Effect of aluminum on microstructure and property of Cu–Ni–Si alloys

Abstract

The effect of aluminum on the microstructure and properties of Cu–Ni–Si alloys has been investigated using hardness test, electrical conductivity measurement, optical microscopy, X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy. Compared with Cu–Ni–Si alloy, Cu–Ni–Si–Al alloy had finer grains. After homogenization treatment at 940°C for 4h, hot rolling by 80% at 850°C, solution treatment at 970°C for 4h, cold rolling by 50% and ageing treatment at 450°C for 60min, properties better than Cu–Ni–Si alloy have been obtained in Cu–Ni–Si–Al alloy: hardness was 343HV, electrical conductivity was 28.1% IACS, tensile strength was 1080MPa, yield strength was 985MPa, elongation percentage was 3.1% and stress relaxation rate was 9.83% (as tested at 150°C and loading for 100h). β-Ni3Si and δ-Ni2Si formed during the ageing process and the crystal orientation relationship between matrix and precipitates was : (02̄2̄)Cu(01̄1̄)β(010)δ, [100]Cu[100]β[001]δ; (111̄)Cu(111̄)β(02̄1)δ, [112]Cu[112]β[012]δ. Addition of Al promoted the precipitation, and effectively enhanced the anti-stress relaxation property. Quasi-cleavage fracture with shallow dimples appeared in designed Cu–Ni–Si–(Al) alloy.