Achieving high strength and high electrical conductivity Cu-Cr-Zr alloys by continuous extrusion and thermomechanical treatment

A high strength and high electrical conductivity Cu-Cr-Zr alloy was obtained by continuous extrusion and thermomechanical treatment. Without solution treatment of the raw material, the combined process can promote the microhardness, tensile stress, and electrical conductivity to 200.4 HV0.3, 607 MPa, and 79.3 % IACS, respectively. The excellent comprehensive properties were obtained from systematically performed experiments. It was found that direct aging of as-cast or extruded alloy can not enhance the mechanical strength significantly compared with that of the extruded-rolled alloy, implying that the dislocation density plays a crucial role in the precipitation process. Cold rolling with a reduction rate of 80 % can enhance the dislocation density dramatically, promoting the precipitation process at the aging temperature of 400 degrees C. Then, the contribution of the precipitation strengthening mechanism on the total yield stress increases from 16.4 % in the extruded state to 26.4 % in the extruded-rolled-aged state. The precipitation sequence during the process was characterized as mainly meta-stable f.c.c. Cr after extrusion to stable b.c.c. Cr and Cu4Zr after thermomechanical treatment. The orientation relationship between the Cu matrix and Cu4Zr precipitates is: [011](Cu)//[100](Cu4Zr), (0 (2) over bar2)(Cu)//(040)(Cu4Zr). The investigation provides new insights into manufacturing high-performance Cu-Cr-Zr strips.