1 test materials and test methods test material Cu (purity 99.95%) as the matrix, plus the main alloy element is Ni (purity 99.95%), and small amounts of alloying elements Ti, Co, Mo, and rare earth. The medium frequency induction furnace is used for melting, casting into a cylindrical test bar of 10 mm, cutting into small samples, grinding the sample after heat treatment, etching in 3% FeCl 3 + 10% HCl aqueous solution, in the OLYMPUS PMG3 metallographic phase. The microstructure was observed under a microscope. The hardness was tested on a HVS-1000 Vickers hardness tester. SEM observation was performed on KYKY-2000B.
2 Test results and analysis 2.1 Heat treatment process and hardness In order to study the effect of solid solution and failure heat treatment on the microstructure of the alloy, the temperature and time of solid solution and failure were screened. According to the Cu-Ni phase diagram, the solution temperature is selected in the range of 980-1200 ° C, and the solution temperature is quenched at intervals of 20 ° C for 5-10 h. The solution temperature of the alloy is determined to be 1160 ° C, and the solid solution time is 8 h. The hardness of the alloy is the lowest (HV = 118.3). The samples after solution treatment at 1160 ° C × 8 h were treated at 500 ° C for 2 h and 4 h respectively to determine a reasonable aging temperature of 500 ° C, and the aging time was 4 h. At this time, the hardness of the alloy rose back to High value (HV=239.3). The specific experimental results are shown in Table 1.
Table 1 Â Hardness of alloy under different heat treatment processes | ||
Numbering | status | H V (average hardness) |
1 | Cast state | 257 |
2 | 1160 ° C × 5 h water quenching | 191.4 |
3 | 1160 ° C × 6 h water quenching | 172.4 |
4 | 1160 ° C × 7 h water quenching 159.4 | 　 |
5 | 1160 ° C × 8 h water quenching | 118.3 |
6 | 1160 ° C × 8 h water quenching + 500 ° C × 2 h air cooling | 138 |
7 | 1160 ° C × 8 h water quenching + 500 ° C × 4 h air cooling | 239.3 |
2.2 Results Analysis The as-cast microstructure of copper alloy electrical contact materials consists of coarse dendrites [Fig. 1(a)], which has high hardness and high brittleness, which is not conducive to the processing of materials. After 1160 ° C × 5 h solution water quenching treatment, the alloy phase in the structure began to dissolve, and the sharp transmissive structure in the alloy became smooth (Fig. 1 (b)], and the hardness was greatly reduced. When the solid solution holding time is extended to 1 h at 1160 °C, the alloying elements Ni, Ti, Co, Mo, etc. in the alloy are fully dissolved into the α solid solution to form a solid solution based on the α phase. During the water quenching process, the α phase is too late to change. The uniform quenching structure of a single unit [Fig. 1 (c)], the hardness is reduced to a minimum. The alloy is solution treated at 1160 ° C for 8 h, and then subjected to air cooling treatment at 500 ° C for 4 h. The obtained structure is shown in Fig. 1 (d), and the metallographic structure is still a single uniform α phase.
It can also be seen from the secondary electron image of SEM that the alloy is uniformly treated after 1160 ° C × 8 h solution, and the particle diameter tends to be uniform. See Figure 2 (a) for EPMA fixed-point composition analysis. The composition is Cu and Ni, and almost no alloying elements such as Ti, Co, and Mo appear. It is indicated that the alloy is subjected to solid solution quenching treatment at 1160 ° C for 8 h to obtain a Cu-Ni single phase solid solution structure with uniform composition. [next]
Observed under SEM, the alloy was solution treated at 1160 ° C for 8 h, and then subjected to air-cooling aging treatment at 500 ° C × 4 h. The structure consisted of small phase fine particles with approximately equal diameter and uniform distribution, as shown in Fig. 2(b). Analysis by EPMA, in addition to mainly containing Cu, Ni, a small amount of Ti, Co, Mo exists in these particle components. This can be considered as a supersaturated α solid solution obtained by quenching, which is an unstable phase from the viewpoint of thermodynamics. Therefore, in the subsequent aging process at 500 ° C, the α phase is desolvent precipitated, and a small amount of alloying elements Ti and Co in the alloy. Mo, etc. form a diffusely distributed second phase particle with Cu and Ni, which significantly increases the hardness of the alloy.
3 Conclusion
(1) The microstructure and hardness of the copper alloy (Cu-20Ni-X) electrical contact material were changed by 1160 ° C × 8 h solution water quenching treatment to obtain a uniform single-phase solid solution structure with reduced hardness and plasticity. The processing performance is improved, and the material is processed into different shapes of electrical contact contacts during the punching, squeezing and drawing process.
(2) It is quenched by solid solution water at 1160 °C×8h, and then treated by air-cooling aging treatment at 500°C×4h. The hardness of this material rises and has high strength and wear resistance, which meets the requirements of its use. The strengthening mechanism can be considered as the first The dispersion of two-phase particles is precipitated.
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