Finite element and metallurgical study of properties of deformed pure copper by ECAE at various strain rates

Abstract

In this work, annealed pure copper is deformed by equal channel angular extrusion (ECAE) for a maximum of eight passes. Mechanical properties of the extruded material are obtained at tension velocities of 0.5 mm/min, 200 mm/min and 8 m/s. It is found that the maximum increase of ultimate strength occurs after the second pass for the V = 200 mm/min. The total increase of ultimate strength after eight passes is around 100%. Hardness increases to a maximum of 36% after eight passes. The elongation decreases for the second and fourth passes but increases after sixth and eighth passes. The reason is believed to be due to the formation of equiaxed grains and gradual decrease in dislocation density at the same time after the sixth pass. As the number of equiaxed grains increases, a high rate of dynamic recovery gives rise to further decrease in dislocation density or in other word to decrease in strain hardening. Therefore, after the sixth pass, elongation continues to increase. At the same time, tensile strength also keeps increasing but at a slower rate. Fracture mechanism of extruded specimens was studied at strain rates to a maximum of 4 × 103 s−1. Fractography of specimens shows that fracture mechanism is strain rate independent. ECAE process is simulated using the DEFORM-3D software through a three-dimensional analysis. Grain refinement is simulated by forcing the element size to zero. It is found that for a very fine mesh, the PEEQ converges to 1.51. The value of predicted PEEQs is not rate sensitive and is almost the same for all punch speeds considered in the simulations.