Mechanical properties optimization and microstructure analysis of pure copper gradient laminates via rolling

Abstract Heterostructured (HS) material with extraordinary mechanical properties has been regarded as one of the most promising structural materials. In this paper, heterogeneous lamella structure (HLS) Cu laminates composed of surface elongated-grain layer and center equiaxed-grain layer were fabricated via rolling bonding and annealing. In order to study the interface effect on mechanical properties of gradient structured materials，both the laminate metal composite (LMC) and the non-composite laminate (NCL) were fabricated by cold-rolling pretreatment of the center layer (60% reduction) and cold-rolling bonding of the whole blank (67% reduction). Then by controlling the post-annealing regimes, the HLS was obtained and the microstructure of each layer was optimized, and a larger degree of microstructure heterogeneities such as grain size, misorientation angle and grain orientation were obtained, which resulted in obvious mechanical differences. Tensile tests of HLS, surface layer, center layer and NCL specimens reveal that the HLS annealed at 300°C/1h has a significantly higher strength than the center layer and a higher elongation than the surface layer. The HLS have a tensile strength and elongation at fracture of 278.08 MPa and 46.2%, respectively, which shows good balance of strength and plasticity. The main reason for the improved properties is the strengthening or strain hardening generated by the inhomogeneous deformation of the heterogeneous layers in the laminate and the mutual constraint acquired by the distinct layers with strong mechanical differences. The HLS has an interfacial bonding strength of 178.5 MPa, which plays a vital role in the coordinated deformation of heterogeneous layers. The method of obtaining gradients in homogeneous materials proposed in this study provides a new way of thinking and enriches the theoretical basis for the comprehensive performance improvement of traditional metallic materials.