Effect and mechanism of room temperature rolling, cryogenic rolling and heat treatment on mechanical properties and electrical conductivity of Cu-Ni-Si alloy with continuous directional solidification

Simultaneously improving the mechanical and electrical conductivity of copper alloys has become an important challenge. In this paper, columnar crystal Cu-Ni-Si alloy materials were prepared using continuous unidirectional solidification method, and the effects of room temperature rolling (RTR), cryogenic rolling (CR) and subsequent aging treatment on the microstructure, mechanical and electrical properties of C70250 copper alloy were investigated. The results show that the material has good tensile strength (886 MPa), elongation after break (5.2%) and electrical conductivity (42.4% IACS) when the columnar crystal C70250 copper alloy is cryogenic rolled with 95% depression rate and aged at 450 °C for 1 h. After severe rolling deformation, both RTR and CR C70250 copper alloy produce uniform fibrous structure. Large deformation CR can exhibit higher dislocation density compared with RTR C70250 copper alloy, high lattice distortion results in the transformation of the matrix into an amorphous structure, which has a very strong promotion effect on solute atom diffusion and recrystallization. The precipitation of the fine Ni2Si cluster phase with average size of ∼3.2 nm can be accelerated in a shorter aging time compared to RTR, while the uniform fibrous structure after CR can rapidly recrystallize to produce uniform ultra-fine grains with diameter of ∼550 nm. The strength of the cryogenic rolling alloy can significantly increase through precipitation strengthening, fine grain strengthening and dislocation strengthening. This provides a feasible strategy to improve the overall performance of Cu-Ni-Si alloys.