Effect and Mechanism of Solidified Microstructure on Deformation Behavior, Mechanical Properties, and Residual Stress of Cu-Ni-Si Alloy

Abstract

Cu-Ni-Si alloy is the key raw material for the lead frame of large integrated circuits. The disordered grain orientation of alloy billet, high hardening rate, residual stress, and poor surface quality of cold working strips seriously affect its processability. In order to improve the cold-working properties of Cu-Ni-Si alloy, two kinds of C70250 copper alloy strips were produced through hot mold continuous casting (HMCC) and cold mold continuous casting (CMCC) technology. The effects of solidified microstructure on the cold-working deformation behavior, mechanical properties, and residual stress of the alloy were studied. The results show that C70250 copper alloys with columnar grain and equiaxed grain were prepared through HMCC and CMCC. After a 98% reduction in cold rolling, columnar grain strip surface quality was very good, and the elongation was still as high as 3.2%, which is 2.9 times that of equiaxed grain alloy. The residual stress of equiaxed grain strips reached 363 MPa, which is 2.7 times that of columnar grain strips. During the cold rolling process, equiaxed grain strips are prone to cause intersecting plane dislocations, stacking faults, shear bands, and grain breakage during large deformation cold rolling. The columnar grain strip causes parallel plane dislocations, stacking faults, and shearbands. Furthermore, the deformation structure was found to be uniform, and, ultimately, the alloy formed a fibrous structure. Therefore, the elongation and latter distortion of columnar grain strips improved after being put through large deformation cold rolling, which greatly reduced residual stress.