| The mechanical and electrical-conductivity properties,microstructure,aging precipitation behavior and stress relaxation behavior of Cu-1.6Ni-1.2Co-0.6Si alloy were investigated by means of mechanical and electrical-conductivity properties text,optical microscope observation,X-ray diffractometer,scanning electron microscopy with energy dispersive spectrometer and back-scattered electron detection device,transmission electron microscopy and 3D-atomic probe.The main conclusions were summarized as follows:(1)The optimum processing and heat treatment processfor Cu-1.6Ni-1.2Co-0.6Si alloys was that:solutionized at 950℃ for 10min+quenching+first-aged at 500℃for 2h+cold-rolled for 50%deformation+re-aged at 350℃ for 12h,the microhardness and electron conductivity of the final alloy was 253.43HV and 46.21%IACS respectively increased than first-aging alloy 56.58HV and 11.09%IACS.The elastic modulus,elongation rate,tensile strength and yield limit of the re-aging alloy reached 126.32GPa,4.68%,820.46MPa and 619.84MPa.The mechanical properties of the second-aging alloy were better than those of the first-aging alloy.(2)These re-aged precipitates have the same structure and composition as first-aged precipitates,both which are identified to be the orthorhombic(Ni,Co)2Si.The element composition ratio of the precipitated phase was determined to Ni:Co:Si=1:1:1 by elemental composition analysis and the chemical formula was δ-NiCoSi.The crystal orientation relationship between matrix and precipitates is that:(001)cu//(001)p and[110]Cu//[010]p.(3)Re-aged precipitates are finer and denser than first-aged precipitates.The hardness enhancement of the alloy after re-aging is mainly attributed to the finer and denser 8-NiCoSi precipitates.The precipitation of re-aged precipitates is promoted by the high density dislocation formed during cold-rolling.This is due to the higher dislocation density of the second-aging alloy,which provides a fast channel for the diffusion of solute atoms and reduces the precipitation phase energy,so as to diffuse the nucleation.Meanwhile,the lower aging temperature lead to the lower element diffusion coefficient,and inhibited to the precipitation phase growth.So the secondary aging precipitation phase is smaller.(4)The phase change dynamics equation and the conductivity change equation of the Cu-1.6Ni-1.2Co-0.6Si alloy re-aging at 350℃ are as follows:f-1-exp(-0.0515t0.515)and σ=29.5+23.43(1-exp(-0.0515t0.515)).(5)The stress relaxation rate of the re-aging Cu-1.6Ni-1.2Co-0.6Si alloy stress relaxtionzied between 25℃ and 150℃ is lower than that of the first-aging alloy,indicating that the stress relaxation stability of the re-aging alloy is better than that of the first-aging alloy.According to Maxwell’s viscoelastic theory,the formula for the change of the residual stress with time in the stress relaxation process of Cu-1.6Ni-1.2Co-0.6Si alloy after re-aging is derived:stage1(0h-5h):lnσ=6.204-7.14*10-3t;stage2(>5h):lnσ=5.876-7.88*10-5t。... |
