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Ultrafine-grained (UFG) microstructures with an average grain size of 100–300 nm are achieved in solution-hardened AZ31 Mg–Al–Zn alloy prepared by friction stir processing equipped with a rapid heat sink. The mean hardness of the UFG region reaches ∼120Hv, which is more than twice as high as that of the AZ31 matrix. The grain refinement kinetics are analyzed and the results are self-consistent.
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Achieving ultrafine grain size in Mg–Al–Zn alloy
by friction stir processing
C.I. Chang,
X.H. Du
and J.C. Huang
Institute of Materials Science and Engineering, Center for Nanoscience and Nanotechnology,
National Sun Yat-Sen University, Kaohsiung 804, Taiwan, ROC
Department of Materials Engineering, Shenyang Institute of Aeronautical Engineering, Shenyang 110034, China
Received 27 February 2007; revised 6 April 2007; accepted 9 April 2007
Available online 10 May 2007
Ultrafine-grained (UFG) microstructures with an average grain size of 100–300 nm are achieved in solution-hardened AZ31 Mg–
Al–Zn alloy prepared by friction stir processing equipped with a rapid heat sink. The mean hardness of the UFG region reaches
, which is more than twice as high as that of the AZ31 matrix. The grain refinement kinetics are analyzed and the results
are self-consistent.
2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: Friction stir processing; Magnesium alloy; Ultrafine-grained microstructure; Grain refinement
Magnesium alloys are attractive for lightweight
structural applications in the transportation industry
because of their low density and high specific strength
and stiffness [1]. However, the symmetry of the hexago-
nal close-packed crystal structure has the limited num-
ber of independent slip systems, resulting in poor
formability and ductility near room temperature [2].
Fortunately, this can be resolved by the preparation of
an ultrafine-grained (UFG) structure which can bring
about sufficient room temperature ductility and even
superplasticity at high strain rates and low temperatures
[3–5]. Of the many techniques used for achieving UFG
microstructures, severe plastic deformation (SPD) has
been considered to be a promising route [6]. Matsubara
et al. [7] and Lin et al. [8] developed a two-stage extru-
sion plus equal channel angular pressing (ECAP) to fab-
ricate the UFG Mg alloys. The original coarse grain size
can be reduced to less than 10 lm after extrusion at
300 C and is further reduced to around 0.7 lm after
subsequent 8-pass ECAP at 200 C. However, the pro-
cessing is time consuming and the resulting materials
are in a rod shape of finite dimensions. Recently, an-
other trial was undertaken employing friction stir pro-
cessing (FSP) in which the localized heating was
produced by the friction generated between the rotating
tool and the workpiece. During this process, the mate-
rial undergoes intense plastic deformation at elevated
temperatures, resulting in significant grain refinement
via repeated dynamic recrystallization [9–13].
Successful FSP of Mg-based alloys refining the
microstructure of the alloys down to 1–5 lm have been
widely reported recently [14–23]. A UFG structure is
more easily achieved in precipitate-hardened Mg alloys
or Mg-based composites due to the effective pining effect
from the precipitates or added ceramic particles on the
grain boundaries [16–19]. For pure Mg or solute-
solution hardened Mg alloys (such as AZ31) with a
low content of alloying elements, it is difficult to achieve
a UFG microstructure due to the rapid growth kinetics
of the single-phase grains. In fact, FSP has so far failed
to refine the grain size of AZ31 to less than 0.5 lm
In this study, FSP combining rapid heat sink is used
to prepare UFG AZ31 Mg alloys. With just one single
FSP pass under effective cooling, the mean grain size
of the obtained specimens can be refined to an ultrafine
scale (100–300 nm) which is much finer than previous
SPD results [8,24–26] and is also the finest microstruc-
ture obtained by FSP in pure AZ31 alloys to date.
The material for this study was commercial AZ31 Mg
alloy with the chemical composition Mg–3.02Al–
1.01Zn–0.30Mn (in mass%). The as-received billet,
178 mm in diameter and 300 mm in length, possessed
nearly equiaxed grains around 75 lm in size. The
1359-6462/$ - see front matter 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Scripta Materialia 57 (2007) 209–212
average hardness value of the as-received AZ31 billet is
about 50H
. A tool with shoulder diameter, pin tool
diameter and length of 10, 3 and 3 mm, respectively,
was used to perform the FSP. A constant tool rotation
rate of 1200 rpm was adopted and the advancing speed
was 28–33 mm min
. A tool tilt angle of 1.5was used.
In order to obtain rapid heat sinking during FSP, a new-
ly efficient cooling system was designed, as presented
schematically in Figure 1. Based on our previous experi-
ence, we concluded that the primary heat loss during
FSP is made from the bottom of the pin to the back
plate beneath the sample. In order to transfer the heat
generated between the tool and the sample during FSP
as quickly as possible, a thin copper mould and liquid
nitrogen were used. Two tunnels were machined beneath
the surface of the copper mould, and the liquid nitrogen
can be immerged and flowed through.
Vickers hardness tests were conducted on the cross-
sectional plane using a Vickers indenter with a 200 gf
load for 10 s. The grain structures on cross-sectional
planes of the etched specimens were examined by optical
microscopy (OM) and scanning electron microscopy
(SEM). Microstructural and hardness characterizations
in this study are focused on the central and bottom parts
of the nugget zone, where the cooling rate is the highest.
The grain size was measured by Optimas
image analy-
sis software on the SEM micrographs. The grain size
near the top surface layer contacting the tool shoulder
is typically slightly larger due to the higher and longer
heat exposure and the inevitably slower cooling rate.
Figure 2 shows a cross-sectional view of the AZ31
FSP specimen containing the entire nugget zone after
one single FSP pass with an advancing velocity of
28 mm min
. The degree of refinement and the extent
of homogeneity of the final FSP microstructure are the
two aspects that are most noticeable. In Figure 3, the
grain structures in the AZ31 billets after one-pass FSP
with an advancing velocity of 28 mm min
, viewed at
low magnification, show a well-defined equaixed and
highly homogeneous nature. Figure 4 shows the micro-
structures with an advancing velocity of 33 mm min
at higher magnifications. All of these figures show that
the recrystallized fine grains are distributed homoge-
neously in the nugget region. Compared with other
SPD processes, such as extrusion, accumulated roll
bonding (ARB) or ECAP [8,24–26], the UFG micro-
structure obtained in the present study has clearer grain
boundaries and more uniform ultrafine grain sizes with-
out abnormal local grain growth. Such fine grains
appear to be fully recrystallized and do not belong to
subgrain structures with a ‘‘diffused’’ boundary nature.
Figure 5 shows the grain size distribution of the
33 mm min
specimen, which is summarized from
numerous SEM micrographs. It shows that the grain
sizes are mostly scattered from less than 100 to
500 nm, and more than 80% of the grains are refined
to less than 300 nm. The average grain size is typically
around 200–280 nm.
The ultrafine grains lead to pronounced hardening, as
demonstrated by the microhardness tests. The typical
microhardness values, H
, in the UFG zone of the
FSP specimens are depicted in Figure 6. The highest
reaches 128, with the mean hardness values around
, which is even higher than those observed in the
FSP AZ31 based composites [15,16,19]. In the AZ31
matrix away from the nugget, H
remains at around
50, indicating that the ultrafine grain structure in the
Pure AZ31 plate
Liquid nitrogen
Copper mould
Figure 1. Schematic drawing of the newly designed cooling system.
Figure 2. Photograph of the cross-section of the AZ31 FSP specimen
after a single FSP pass with an advancing speed of 28 mm min
Figure 3. SEM micrograph at low magnification showing the uniform
UFG structure in the AZ31 alloy after one-pass FSP at 28 mm min
with liquid N
Figure 4. SEM micrographs for the FSP AZ31 alloy at an advancing
speed of 33 mm min
210 C. I. Chang et al. / Scripta Materialia 57 (2007) 209–212
FSP nugget has strengthened the alloy 2.4-fold. Since
there is no twin observed in such fine grains, the harden-
ing is postulated to be a result of the UFG microstruc-
ture plus the retained matrix dislocations.
Some previous works have demonstrated that the
inability in preparing UFG microstructures in pure
Mg or Mg alloys with low content of alloying elements
by SPD, such as ECAP [27]. This is reasonable from the
physical point of view. Since the lattice and grain
boundary diffusion rates of Mg at working tempera-
tures, e.g. 300 C, are 4.7 ·10
and 2 ·
(where dis the grain boundary width),
respectively [28], both are much higher than the values
of 1.8 ·10
and 1.1 ·10
for Al
counterparts [28]. The achievement of ultrafine and uni-
form grain structures is accomplished by the combina-
tion of a high degree of SPD and a sufficiently rapid
heat release. To clarify the mechanism for the formation
of UFG, the relationship between the Zener–Hollomon
parameter, Z, and the average recrystallized grain size,
d,inlm, can be used because recrystallization proceeds
during the course of FSP. First, the strain rate and
working temperature of the nugget region experienced
during FSP need to be determined.
The material flow strain rate, _
e, during FSP may be
estimated by the torsion-type deformation as [22]:
where R
is the average material flow rate (assumed to
be about half of the pin rotational speed, namely 1200/
2 rpm), and r
and L
are the effective (or average) radius
and depth of the dynamically recrystallized zone. An
effective radius, r
, that can represent the average radius
for all parts of the materials inside this zone is assumed
to be equal to about 0.78 (or p/4 [29]) of the observed
zone boundary radius (1.7 mm in the current case). A
similar argument can also be applied to L
(0.78 ·
3 mm). Thus, _
ecan be calculated to be 36 s
the previous work [22], the relationship between Zand
din lm for the AZ31 alloy during FSP can be estimated
as: lnd= 9.0–0.27 ln Z, where Z¼_
eexpðQ=RT Þ,Qis the
activation energy for lattice diffusion (135 kJ mol
and RT has its usual meaning. In this case, with an aver-
age grain size of 0.3 lm and a strain rate of 36 s
the working temperature can be calculated to be
200 C. Note that the heating history during FSP in
Mg alloys without rapid cooling design is typically a
heating stage from room temperature to 400 Cover
30 s, followed by a cooling stage to room temperature
over 100s, as monitored by the inserted thermal couples
[22]. In the present FSP case under effective rapid cool-
ing, the heat generated during FSP can be conducted
away quickly, as reflected by the low calculated working
temperature of 200 C.
Watanabe et al. [30] reported that the grain size after
dynamic recrystallization, d
, was dependent on the ini-
tial grain size, d
. They proposed that the initial grain
size and the Z-parameter of Mg alloys could be related
by the following empirical equation:
ðdrec=dinit Þ¼103Z1=3¼103_
eexpðQ=RT Þ
Using the initial grain size of 75 lm and the estimated
working temperature of 200 C, the achievable grain size
after dynamic recrystallization based on Eq. (2) will be
about 250 nm, which is consistent with the current exper-
imental result. Here, precipitates that are often helpful to
stabilize the microstructure (the Zener pining) are not
available because the Mg
precipitates in the
AZ31 alloy dissolve into the matrix above 200 C[31].
Therefore, the low working temperature in the current
case is critical in achieving the UFG microstructure for
the AZ31 alloy. It is known that one-pass FSP can only
produce UFG structures along the weld line. In order to
achieve a wider area with such microstructures, it is nec-
essary to use multiple overlapping FSP using robot con-
trol. Experimental trials in the laboratory using multiple
FSP passes under liquid N
cooling ensure the same fine
grain structures. It is possible to scale up the current pro-
cessing route for possible engineering applications.
In short, the ultrafine grain size in solid solution-
hardened AZ31 Mg alloy is successfully achieved by
one-pass FSP coupled with rapid heat sink. The results
can be summarized as follows:
(1) With proper control of the working temperature his-
tory, an ultrafine and uniform grained structure can
be achieved. The grain boundaries are well defined
and the mean grain size can be refined to 100–
300 nm from the initial 75 lm by a single FSP pass.
(2) The ultrafine-grained structure can drastically
increase the microhardness from an initial 50 up
to 120H
, or an increment factor of 2.4.
200 300 400 500 600 700 800 900
Percentage, %
Average grain size, nm
Figure 5. Grain size distribution chart of the UFG microstructure in
FSP AZ31 alloys.
-4 -2 0 2 4
(UFG region)
Retreating Side
Vickers hardness, /Hv
33 mm/min
28 mm/min
Distance from weld center, d/mm
Figure 6. Microhardness (H
) profile measured on cross-sectional
planes for the FSP AZ31 alloy.
C. I. Chang et al. / Scripta Materialia 57 (2007) 209–212 211
(3) The estimated high strain rate and low working
temperature during FSP with rapid heat sink agree
self-consistently with the achieved ultrafine grains.
The authors gratefully acknowledge the sponsorship
from National Science Council of ROC under the
project NSC 94-2216-E-110-010. X.H.D. is grateful for
the post-doctoral sponsorship from NSC under contract
NSC 95-2816-E-110-001.
[1] K.U. Kainer, F. von Buch, in: K.U. Kainer (Ed.),
Magnesium Alloys and Technologies, DGM, Weinheim,
2003, p. 1.
[2] P.G. Patridge, Met. Rev. 118 (1967) 169.
[3] C.C. Koch, D.G. Morris, K. Lu, A. Inoue, Mater. Res.
Soc. Bull. 24 (1999) 54.
[4] J.R. Weertman, D. Farkas, K. Hemker, H. Kung, M.
Mayo, R. Mitra, Mater. Res. Soc. Bull. 24 (1999) 44.
[5] S.X. McFadden, R.S. Mishar, R.Z. Valiev, A.P. Zhilyaev,
A.K. Mukherjee, Nature 398 (1999) 684.
[6] T.C. Lowe, R.Z. Valiev (Eds.), Investigations and Appli-
cations of Severe Plastic Deformation, Kluwer, Dordr-
echt, 2000.
[7] K. Matsubara, Y. Miyahara, Z. Horita, T.G. Langon,
Acta Mater. 51 (2003) 3073.
[8] H.K. Lin, J.C. Huang, T.G. Landon, Mater. Sci. Eng. A
402 (2005) 250.
[9] R.S. Mishra, M.W. Mahoney, Mater. Sci. Forum 507
(2001) 357.
[10] R.S. Mishra, M.W. Mahoney, S.X. McFadden, N.A.
Mara, A.K. Mukherjee, Scripta Mater. 42 (2000) 163.
[11] J.Q. Su, T.W. Nelson, C.J. Sterling, Scripta Mater. 52
(2005) 135.
[12] Y.S. Sato, Y. Kurihara, S.H.C. Park, H. Kokawa, N.
Tsuji, Scripta Mater. 50 (2004) 57.
[13] Y.J. Kwon, I. Shigematsu, N. Saito, Scripta Mater. 49
(2003) 785.
[14] A.H. Feng, Z.Y. Ma, Scripta Mater. 56 (2007) 397.
[15] Y. Morisada, H. Fujii, T. Nagaoka, M. Fukusumi, Mater.
Sci. Eng. A 419 (2006) 344.
[16] Y. Morisada, H. Fujii, T. Nagaoka, M. Fukusumi,
Scripta Mater. 55 (2006) 1067.
[17] C.J. Lee, J.C. Huang, Mater. Trans. 47 (2006) 2773.
[18] C.J. Lee, J.C. Huang, P.J. Hsieh, Scripta Mater. 54 (2006)
[19] C.I. Chang, Y.N. Wang, H.R. Pei, C.J. Lee, J.C. Huang,
Mater. Trans. 47 (2006) 2942.
[20] F.Y. Hung, C.C. Shih, L.H. Chen, T.S. Lui, J. Alloys
Compd. 428 (2007) 106.
[21] J.A. Esparza, W.C. Davis, E.A. Trillo, L.E. Murr, J.
Mater. Sci. Lett. 21 (2002) 917.
[22] C.I. Chang, C.J. Lee, J.C. Huang, Scripta Mater. 51
(2004) 509.
[23] W. Woo, H. Choo, D.W. Brown, P.K. Liaw, Z. Feng,
Scripta Mater. 54 (2006) 1859.
[24] T.C. Chang, J.Y. Wang, C.M. O, S. Lee, J. Mater. Proc.
Techn. 140 (2003) 588.
[25] M.T. Perez-Prado, J.A. del Valle, O.A. Ruano, Scripta
Mater. 51 (2004) 1093.
[26] M. Eddahbi, J.A. del Valle, M.T. Perez-Prado, O.A.
Ruano, Mater. Sci. Eng. A 410 (2005) 308.
[27] A. Yamashita, Z. Horita, T.G. Langdon, Mater. Sci. Eng.
A 300 (2001) 142.
[28] H.J. Forst, M.F. Ashby, Deformation-Mechanism Maps,
Pergamon Press, Oxford, 1982, p. 21 and p. 44.
[29] A.J. Ardell, Metall. Trans. 16 A (1985) 2131.
[30] H. Watanabe, H. Tsutsui, T. Mukai, H. Ishikawa, Y.
Okanda, M. Kohzu, K. Higashi, Mater. Trans. 42 (2001)
[31] T.B. Massalski, H. Okamoto, P.R. Subramanian, L.
Kacprzak (Eds.), Binary Alloy Phase Diagrams, ASM
International, Materials Park, OH, 1990, p. 2444.
212 C. I. Chang et al. / Scripta Materialia 57 (2007) 209–212
... Many studies have conducted on FSP to further refine the grains in the stir zone through different methods [28][29][30][31][32]. C.I. Chang et al. used a thin copper mold and liquid nitrogen to realize a rapid heat sink, ultrafine grain size (about 100-300 nm) was obtained in AZ31 Mg alloy [29]. ...
... Many studies have conducted on FSP to further refine the grains in the stir zone through different methods [28][29][30][31][32]. C.I. Chang et al. used a thin copper mold and liquid nitrogen to realize a rapid heat sink, ultrafine grain size (about 100-300 nm) was obtained in AZ31 Mg alloy [29]. Y.M. Xie et al. processed a deformation-driven metallurgy (DDM) procedure on aluminum (Al) matrix composites, it was a process like the PLFSP. ...
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A novel material processing method, friction stir-surface mechanical attrition treatment (FS-SMAT) was conducted on pure magnesium plate and AZ31 magnesium alloy plate. Two types of stir tools, spherical stir tool and plane stir tool, are designed to process FS-SMAT to reduce the heat input compared with the traditional friction stir processing (FSP). Microstructure evolution during FS-SMAT and its effect on mechanicl property are investigated. These two stir tools have different effect on microstructure and mechanical property due to their specific shapes where different heat input and plastic deformation can be produced during FS-SMAT. Using a spherical stir tool, the grain size of pure magnesium plate was refined to 1.74 μm. The micro-hardness was improved from 40 HV to 63 HV. In contrast, after FS-SMAT with a plane stir tool, the grain size and micro-hardness of AZ31 magnesium alloy are 0.91 μm and 125 HV, respectively.
... The most typical use of FSP is to change the mechanical characteristics and microstructure of metallic components with thin surface layers regulated [46][47][48][49]. Homogeneity and densi cation of the FSP zone [50] and the elimination of manufacturing process aws [6] have both been shown to be effective methods for achieving signi cant microstructure re nement. Mehdi et al. [51] effective fabrication of an aluminium matrix composite (AMC) with nanoparticles of SiC and investigation of the microstructure and mechanical characteristics of the multi-pass FSP/SiC of AA6082-T6. ...
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This work is an attempt to fabricate aluminum (AA 5049) matrix composites (AMCs) reinforced with electrospun polyacrylonitrile (PAN) nanofibers and consisting of exfoliated graphite nanosheets (EGNS/PAN) by utilizing friction stir processing (FSP) to improve the mechanical characteristics of AA 5049. PAN and EGNS/PAN nanofibers were fabricated using the electrospinning technique. The average diameter of the electrospun PAN nanofibers is 195 ± 57 nm, and after EGNS incorporation is 180 ± 68nm. The incorporation of nanofiber reinforcement can enhance the mechanical characteristics of AA5049. The mechanical characteristics of AA5049 can be enhanced by the procedure of incorporating nanofibers, making them an ideal choice for applications in the automotive and aerospace industries. PAN and EGNS/PAN nanofiber reinforcement enhanced the hardness to 89 and 98 Hv, respectively. Also, the ultimate tensile strength was raised to 291 MPa and 344 MPa, respectively.
... However, we found CoreFlow TM has a potential of rapidly screening chemical compositions for high performance metallic wires and producing bespoke wires of theoretically unlimited lengths from the base material in a single step without extra external heat input. CoreFlow TM is believed to have similar effects on Mg alloys to what FSP can possibly do, such as grain refinement, second phase particle redistribution, texture modification and thus improving the mechanical properties [27][28][29][30][31][32]. To validate our hypotheses, as-received AZ31B plates were used for wire extrusion. ...
Full-text available
Mg-3Al-1Zn-0.2Mn (wt.%, AZ31B) wires were successfully produced from commercial hot-rolled plates in one step using the CoreFlowTM process, a novel stationary shoulder friction stir extrusion manufacturing. CoreFlowed AZ31B wires exhibited fine grains with a heterogeneous grain size distribution of 6.5 ± 4.2 μm along the transverse direction (TD) compared with the as-received material. A weakened texture was also obtained in CoreFlowed AZ31B, with basal poles aligned parallel to TD shift toward extrusion direction (ED) from wire center to edge. Periodic needle-like regions with a distinctively different orientation from neighbouring regions were observed at the sample edge. The engineering ultimate tensile strength (UTS) and elongation (El) of the CoreFlowed sample was 258 ± 5 MPa and 22.3 ± 0.8%. The El was significantly increased by 58% with equivalent UTS compared to the as-received material. Such a good combination of strength and ductility is attributed to grain refinement with heterogeneity, texture weakening, and homogeneously redistributed second phase particles.
... Recently, for preparation of magnesium alloys, Friction stir Processing (FSP) is being used as a promising approach for limitation of defects, homogenization and grain refinement. (Gandra et al. 2011, Nia et al. 2014) Moreover, the corrosion rate of Mg alloys can also be minimized during friction stir processing by producing surfaces strengthened by intermetallic phases (Chang et al. 2007). ...
Friction stir processing was done for surface modification of cast Magnesium-Aluminum alloy. The microstructural characteristics related to different phases of untreated cast Magnesium-Aluminum alloy, friction stir processed under different process parameters like rotational speeds at 380rpm and 545 rpm with 31.5 mm/min transverse speed with and without pure aluminum powder were investigated by Metallurgical microscopy at lower magnification and scanning electron microscopy at higher magnification. Pure aluminum powder of fine size (~19µm) was filled in the groove made at the center of the Magnesium-Aluminum alloy plate which cover 33 vol% of pure aluminum during friction stir processing. The electrochemical behavior of the Magnesium-Aluminum alloy, Friction stir processed Magnesium-Aluminum alloy without aluminum powder and Friction stir processed Magnesium-Aluminum alloy with pure aluminum powder were investigated using Potentiostat in 5 wt % sodium chloride (NaCl) solution.Surface of all conditions specimens were analyzed for the phases present on the surface by X-Ray Diffractometer (XRD) which revealed different peaks of α-Mg phase, β-phases (Mg17Al12) and Pure Aluminum . In friction stir processed Magnesium-Aluminum alloy double pass with aluminum powder all these peaks were observed. The electrochemical corrosion tests revealed the least corrosion rate (0.603 X 102mpy) for friction stir processed double pass with aluminum powder amongst all the tested specimens. The improvement in corrosion resistance of friction stir processed double pass with aluminum powder is because of more formations of the β-phases (Mg17Al12) and aluminum dissolved in the α-Mg phase.
... The pressing speed of the stirring head was 10 mm/s. In FSP, the grain size of the material is affected not only by the temperature and strain rate of the stir zone, but also by the cooling rate [13][14]. To reduce heat input and inhibit the excessive grain growth in the stir zone, some scholars carried out FSP experiments under water and found that the effect of material modification was significantly improved [15][16]. ...
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Friction stir processing (FSP) is a method to produce severe plastic deformation (SPD) of materials, which can well improve and optimize the microstructure and mechanical properties of Mg-Li alloy. In this paper, the FSP experiment of LA103Z Mg-Li alloy was conducted, and the influence of process parameters on the microstructure, tensile strength, elongation after fracture and fracture morphology of the material was studied. The microstructure of the Mg-Li alloy after FSP was significantly refined. With the increasing rotational speed of the stirring head, the grain boundaries became clearer and more distinguishable, and the low angle grain boundaries transformed into the high angle grain boundaries. With the increasing feed speed of the stirring head, the grain refinement became more pronounced, and the dispersion of α-Mg phase in the stir zone became more uniform and distributed at the grain boundaries. When the rotational speed and the feed speed of the stirring head were 800-1000 r/min and 100-200 mm/min respectively, the comprehensive performance of the Mg-Li alloy plate after FSP was expected to be optimal.
... Wrought Mg alloys could be formed into complicated shapes using high temperature forming like quick plastic forming and superplastic forming [19]. Previous endeavours in the direction of friction stir processing of AZ31 alloy have investigated the effect of prior heat treatment of the base material [20] and rapid heat sink [21] on the attained microstructure. Some of the experimental studies have probed the influence of the FSP tool parameters on the hardness of the AZ31 alloy [10,22]. ...
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The present study has expounded the effect of high temperatures on the tensile deformation of AZ31 magnesium alloy processed through a single-pass of friction stir processing (FSP). The major operation parameters, namely rotation speed and traverse speed of the FSP tool, were varied which led to extensive dynamic recrystallization (DRX) in the stir zone (SZ) engendering maximum grain refinement of about 63% as compared to the base metal. The lowest average grain size ∼ 5.66 μm was attained after a single FSP pass. Optical microscopy (OM) was followed by the uniaxial tensile tests at three different temperatures of 350, 400 and 450 ºC at a constant strain rate of 1.3 × 10⁻³/s. As the deformation temperature was raised, the flow stress reduced and led to appreciable increments in the processed material’s tensile elongations. The maximal elongation to fracture of 160% was observed in the friction stir processed (FSPed) sample possessing the finest grains.
The aim of this work is to develop magnesium matrix surface composite (MMSC) using the commercially pure magnesium (Mg) plate by friction stir processing (FSP) by adding b-tricalcium phosphate (TCP), Al and nano-Ca in various fractions. The as-processed MMSCs were also aged at 300°C for 60 min. The Mg 2 Ca phase is more thermally stable during the aging period than the b-phase. The maximum Young's modulus (E) was achieved in as-processed MMSC alloyed using Al and Ca and reinforced with TCP, and no significant deterioration was noted after aging. The hardness varied owing to the presence of b-phase, Mg 2 Ca and other phases. The as-processed MMSCs significantly improved the recovery of shape after plastic deformation than the pure Mg. Aging process further increases the recovery of shape and highest recovery was achieved in aged MMSC with Ca alloying and reinforced with TCP. The as-processed MMSCs reinforced with TCP and alloyed using Al and Ca demonstrated better corrosion resistance than the pure Mg. However, aged MMSCs are generally possess lower corrosion resistance than the Pure Mg. This study essentially showed how the FSP approach may impose a variable deterioration behavior on a static Mg characteristic to create controlled and customized biodegradable material.
The transportation sector is dominated by compression ignition (CI) engines. Their high power output, portability, efficiency, and overall prevalence in vehicles have resulted in their status as the largest petroleum consumer in any field. The present research aims to reduce petroleum reliance by using biodiesel as an alternative fuel to diesel in the CI engine. As a renewable, eco-friendly alternative to fossil fuels, biodiesel requires thorough investigation under operational conditions. The studies on the mixture of diesel and single biodiesel have been carried out for most available plant and animal sources. With the combination of two different biodiesel blends with diesel, very little work has been done, and much potential has been left in this region. This investigation involves examining a 50:50 mixture of biodiesels extracted from non-edible Pongamia pinnata and Neem plant seed oil to blend with diesel. An acid catalyst chemically treats both non-edible oils before transesterification and reduces their free fatty acid (FFA) content. The results show that blends B10 to B30 have better or adjacent values with conventional diesel in fuel consumption and thermal efficiency. With all biodiesel blends, CO and HC emissions were reported to be reduced than that of diesel. As biodiesel is constituted of more oxygen molecules it enables better combustion of fuel in the combustion chamber. The emission of NOX is slightly higher in biodiesel blends when compared with diesel. In conclusion, dual biodiesel blends up to 30%, could be used as substitute to diesel in a conventional CI engine without significantly altering the engine and compromising on the engine's performance and emissions.
Friction stir welding is a well known friction-based process, however many friction-based processes are there which were developed and modified depending upon the applications. FSW is the latest welding process which falls under the solid-state welding processes; it was developed by “TWI” in 1991. Since then, the process utilized for many metals and alloys for joining depending upon the application. Specifically, for the metallurgical incompatible metals and alloys, the process is very much effective. Friction welding is also one such process which is the most compatible with the dissimilar metal/alloys joining. Friction stir processing (FSP) is the process which is a single process which is used for many applications, based on the application's name of the FSP changes a bit. This article discusses the applications of friction-based processes.
Friction Stir Processing (FSP) is a surface modification approach by which the surface characteristics of materials can be improved. The materials that are subjected to the FSP can significantly alter the tribological well as the mechanical and metallurgical features by transforming a heterogenous microstructure to a more homogeneous and refined microstructure. In the present work, Zirconia (ZrO 2 ) and Boron Carbide (B 4 C) nanoparticles along with Graphene Nano platelets (GNP) were reinforced into the surface of the Aluminum AA6061-T6 alloy by FSP. Studies on the effects of the reinforcement on the mechanical and microstructural changes were carried out. As a result of the FSP, the reinforcement particles are uniformly dispersed on the substrate material’s surface. The zirconia/graphene reinforced aluminum composite (Al-ZrO 2 -GNP) has a significant improvement in hardness about 130% when compared to the as-received AA6061 alloy whereas the hardness of B 4 C/graphene reinforced composite has shown an increase of 87% when compared with the base metal. X-Ray Diffraction (XRD), Scanning Electron Microscope, and Field Emission Scanning Electron Microscope images reveal the presence of the reinforcement particles and microstructural changes in the friction stir processed aluminum alloys. The Tensile properties of the developed composites have also increased reasonably when compared to the base metal. Wear analysis was carried out and it was found that the B 4 C/graphene reinforced surface composite has higher wear resistance (40% increase) when compared to the ZrO 2 /graphene reinforced surface composite (22%increase).
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Mg-AZ31 based composites with 10-20 vol% nano-sized ZrO2 and 5-10 vol% nano-sized SiO2 particles were fabricated by friction stir processing (FSP). The clusters of the nano-ZrO2 and nano-SiO2 particles, measuring 180-300 nm in average, were relatively uniformly dispersed. The average grain size of the Mg matrixes of the composites varied within 2-4 mu m after four FSP passes. No evident interfacial product between the ZrO2 particles and Mg matrix was found during the FSP mixing ZrO2 into Mg-AZ31. However, significant chemical reactions occurred at the Mg/SiO2 interface to form the Mg2Si phase. The mechanical responses of the resulting nano-composites in terms of hardness and tensile properties of these Mg/nano-ZrO2 and Mg/nano-SiO2 composites were examined and compared. The grain refinements and the corresponding hardening mechanisms are also analyzed and discussed.
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The nano-sized SiO2 particles were added into the AZ61 Mg alloys via friction stir processing (FSP) to a volume fraction of 5-10%. After four FSP passes, the 10% composites had uniform dispersion of particles and grain size of 0.8 mu m. This composite exhibited high strain rate superplasticity, with a maximum ductility of 470% at 1 x 10(-2) s(-1) and 300 degrees C or 454% at 3 x 10(-1) s(-1) and 400 degrees C while maintaining fine grains less than 2 mu m in size.
Abstract The aim of this work is to compare the microstructure, the texture, as well as the thermal stability of an AZ31 Mg alloy processed via two different severe plastic deformation processing techniques, namely large strain hot rolling (LSHR) and equal channel angular pressing (ECAP). The microstructure was characterized by optical microscopy and the texture was measured both by X-ray diffraction and electron backscatter diffraction (EBSD). The microstructure obtained via LSHR has average grain sizes around 3 �m, but it is quite heterogeneous. Additionally, a well-defined basal texture develops. ECAP gives rise to a more homogeneous and slightly coarser microstructure, with an average grain size of 7�m and a shear type texture. The higher resistance of the extruded sample to secondary recrystallization after severe post-deformation annealing is attributed to a texture effect. © 2005 Elsevier B.V. All rights reserved. Keywords: Magnesium; Severe plastic deformation; Equal channel angular extrusion; Large strain rolling
Dynamic recrystallization (DRX) behavior was systematically examined in two commercial Mg-Al-Zn alloys in order to clarify the relationship between deformation conditions and the resulting microstructure. The materials were deformed by upset forging at temperatures ranging from 473 to 673 K at an initial strain rate of 3.3× 10-2 s-1. Grain refinement was observed during deformation. It was found that the dynamically recrystallized grain size decreases with an increasing Zener-Hollomon parameter and/or a decreasing initial grain size. A phenomenological constitutive equation was developed in order to provide a guideline for the control of the grain size of hot deformed AZ61 alloy.
The development of low temperature superplasticity and texture is examined in an AZ31 Mg alloy after extrusion and processing by equal-channel angular pressing (ECAP). It is demonstrated that an elongation of ∼460% may be attained at a temperature of 150 °C, equivalent to 0.46 Tm where Tm is the absolute melting temperature. This result demonstrates the potential for achieving low temperature superplasticity. The experimental results show that the mechanical properties of the alloy are influenced by the different textures present after extrusion and after extrusion and subsequent processing by ECAP.
Friction-stir processing (FSP) induces significant texture variations in magnesium alloys. Diffraction peak intensities measured using spatially-resolved neutron-diffraction scanning provide the quantitative changes in the texture across the processing line. The relationship between the texture distribution and the tensile behavior of a FSP AZ31B Mg alloy is discussed.
Magnesium alloy is the lightest metal that can be employed for structural use. However, it is commonly recognized that magnesium possesses poor formability at room temperature because of its hexagonal closed packed structure. It is then highly desirable to refine the grain structures in order to apply superplastic forming technique. Among the hot forming processes for refining grain structure, the most practical technique is rolling combined with suitable heat treatment which can be scaled for large bulk sheet or plate sample fabrication. Results of grain refining by this processes are presented. Processed AZ31 was studied with optical and transmission electron microscopy as well as X-ray diffraction. Tensile tests at room and high temperatures were also performed using the Instron machine, and their properties are correlated with the microstructures.