Super-high Strength Cu - 6.0 - Si Ni - 1.4-0.15 Mg - 0.1 Microstructure And Properties Of Cr Alloy

A super high strength, high electrical conductivity, high tress relaxation resistant Cu-6.0Ni-1.4Si-0.15Mg-0.1Cr alloys have been developed in this paper. The mechanical property, electrical conductivity, kinetic of transformation, microstructure of phase and stress relaxation property have been investigated by means of mechanical and conductivity properties measurement, thermal simulation, OM, SEM and TEM observation, X-ray diffraction and select-area electron diffraction. The main conclusions have been gained and were listed as following:1. The appropriate heat treatment process of Cu-6.0Ni-1.4Si-0.15Mg-0.1Cr alloys was that:homogeneous treated at940℃for4hâ†'hot rolled at850℃by80%â†'solution treated at980℃for4hâ†'cool rolled by50%â†'aged at450℃for30min, and the properties of the Cu-6.0Ni-1.4Si-0.15Mg-0.1Cr alloy are that:σb=947.7MPa, σ0.2=909.2MPa, HV=341.8, g=29.1%IACS,δ=4.5%.2. The effects of the deformation temperature and strain rate on the peak value of flow stress of Cu-6.0Ni-1.0Si-0.5Al-0.15Mg-0.1Cr alloy have been investigated by a quantitative analysis. The results were that:the relationship between the rheological stress peak and strain rate can be expressed by hyperbolic sine equation; the relationship between the peak value of flow stress and deformation temperature was linear one; the activation energy of alloy was854.73kJ/mol; and the relationship of peak value of flow stress, strain rate and temperature can be expressed as follow: ε=[sinh(0.008209σ)]8.6exp[91.2-(854.73/RT)]3. The behavior of phase transformation kinetic of the Cu-6.0Ni-1.4Si-0.15Mg-0.1Cr alloy during aging has been investigated through measuring the variation of electrical conductivity with aging time. The Avrami phase transformation equation at400℃,450℃and500℃were that:f=1-exp(-0.019t0.890),f=1-exp(-0.181t0.483) and f=1-exp(-0.228t0.433), respectively.4. Strengthening mechanism of the Cu-6.0Ni-1.4Si-0.15Mg-0.1Cr alloy during aging were ordering strengthening and precipitation strengthening. The precipitated phases are β-Ni3Si (prime cubic structure) and8-Ni2Si (prime orthorhombic structure), the δ’-Ni2Si was a variant of δ-Ni2Si and had the same crystal structure parameter as that of δ-Ni2Si. The crystal orientation relationship between the precipitates and copper matrix were determined as:(022)c||(O11)β||(010)δ,[100]u||[100]β||[001]δ;(022)Cu||(011)β||(100]δ,[100]Cu||[100]β||[001】δ5. The stress relaxation rate curves can be divided into two stages. The first stage was0to2h, the stress decreases rapidly; the second stage was2h to100h, the stress decreased slightly and reached to a constant value. Under the action of temperature and stress for long time, the dynamic recovery and recrystallization occurred. The stress relaxation behaviors of the Cu-6.0Ni-1.4Si-0.15Mg-0.1Cr alloy were modeled according to the MAXWELL elasticity-viscoplasticity model and can be expressed by lnσ=-t/tr+C. The equations were proposed and showed the alloy can be used for1000h at the temperature of25℃and100℃, and then the relaxation quantity is6.62%and10.49%.