Field of the Invention
[0001] The present invention relates to the field of copper alloy manufacturing, and in
particular to a softening-resistant copper alloy, a preparation method thereof and
applications thereof, belonging to the technical field of novel alloy materials.
Description of the Prior Art
[0002] Welding is a manufacturing technology that joins metals or other materials by heating,
at high-temperature or under high-pressure.
[0003] At present, there are mainly three methods for joining materials: fusion welding,
pressure welding and braze welding. During the welding process, a workpiece and the
solder are molten to form a molten area, and the molten pool is cooled and solidified
to form a connection between the materials. During this process, it is usually necessary
to apply a pressure. There are a variety of sources of energy for welding, including
gas flame, electric arc, laser, electron beams, friction, ultrasonic waves and the
like. Before the end of the 19
th century, the only welding process was metal forging already used by the blacksmith
for hundreds of years. The earliest modern welding techniques appeared at the end
of the 19
th century, first arc welding and oxygen-fuel welding and then resistance welding. In
the early 20
th century, as the first and second world wars happened, the demand for cheap and reliable
connection methods for military materials was extremely high, so that the development
of the welding techniques was also facilitated. With the extensive use of welding
robots in industrial applications, researchers are still studying the nature of welding
and continuing to develop new welding methods to further improve the welding quality.
[0004] Throughout the development of modern welding techniques and equipment, the automation
of welding equipment and the improvement of production efficiency are major driving
forces for the development of welding techniques. Since copper alloys are good in
strength and electrical performance, many consumables in the welding equipment use
copper and its alloys, for example, electrode caps in resistance welding, conductive
nozzles in braze welding and the like. With the use of modern automatic equipment,
particularly welding robots, the requirements on copper alloys used for conductive
nozzles, electrode caps and the like, particularly their ability to resist against
high-temperature softening, are increasing. During the welding process, due to the
need for heating, high temperature or high pressure, the actual copper alloy consumables
are often used at a very high temperature, so the requirements on the copper alloys
are also increasing. In other fields, there are also examples of using materials in
a high-temperature environment. For example, electrified railway contact lines are
also to be used for a long period of time at a relatively high temperature. Therefore,
it is urgent to develop a copper alloy with better high-temperature softening resistance.
[0005] At present, the actually popularized products, such as conductive nozzles for welding
equipment, electrode caps and electrified railway contact lines, mostly use conventional
copper chromium zirconium alloy (e.g., American Standard C18150) which has been widely
applied in the above fields due to its excellent strength and electrical conductivity.
However, with the gradual increase of the level of mechanical automation, a strategy
of replacing manpower with machines basically comes into use in welding and other
industries, in order to improve the production efficiency. This change will present
new requirements on the raw material performances of parts, among which high-temperature
softening resistance comes first. This is because the wear of the parts will be less
if the high-temperature softening resistance is better. Accordingly, the service life
of the parts is prolonged and the precision during the welding process is also improved.
At present, the conventional copper chromium zirconium alloy (e.g., American Standard
C18150) has a high-temperature softening resistance that a hardness loss value is
above 15% below 580°C. This already cannot meet the development requirements of the
related industries. Therefore, improving the high-temperature softening resistance
of materials becomes an urgent need at present.
Summary of the Invention
[0006] An objective of the present invention is to provide a copper alloy with better high-temperature
softening resistance, in order to solve the problem that the high-temperature softening
resistance of the existing copper chromium zirconium alloy is to be improved.
[0007] To solve the technical problem, the softening-resistant copper alloy, comprises:
0.1%-1.0 wt% Cr, 0.01% -0.2 wt% Zr, 0.01%-0.10 wt% Si, and ≤0.10 wt% Fe, and with
the remaining of copper and inevitable impurities, characterized in that, the microstructure
of the copper alloy comprises: an elemental Cr phase, a Cu
5Zr phase, and a Cr
3Si phase. In the copper alloy of the present invention, the high-temperature softening
resistance effect of the material is improved by adding a proper amount of Si to form
a compound Cr
3Si, and the strength and the high-temperature softening resistance of the material
are further improved by strengthening the copper alloy matrix by the elemental Cr
phase and the Cu
5Zr phase, using the synergistic effect of the Cr
3Si phase and the elemental Cr phase and by controlling the content of the impurity
Fe.
[0008] The effects of the alloy elements and the related precipitated phases in the copper
will be described below.
[0009] The solid solubility of chromium in copper at the normal temperature is very small
(less than 0.5%), but the solid solubility of chromium in copper at a high temperature
is relatively high (up to 0.65%). Therefore, chromium is able to realize precipitation
strengthening and used as a main strengthening element in the copper alloy of the
present invention. In the copper alloy, dispersion strengthening phase particles of
the elemental Cr can be obtained by heat treatment, so the copper matrix is strengthened.
While strengthening the copper matrix, Cr will also form a compound Cr
3Si with Si solid-dissolved in the copper matrix. Researches have indicated that the
compound Cr
3Si is a compound phase that is stable at a high temperature and will not be dissolved
even at a high temperature of 800°C, so that the high-temperature softening resistance
is very high. The content of chromium in the copper alloy of the present invention
is 0.1% to 1.0%. If the content of chromium is less than this range, Cr and Si are
difficult to form Cr
3Si or can form a small amount of Cr
3Si so that the desired effect cannot be achieved; however, if the content of chromium
is greater than this range, chromium will be largely precipitated to form a strengthening
phase, so that the chromium will be largely accumulated at the crystal boundary and
the plasticity of the material is damaged.
[0010] Zirconium has a certain solubility in the copper alloy. By adding zirconium, the
recrystallization temperature of the copper matrix can be increased and the high-temperature
softening resistance of the copper alloy can be thus improved. Moreover, zirconium
and copper will form an intermediate compound Cu
5Zr, strengthening the copper matrix and also improving the electrical performance
of the copper alloy. The content of zirconium in the copper alloy of the present invention
is 0.01% to 0.2%. If the content of zirconium is less than this range, the desired
effect cannot be achieved; however, if the content of zirconium is greater than this
range, although the alloy can be strengthened, the electrical conductivity of the
alloy will be greatly reduced and the overall performance of the alloy will be influenced.
[0011] Silicon has a certain solid solubility in copper. Silicon can strengthen the copper
alloy matrix, but will greatly influence the electrical conductivity of copper and
will greatly reduce the electrical conductivity of the copper alloy. However, when
there is a proper amount of chromium in the copper alloy, silicon and chromium can
form a Cr
3Si phase compound. Since Cr
3Si is a precipitated phase, the electrical conductivity of the material can be greatly
improved after Cr
3Si is precipitated, so that the overall performance of the copper alloy is positively
influenced. The content of silicon in the copper alloy of the present invention is
0.01% to 0.1%. If the content of silicon is less than this range, the Cr
3Si phase formed in the copper alloy is not enough to achieve the desired effect; however,
if the content of silicon is greater than this range, although sufficient Cr
3Si phase can be formed, the precipitation of Cr will be greatly reduced and the overall
performance of the alloy will thus be influenced.
[0012] In the present invention, Fe is controlled as an impurity element. A small amount
of Fe facilitates the improvement of strength, but a too high content of Fe will affect
the electrical conductivity. Therefore, in the present invention, the content of Fe
is controlled below 0.01wt%.
[0013] The elemental Cr phase, the Cu
5Zr phase and the Cr
3Si phase in the microstructure of the copper alloy of the present invention have the
following effects.
[0014] As a primary phase of alloy, the Cr
3Si phase is generated during the liquid state and crystallization process of the alloy,
is stable in both structure and performance at a high temperature, and will not be
dissolved at 800°C while still maintaining its original structure. Accordingly, the
high-temperature softening resistance of the alloy can be greatly improved. As one
of main precipitation strengthening phases in the copper alloy of the present invention,
the Cu
5Zr phase is completely dissolved in the copper matrix to form a supersaturated solid
solution after solid solution treatment on the alloy, then precipitated out of the
copper matrix during the subsequent aging process and dispersedly distributed in the
alloy. After the Cu
5Zr phase is precipitated, a pinning effect on the dislocation is achieved, so that
the strength and hardness of the copper matrix are improved. Meanwhile, due to the
precipitation of the Cu
5Zr phase, the copper matrix becomes pure, the inhibition of electrons is reduced,
the electrical resistivity is reduced, and the electrical conductivity is thus greatly
improved. Another strengthening phase in the copper alloy of the present invention
is the elemental Cr phase. Similarly to the generation principle of the Cu
5Zr phase, the elemental Cr phase is also generated during the heat treatment of the
alloy. The elemental Cr phase is completely dissolved in the copper matrix to form
a supersaturated solid solution after the solid solution treatment, then precipitated
out of the copper matrix during the subsequent aging process and dispersedly distributed
in the alloy. As the most important strengthening phase in the alloy of the present
invention, the elemental Cr phase plays a crucial role in the improvement of the strength
of the alloy.
[0015] The three main strengthening phases in the alloy of the present invention exist independently
and have a certain dependence. The addition of a suitable proportion of alloy elements
to form a rational proportion of phases is very important for the performance of the
alloy. The elemental Cr phase, as the main strengthening phase in the alloy, plays
a leading role in the strengthening of the alloy; the Cr
3Si phase, as a high-temperature phase, plays a leading role in the high-temperature
softening resistance of the alloy; and, the Cu
5Zr phase, as another moderate strengthening phase, can strengthen the alloy and can
also increase nucleating particles, refine the elemental Cr phase and the Cr
3Si phase and allow the elemental Cr phase and the Cr
3Si phase to be dispersedly distributed, so that both the strength and the high-temperature
softening resistance are further improved.
[0016] Preferably, the elemental Cr phase and the Cr
3Si phase satisfy the following relationship:
if the weight of the elemental Cr phase is X and the weight of the Cr
3Si phase is Y, then 0<X/Y<20.
[0017] When the strengthening phases satisfy this ratio, both the high-temperature softening
resistance and the strength of the copper alloy will be greatly improved. When the
ratio of the strengthening phases is greater than 20, the amount of the Cr
3Si phase in the alloy is very small. As a result, the high-temperature softening resistance
of the alloy cannot satisfy the requirements.
[0018] Preferably, the copper alloy further comprises: 0.0001% - 0.10 wt% Mg. By providing
magnesium in this proportion, magnesium can be dissolved in the copper matrix to strengthen
the copper alloy, with little influence on the electrical conductivity of the copper
alloy; and meanwhile, oxygen in the copper alloy can be effectively eliminated, so
that the content of oxygen in the copper alloy is reduced and the quality of the material
is improved.
[0019] Preferably, the copper alloy further comprises: 0.01% to 2.5 wt% of any one or more
of Co, Zn, Mn, Sn and Nb, and their total amount does not exceed 3.5 wt% of the copper
alloy. By adding the above alloy elements in the copper alloy, solid solution strengthening
can be realized, the recrystallization temperature of the material is increased, and
the softening temperature of the material is further increased. However, the amount
of addition of the above alloy elements should not be too large, otherwise the electrical
conductivity of the material will be greatly reduced.
[0020] Preferably, the softening temperature of the copper alloy is greater than or equal
to 580°C. When the softening temperature of the copper alloy is greater than or equal
to 580°C, the demands for various welding processes by the material can be greatly
increased, and the service life of the welding material is prolonged.
[0021] The softening temperature of the copper alloy is determined by tests. Generally,
when the material is kept at a certain temperature for 2 hours and then cooled in
water, the hardness of the treated material is tested. If the hardness loss of the
treated material is within 15%, it is considered that the material is not softened
at this temperature; or otherwise, it is considered that the material is softened.
The softening temperature of the conventional copper chromium zirconium alloy is about
550°C. If the conventional copper chromium zirconium alloy is kept at 550°C for 2
hours and then cooled in water, the hardness loss of the treated material is about
13% to 15%; and, if the conventional copper chromium zirconium alloy is kept at 580°C,
the hardness loss is far greater than 15%.Therefore, the softening temperature of
the conventional copper chromium zirconium alloy is 550°C .However, for the copper
alloy of the present invention, under the above experimental conditions, the hardness
loss of the material at 550°C is 4% to 8%, and the hardness loss of the material at
550°C does not exceed 10%. Therefore, the softening temperature of the copper alloy
of the present invention is greater than or equal to 580°C.
[0022] The present invention further discloses a method for preparing copper alloy, the
method comprising: alloying and refining-casting into an ingot-ingot sawing, heating
and extruding-solid solution heat treatment-stretching and drawing-aging heat treatment-straightening
and finalizing;
characterized in that, the casting temperature for the alloying treatment and the
covered refining is 1150°C to 1350°C; the temperature for the hot extrusion is 850°C
to 950°C; the temperature for the solid solution treatment is 850°C to 1000°C; the
cooling medium is water, and the cooling rate is 10°C/min to 150°C/s; the machining
rate of the cold stretching and drawing is 20% to 60%; the temperature for the aging
heat treatment is 420°C to 520°C; and the copper alloy is insulated for 2h to 4h.
In the material produced by this production process, the elemental Cr phase, the Cu
5Zr phase and the Cr
3Si phase are rational in size and more dispersive in distribution, so that various
performances of the copper alloy of the present invention are improved.
[0023] The present invention discloses a method of using the copper alloy, the method comprising
using the softening-resistant copper alloy in contact lines and welding materials..
[0024] Compared with the prior art, the present invention has the following advantages:
- 1. In the copper alloy of the present invention, the high-temperature softening resistance
effect of the material is improved by adding a proper amount of Si to form a compound
Cr3Si, and the strength and the high-temperature softening resistance of the material
are further improved by strengthening the copper alloy matrix by the elemental Cr
phase and the Cu5Zr phase, using the synergistic effect of the Cr3Si phase and the elemental Cr phase and by controlling the content of the impurity
Fe.
- 2. Since the softening temperature of the copper alloy of the present invention is
greater than or equal to 580°C, the requirements on various performances of the copper
alloy in the fields of welding and contact lines are better satisfied.
Detailed Description of the Preferred Embodiment
[0025] To enable a further understanding of the present invention content of the invention
herein, refer to the detailed description of the invention and the accompanying drawings
below:
To avoid repetition, the technical parameters involved in the specific implementations
will be uniformly described below, and will not be repeated in embodiments.
wt%: weight percentage.
%IACS: used for representing the electrical conductivity of a metal or alloy (reference
to the standard annealed pure copper).The electrical conductivity of the standard
annealed pure copper is generally defined as 100%IACS, i.e., 5.80E+7(1/Ω·m) or 58(m/Ω·mm2). The value is the ratio of the resistivity (in volume or mass) specified by the
International Annealed Copper Standard to the resistivity of the sample in the same
unit multiplied by 100.
HR: Rockwell hardness.
Rem.: remaining amount.
Embodiments 1-20
[0026]

[0027] The finished softening-resistant copper alloy products in Embodiments 21-40 of the
present invention were obtained by preparing materials according to the components
and their mass percentages of the softening-resistant copper alloy in Embodiments
1-20 in Table 1, then smelting, casting into an ingot, processing and molding, heating
to 450°C to 520°C at an average heating rate of 1 °C/min to 30°C/min and holding this
temperature for 2h to 4h (Embodiments 21-40 where the finished products were obtained,
corresponding to the components and their mass percentages of the softening-resistant
copper alloy in Embodiments 1-20, respectively).
[0028] The microstructures of the finished softening-resistant copper alloy products in
Embodiments 21-40 were analyzed. The results of analysis are shown in Table 2.
[0029] In the softening-resistant copper alloys in Embodiments 21-40 of the present invention,
microscopic intermediate phases and elementary substances with different properties
are formed by various added alloy elements and a particular aging process, and the
microscopic phases are dispersedly distributed in the copper matrix, so that various
performances of the copper alloys are effectively improved. The related phases and
their contents in the softening-resistant copper alloys in Embodiments 21-40 of the
present invention are shown in Table 2.
Table 2: Intermediate phases and their contents in the softening-resistant copper
alloys in Embodiments 21-40 of the present invention
Embodiment Second phase |
Cr(wt%) |
Cr3Si (wt%) |
Cu5Zr (wt%) |
Embodiment 21 |
0.0525 |
0.0975 |
0.0495 |
Embodiment 22 |
0.1045 |
0.0975 |
0.072 |
Embodiment 23 |
0.0435 |
0.1755 |
0.8505 |
Embodiment 24 |
0.119 |
0.143 |
0.1215 |
Embodiment 25 |
0.154 |
0.169 |
0.1305 |
Embodiment 26 |
0.224 |
0.169 |
0.207 |
Embodiment 27 |
0.2375 |
0.2275 |
0.216 |
Embodiment 28 |
0.251 |
0.247 |
0.2655 |
Embodiment 29 |
0.1525 |
0.4225 |
0.27 |
Embodiment 30 |
0.337 |
0.299 |
0.324 |
Embodiment 31 |
0.486 |
0.182 |
0.3555 |
Embodiment 32 |
0.3115 |
0.4355 |
0.3825 |
Embodiment 33 |
0.0312 |
0.624 |
0.4095 |
Embodiment 34 |
0.469 |
0.403 |
0.5175 |
Embodiment 35 |
0.609 |
0.273 |
0.5715 |
Embodiment 36 |
0.7855 |
0.1235 |
0.6705 |
Embodiment 37 |
0.7195 |
0.2015 |
0.6615 |
Embodiment 38 |
0.5155 |
0.5135 |
0.792 |
Embodiment 39 |
0.419 |
0.533 |
0.7965 |
Embodiment 40 |
0.4365 |
0.6305 |
0.873 |
Comparison embodiment |
0.92 |
- |
0.2295 |
[0030] The materials were prepared according to the components and their mass percentages
of the softening-resistant copper alloy in Embodiments 1-20 in Table 1, and then treated
under the following conditions: the casting temperature for the alloying treatment
and the covered refining was 1150°C to 1350°C, the temperature for hot extrusion was
850°C to 950°C, the temperature for solid solution treatment was 850°C to 1000°C,
the cooling medium was water, the cooling rate was 10°C/min to 150°C/s, the machining
rate of cold drawing was 20% to 60%, the temperature for aging heat treatment was
420°C to 520°C, and the temperature holding time was 2 h to 4 h. Finally, the finished
softening-resistant copper alloy bar products in Φ8 in Embodiments 41-60, corresponding
to the components and their mass percentages of the softening-resistant copper alloy
in Embodiments 1-20, were obtained by finishing.
[0031] The tensile strength, hardness, electrical conductivity and softening temperature
of the softening-resistant copper alloy bars in Embodiments 41-60 of the present invention
were tested by methods specified by the related national and industrial standards.
The test results are shown in Table 3.The room-temperature tensile tests were carried
out by an electronic universal mechanical property testing machine according to
GB/T228.1-2010 Metal Material Tensile Test Section 1: Test at Room Temperature. The samples were
circular cross-section proportional samples having a proportional coefficient of 5.65.The
electrical conductivity tests were carried out according to
GB/T228.1-2010 Test Methods for Electrical Performance of Electric Wires and Cables Section 2: Metal
Material Resistivity Test. As the test instrument, a ZFD microcomputer bridge DC resistance
tester was used, and the samples were 1000 mm in length. The electrical conductivity
was represented by %IACS. The hardness tests were carried out by a hardometer according
to
GB/T 230.1-2009 Metal Material: Rockwell Hardness Test.

[0032] In the present invention, the tensile strength is higher than or equal to 470MPa,
the Rockwell hardness is above 75, and the electrical conductivity is above 75%IACS.
[0033] Embodiments 61-80 The components and their mass percentages of the softening-resistant
copper alloys in Embodiments 61-80 are the same as those in Embodiments 41-60. That
is, the materials were prepared according to the components and their mass percentages
of the softening-resistant copper alloy in Embodiments 1-20 in Table 1, and then treated
under the following conditions: the casting temperature for the alloying treatment
and the covered refining was 1150°C to 1350°C, the temperature for hot extrusion was
850°C to 950°C, the temperature for solid solution treatment was 850°C to 1000°C,
the cooling medium was water, the cooling rate was 10°C/min to 150°C/s, the machining
rate of cold drawing was 20% to 60%, the temperature for aging heat treatment was
420°C to 520°C, and the temperature holding time was 2h to 4h. Finally, the finished
softening-resistant copper alloy bar products in Φ8 were obtained by finishing.
[0034] The softening temperature tests were carried out by methods specified by HB5420-89
Copper and Copper Alloys for Resistance Welding Electrodes and Auxiliary Devices.
The test temperature was 580°C. The test results are shown in Table 4.
Table 4: Test results of the softening temperature of the softening-resistant copper
alloy bars in Embodiments 61-80 of the present invention
Embodiment |
Original hardness (HRB) |
580°C |
Hardness after softening (HRB) |
Softening rate (%) |
Embodiment 61 |
75 |
70 |
6.67 |
Embodiment 62 |
77 |
71 |
7.79 |
Embodiment 63 |
75 |
69 |
8 |
Embodiment 64 |
78 |
73 |
6.41 |
Embodiment 65 |
78 |
72 |
7.69 |
Embodiment 66 |
80 |
75 |
6.25 |
Embodiment 67 |
81 |
77 |
4.94 |
Embodiment 68 |
80 |
76 |
5 |
Embodiment 69 |
82 |
76 |
7.32 |
Embodiment 70 |
81 |
75 |
7.41 |
Embodiment 71 |
84 |
79 |
5.95 |
Embodiment 72 |
86 |
80 |
6.98 |
Embodiment 73 |
82 |
78 |
4.88 |
Embodiment 74 |
87 |
81.5 |
6.32 |
Embodiment 75 |
85 |
80 |
5.88 |
Embodiment 76 |
85 |
81 |
4.71 |
Embodiment 77 |
87 |
81 |
6.90 |
Embodiment 78 |
86 |
80 |
6.98 |
Embodiment 79 |
86 |
81 |
5.81 |
Embodiment 80 |
88 |
82 |
6.82 |
Comparison embodiment |
85 |
69 |
18.8 |
[0035] It can be know from the above embodiments that, in accordance with the standard test
methods, the hardness loss of the copper alloy of the present invention at 580°C is
below 8%, while the hardness loss of the conventional copper chromium zirconium alloy
in the comparison embodiment is greater than 18%. It is indicated that the high-temperature
softening resistance of the copper alloy of the present invention is greatly improved.
Application embodiment
[0036] The softening-resistant copper alloy bars in anyone of Embodiments 41-60 are machined
into appliances for welding.
[0037] The softening-resistant copper alloy bars in anyone of Embodiments 41-60 are machined
into contact lines for electrified railways.
[0038] In conclusion, the softening-resistant copper alloy of the present invention has
high strength, good electrical performance and excellent high-temperature softening
resistance, and is particularly applied in industrial fields such as welding appliances
and contact lines for electrified railways.