Vj
DOI 10.1515/jmsp-2014-0007
Received February 16, 2014; accepted June 9, 2014.
1 Introduction
Many of the metals can be joined together by the current
advancements in the welding technologies, but there are
many unsolved problems in joining of dissimilar alloys.
There is also an increasing trend towards the use of dis-
similar joints in the shipbuilding, military, aerospace
andautomobile industries. The sound joint is the highest
concern through the design of the parts especially for such
places where quality of the joints has more priority than
other concerns. Most of the thinking about the replace-
ment of the materials is that it will help to reduce the
fuel consumption, cost of production and reduction in
the amount of energies spent on heavier materials. For
instance, the use of aluminum alloys and steels for some
of sensitive components is relatively influenced by the
current regulations to encounter fuel efficiency standards
[1, 2]. The result of this shift is to provide improved weld-
ing technologies to join materials together since some
components still are needed to be made of hard and
toughened materials. There are, however, numbers of
works on the application of different welding technol-
ogies to bond heavy-duty materials but the problem of
losing the strength in the bond area is always a big chal-
lenge [3, 4]. For the case of welding different aluminum
alloys to the steels, large electrochemical difference of 1.22
volts, the subsidiary precipitates, different thermal prop-
erties, dissimilar thermal expansion, heat capacity and
thermal conductivity, different lattice transformation and
melting points (660 °C for Al alloy and 1497 °C for steel)
and nearly zero solid solubility are creating distortion, for-
mation of cavities and cracks in the joined area. Laser roll
bonding [5], impact welding [6], friction welding [7], ultra-
sonic welding [8], diffusion bonding [9], explosive weld-
ing [10], friction stir welding [11], laser brazing/welding
[12, 13], magnetic pulse welding [14] and laser pulse
welding [15, 16] are the typical welding processes that
have been applied to join different grades of the steels to
the aluminum series. However, the key point in the devel-
opment or improvement of the welding techniques was a
way to control the size and quantity of the Al/Fe inter-
metallics by controlling the heat input or seizing the for-
mation of the intermetallics. The synergy of welding pa-
rameters e.g. temperature, time, pressure and atmosphere
and type of the intermetallics is an important issue which
has never been given attention for improving the quality
of the joints.
In the present review, current application of the
joining techniques and the synergy of the welding param-
eters with intermetallics for making stronger bonds
between different aluminum alloys and different classes
*Corresponding author: R. Kovacevic: Research Center forAdvanced
Manufacturing and Technology (RCAM), Southern Methodist
University, Dallas, Texas, USA.
E-mail: kovacevi@lyle.smu.edu
M. Nikodinovski: U.S. Army RDECOM-TARDEC, Warren, Michigan, USA
P. Chenier: Onodi Tool & Engineering Co., Melvindale, Michigan, USA
M. Mazar Atabaki, J. Ma, M. Harooni: Research Center for Advanced
Manufacturing and Technology (RCAM), Southern Methodist
University, Dallas, Texas, USA
 M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview
of steels are presented. However, the most recent research
works on the investigation of the bonds are reviewed and
some solutions to solve the problems in joining of the
steels to aluminum alloys are discussed.
2 Recent technologies for joining
aluminum alloys to steels
Before exploring any of the bonding processes it might be
better to explain a little bit about the techniques that have
been applied so far to join the aluminum alloys and steels
and then have an overview of the physical phenomenon
during the fusion and solid state welding methods. As
thewelding processes are fundamentally categorized into
two main streams, fusion and solid state, there are physi-
cal, chemical, mechanical and even statistical analysis to
explain the reactions during the joining of the aluminum
alloys and steels. In the fusion bonding of the metals the
heat source generates a temperature field which is very
inhomogeneous and varies over time. Thermal variation
occurs in the regions of the heat sources and adjacent
areas. The microstructural variations in the fusion zone,
deformed area and heat affected zone dominate the
changes in the total behavior of the bonds as a result of
non-uniform heating and solidification. Extreme crack
propagation, intermetallic formation, porosity and other
imperfections arise in connection with the typically inho-
mogenous phase changes and solidification. Consider-
able residual stresses, weld shrinkage, welding distortion
and deformations are a few examples of the unwanted
consequences which somehow would lead to brittle
fatigue fracture, shape instability and stress corrosion
cracking. As the formation of FexAly phases is necessarily
irresistible an excessive formation of the intermetallics
lead to the brittleness of the bonds. The formations of the
intermetallics are mostly because of the interactions of
welding parameters like temperature, time, pressure and
atmosphere with the chemical composition of the metals.
This can be clearly described by the ideal phase diagram
of the aluminum and iron (see Fig. 1).
In the atomic scale the atoms of the aluminum and
steel can be interchanged during the joining processes
as a function of the number of vacancies, diffusion of
small solutes and movement of the grain boundaries. The
equilibrium phase diagram shows the interaction of tem-
perature and elemental concentration will cause seven
non-stoichiometric intermetallics (Fe3Al, FeAl (α2), FeAl2,
Fe2Al3 (ɛ), Fe2Al5 and FeAl3, FeAl6). Table 1 designates the
most important characters of theses intermetallics.
The formation of the intermetallic phases is relied on
three main thermodynamical factors, including the chem-
ical potential of the aluminum and iron elements, the
nucleation of the phases at the beginning of the interdif-
fusion and mobility of the alloying elements during the
Fig. 1: The dual phase diagram of the Fe-Al [improved version of 3].
M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview 
welding processes. However, the enthalpy of the forma-
tion of the intermetallics can be declared to be a linear
relationship by the following equation [20].
xx
Al Fe
ef ef ef
Al Al Fe Fe Al Fe
HX H X H H
Δ = Δ + Δ −Δ (1)
where XAl and XFe, are mole fractions of the Al and Fe, ΔH
the formation enthalpy of the intermetallic at the room
temperature,
ef
Al
HΔ
,
ef
Fe
HΔ
are dissolution heat effects of
one mole atoms of Al and Fe in the solvent and
xx
Al Fe
ef
Al Fe
HΔ
is the heat effect accompanying the dissolution
of one gram-atom of the intermetallic. The thermody-
namic reactions between the aluminum and steel can also
be presented by the Scheil’s relations as it is shown in
Fig.2. However, based on the method of the welding and
influence of the joining parameters the intermetallics vary
in size, type and distribution. The following sections are
mostly dedicated on describing these interactions.
2.1Fusion welding methods
2.1.1 Gas metal arc (MIG) welding and tungsten
inert gas (TIG) welding techniques
The MIG and TIG processes have the advantage of having
high heat input and since a flux is not used, there is little
chance for the entrapment of slag in the weld metal result-
ing in high quality welds. The shielding gas also protects
the arc and causes little loss of the alloying elements and
variety of the steels and aluminum alloys can be welded
by this process. However, the high heat input in these
processes is a big challenge to make the intermetallics
formed in the weld zone. For example, one of the alumi-
num alloys (2B50) and stainless steels (1Cr18Ni9Ti) were
welded by MIG welding using Al-Si filler metal (4043). The
influence of the aluminizing coating and galvanized zinc
coating on the fusion metal spread-ability was studied
[22]. The results showed that the aluminized coating did
not improve the appearance of the weld bead and there
were many micro-cracks in the middle of the weld zone.
The fracture, as a result, mostly happened at the interfa-
cial of the welds showing just 60 MPa ultimate tensile
strength. The study indicated that the intermetallic com-
pound (Al4.5FeSi) would be formed in the fusion zone near
the interface of the weld zone and heat affected area. The
thickness of the intermetallic compound layer was de-
clared to be around 5 μm to 15 μm for the heat input of
0.846 KJ/cm [22]. In another research, the aluminum alloy
was joined to the stainless steel by the MIG welding and
the intermetallic layer with a thickness greater than 40 μm
was achieved [23]. In the other study, a thin aluminum
alloy sheet (5A02) was welded to stainless steel 304
usinga flux-cored Zn-15%Al alloy wire. It was shown that
annealing at 280 °C for 30 min after the welding could
enhance the strength of the welds. The thickness of the
intermetallic layers was reported to be around 1.5 μm
[24,25]. However, the grains were refined during the TIG
welding by an ultrasonic technique and post weld heat
treatment at 280 °C attaining better tensile strength [26].
TIG welding of an aluminum alloy (5A06) to austenitic
stainless steel was also performed by applying alumi-
num-based filler metal and non-corrosive flux (see Fig. 3).
The results indicated the formation of different brittle in-
termetallics with the thickness of 5 μm to 35 μm [27]. The
intermetallic phases were τ5-Al7. 2 Fe2Si, η-Fe2Al5 and FeSi2,
giving an average tensile strength of 140.0 MPa and having
the fracture in the fusion zone. The formation of these
phases was also predicted by solidification path in a
ternary phase diagram (see Fig. 4).
Cold metal transfer was another solution for join-
ing an aluminum alloy and galvanized steel [4]. A pure
Table : Stability range, crystal structure and hardness of the intermetallics [–].
Phase Stability range
(at.%)
Crystal structure Vickers
hardness
Activation
energy (eV)
Density
(g/cm)
Fe solid solution – BCC – –
γ-Fe –. FCC – –
FeAl – BCC – . .
FeAl – Ordered BCC – .
FeAl– Complex cubic – –
FeAl–. Triclinic – – .
FeAl– BCC Orthorhombic – . .
FeAl.–. Highly complex Monoclinic BCC – – .
FeAl . –
Al solid solution .– FCC – –
 M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview
aluminum (99.8% wt.) was used for this study and it was
shown that the thickness of the intermetallics, mainly
trapezoidal equiaxial Fe2Al5 and elliptical FeAl3, could be
reached to 2.3 μm. The scanning transmission electron
microscopy (STEM) micrographs of this study showed
microtwins and Grisslile dislocations within the interme-
tallics (Fig. 5). The FeAl3 was said to be a kind of mono-
clinic phase with the lattice constants of α= 1.5489 nm,
b= 0.8083 nm, c= 1.2476 nm, β= 107.70°. An alternative
MIG welding process, alternate-current double-pulse gas
metal arc welding, has been proposed for joining a thin
aluminum alloy (5052) to galvanized mild steel in the lap-
joint configuration with the help of an aluminum filler
wire (A4047) [29]. Despite the fact that it was a novel idea,
the bonds weakened because of the nucleation and growth
of Fe2Al5, FeAl3 and Fe3Al.
The cold metal transfer welding of thin aluminum
alloy bonded to a mild steel (Q235) by the help of alumi-
num filler metal (Al4043) caused the reduction in the
thickness of the intermetallics [30].
2.1.2Resistance spot welding
The resistance spot welding is an efficient welding method
and the deformation of the work-pieces is very low in com-
parison to the other joining methods. However, the weld
strength is significantly lower when compared to other
Fig. 2: The calculated possible reactions between aluminum and iron [21].
M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview 
processes. This makes the process suitable for only certain
applications. The schematic of the resistance spot welding
is presented in Fig. 6. There are some reports on the joining
of the steels to aluminum alloys by the resistance spot
welding. In one of the researches, the welding current
during the bonding process was altered between 5 kA and
12 kA at the welding time of 0.2 s and an electrode force of
2 kN. The thickness of the reaction layer was thin at the
peripheral region and it was thicker in the middle of the
bond area. The fracture crack was significantly propa-
gated through the aluminum alloy (A5052) in the periph-
eral region of the weld and through the reaction layer in
the central region of the weld, from an intermetallic layer
with the thickness of about 1.5 μm [31, 32]. A comparison
was made for the reaction layers formed at the A5052/
SUS304 interface and A5052/SPCC interface indicating the
reaction layer at the interface of the A5052/SUS304 was
thinner than the one formed for the A5052/steel plate cold
commercial (SPCC) (see Fig. 6).
It was shown that there is a relationship between the
welding current and the nugget diameters during the re-
sistance spot welding of the A5052/SPCC and A5052/
Fig. 3: (a) Schematic of the butt TIG welding for joining the aluminum to steel and (b) formation of the cracks at the interface [27, 28].
Fig. 5: (a) STEM micrograph of the finger-like intermetallics,
(b)schematic of all the phases and their defects and (c) bright
fieldTEM micrograph of an Al5Fe2 showing Glissile dislocation
half-loops [4].
Fig. 4: Ternary phase diagram of the Al-Fe-Si system at 600 °C [27].
 M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview
SUS304 bonds. The nugget diameter was increased with
enhancing the welding current. Under the same spot
welding current, the nugget of A5052/SPCC bonds pre-
sented nearly the equal diameter, while the A5052/SUS304
bonds exposed larger nugget diameter because of the
poorer electrical conductivity and specific heat of the
SUS304 [33, 34].
In another work, in order to overcome the problems
associated with the direct resistance spot bonding of the
aluminum alloys to steels a transition layer was intro-
duced as a compatible material to both sides of the bond
zone [35]. The interlayer was cold-rolled to the aluminum
side and then the bond was made under the copper tips of
the spot welding machine. The fatigue results showed
higher fatigue strength of the joints with transition layer
than that of purely spot welded coupons. The work was
extended by applying the finite element method to explore
the effect of the transition material on the bond quality
[36]. It was shown that the nugget on the steel side has a
regular and elliptical shape with dendritic grain structure
while the side of aluminum showed a top-cap ellipsoidal
structure with the formation of pores and cavities inside
the cap. This finite element analysis suggested the heat for
the nugget formation on the aluminum side was vastly
conducted from the steel side.
2.1.3 Laser welding and electron beam welding
The laser welding can also be considered for joining of
aluminum to steel because of the precise positioning of
heat source with exact placing of the energy spot, low
thermal distortion and low post welding operation times.
However, depending upon type, the lasers are very expen-
sive, due to minor production quantities. For an open and
thus flexible handling technology, an isolated and corre-
spondingly secured working room is necessary. In com-
parison to other procedures, the production time is also
longer. On the other hand, based on the need in some
industries, the steels and aluminum alloys were welded
by the laser technologies. For example, a type of low
carbon steel (structural steel) was laser welded to an alu-
minum alloy (A5754) in the keyhole welding mode with
the overlap configuration. For reducing the formation of
intermetallics during the bonding process the effect of
laser power, pulse duration and overlapping factor were
studied. With enhanced laser power, pulse duration and
overlapping factor the amount of intermetallic compo-
nents inside the weld region was increased whereas de-
creasing the main parameters produced inadequate pene-
tration depth and cavity (Fig. 7). It was indicated that the
appropriate tensile strength can be achieved when the
amount of the intermetallics is reduced to the lowest
possible amount [15]. It was believed that when the pene-
tration depth is limited between 1560 and 1630 μm, an
appropriate surface quality and lower amount of inter-
metallics can be created. In this investigation, the amount
of the intermetallics was measured by the following
relationship:
100
Total
A
IA
= ×
(2)
Fig. 6: (a) Schematic of the resistance spot welding for joining the aluminum alloy (A5052) and stainless steel (steel plate cold commercial
(SPCC)) and (b) bright field image of the interface showing FeAl3 and Fe2Al5 formed at the interface [32].
M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview 
where ITota l is the total amount of the intermetallics, A the
area of intermetallic components and A is the area of the
weld zone.
The laser brazing was a solution proposed by some of
the references. It allows having a localized fusion of the
materials ensuing in the control of the growth of the inter-
metallics. For example, a filler wire composed of 85% Zn
and 15% Al was used to join the aluminum to steel and the
process parameters were optimized by the Taguchi Method
[37]. The tensile strength of about 200 MPa was reported
while a significant fracture was seen in the heat-affected
zone [38, 39]. The thickness of intermetallics was within
the range of 3–23 μm. In another work [40], the steel
(JSC270CC) and aluminum alloy (A6111-T4) was welded
by a dual-beam YAG laser with the continuous wave
andpulse wave modes. Formation of a 10 μm thick semi-
circular intermetallic layer at the bottom of the weld zone
and shearing strength of 128 MPa were reported. Conduc-
tion mode laser welding of a thin galvanized steel and an
aluminum alloy (A5083-H22) also confirmed the forma-
tion of FeAl3 and Fe2Al5 [41]. The other type of silicone-base
filler alloys (A4047) was applied to join AA6022 to two
different galvanized steels but as the intermetallics were
formed the strength of the joints were not higher than 55
to 75% of the aluminum alloys [42].
A defocused laser beam was used to join aluminum
alloy (A6111) and low-carbon steel (SPCC) in a lap-joint
configuration. It was reported that since the depth of the
molten pool in the steel side kept about 90% of the steel
thickness, the area near the upper surface of the alumi-
num could be melted with the semi-elliptical shape [43,
44]. However, the maximum shear strength of the lap joint
was around 70% of the A6111-T4 and needle-shape inter-
metallics were formed in the molten pool confirming the
presence of Al13Fe4, Al5Fe2, Al2Fe, FeAl, Fe3Al and Al6Fe
(see Fig. 8).
The other alloy from the aluminum alloy series
(AA6016) was laser brazed to low-carbon galvanized steel
with different thicknesses, by a zinc-based aluminum
filler alloy. The work shows that Fe2Al5Znx type intermetal-
lics with 10-μm thickness can be formed in the bond area
[45]. In an interesting research [46], a 10 kW fiber laser
with a tightly focused spot diameter of 200 μm was em-
ployed to join a stainless steel (304) and aluminum alloy
(A5052). The study was given an indication of the influ-
ence of the laser beam density on the geometry and feature
of the weld, based on a high speed charge-coupled device
(CCD) camera. The weldability of aluminum (AA1100) and
stainless steel (AISI409) by the pulsed Nd: YAG laser
welding process was also studied and the influence of
the pulse duration and power density on weld width,
penetration, bond area and porosity was qualitatively ex-
plained concerning material-dependent variables such as
the thermophysical properties of the parent alloys [47].
The power density required for melting the aluminum was
reported to be almost 4.5 times higher than the stainless
steel. Galvanized steel was joined by the laser brazing
tothe aluminum alloy (A4043) using a fiber laser in the
keyhole mode and the presence of α (τ5)-Al8Fe2Si, θ-Al13Fe4
and ζ-Al2Fe, causing the maximum strength of 162 MPa
and brittle fracture was reported [48]. Some of the specific
joint shapes essentially needed a design for the filler alloy
to fill the gap between the two components. Two different
galvanized steel flanges were laser brazed using a zinc-
based filler wire with Nd-YAG laser where the formation of
different intermetallics was recorded [49]. The interesting
point in the research was the suggestion on the use of a
pre-heating of steel by the second-heat source such as
laser towards the steel side during the bonding. The other
recommendation which might affect the dimension and
geometry of the intermetallics was a method to sink the
heat out of the bond area in order to reduce the heat input
Fig. 7: SEM micrograph of the bond shows FeAl3, Fe2Al5 and pores [15].
Fig. 8: X-ray diffraction pattern shows the presence of different
kinds of intermetallics on the fracture surface of the coupons [43].
 M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview
within the molten pool. The copper backing blocks are
very familiar in the welding industry and their use was
studied to control the heat flow with the successful report
on the reduction of the intermetallic layers during the
laser welding of a high strength steel (Dual-TEN 590 steel)
and A6022-O aluminum alloy [50].
Furthermore, the influence of the penetration depth
in the key-hole mode of the laser welding of aluminum
alloys (A6016, 6056 and 6061-T6) to a low carbon steel (DC
04) showed that the presence of FeAl3 and Fe2Al5 with the
20 μm and 5 μm is a kind of irresistible response to the
fusion laser welding process [13, 51]. However, the medium
penetration through the steel provided interlocking be-
havior of the joints achieving a little bit higher strength,
since the aluminum was at the top [13]. Application of bi-
metals for the laser welding process was another resolu-
tion presented by Liedl et al. [52] in which the bimetal
wires can be roll-welded (Al/steel strips). It was also some
indications of using different interlayers to improve the
joints quality by relying on the good mechanical proper-
ties of the filler alloys. For example, a nickel alloy was
used in the laser conduction brazing, having the steel at
the top and a slight penetration into the aluminum sub-
strate with the presence of [Fe, Ni, Cr, Mn]n Al3, Al0.9Ni1.1
and FeAl3 intermetallics at the interface [53].
Electron beam welding was the other method to bond
aluminum alloy and steel where a silver interlayer was
used in the sandwich coupons. The joint was full of Ag2Al
intermetallic which its amount was highly dependent on
the electron beam power and beam offset [54]. When the
beam offset was large enough two other intermetallics
namely FeAl and FeAl3 were formed. However, the bonds
were weaker than the both parent metals. However, there
are only a few studies and low interest on the usage of this
method to join steels and aluminum alloys.
2.2Solid state welding methods
2.2.1Ultrasonic welding
The ultrasonic welding is a suitable and fast process for
the small and tiny components but it cannot be used
for the complicated geometries and thick materials. A
main advantage in welding aluminum to steel is the fact
that the vibrations break the oxide layer of the aluminum
alloy and transport it to the boundary regions. As a result,
mechanical and chemical surface cleaning is not neces-
sary. The feasibility of applying this technique was studied
for joining aluminum to steel by a 15 kHz ultrasonic in
a butt joint configuration with a vibration source. The
technique applied eight bolt-clamped Langevin type PZT
trans ducers and a 50 kW static induction thyristor power
amplifier [8]. It was shown that the large vibration ampli-
tude of 25 μm, static pressure of 70 MPa and welding time
of 1.0–3.0 s can produce a reasonable high strength joint
(Fig. 9).
2.2.2Magnetic pulse welding
In the magnetic pulse welding, the magnetic field gener-
ated by a coil focused by a field shaper is limited to a small
area. The magnetic field only generates enough pressure
under the condition that the coupon is a good electrical
conductor. There is also a limitation in the size of the coil
and the thickness of materials and this is mainly because
of the needs for more energy. It is also very difficult to find
an optimum spacing between the parts to be welded,
which is important to generate the appropriate impact
speed. However, some of the aluminum alloys (A1050,
A2017, A3004, A5182, A5052, A6016, and A7075) were
joined to a steel (SPCC) by the magnetic pulse welding
[14]. The breakthrough in the study was the design of
the electrical coils which had T-shape and E-shape flat
surfaces (Fig. 10).
The eddy current i and the magnetic pressure p can be
given as [14]:
(3)
( )
22 2
002
(1 exp( ))
22
i
BB
Bx
p
μμ δ



= = −




(4)
Fig. 9: The relationship between vibration amplitude, input power
and weld strength of joint between the pure aluminum and
electrolytically polished stainless steel [8].
M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview 
where κ, μ, τ, Bo, and Bi are the electrical conductivity,
magnetic permeability, thickness, and magnetic flux den-
sity for the lower and upper surfaces of dissimilar sheets,
respectively. The depth of skin effect can be obtained by
δ= √(2/ωκμ), where ω is the angular frequency of chang-
ing field [14]. A kind of wave morphology and the inter-
mediate layer was observed along the bond interface. Ad-
ditionally, grain refinement in the A6111 matrix near the
weld interface has been recorded [55]. High shear strength
of the joints was reported because of the greater penetra-
tion of the magnetic field in the center of the bond area
but the edges of the bonds showed the weakness of the
prepared bonds [56].
2.2.3Roll bonding
The cold roll bonding requires the surfaces to be clean for
the interatomic connections and as the surface cleanliness
is difficult to achieve without a controlled atmosphere the
process is limited for the joining of aluminum to steel com-
ponents. However, one of the low carbon steels (stw22)
was welded to an aluminum alloy (Al1350) at different pre-
heat temperatures by this process [57]. After using the
peeling test, the study showed that the brittle surface
between the aluminum and steel was the main cause of
the failure. It was also shown that the main parameters
controlling the bond behavior are the rolling speed, pre-
heating and roll-strip frictional condition [58–61].
2.2.4Diffusion bonding
The diffusion welding process gives minimal shape
change to the parts and there is not any need for the
post-finishing processes but the process is comparatively
slow joining technique. The key to a good bond lies in
choosing the process conditions and cleanness of the
materials because the joint needs to form successfully
with both parent materials, while controlling deforma-
tion. In one of the studies [62], diffusion bonding was
applied to join an austenitic stainless steel (316) to two dif-
ferent aluminum alloys (A1100 and A6061), using silver
interlayer coated on the surface of the parent metals by a
hot hollow cathode faying surface coating technique and
then the joints were aged at different temperatures. There
was a vast reduction in the reported mechanical pro-
perties emanating from the initiation and growth of inter-
metallics between the alloys. The microscopic analysis
showed the formation of Ag2Al and Ag3Al at the faying
surface of the aluminum alloy. It was shown that the
coupons aged at 423 K gives lower development of the
intermetallic with respect to the time of the aging (see
Fig.11).
In the other investigation, Al1060 and steel (1Cr18Ni9Ti)
were joined together using the vacuum furnace by Al-Si
alloy as the strip layer. The interface of the joints showed
Fig. 10: The coil designs for the magnetic pulse welding (a) T-shape
and (b) E-shape [14].
Fig. 11: The dependency of the strength of the bonds prepared by
the diffusion welding between stainless steel (304) and aluminum
alloy (1100) on the total thickness of the intermetallic layer [62].
 M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview
the massive formation of δ (Al, Fe, Si) and α-Al (Si),
with reportedly less brittleness of the interfaces [63]. It
was found that during the diffusion bonding at 873 K
theFeSiAl5, FeAl3 and Fe3Al intermetallics can be formed
[64–68]. The mass balance equation at the boundary
between Fe3Al and FeAl3 can be said to have the following
form [69]:
12
12 1 2
( ) () ()
CC
dCC
CC D D
dt x x
ξ
∂∂
−=− +
∂∂
(5)
where D1 is the diffusion coefficient of Fe in Fe3Al and D2 is
the diffusion coefficient of Fe in FeAl3. The diffusion of the
aluminum to the steel can be estimated by the Boltzmann
solution of Fick’s second law [70, 71]:
1
1
2
S
S
C
SS
bS
C
x
D xdC
tC
=
(6)
where x is the position of the solute, tb is the diffusion
brazing time, and CS is the concentration of the solute in
the steel. It was recommended that the development of the
intermetallics is a diffusion-controlled process since the
thickness of the layers proved a linear link to the square
root of the diffusion time [72]. Therefore, the growth of the
intermetallic layer (Y) can be explained by:
4
3 0.5 9 10
5.74 10 exp( )
FeAl
Yt
RT
×
=×−
(7)
3
5
5 0.5
1.39 10
2.75 10 exp( )
Fe Al
Yt
RT
×
=×−
(8)
where K0 and K are constant, R is the gas constant, Q is the
activation energy for growth of the intermetallic and T is
the process temperature. The activation energies for the
growth of the FeAl and Fe3Al intermetallics were alleged to
be 180 and 260 kJ mol1, respectively [73]. It was suggested
that the development of the Fe2Al5 was mainly controlled
by the diffusion interaction and follows a parabolic law,
whereas the development of FeAl3 is completely linear
and controlled by the reaction on the interface [73, 74].
However, the growth rates and activation energies of
theFe2Al5 and FeAl3 were reduced by the increase in the
amount of Si in the aluminum alloy. Fig. 12 shows the
electron backscatter diffraction inverse pole figure maps
of the different intermetallic layers between steel and alu-
minum alloy. It was demonstrated that the reaction of the
steel with Al-5 wt.% Si at 600 °C lead to thicker reaction
layers in comparison to the reaction of the steel with pure
aluminum [74].
In the tensile test experiment, it was shown that the
interfacial failure mostly occurred for the pure aluminum/
steel joints with the intemetallic layer thickness of 7 μm.
The failure in the Al-5 wt.% Si/steel joints occurred within
Fig. 12: Electron backscatter diffraction inverse pole figure maps for different reaction layers between steel and aluminum alloys:
(a) the interdiffusion at 675 °C for 30 s for the Al-5 wt.% Si/steel, (b) the interdiffusion at 675 °C for 30 s for pure aluminum/steel,
(c) the interdiffusion at 600 °C for 1 h (top) and 16 h (bottom) for pure aluminum/steel and (d) the interdiffusion at 600 °C for 16 h
for Al-5 wt.% Si/steel [74].
M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview 
the η phase with the thickness of 1.6 μm [75]. Direct
bonding of pure aluminum (in a cubic form) and stainless
steel 304 and 316 (in a cylindrical shape) was performed,
without heating, in an ultra-high vacuum since the prepa-
ration of the specimens was a kind of troublesome process
by activating the surface using argon fast atom beam for
long hours under the pressure of 6.0 × 105 Pa followed by
close contact under an external pressure of 960 N [76]. The
maximum tensile strength of 100 Mpa was reported for
this technique.
2.2.5Explosive welding
Explosive welding of the dissimilar materials is relatively
easier than other welding processes and extremely big
surfaces can be joined. The welds also can be created
without any significant effect on the microstructure of the
parent metals. The most important point in this process is
that broad range of the thicknesses can be joined or
cladded without having an influenced heat affected area
and porosity in the bond zone. However, the use of the
explosive materials in the industrial scale is very limited
because of the storage problems and effects of the explo-
sion. In one of the most recent works, bimetals were
fabricated from a high strength low alloy steel (1.45 wt.%
Mn-0.2 wt.% Si-0.186 wt.% ) and dual phase steel joined to
the aluminum alloy, separately by the explosive welding
and the shear strengths of 420 MPa and 720 MPa were
reported, respectively (Fig. 13) [77]. An aluminum alloy
(AA5083) and a steel (SS41) were explosively-cladded
while an aluminum alloy (AA1050) was at the interface of
the specimens [78]. It was demonstrated that the bond
zone was composed of FeAl3.
The bonding interface of explosively-welded alumi-
num and steel with three different explosive materials
showed that the waves with curled front can be formed by
the superplastic deformation, but presence of dispersed
AlFe, Al2Fe, Al3Fe and Al6Fe intermetallics were reported
in the bond area [79, 80]. The point is that structural tran-
sitions made of more materials by the explosive welding
are one of the prospect technologies that should be more
developed. There is a shortage of theoretical investiga-
tions for these joints prepared by the explosive welding
but in one of few studies the interfacial toughness of the
aluminum and steel joints was studied by the compact
tensile test and four points bending test, showed that the
temperature of the bonds at the interface should not
exceed 300 °C during the welding process [81]. A triple
cladding layer made of steel (A516)/pure aluminum
(AA1050)/aluminum alloy (AA5083) was heat treated and
the effect of heating on the shear stress of the bonds were
shown to decrease by increasing the time and tempera-
ture, because of the increase in the quantity and thickness
of the interlayer [82]. The surface cleaning, type of the
explosive materials and set-up the weld pieces are the
Fig. 13: The microstructure of the (a) high strength low alloy steel to aluminum and (b) aluminum to dual phase steel welded by the explosive
welding and (c) schematic of the bonding process [10].
 M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview
prominent parameters controlling the bonding process to
reach a high quality joint or clad [83, 84].
2.2.6 Friction welding, friction stir welding
and friction spot welding
One of the joining techniques that were more extensively
than the others was investigated for the joining of alu-
minum to the steels was friction-based welding process.
For example, many works were dedicated for friction stir
welding while few findings were mentioned for resistance
spot welding and some others. Friction welding and fric-
tion stir welding can join the dissimilar materials in a
full-strength weld without sacrificing weld integrity or
strength. As compared to conventional flash or resistance
butt welding, friction/inertia welding produces improved
welds at higher speed and lower cost, less electric current
is required, and costly copper fixtures to hold components
are eliminated. Plus, heat is localized at the weld and is
quickly dissipated so that there is only a slight effect on
the parent metals. The heat affected zone adjacent to the
weld is confined to a narrow band and therefore does not
affect the temperature of the surrounding area. For in-
stance, aluminum alloys (AA6082 and AA5052) and stain-
less steel (AISI 304) were welded by friction welding
process [7]. It was revealed that the center of the cylindri-
cal bond was the weakest because of the short upset time
while the longer upset time originated the intermetallics
at the bond interface [85]. An argon atmosphere was used
during the friction welding of aluminum alloy to steel,
giving stronger interface but the formation of chromium
oxide was not fully eliminated by this method [86]. In ad-
dition, the formation of FeAl3 as a function of diffusion
time was also confirmed [87]. The feasibility of the inertia
friction welding of an aluminum alloy (6061-T6) and steel
(1018) was studied [88, 89]. The maximum tensile strength
of 250 MPa was achieved when the upset pressure was set
at 60 MPa although failure was seen to be on the alumi-
num side after the bonding process and the thickness of
the intermetallics (FeAl and Fe2Al5) was reported to be
about 0.350 μm [90]. Another aluminum alloy (AA1050)
was welded to stainless steel (AISI 304) by rotary friction
welding; both in the cylindrical form and fracture through
the aluminum side was reported [91]. The alloys grain size
also might have an effect on the final properties of the
bonds which it was taken into account by Yufeng et al.
[92].
The characterization of the friction stir welded alumi-
num alloy (A3003-H112) to stainless steel (304) showed
that the strength in the center of the bonds and on the
advancing side was higher than that at the retreating side
[93]. In the other investigation, friction stir lap joints of
aluminum alloy (AC4C) and zinc-coated steel, where the
coupons surfaces were prepared by different techniques,
were studied. It was demonstrated that the joints between
AC4C and as-received zinc-coated steel has higher fracture
strength than the joints of AC4C and surface treated steel
[94]. The other alloy from the aluminum (A5083) was fric-
tion stir welded to steel (SS400) and it was shown that in-
creasing the rotational speed and pin length causes the
reduction in the shear strength of the bonds because of
the presence of a thick FeAl3 at the bond interface [95, 96].
It was stated that having 10 mm pre-hole in the specimen
for the friction spot welding is fine enough to achieve the
maximum shear strength [97]. The significant influence
ofthe pin depth and formation of Al5Fe2 and Al13Fe4 was
confirmed by the examination of the pure aluminum/low
carbon steel bonds prepared by the same solid state
welding method [98]. However, Al4Fe with a hexagonal
close-pack structure with a thickness of 0.250 μm was
identified for the joints prepared by friction stir welding of
A6056 and steel (304) [99].
The other aluminum alloy (5052) and steel (A36) were
friction stir-welded and it was shown that increasing the
upset pressure to 137.5 MPa and friction time of 0.5 s can
give a final strength of 202 MPa [100]. A German-based
research institute (German Aerospace Center-DLR) also
patented the friction stir welding of aluminum alloy
(A6056-T4) and stainless steel (304) by an adapted milling
machine, but there was not any evidence of the maximum
strength of the joints [101]. A5083 has been welded to a
mild steel (SS400) by the friction stir welding and a tensile
strength was lower than of the aluminum alloy, as a reason
of the formation of brittle intermetallics at the upper
portion of the bond area [102]. It was correspondingly
shown that the counterclockwise rotation of the pin would
not lead to the joining of the coupons and maximum
tensile strength can be achieved at the pin offset of 0.2 mm
to the steel side. The influence of the annealing, as the
post heat treatment process, at 300 °C and 350 °C on the
strength of the joints made of steel and aluminum by
the friction stir welding was shown that the extended
soaking time for the post weld heat treatment lead to the
higher strength. This was because of the solution of inter-
metallics and final size of the phases (0.49 μm) [103]. The
critical thickness of 2.6 μm for the optimum bond strength
was reported. To investigate the effect of bonding parame-
ters, pure aluminum and structural steel were joined and
the presence of Al3Fe was confirmed as a function of the
tool speed [104]. Among the analysis for investigating the
friction stir bonded specimens, scanning electron micros-
M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview 
copy (SEM) combined with electron backscattered diffrac-
tion (EBSD) might be an interesting tool to explore the
reactions within the bond area. For instance, in a study
after aluminum alloy (AA6181-T4) was friction stir-welded
to high-strength steel (DP900) examined and a plastic
flow of the material was meticulously studied by EBSD
analysis (see Fig. 14) [105].
One of the important aluminum series which is mostly
used in the aerospace industry (7075-T6) has been friction
stir welded to mild steel with the tool rotation speed of
400–1200 rpm and the weld travel speed of 100 mm/min
[106]. It was observed that the joint strength enhanced by
the reduction of the intermetallic thickness. Jiang and
Kovecevic [107] exhibited the friction stir welding of a rel-
atively thick aluminum alloy (6061), 6 mm, to a structural
steel (AISI1018) in butt joint configuration and showed
that the thickness of Al13Fe4 and Al5Fe2 can be controlled.
In the continuous work, the offset distance of the tool
wasconsidered as the main parameter during the friction
stir welding of the relatively thick aluminum alloy and
structural steel [108]. The study was focused on the moni-
toring of the tool wear with acoustic emission sensors (see
Fig. 15). The presence of Al13Fe4 and Al5Fe2 was confirmed
in the bond interface and the pin was worn for the rota-
tional speed of 917 rpm and travel distance of 100 mm.
Moreover, a designed tool made of Tungsten-Rhenium
(W-25%Re) was applied through the study with a pin com-
prising a triflute with brinks [109].
A regular aluminum alloy (A6013-T4) was joined to
the stainless steel (X5CrNi18-10) by the friction stir welding
showed fatigue properties of 30% lower than the alumi-
num alloy [110]. The other type of the aluminum alloy
(6016) and high strength steel with different thicknesses
were friction spot welded. Different intermetallics (FeAl3,
Fe2Al5 and FeAl2) were formed, in relation to the pin pene-
tration and rotational speed (see Fig. 16) [111]. The result
of the study by Bozzi et al. [111] can be confirmed by the
outcome of the research done by Qiu et al. [112] where an
aluminum alloy (A5052) and a mild steel with a thickness
of 1.0 mm were bonded by this method. The other type of
the aluminum alloy (5186) was likewise friction stir welded
to mild steel and two intermetallics, Al6Fe and Al5Fe2, were
observed in the bond area [11].
The thickness of the intermetallics was stated to be
a function of dwell time (X= (Dt)0.5) as the pin stays in
itsposition for longer time [113]. Moreover, a thin alumi-
num alloy (6061-T6) was friction spot welded to mild
steel where a round dent was made on the aluminum
Fig. 14: (a) The EBSD analysis locations, (b, c) orientation of the grains, (d, e) grain shape orientation, (f) grain aspect ratio, and (g) grain
size distribution [105].
 M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview
side before the bonding but despite the fact that the
pre-plasticized area should help to improve the bond
quality some unexpected intermetallics like Al6Fe were
formed in the bond zone [114]. Friction spot welding of
AA5754 and galvanized steel HX 340LAD was also con-
ducted and the presence of Fe2Al5 at the interface was
reported [115].
On the other hand, for the thin plates of aluminum
alloys with the thickness of less than 1 mm the friction stir
welding process can cause the distortion of the coupons
so there is a proposed method “Friction stir knead
welding” in which the tool does not have a pin in the head
of the tool with a groove inside it leading to the higher
welding speed [116]. This improvement on the tool design
was implemented on the steel DC04 and aluminum alloys
of the AA5182 and AA6061. There is also another report on
the usage of the friction stir welding where an aluminum
alloy was welded to a cast iron by a frictional consumable
bit and an insert metal made of steel [117]. As the cast iron
contains the graphite flakes the rotation of the bit has not
showed any bond formation so the rotation of the bit was
implemented on the aluminum side. In other progress
[118], friction stud welding was introduced with the ad-
vantage of breaking the aluminum oxide layer faster than
the conventional friction welding technique but there
were still long cracks, provided by the expansion of
intermetallics, at the bond interface.
2.3Mixed welding techniques
The mixing of welding techniques is on the front line of
the current researches. The mixing of the welding pro-
cesses can help the improvement of the heat input and
compensate the drawbacks of the other heat sources. For
example, TIG welding was combined with friction stir
welding to join a stainless steel alloy (STS304) to an alu-
minum alloy (Al6061). This combination gives 93% tensile
Fig. 15: (a) Schematic of the acoustic emission monitoring and (b) location of the pin during the friction stir welding of aluminum alloy (6061)
to a structural steel (AISI1018) [108].
Fig. 16: Transmission electron microscope micrographs of the
intermetallics (a) diffraction patterns of FeAl2 and Fe2Al5 and (b)
micrograph of FeAl3 [111].
M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview 
strength of the aluminum alloy, higher than the joints
with friction stir welding alone [119]. Laser roll bonding is
the other process that benefits from the assistance of the
pressure on the top of the bond zone. Laser heating could
give higher temperature in a short period of time and its
combination with roll bonding for the aluminum and steel
alloys was reported to be non-effective as the significant
formation of intermetallics (FeAl, FeAl3, Fe2Al5 and Fe3Al)
was detected [5, 120]. In the other mixed method, resis-
tance spot welding and brazing were mixed to join alumi-
num alloys (6××× series) and low carbon steel where the
bonds did not display enough strength [121]. The mixed
method of TIG welding and laser welding was one of the
works that demonstrated that the heat conduction from
the steel side to the aluminum could lead to the partial
melting of the aluminum side, resulting in the linear
interaction between the alloying elements, presence of
complex intermetallics and ultimate strength of 250 MPa
[122, 123]. Other combined methods proposed the mixture
of the friction stir welding and brazing with the zinc inter-
layer [124]. The process shows the interaction layer can be
controlled by the bonding parameters since the reacted
layer thickness of less than 10 μm was reported (Fig. 17).
There is also a report on the joining of aluminum alloy to
stainless steel 316L with the cold spray technique where 3
to 8% porosity was reported to be the drawback of the
process for the bonding of the dissimilar materials [125].
However, there are some novel efforts to combine
the welding techniques and quenching systems in the
Research Center for the Advanced Manufacturing in the
Southern Methodist University which might be resulting
in the development of a combined bonding method to join
thin and specifically thick components of the aluminum
alloys and advanced steels. The result of the studies will
be presented somewhere else with more vision into the
details of the mechanical and metallurgical phenomenon
elaborated in the bonding processes. The ideas of the
welding strategy is for the thin and thick plates of alumi-
num alloys and steels where they will be bonded by
the TRICLAD as the insert metal-composite and hybrid
laser welding, conduction laser welding and friction stir
welding techniques. In the laser conduction method a
defect-free two-pass laser partially penetrated lap joint of
galvanized steel to aluminum can be achieved. With the
optimal preheating and welding parameters, the thick-
ness of the Al-rich intermetallics could be controlled at
around 5 μm. The zinc presented in the intermetallics
could improve the strength of the galvanized steel to alu-
minum lap joints (see Fig. 18). The transitional joint of the
aluminum alloys to steels can also be achieved for the
thick plates if the multi-interlayered transition insert
made of steel and aluminum by solid-state welding pro-
cesses, especially by explosive welding, for decreasing the
level of bonding temperature and heat input to eliminate
the formation of the intermetallics. The process then can
be extended to the fusion welding methods like hybrid
laser arc welding or friction stir welding of the aluminum
alloy to another aluminum alloy in one side and steel to
Fig. 17: The schematic of the mechanism of the joining in the combined technique of gas tungsten arc welding and brazing [124].
 M.M. Atabaki et al., Welding of Aluminum Alloys to Steels: An Overview
the other type of the steel in the other side (Fig. 18).
However, the use of other welding techniques like friction
stir welding is in progress where the design of a tool can
be a good target to improve the quality of the joints.
3Conclusions
The attempt of the present review was to bring the
recentworks on the joining of the aluminum alloys to the
steels into the highlight. There were generally great steps
towards the better understanding of the applied welding
processes for the joining of the aluminum alloys and steels
but for having desirable weldments more efforts have to
be putting forward. The removal of the intermetallics was
a kind of effortless process especially in the fusion welding
techniques. The ideal case might be the design of thicker
multi-interlayers to completely eliminate the presence of
intermetallics in the weldments. More investigations are
also needed to find the optimum welding parameters.
However, the Al-Fe system is a very complex system and it
still needs serious work for modeling the phase equilib-
rium under the non-isothermal condition such as the
solidification process in the various welding techniques.
Hence, it can be concluded that a comprehensive studies
are needed for the specific joining techniques with all pos-
sible input parameters as well as multiple performance
measurements.
Heat generation, fluid flow and plastic flow should
beconsidered and perfectly adopted for the design of the
welding processes, in the case of aluminum and steel
alloys. The problem of the intermetallic formation can be
solved if the required techniques eliminate the reactions
between the iron and aluminum during the heating pro-
cesses. Further analysis, like structural analysis, residual
stress analysis, molten pool tracking, phase analysis and
the welding physics behind the initiation and extension of
the intermetallics is required for the development of the
state of the art welding technology. More works on the
simulation and modeling of the welding processes are
essential to explore the effect of the bonding processes on
the microstructure and mechanical properties. Finite ele-
ment method, finite difference method, phase field mod-
eling and molecular dynamic modeling are examples of
the more effective methods to discover the phenomenon
involved in the bonding of the aluminum alloys and steels.
Funding: The authors would like to thank the financial
support of the Onodi Tool & Engineering Company.
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... As a solution to these problems, Friction stir welding (FSW) has become a promising key for dissimilar joining in the solid-state joining process [3]. This process with relatively small heat input is characterized to provide the formation of limited IMCs. ...
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The dissimilar lap joining of 1050 Al alloy with thickness of 0.5 mm and commercial pure copper with thickness of 1.0 mm has been carried out by Friction Stir Welding (FSW). The influence of process parameters on Al-Cu dissimilar joint characteristics was investigated. The tensile-shear test results indicated that a higher heat input with increasing rotational speed and decreasing travel speed contributed to a higher tensile-shear load. The maximum tensile-shear load of the Al-Cu dissimilar joint was 913 N when obtained under a rotational speed of 600 rpm and a travel speed of 60 mm/min. According to the Al-Cu joint electrical resistance test, the minimum electrical resistance value was about 70 µΩ, which corresponded with the maximum tensile shear load. It can be inferred that the defect-free welded joint and sufficient joining area contributed to smooth current flow.
... Joining processes such as brazing [2,3], soldering [4,5], arc welding [6,7], laser welding [8,9], hybrid welding [10,11], electron beam welding [12,13], resistance welding [14,15], ultrasonic welding [16,17], friction crush welding [18,19] and other types of welding processes have been covered in literature. Arc welding processes among all these processes appear as not recommended processes for obtaining felicitous dissimilar welds such as Al-steel based on features of the arc-induced melting and hardening process such as the evolution of brittle intermetallic compounds (IMCs) [20]. Thus, other joining processes have been studied where no melting occurs for both parent metals. ...
Article
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Friction stir brazing (FSB) is a new technology developed for its ability to join similar and dissimilar metals and alloys resulting in a joint with considerable characteristics through the use of interlayer (braze) material under the action of a pinless rotating tool and other FSB parameters. The frictional heat during FSB is responsible for the melting of the braze material between the two workpieces, while the shoulder action must be satisfactory for the extrusion of the excess braze liquid phase depending on the FSB parameters used. The parameters of FSB also have a considerable impact on the microstructure and mechanical characteristics of friction stir brazed (FSBed) joints. Sound interfacial bonding can be observed in the central zone of FSBed joints, where intermetallic compounds (IMCs) can be formed by direct diffusion among the dissimilar workpieces after extrusion of liquid phase rather than by mechanical mixing or solidification of braze material. Increasing the transverse speed at a constant rotational speed has an influence on the peak temperature, but it remarkably reduces the holding time owing to the increased cooling rate. The use of vibration in the FSB increments the fluidity of the molten braze material among the joining workpieces resulting in a more homogeneous distribution of IMCs particles. In this review article, FSB parameters, bonding mechanisms, as well as the microstructure, and mechanical properties of FSBed joints are reviewed.
... However, melting forms a layer of brittle intermetallic phases between aluminum and steel [3] or even unexpected phases between the same grade of materials [4,5]. Different modifications of RSW can reduce unwanted phases [6,7]; however, the welding process becomes more complicated and the mismatch in the aluminum-steel bonding remains [8,9]. ...
Article
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In the present study, AA2024 aluminum alloy and AISI304 stainless steel were welded in a lap joint configuration by Probeless Friction Stir Spot Welding (P-FSSW) with a flat surface tool. A full factorial DOE plan was performed. The effect of the tool force (4900, 7350 N) and rotational speed (500, 1000, 1500, 2000 RPM) was analyzed regarding the microstructure and microhardness study. A two-dimensional arbitrary Eulerian–Lagrangian FEM model was used to clarify the temperature distribution and material flow within the welds. The experimental results for the weld microstructures were used to validate the temperature field of the numerical model. The results showed that the tool rotation speed had an extensive influence on the heat generation, whereas the load force mainly acted on the material flow.
... Among the efforts made by experimenters in improving the quality of dissimilar joints is the incorporation of an interlayer between the BMs. Several interlayers including aluminium, copper, zinc, nickel, titanium, molybdenum and Carbon Fibre-Reinforced Polymer (CFRP) have been reported [15][16][17]. A suitable interlayer has the ability of retarding oxide formation and facilitates the release of residual stresses between the BMs [18]. ...
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This article investigated the mechanical performance and corrosion behaviour of a diffusion-bonded A5083 aluminium/A36 mild steel dissimilar joint with a Gallium (Ga) interlayer. The bonding parameters were the bonding temperature (525 and 550 °C), holding time (60 and 120 min) and surface roughness (800 and 1200 grit). Property characterisation was achieved using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) analysis, Vickers microhardness tester, Izod impact tester and potentiodynamic polarisation testing. The results revealed that the significance of the bonding parameters was in the order bonding temperature > surface roughness > holding time. Increasing the bonding temperature resulted in an increase in the impact strength and a corresponding reduction in the corrosion rate and microhardness. However, increasing the grit size decreased the microhardness and a corresponding increase in the impact strength and corrosion rate. The impact strength and corrosion rate decreased with the increasing holding time while the microhardness followed a reverse trend. It was also discovered that incorporating the Ga interlayer resulted in a 67.9% improvement in the degradation rate.
... However, the difficulties related to these two metals' joints are well known, mainly related to the generation of intermetallic compounds such as the Al x Fe y binary phases. Nevertheless, the incorporation of Friction Stir Welding (FSW) technology allows a positive impact in this area since it allows manufacturing welded joints with promising characteristics, mainly due to the control in the formation of intermetallic compounds (IMCs) [2]. For the automotive and aerospace sectors, one of the technologies that employ dissimilar welding is tailor-welded blank (TWB), where two or more metal sheets with different properties or thicknesses are welded to form a piece [3][4][5][6]. ...
... However, the difficulties related to these two metals' joints are well known, mainly related to the generation of intermetallic compounds such as the Al x Fe y binary phases. Nevertheless, the incorporation of Friction Stir Welding (FSW) technology allows a positive impact in this area since it allows manufacturing welded joints with promising characteristics, mainly due to the control in the formation of intermetallic compounds (IMCs) [2]. For the automotive and aerospace sectors, one of the technologies that employ dissimilar welding is tailor-welded blank (TWB), where two or more metal sheets with different properties or thicknesses are welded to form a piece [3][4][5][6]. ...
Article
The environmental crisis has raised serious concerns regarding fuel consumption, inciting a race to reduce vehicles’ weight. The design of structures combining different materials is a common factor in various industries, where the synergy between steel and aluminum is the starting point for many applications. Metallurgical challenges and the implementation of joining processes for thin sheets are some challenges that friction stir welding has overcome in the last two decades. In this manuscript, the methodology for joining aluminum alloy 6063-T5 and SAE 1020 steel, in thin sheets, employing friction stir welding, is presented. The research evaluated the offset in obtaining joints with complete joint penetration, heat generation, and microstructural changes. Joints with no defects were obtained, with a low thermal input, which favored the formation of tiny grain size in the stir zone, as well as an interface free of intermetallic compounds.
Thesis
Das Gewicht von Fahrzeugkarosserien kann durch den Einsatz von Leichtbauwerkstoffen reduziert werden, in der Massenproduktion ist die Kombination von Aluminium und Stahl besonders interessant. Unabhängig von ihren unterschiedlichen Schmelztemperaturen können Aluminium und Stahl durch das Metall-Ultraschallschweißen im festen Werkstoffzustand energieeffizient, schnell und ohne Zusatzwerkstoffe verbunden werden. Zur Herstellung eines großflächigen Werkstoffkontaktes auf mikroskopischer Skala wird eine Anpresskraft mit hochfrequenten Schwingungen überlagert, die sich in den Bauteilen ausbreiten und bereits vorhandene Schweißpunkte beeinflussen können. In dieser Arbeit wurde daher ein Prozess entwickelt, um die Aluminiumknetlegierung AA6005A-T4 mit dem feuerverzinkt-geglühten Dualphasenstahl HCT980X+ZF100 sowie dem feuerverzinkten, niedriglegierten Stahl HX380LAD+Z100 durch aufeinanderfolgend erzeugte Schweißpunkte zu verbinden. Die zentralen Prozessparameter wurden mithilfe einer statistischen Versuchsplanung ermittelt und auf hohe und gleichzeitig zuverlässige Zugscherkräfte optimiert. Zur Analyse der Fügeprozesse wurden Temperaturmessungen in der Schweißzone, die Zeitverläufe der Leistung des Ultraschallgenerators sowie die Schweißzeiten selbst herangezogen. Ferner wurden licht- und rasterelektronenmikroskopische Untersuchungen inklusive energiedispersiver Röntgenspektroskopie an Quer- und Längsschliffen sowie an Bruchflächen der Schweißverbindungen nach der Zugscherprüfung durchgeführt. Die Prozess- und Verbundeigenschaften wurden sowohl durch die spezifische Position und Reihenfolge der Schweißpunkte als auch durch die Zinkschichten der Stahlbleche beeinflusst. Den Abschluss der Arbeit bildet die Erarbeitung eines Bindungsmodells für das vorliegende Multi-Material-System. Die Erkenntnisse können zur Entwicklung zukünftiger Anwendungen des Metall-Ultraschallschweißens in Aluminium/Stahl-Strukturen mit mehreren Verbindungsstellen beitragen.
Article
This article presents the application of an adhesion promoting highly crosslinked ultrathin organic-inorganic hybrid layer applied to steel which promotes the subsequent joining process based on plastic deformation. The tensile shear results show that a significant increase of the bond strength between low-alloy steel (DC04) and aluminum (AW1050A H111), upon cold-pressure welding (CPW), could be achieved. Electrografting of an ultra-thin film of 1,2-bis(triethoxysilyl)ethane (BTSE) films on the steel surface was done from ethanolic solutions containing zinc ions. Based on surface spectroscopic analysis it is shown that silanol moieties present in the organosilane deposits can form stable chemical bonds with both the iron oxide covered steel and the aluminum oxide covered aluminum alloy. The successful modification of metal oxide surfaces with BTSE has been demonstrated via SEM-EDX, AFM, PM-IRRAS, and XPS measurements. In addition, electrochemical analysis of the BTSE:Zn films showed that the films lead to very good corrosion properties even at low thicknesses.
Article
Refill Friction Stir Spot Welding (Refill FSSW) allows welding dissimilar materials providing excellent bonding between both parts. On this work, a multi-scale analysis of load-controlled Refill FSSW was performed to analyze dissimilar AA6016-T4 and Zn-coated DX56D steel joints. These were produced using optimized process parameters and analyzed in both as-welded and bake-hardened conditions. During the process, fusion and subsequent dispersion of Zn favored the formation of a semi-solid structure characterized by an intense microsegregation. Therefore, incipient melting of Zn-rich phase followed by eutectic reaction was observed. The presence of liquid phases along the grain boundaries led to a complex relationship between mechanical properties, microstructure and processing variables. Joints with enhanced mechanical properties were produced by limiting the growth of intermetallic compounds (IMC) at the interface, which coupled with stir zone (SZ) strengthening due to Zn dispersion, led to less pronounceable secondary bending effects. The bake hardening process was also found to have a substantial influence on diffusion-dependent mechanisms and, consequently, on the final performance of the welded joint. The results highlighted a great potential of load-controlled Refill FSSW for producing high-strength dissimilar joints in short cycles, which is desirable for applications in the automotive industry.
Article
Conduction mode laser welding was employed to accomplish lap joining of a 6061 aluminium alloy with a galvanized interstitial-free steel in the aluminium-on-steel configuration, through laser induced reactive wetting of molten aluminium on solid steel. Orthogonal experimental design arrays (33) were used to evaluate different process parameter combinations and identify optimal processing parameters for achieving maximum joint strength. Detailed mechanical and microstructural characterizations of the joint interfaces were used to identify mechanisms for formation and growth of the intermetallic compounds (IMC), as well as joint failure on tensile loading. Inter-relationships between processing parameters, characteristics of the IMC layer, and joint strength were critically examined. Optimum IMC layer width and thickness for obtaining maximum joint strength for the present joint configuration was determined.
Article
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The tensile strength and energy absorption of dissimilar metal friction welds between 6061 aluminum alloy and SUS304 stainless steel at high rates of loading are determined using the split Hopkinson bar. Round tensile specimens machined from as-welded butt joints of 12 mm diameter are used in both static and impact tension tests. Friction welding is conducted using a brake type friction welding machine under two different welding conditions. The effects of welding parameters and loading rate on the tensile properties are investigated. It is demonstrated that the tensile properties are greatly affected by the welding conditions, and are slightly enhanced with increasing loading rate. Macroscopic observations reveal that the fracture mode of the friction welded butt joints varies with loading rate, depending on the welding conditions. Microhardness measurements are performed to examine the extent of the heat—affected zone (HAZ) across the weld interface. The slight enhancement in the tensile properties with increasing loading rate is primarily due to the strain rate dependence of the thermally- softened 6061 aluminum alloy base material.
Article
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The authors tried to butt-joint weld an aluminum alloy plate to a mild steel plate using friction stir welding. This study investigated the effects of pin rotation speed, position of the pin axis, and pin diameter on the tensile strength and microstructure of the joint. The main results obtained are as follows: Butt-joint welding of an aluminum alloy plate to a steel plate was easily and successfully achieved. The maximum tensile strength of the joint was about 86% of that of the aluminum alloy base metal. Many fragments of the steel were scattered in the aluminum alloy matrix, and fracture tended to occur along the interface between the fragment and the aluminum matrix. A small amount of intermetallic compounds was formed at the upper part of the steel/aluminum interface, while no intermetallic compounds were observed in the middle and bottom regions of the interface. A small amount of intermetallic compound was also often formed at the interface between the steel fragments and the aluminum matrix. The regions where the intermetallic compounds formed seem to be fracture paths in a joint.
Article
The formation of intermetallic reaction layers and their influence on mechanical properties was investigated in friction stir welded joints between a low C steel and both pure Al (99.5 wt.%) and Al-5 wt.% Si. Characterisation of the steel/Al interface, tensile tests and fractography analysis were performed on samples in the as-welded state and after annealing in the range of 200-600 • C for 9-64 min. Annealing was performed to obtain reaction layers of distinct thickness and composition. For both Al alloys, the reaction layers grew with parabolic kinetics with the phase (Al 5 Fe 2) as the dominant component after annealing at 450 • C and above. In joints with pure Al, the tensile strength is governed by the formation of Kirkendall-porosity at the reaction layer/Al interface. The tensile strength of joints with Al-5 wt.% Si is controlled by the thickness of the phase (Al 5 Fe 2) layer. The pre-deformation of the base materials, induced by the friction stir welding procedure, was found to have a pronounced effect on the composition and growth kinetics of the reaction layers.
Article
Low-carbon steel and aluminum Alloy 5052 sheets were diffusion welded using different conditions of time, temperature, and pressure in order to understand the kinetics of diffusion and the microstructure of the interface layer. High pressures accelerated intermetallic compound formation at the interface. The interface layer consisted of aluminum-rich brittle intermetallic compounds (FeAl3 and Fe2Al5), which made the joints brittle. In laser roll welding, steel and aluminum sheets in a lap-joint configuration are subjected to laser heating and immediate rolling for intimate contact. Laser heating provides high temperature in a short time for melting of the aluminum alloy and diffusion. It results in formation of a thin interface layer. When the temperature is above 1473 K (1200degreesC), formation of iron-rich (Fe-rich) intermetallic compounds (FeAl and Fe3Al) is encouraged. Travel speed and roll pressure were varied and resultant joints were characterized by optical microscopy, electron-probe microanalysis (EPMA), scanning electron microscopy (SEM), X-ray diffraction, and tensile shear testing. The laser roll welded interface layer contains brittle aluminum-rich (Al-rich) intermetallic compounds on the aluminum side and slightly ductile Fe-rich intermetallic: compounds on the steel side. As the travel speed increases, thinner interface layers are formed and the percentage of Fe-rich intermetallic compounds in them increases. This increases the shear strength of the joints from 11.0 to 55.9 MPa. Interface layers with a thickness of 4 to 5 mum, containing 25 to 40% Fe-rich intermetallic compounds, gave maximum shear strength.
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This paper summarizes work on finite element modeling of nugget growth for resistance spot welding of aluminum alloy to steel. It is a sequel to a previous paper on experimental studies of resistance spot welding of aluminum to steel using a transition material. Since aluminum alloys and steel cannot be readily fusion welded together due to their drastically different thermal physical properties, a cold-rolled clad material was introduced as a transition to aid the resistance welding process. Coupled electrical-thermal-mechanical finite element analyses were performed to simulate the nugget growth and heat generation patterns during the welding process. The predicted nugget growth results were compared to the experimental weld cross sections. Reasonable comparisons of nugget size were achieved. The finite element simulation procedures were also used in the electrode selection stage to help reduce weld expulsion and improve weld quality.
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The bonding of steel plate to aluminum liquid was conducted by using rapid solidification. The influence of diffusion time on interfacial structure was studied. The results showed that under the condition of 750°C for the temperature of aluminum liquid and 200°C for the preheat temperature of steel plate, when the diffusion time was shorter than 4.3 s, there was only Fe-Al solid solution at the interface. When the diffusion time was longer than 4.3 s, Fe-Al compound began to form at the interface. The relationships between the diffusion time t and the thickness of Fe-Al compound layer H are as follows: H=-9.72+2.62t-0.08t2(4.3 s≤t≤15 s) and H=2.79+0.647t-0.033t2 (t>15 s).
Article
In friction stud welding of a steel stud to an Al plate, even when an upsetting action was not introduced, intimate contact at the initial interface could be achieved. However, a crack roughly parallel to the initial interface was present within the softer Al plate, but not along the initial interface. A small amount of intermetallic compound indicated the crack did not result from embrittlement of the Al base metal, but was related to the torsion of the steel stud. This torsion crack could be the result of a combination of factors, including the following: 1) shift of actual friction interface from initial interface into the softer Al plate to form a secondary friction interface within the Al plate when strong interfa-cial bonding was established at the initial interface, 2) very long stopping stage time and, in particular, 3) the lack of joining pressure. When upsetting (24.8 MPa) was introduced manually, the debonding crack at the secondary friction interface could be closed at/after the moment of dead stop of the motor and the joint became so strong that most of the Al in the central bonded region adhered to the steel stud end after the tensile test.
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The method involves roll-bonding aluminum sheet to hot-dip aluminum-coated steel. The substrate is low carbon rimmed steel with nitrogen addition. Sheets with various cladding thicknesses 350 mm wide have been produced by a mill which consisted of a remodeled four-high reversing mill with 200 mm diameter work rolls, high-frequency induction heating equipment, and three pay-off reels. The mechanical properties, microstructures of the interface, adhesion of the coating layer and formability have been investigated.
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Today, continuing ecological pressure, energy and fuel problems, and global competition have led companies to search for new automobile designs. One of the main targets in studies for optimizing fuel-efficient and environmentally friendly automobile designs is to save material and weight without sacrificing quality and safety. One of the biggest advantages in using different materials is to reduce the construction weight as much as possible. The easiest and most economical solution to manufacture such constructions is to use lighter-weight materials. In the automotive industry, there has been an increasing use of light metals, such as aluminum, magnesium, and composite materials. The different materials can be welded by using the laser process, which is not possible with conventional manufacturing processes. Metal plates were compressed with a specially manufactured fixture with the steel on top of the aluminum to prevent root openings at the joint faces.