Improvement in strength and thermal conductivity of powder metallurgy produced Cu–Ni–Si–Cr alloy by adjusting Ni/Si weight ratio and hot forging

• Two major improved approaches were used to produce a P/M Cu–Ni–Si–Cr alloy.
• The approaches include the reduction of Ni/Si ratio and the extra hot forging.
• Various heat treatment parameters were conducted to the alloy.
• Microstructures, thermal and mechanical properties of the samples were studied.
• Mechanical and thermal properties were substantially improved.

To further enhance the mechanical and thermal properties of a powder metallurgy (P/M) produced Cu–Ni–Si–Cr alloy, two major improved approaches compared to previous work were conducted. First, chemical composition (wt.%) of Cu–7.0Ni–1.75Si–0.5Cr P/M copper alloy consisting of a Ni/Si weight ratio of 4.0 was produced to provide the desired mechanical and thermal properties; second, after consolidation of the powder by hot pressing and sintering, an extra hot forging process was conducted to tackle the defect of the prior particle boundary (PPB), and to remove the residual porosity in the ingot.After proper heat treatment, the nano-sized Ni–Si precipitates, e.g. δ-Ni2Si and β-Ni3Si, were formed in order to promote the strength and hardness of the P/M Cu–7.0Ni–1.75Si–0.5Cr alloys. From the test results, it was found that the P/M produced copper alloy has a good combination of average sub-grain size, mechanical properties and average thermal conductivity. When compared to our previous work, the improved P/M copper alloy produced in this study provides approximately a 6.3% increase in tensile strength, a 12.1% increase in yield strength, a 13.3% increase in hardness and a 27% increase in thermal conductivity, which makes it even more suitable for application in mold tooling.