Copper And Aluminum Composite Line Of Contact With The Silver-copper Alloy High-temperature Deformation Behavior Research

Cu-Ag alloy is a kind of material with a series of advantages on high electrical conductivity, high thermal conductivity, high anti-magnetic, high corrosion resistance, high ductility and good forming ability, which is used to make the contact wire in the electrified railway . In this paper, the investigation of the hot deformation behavior and the microstructure evolution at high temperature abut the silver-copper rods is made by the experiment of one-pass and isothermal hot compression on Gleeble-1500 thermal simulator. Dependence of high-temperature flow stress on strain rate, strain temperature and strain capacity is investigated. The strain capacityεis 0.8, the strain temperature is from 700～950℃and the strain rate is from 0.01～10s^-1. Collect experimental data and draw out the true stress - true strain curve. The interrelations of flow stress, strain rate, strain and temperature have been studied with the aid of regression analysis, and solute out the material constant. And high-temperature flow stress mathematical equations and mathematical models of dynamic recrystallization are established. The regularity of the evolution of microstructure is analyzed after hot compression. And the mechanism of dynamic recovery and dynamic recrystallization during hot deformation are preliminary discussed. Get the following key conclusions:1. There are peak stress and different dynamic softening phenomenons in the flow stress curves at all experimental conditions. In the same strain rate, the deformation temperature is higher, the dynamic softening is more obvious. With the increase of the temperature, the true strain corresponding to the peak stressε_p shifts to the left and the true strain corresponding to the steady-state stressε_ss shifts to the right. When the temperature is constant, with the increasing of the strain rate,ε_p has the trend to shift to the right, whileε_ss shifts to the left.2. The material constants are derived by the methods of graphing, linear regression, and the results are as follows: Q = 258.07KJ/mol, n = 8.9427,α= 0.0164, A = 9.3314×10^-10s^-1.3. The semi-empirical equations of the flow stress at elevated temperature are derived from experimental data by multiple linear regression analysis. Considering the influence of hot deformation conditions on the hardening rate and the dynamic softening rate, we also use Laasraoui and Jonas's flow stress model before peak stress and the Jonson-Mehl-Avrami model which is used to describe the kinetics of recrystallization to establish the flow stress model at elevated temperature. In addition, according to JMAK recrystallization theory, the critical strain, the volume fraction of dynamic recrystallization, dynamic recrystallization grain size are established.4. The samples are more likely to occur dynamic recrystallization on high temperature and low strain rates, but it is difficult to occur on low temperature and high strain rates, and the deformation temperature is higher, strain rate is lower, discontinuous dynamic recrystallization phenomenon will appear. In addition, in the same deformation conditions, the central part of the sample is more likely to occur dynamic recrystallization. The microstructure will be equiaxed and twin-axis crystal after dynamic recrystallization, and the grain is more structured. The recrystallized grains will grow with the increasing of the strain.5. The dynamic crystallization nucleation cores are formed and the grain grows by the rotation and the congregation of the grain during hot deformation of the material.