Microstructure, Mechanical And Electrical Properties Of Copper And Copper Alloy Fabricated By Severe Plastic Deformation

Severe plastic deformation (SPD) is an effecitive method for fabricating bulk ultrafine-grained materials and sufficiently excavating the materials'latent capacity. Equal channel angular pressing (ECAP) and cyclic channel die compression (CCDC) have a potential for industrial application. In this paper, numerical simulations and experiments were conducted on CCDC of pure copper and ECAP of CuCrZr alloy. The developed exploratory work and achievements are listed as follows:1) The microstruture evolution of pure copper was examined by optical microscopy and scaning electron microscopy after CCDC. The properties change were investigated by microhardness test, tensile test and electrical conductivity measurement. The results show that grains can be obviously refined by CCDC same as other SPD technologies. The microhardness and tensile strength increase obviously, but the elongation to failure and electrical conductivity decrease. The fracture feature is still ductile and the electrical conductivity is high relatively. These illustrate that CCDC technolgy has the potential to fabricate pure copper with high strength and high electrical conductivity. The height-width ratio has effect on the grain refinement process, but has little effect on tensil strength. The equiaxed grains can be obtained easily by route B than route A. The thermal stability of pure copper decreases after subjecting to severe plastic deformation, static recrystallization occurs at the temperature range of 230 to 270℃.2) The cyclic channel die compression process of pure copper was investigated by numerical simulation. The effect of height-width ratio of the sample, processing routes and friction on effective strain distribution and deformation load were analysed. The simulation results show that the effective strain distribution is inhomogeneous after CCDC due to the effect of friction between tools and sample. The higher effective strain appears in the center of sample. The strain inhomogeneity increases with increasing the friction coefficient. The deformation degree of per pass increases with increasing the height-width ratio of the sample, but the deformation load is also enhaced. The effect of the processing route is samll on the deformation load and average effective strain, but its effect is obvious on the effective strain distribution.3) The equal channel angular pressing process of CuCrZr alloy was investigated by numerical simulation. The effect of die geometry and extrusion condition on effective strain distribution and deformation load were analysed. The simulation results show that the effective strain, deformation load and temperature rise increase obviously with the decrease of die angle. The appropriate outer and inner corner angle can effectively decrease maximum deformation load and increase the strain homogeneity. With increasing the friction coefficient, the maximum extrusion load is enhanced, while the effective strain at the bottom of the sample also is increased. The distribution of effective strain is more homogeneous after four passes ECAP by route Bc.4) The microstruture evolution of solid solution CuCrZr alloy was examined by optical microscopy and scaning electron microscopy after ECAP. The properties of CuCrZr alloy after different treatments were investigated by measuring the hardness and electrical conductivity. The results show that the grain size of the alloy can be refined to submicrometer level after 10 passes ECAP. The ultrafine grain is equaixed and uniform. The hardness increases drastically after ECAP, while the electrical conductivity decreases appreciably. The well combination of hardness and electrical conductivity can be obtained after aging 2 hours at 500℃for the unECAPed alloy. The electrical conductivity is 80.2%IACS and the Vickers hardness is 158 HV. The peak Vickers hardness respectively reaches 202 HV aging 8 hours at 375℃and 200 HV aging 1 hour at 400℃for the alloy after 6 passes ECAP. The ECAP treatment before aging enhances the peak hardness and reduces the time and temperature of peak hardness compared with direct aging after solid solution. The well combination of hardness and electrical conductivity can be obtained after aging 1 hour at 400℃for the 6 passes ECAPed alloy. The electrical conductivity is 81.1%IACS and the Vickers hardness is 200 HV. The results illustrate that the aging kinetics process can be accelerated after ECAP before aging, better comprehensive properties can be obtained compared with conventional cold plastic deformation technologies. The softening temperature is about 530℃, however, the Vickers hardness even remains 161HV at 550℃for the 10 passes ECAPed sample, which indicates that the softening resisitance of CuCrZr alloy do not decrease after ECAP. It can be attributed to the grain refinement and the precipitation of precipitates is accelerated due to abundant lattice distortion and high stored energy, which makes the precipitates are more dispered and fine. The precipitates pin the movement of grain boundaries and dislocation. The excellent comprehensive properties are still attained at elevated temperature.The investigation results show that CCDC and ECAP technology similarily can greatly refine the grain and enhance properties of materials same as other SPD technologies. Combining severe plastic deformation and alloying, a new approach is provided for fabricating high strength, high elecrical conductivity and high heat resistance copper alloy by subsequent microstructure control.