Content uploaded by Aldona Garbacz-Klempka
Author content
All content in this area was uploaded by Aldona Garbacz-Klempka on Sep 22, 2014
Content may be subject to copyright.
ARCHIVES
of
FOUNDRY ENGINEERING
DOI: 10.2478/afe-2014-0041
Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences
ISSN (2299-2944)
Volume 14
Issue 2/2014
79 – 84
ARCHIVES of FOUNDRY ENGINEERING Volume 14, Issue 2/2014, 79-84 79
Research on Technology of Alloyed Copper
Casting
St. Rzadkosz a*, M. Kranc b, A. Garbacz-Klempka a, M. Piękoś a, J. Kozana a, W. Cieślak a,
a AGH-University of Science and Technology, Faculty of Foundry Engineering, Reymonta 23, 30-059 Krakow, Poland
b Foundry Research Institute, Zakopiańska 73, Krakow, Poland
*Corresponding author. E-mail address: rzadkosz@agh.edu.pl
Received 31.03.2014; accepted in revised form 10.04.2014
Abstract
The work presents experiment results from the area of copper casting technology and chosen examples of alloyed copper. At present,
copper casting technology is applied in many branches of industrial manufacturing, especially in the sector of construction,
communications, arms and power engineering. Alloyed copper, containing slight additions of different elements and having special
physio-chemical properties, is used in a special range of applications. Copper technology and alloyed copper analyses have been presented,
these materials being used for cast manufacturing for power engineering. The quality of casts has been assessed, based on their
microstructure analysis, chemical content and the cast properties. During the research, special deoxidizing and modifying agents were
applied for copper and chosen examples of alloyed copper; also exemplary samples were tested with the help of metallographic analysis,
electrical conductivity and gaseous impurities research.
Keywords: Casting technology, Copper, Alloyed copper, Copper deoxidation, Heat treatment
1. Introduction
Modern industry, and especially the sector of power
engineering and electronics, sets very high standards for the
materials used there. They should be characterised by high
physical and functional properties, such as high electrical and
thermal conductivity, high strength, resistance to abrasion and
corrosion [1-4]. The basic material used for casts manufactured
for power engineering industry is copper. Its electrical
conductivity is the highest of all technical metals used in casting
(58MS). However, the mechanical properties of copper are
relatively low, that is why, often small additions of other elements
are introduced, which improve resistance to mechanical wear.
One of the copper alloys meeting high strength and functionality
requirements, and also characterised by good thermal and
electrical conductivity is chromium copper. [5]
Producing chromium copper casts is connected with
technological problems, especially during melting and liquid
metal preparation process. This is caused by unfavourable
properties of the material, among others significant differences in
melting temperature and specific gravity of the alloyed elements,
namely of Cu and Cr. But the greatest difficulties are caused by
their different oxygen affinity. [5]
Copper, having low activity in comparison to oxygen, creates
easily soluble oxides, while chromium creates Cr2O3, which is
insoluble and difficult to remove from the bath. It it the reason of
many defects lowering the cast properties, mainly through
creating discontinuities of structure, which has direct influence on
strength parameters; thermal and electrical conductivity. High
shrinkage and the proclivity to create slag which is difficult to
remove, causes the appearance of shrinkage cavities and slag
inclusions. A negative phenomenon resulting from high
chromium affinity for oxygen is a significant melting loss,
Unauthenticated | 10.248.254.158
Download Date | 9/22/14 10:40 PM
80 ARCHIVES of FOUNDRY ENGINEERING Volume 14, Issue 2/2014, 79-84
causing changes of chemical composition and physio-chemical
properties of the material melted. [7-8]
The difficult technology of melting and casting copper and
alloyed copper poses a set of challenges. Conducting research and
attempts of optimization of the melting technology and refining
the metal bath of copper and alloyed copper is indispensable for
achieving the highest levels of cast quality.
2. Researching copper casts
2.1. Researching copper melting and deoxi-
dation technologies
Copper casts were analysed from the perspective of melting
parameters and the efficiency of the influence of deoxidation
technology on the structure and properties of copper and copper
alloys. Also, the influence of modifying elements applied in the
refining agents was tested in order to obtain the optimal cast
properties, of among others, primary coils used in power
engineering. Microstructure changes and cast properties were
analysed. The most important copper properties are electrical and
thermal conductivity as well as mechanical properties of casts.
Next, the resistivity to corrosion was tested. The high values of
the above-mentioned properties are obtained by the proper
preparation of liquid metal, mainly by removing gaseous
impurities. Oxygen and hydrogen are gasses, which are absorbed
in copper. Their presence causes porosity (Fig. 1) and
unfavourable eutectic microstructure in casts. [6-8]
Fig. 1. Gaseous porosity in the copper cast section
Nowadays, to remove impurities a range of elements with
high affinity for oxygen is used, the most important of them being
phosphorus, lithium, magnesium, boron and beryllium. Electrical
conductivity was analysed with the help of SIGMA TEST 2.067,
a conductivity testing appliance, manufactured by Forster.
Strength parameters were tested on the machined samples cast
into ceramic moulds. The samples cut from the casts were
machined with Metasinex metalographic grinder, and next the
samples were polished using Montasupal machine. The polished
sections were etched by a mixture of acids. The microstructures
were observed with the help of metallographic microscope of
Nikon Eclipse LV150 type, with a magnification of 50x – 500x.
The exemplary results for copper deoxidized with different agents
are collated in Table 1.
Table 1.
Deoxidizing influence on the oxygen content and electrical
conductivity of copper
Agent Amount,%
Electrical
conductivity
MS
Oxygen content
O2 [ppm]
1
-
-
24
2260
2
-
-
30
1290
4
Logas
0,15
54
73
5
CuP12
0,2
48
98
6
CuP12
0,3
55
34
8
Li
0,05
54
39
9
P3
0,5
55
93
10
ODM2
0,3
55
16
11
Kupmod 2B
0,2
53
24
The analysis of deoxidizing treatments shows varied influence
of different agents. Phosphor introduced into the metal bath
causes reduction of copper oxide (I) 5Cu2O + 2P = P2O5 + l0Cu
[1], and in the final stage it increases the flowing power of the
liquid metal, which allows the slags, oxides and other impurities
to float to the surface of copper bath. This treatment makes it
possible to obtain a structure free from solid non-metallic
inclusions, which in an obvious way influences technological
properties of an alloy.
Introducing active lithium into the metal bath causes an
intense reaction with oxygen in the deoxidizing process
temperature, according to 2Li + O2 → Li2O + 136 kcal. Also, it
reacts with hydrogen, according to Li +1/2H2=:LiH + 22 kcal. The
created lithium oxide floats to the surface and passes into the slag,
but the lithium hydride solves into the bath and lowers the metal
properties [2]. Strong deoxidizing properties of boron are
connected with active binding of oxygen into an oxide. B2O3
oxide reacts with oxidized copper, creating 2Cu2O.B2O3 [6]. The
addition of 0,02% of beryllium is introduced into copper in CuBe
treatments. Copper deoxidized with beryllium does not show
porosity or surface defects, also it has high thermal conductivity
and increased strength. Microstructures characteristic for copper
in the original state, and also after melting and deoxidizing
process are presented in Figure 2.
Modern refining technologies for liquid metal that is designed
for special casts are more and more efficient and they make it
possible to obtain high purity material.
The effect observed in copper caused by different deoxidizing
or deoxidizing and modifying agents is distinctly visible. Also,
deoxidizing copper with the help of different complex formulas is
interesting because they influence the microstructure and oxygen
content to a significant degree.
Copper as matrix shows high values of electrical and thermal
conductivity and it is rather resistant to atmospheric corrosion,
however, pure copper has relatively low strength.
Well-deoxidized copper was used in further research for
preparing melts of alloyed copper. Within the scope of our
research, structure and properties of various kinds of alloyed
Unauthenticated | 10.248.254.158
Download Date | 9/22/14 10:40 PM
ARCHIVES of FOUNDRY ENGINEERING Volume 14, Issue 2/2014, 79-84 81
copper were investigated, including slight additions of, e.g.,
chromium, nickel, zirconium, silicon, beryllium, iron, titanium
and other elements.
a)
b)
Fig. 2. Original copper microstructure. Oxygen content 2600 ppm.
Dendritic crystallites of copper are visible (light) on the Cu-Cu2O
eutectic background (dark) (a). Copper microstructure after the
deoxidizing CuP treatment. Oxygen content 230 ppm. Dendritic
crystallites of copper are visible (light) and Cu-Cu2O eutectic
precipitates (dark) in the interdendritic regions (b). Magn. 200x.
Particular properties of some kinds of alloyed copper are
connected not only with its chemical content but also with the
alloy structure and the refining treatment applied. These alloys
show relatively low technological properties as well as a tendency
for many casting defects, which decrease their physio-chemical
properties.
A difficult technology of the above-mentioned materials
requires further research aimed at implementing new solutions
that would result in their increased quality. [9-12]
A lot of attention is paid to the problems of shaping structures
of the Cu-Cr, Cu-Cr-Zr, Cu-Ni-Si, Cu-Ni-Cr alloy types, among
others. Within the research framework, macro-and microstructure
of the alloys was analysed, as well as their intermetallic phases
and properties of the chosen alloys. The influence of deoxidation
processes, refining and modifications on the structure and
properties of the alloys was investigated. Protective and refining
slags were applied during melting, as well as characteristic micro-
additives, deoxidizing and modifying the structure of the chosen
alloys. Also, the properties were analysed in connection with the
heat treatment parameters. During the stock melting process, to
minimize the non-returnable losses, the argon protective
atmosphere was used or protective coating in the form of
charcoal, as well as protective-refining slags, with fluoride salts
were applied. The effects were assessed form the point of view of
changes in macro- and microstructure, changes of mechanical
properties and electrical conductivity. High conductivity copper
and electrolytic copper were used as metal stock.
2.2. Casting of chromium copper
Chromium copper is used for manufacturing welding
electrodes, electrical cable connectors, switches, collectors,
machine parts subject to intense abrasion under electric voltage
and high temperatures, heat exchangers, parts of blast-furnace
burners and blowpipes as well as parts of valves, nuclear reactors
and rocket engines. A characteristic feature of this material is its
relatively high electrical conductivity in comparison with other
copper alloys. A great advantage of chromium copper is its heat
workability, resulting from changeable solubility of chromium in
copper. The maximum solubility of chromium in copper in solid
state is in the temperature of 1076.6°C and it equals 0.89%. It
decreases in step with decreasing temperature, and, for example in
700°C – 0.07%, in 400°C it is 0.02% and it falls to 0.01% in room
temperature [5].
Table 2.
The influence of chromium additions on copper properties
Cr addition, %
Rm, MPa
A5, %
MS
HV
0
150,20
48
57
50
0,4
192,50
36,1
45,2
105
0,8
255,30
30,8
35,4
162
1,3
271,00
22,2
27,4
191
1,6
282,70
20,8
23
210
2,1
270,50
15
19,5
208
2,4
248,10
11,4
16
214
The attempts at obtaining chromium copper with optimal
functional properties are connected with examining the
deoxidation process. The tests were carried out on samples
obtained from alloys containing from 0.4 to 2.4 % of Cr (Table 2).
The electrical conductivity tests show that this property decreases
as the chromium content grows. During our investigations
different formulas were used, but in this paper the exemplary
results are shown for the formulas containing phosphor and boron
in Table 3 and in Figure 3-4.
Table 3.
The influence of deoxidation on electrical conductivity of
chromium copper
No.
Alloy Deoxidizer
Conductivity,
MS
Oxygen,
ppm
13
pure Cu
-
53
200
14
CuCr (1,4%Cr)
-
26
61
15
CuCr (1,4%Cr)
CuP (0,22%)
27
75
16
CuCr (1,8%Cr)
-
20
550
17 CuCr (1,8%Cr)
Desofin0,26
%
24 50
18
CuCr (1,8%Cr)
CuB2 1,5%
23
65
a)
b)
Fig. 3. The microstructure of chromium copper CuCr1.3, cast into
a ceramic mould. Magnification 500x. Etched with Mi 17 (a). The
microstructure of chromium copper CuCr1.3, deoxidized with
0.1% P, cast into a ceramic mould. Magnification 500x. Etched
with Mi 17 (b)
Unauthenticated | 10.248.254.158
Download Date | 9/22/14 10:40 PM
82 ARCHIVES of FOUNDRY ENGINEERING Volume 14, Issue 2/2014, 79-84
a)
b)
Fig. 4. The microstructure of chromium copper CuCr1.8, cast into
a ceramic mould. Magnification 500x. Etched with Mi 17 (a). The
microstructure of chromium copper CuCr1.8 with 1% CuB2
addition, cast into a ceramic mould. Magnification 500x. Etched
with Mi 17 (b)
2.3. The influence of zirconium additions
Among many modifying agents, there were analysed
additions of nucleation elements such as zirconium, boron,
titanium, vanadium, tungsten, as well as salt formulas of the
above-mentioned elements; used as modifying mixtures or
complex, modifying and oxidizing slags (Table 4). After
introducing zirconium additions its positive influence on the
structure of chromium copper can be observed.
At the same time, zirconium additions lower electrical
conductivity of chromium copper.
Table 4.
The conductivity of alloyed copper CuCr and CuCrZr
No.
Alloy
Conductivity, MS
1
pure Cu
50
2
CuCr (1,5%Cr
24
3
CuCr (1,5%Cr)
22
4
CuCr (2,2%Cr)
22,5
5
CuCrZr (2,2%Cr, 0,2%Zr)
20,5
6
CuCrZr (2,2%Cr, 0,2%Zr)
20
7
CuCrZr (2,2%Cr, 0,2%Zr)
18,5
8
CuCrZr (2,16%Cr, 0,2%Zr)
18,5
2.4. Heat treatment
Heat treatment is an important element of technological
process, and it is applied with the aim of obtaining casts with high
functional properties. This process consists of two parts: solution
heat treatment and ageing. During solution heat treatment the
casts are first held at the temperature of 20-50°C above the
solidus line, and next there is a quick cooling, most often in water,
with the aim of arresting chromium in the matrix. Soaking time
should be long enough to ensure that all of the chromium is
solved within the whole volume of the cast [7-8]. Solution heat
treatment causes lowering electrical conductivity to the value of
20–24 MS (Table 5).
The second stage of heat treatment is ageing. Is consists of re-
heating and air cooling. Ageing aims at precipitation of Cr from
supersaturated solution in the form of precipitates, which
significantly increase alloy strength. The process in conducted in
the temperature of 450-510°C. The heating takes from 1,5 to 4 h.
After the heat treatment, in the microstructure, there are spherical
chromium precipitates against the background of equiaxial,
recrystallized grains of chromium in copper solution; the hardness
increase after ageing results from dispersive chromium
precipitates in the grains.
Table 5.
The influence of ageing on properties
Time,
h
HB hardness
Conductivity, MS
Ageing temperature
Ageing temperature
0
600
500
450
400
600
500
450
400
0,1
41
41
41
41
20
20
20
20
0,2
42
43
42
41
21
21
21
21
0,5
100
130
62
43
24
22
22
23
1,0
90
120
115
122
34
28
24
38
2,0
80
105
120
130
37
35
32
40
4,0
70
100
115
122
40
40
37
41
8,0
60
100
110
117
40
41
39
41
3. The influence of silicon additions on
the CuNiSi alloy properties
A series of tests were conducted of the influence of nickel,
chromium and silicon additions on the structure and properties of
CuNi2SiCr copper. Next, the simultaneous influence of these
elements was researched, with a changeable amount of silicon
addition. The range of metals examined makes an interesting
group of copper matrix materials, with good physio-chemical
properties, and especially good mechanical features, accompanied
by good thermal and electrical properties. The influence of varied
chromium additions was analysed, within the range of up to
0.6%, as well as varied silicon additions of up to 2.2%.
Microstructure changes were analysed, as well as changes in
hardness and electrical conductivity. These characteristics are
typical of the group of alloys researched, and are decisive about
their application in engineering.
The research conducted showed, that the alloy hardness increases
significantly after introducing 0.6% chromium addition. It is
connected with the fact that in the microstructure there are
chromium phases appearing, located inside the grains at their
boundaries. Also, after introducing into deoxidized copper the
additions of chromium (0.8%) and nickel (2.1%), and casting the
initial samples, the varied additions of silicone were administered,
in the amounts ranging from 0.4 to 2.2%. The tests results were
compared with the test results for the initial sample (Table 6).
Table 6.
The influence of silicone additions on the CuNi2,1Cr0,6Si, cast
into metal mould
No.
Addition
Si, %
Rm, MPa HB A5, %
Conductivity,
MS
0
0
148,4
55
48,8
34
1
0,8
332,6
98
26,8
12,6
2
1,3
360,1
132
14,6
10,1
3
1,7
420,6
145
9,6
9
4
2,2
355,8
164
6
6,5
Unauthenticated | 10.248.254.158
Download Date | 9/22/14 10:40 PM
ARCHIVES of FOUNDRY ENGINEERING Volume 14, Issue 2/2014, 79-84 83
The microstructure was assessed on the basis of the chosen
micro sections. A coarse-grained macro-structure of equiaxial
grains was established, with clearly seen dendritic heterogeneity,
without any gas or shrinkage porosity.
For further investigations the CuNi2Si0,8 alloy was chosen.
The samples to be investigated were cast into metal and sand
moulds. The chosen samples were heat-treated, in order to
establish the possibility of dispersive strengthening of the cast
structure. The exemplary research results of macro-and
microstructures are collated in Figures 5 and 6.
a)
b)
c)
d)
Fig. 5. The microstructure CuNi2Si0,8 sand moulds (a, b), metal
moulds (c,d). Etched with Mi21, Magnification 50x (a,c), 500x
(b,d)
The microstructure of the alloys researched has dendritic
character with small precipitates of intermetallic phases in
interdendritic regions. In the case of metal moulds a greater size
reduction of primary structure is visible, and clearly compact
structure of the solid state. In the sand moulds slow solidification
is conducive to microporosity appearing at places.
After the heat treatment the heterogeneity disappears. There
are only grain outlines of solid state visible in the microstructure,
without the intermetallic phase precipitates from the interdendritic
regions. The changes in microstructure cause changes in strength
properties. The exemplary results of strength tests are collated in
Table 7.
a)
b)
c)
d)
Fig. 6. The microstructure CuNi2Si0,8 after the heat treatment,
sand moulds (a, b), metal moulds (c,d). Etched with Mi21,
Magnification 50x (a,c), 500x (b,d)
Table 7.
Mechanical properties of the CuNi2Si0,8 alloy
No.
Alloy
state
Conductivity,
MS
R
m
,
MPa A5, % HV
1
Lp
9,5
235
7,6
80
2
Lk
15
380
15,2
91
3
Lp-R6
16
320
3,2
118
4
Lk-R6
13
600
2,5
148
Based on the microscopic analysis it can be ascertained that
increasing the chromium content above 0.8% brings about
appearing the intermetallic phase precipitates, especially at the
boundary of intercrystalline grains. According to the data, it is the
original chromium phase. The addition of silicon and nickel
causes the fact that in the microstructure there is a clear, dendritic,
reduced in size structure of solid state, and in the interdendritic
region there may appear Ni2Si phases (Fig 5).
The results of a microstructure (Fig. 7), research conducted
with the help of scanning microscope Hitachi S-4200 coupled
with the system detecting and analysing EDS type of X-ray,
registered at the 15kV accelerating voltage showed - Table 8.
Unauthenticated | 10.248.254.158
Download Date | 9/22/14 10:40 PM
84 ARCHIVES of FOUNDRY ENGINEERING Volume 14, Issue 2/2014, 79-84
Fig. 7. The microstructure CuNi2Si0,8
Table 8.
The microanalysis of phases results for CuNi2Si0.8 alloy (Fig.8)
Element
Int. c/s
Atomic, %
Conc, %
Si
11.69
13.721
6.623
s1mar1
Mn
0.30
0.171
0.161
Fe
0.98
0.552
0.530
Ni
10.68
7.123
7.185
Cu
62.52
78.211
85.409
Si
26.95
27.673
15.041
s2mar2
Mn
0.49
0.275
0.293
Fe
2.60
1.481
1.600
Ni
38.85
35.818
40.685
Cu
28.56
34.283
42.160
Si
3.45
4.325
1.964
s2mar3
Mn
0.00
0.000
0.000
Fe
0.62
0.289
0.261
Ni
2.00
0.940
0.892
Cu
73.24
94.200
96.78
4. Conclusions
In the course of our research it was established that:
− the most important element in copper and alloyed copper
casting is creating the optimal conditions of melting and
efficient impurities extraction with the help of oxygen and
hydrogen. During melting, the possibility of contact of the
bath with any sources of impurities should be limited,
through applying proper protective atmosphere and
protective-refining slags.
− as stock materials pure kinds of copper should be used,
electrolytic copper and CuCr12 master alloy. The furnaces
used should enable fast melting of the metal stock, limiting
the possibility of polluting the metal. One of the ways of
checking the alloy quality is measuring electrical
conductivity of copper. Lower conductivity may indicate
pollution of the bath. An important element of refining
chromium copper is the deoxidation process conducted most
easily with deoxidizing master alloys, such as CuP, CuB2.
− applying modifying treatments causes slight improvement
in the degree of grain size-reduction,
− there is a clear increase in strength parameters and electrical
conductivity after the heat treatment of chromium copper,
− the research confirmed the engineering difficulties present
during the melting process – during the melting and pouring
the liquid metal into the moulds, the parameters must be
strictly observed,
− silicon additions in multicomponent materials on copper
matrix, also with chromium and nickel, clearly improve
technological properties, and, at the same time, their
strength properties.
References
[1] Górny, Z. (1995). Non-ferrous metals and their casting
alloys – melting, casting, structures and properties. Ed.
Foundry Research Institute, Krakow.
[2] Górny, Z. & Sobczak, J. (2001). Modern casting materials
based on non-ferrous metals. Ed. Foundry Research Institute,
Krakow.
[3] Dies, K. (1967). Copper and copper alloys in technique.
Springer Verlag ed., Berlin (in German).
[4] Kurski, K. (1967). Copper and copper technical alloys.
Silesian ed., Katowice.
[5] Rdzawski, Z. (2009). Alloyed copper. Ed. Silesian Univ. of
Technology, Gliwice.
[6] ]Rdzawski, Z., Ducki, K., Jabłońska, M. & Śmiglewicz, A.
(2010). Properties and microstructure of CuNi2Si1 alloy.
Rudy i Metale Nieżelazne. 55(2), pp.78-83.
[7] Rzadkosz, S., Kranc, M., Nowicki, P. & Piękoś, M. (2009).
Refining processes of selected copper alloys. Archives of
Foundry Engineering. 9 (2), pp. 29–34.
[8] Rzadkosz, S., Kozana, J. & Kranc, M. (2013). Researching
the influence of chemical composition and technological
parameters on the quality of copper alloys. Archives of
Foundry Engineering. 13 (spec. issue 1), pp. 153–158.
[9] Rzadkosz, S., Garbacz-Klempka, A. & Kranc, M. (2010).
Structural examinations of selected copper castings. Archives of
Foundry Engineering. 10 (spec. issue 1), pp. 435–440.
[10] Rzadkosz, S., Kranc, M., Garbacz-Klempka, A., Kozana, J.
& Piękoś, M. (2013). Investment casting technology applied
to copper alloys. Archives of Foundry Engineering. 13
(spec. issue 3), pp. 143–148.
[11] Rzadkosz, S., Kranc, M., Nowicki, P. & Piękoś, M. (2009).
Influence of refining operations on a structure and properties
of copper and its selected alloys. Archives of Metallurgy and
Materiale. 54(2) pp. 299–304.
[12] Drápala, J., Kubíček, P., Kostiuková, G. & Jopek, P. (2013).
Study of interaction between copper and melt of lead-free
solders. Metalurgija. 52(4), pp.509-511.
Unauthenticated | 10.248.254.158
Download Date | 9/22/14 10:40 PM
