Microstructure And Mechanical Properties Of Cu-Cr-Zr And Cu-(30～50%) Cr Alloy Developed By Plastic Deformation

The extruding and rolling processes of the Cu-Cr-Zr alloys and the high Cr content Cu-(30~50wt.%) Cr alloy were investigated. Research on the effect of extruding, annealing and aging treatment on microstructures and mechanical properties of the Cu-Cr-Zr alloys and the influence of extruding, rolling, annealing and aging on microstructures and mechanical properties of the high Cr content Cu-(30~50wt.%) Cr alloy have been studied.The results show that the hardness and electrical conductivity of Cu-Cr-Zr alloys were highly dependent on the extruding parameters. The maximum hardness and electrical conductivity was obtained at an extrusion temperature of 650℃, both hardness and electrical conductivity of the extruded alloys had a remarkable decrease when annealed at 850℃for 1.5h. However, that has a great increase when aged at 450℃for 3.5h. It is also observed that the good combination of hardness and the electrical conductivity could be achieved at an extrusion temperature of 800℃and subsequent annealing temperature of 450℃for 3.5h. Because grains of the as-extruded samples were significantly refined after hot extruded at 800℃, and slight Cr phase precipitation can be observed, which resulted in the enhancement of properties. Further precipitation of fine Cr-rich phase particles in the subsequent aging process reinforced both properties.It is generally accepted that the high Cr content of Cu-Cr materials are generally prepared by powder metallurgy. Size of Cr phase particles of Cu-(30~50 wt.%) Cr prepared by casting is much coarser than that prepared by powder metallurgy. Because the Cu matrix and Cr phase are immiscible, the Cu-Cr phase bonding is weak. Thus, the plasticity of the material is poor, which lead it easily cracked in plastic deformation. The study aims to investigate the effect of hot extruding and rolling on microstructures and mechanical properties of these materials. The academic value and important practical production sense are obvious. Hot rolling and extruding were performed on Cu-Cr materials with the Cr content of 30%, 40$ and 50%. The result shows that the hardness and electrical conductivity improved significantly after extruded at 850℃, but the change of the properties was not obvious after aging. After annealing, decrease in micro-hardness presented but the electrical conductivity was constant. The higher Cr content leads higher hardness but lower electrical conductivity. The hardness and electrical conductivity of Cu-(30~50 wt.%) Cr material was reduced after rolling, especially along the rolling direction. The Cr phase was elongated along the extrusion direction. As a result of large extrusion ratio, the grain size of Copper matrix has been refined, the hardness increased. Although the contacting area between Cr phase and copper increased, the copper matrix became more continuous, promoting the improvement of electrical conductivity. The change of Cr phase in the material is not obvious after hot rolling, the copper grain growth resulted in slightly lowered hardness. Increasing of the area of Cr phase and copper contacting resulted in slightly lowered electrical conductivity. The annealing treatment resulted in decreased hardness because of the grain growth in Cu matrix. The effect of age-hardening on properties of such materials is minimal.