Simultaneously enhancing mechanical properties and electrical conductivity of Cu-0.5%Cr alloy as 5G connector material

Abstract

With the rapid development of the 5 G communication, materials such as the high-speed backplane connector and the integrated circuit lead frame require higher strength and electrical conductivity. Copper alloys have been widely concerned due to their excellent electrical conductivity, thermal conductivity and good strength. A new method of preparing the Cu-0.5%Cr alloy by equal channel angular pressing (ECAP), deep cryogenic treatment (DCT) and aging treatment (AT) was proposed. The electrical conductivity, mechanical properties and microstructure of the Cu-0.5%Cr alloy were investigated, and the precipitation kinetics was analyzed. The results show that ECAP deformation and DCT treatment make the grains elongate and refine along the deformation shear direction. After four ECAP passes and DCT (12 h), the lamellar grains with the thickness of 200–300 nm were obtained, and the dislocation density was evidently increased. After the subsequent AT treatment, the fine Cr phase disperses uniformly at the grain boundaries and within the grains, and distributes on the matrix and along the dislocation lines. Compared with the solid solution, the results showed that after four passes of ECAP + DCT (12 h) + AT (425 ℃ × 1 h), the microhardness increased from 60.5 HV to 210 HV, the electrical conductivity changed from 27.9 % IACS to 69 % IACS, the strength improved from 262 MPa to 587 MPa, the elongation to failure decreased from 44.2 % to 21.9 %. The electrical conductivity was enhanced due to the second phase charge analysis showed that the scattering effect on electrons is weakened. The improvement of strength could be attributed to grain refinement and increase of dislocation density. Based on the Avrami empirical equation of precipitation kinetics analysis, the electrical conductivity equation and the phase change kinetics equation were established, and the relationship between aging time and electrical conductivity was established.