The evolution of microstructure and properties of a Cu–Ti–Cr–Mg–Si alloy with high strength during the multi-stage thermomechanical treatment

A Cu–Ti–Cr–Mg–Si alloy with the super-high strength and high electrical conductivity was designed, and the effects of multi-stage thermomechanical treatment on the microstructure and properties of the alloy were investigated. The alloy treated by the multi-stage thermomechanical treatment had a yield strength of 1072 MPa, tensile strength of 1144 MPa, elongation of 6.1% and electrical conductivity of 24.1 %IACS. During the thermomechanical treatment, the nanoscale β′–Cu4Ti particles, Cr precipitates and submicro-particles that mainly consisted of Cu, Ti, Cr and Si elements formed, leading to the high strength of the alloy. β′–Cu4Ti phase with body-centered tetragonal structure had a classic orientation relationship with copper matrix: [001]Cu//[001]β' and [3-10]Cu//[100]β'. The super-high strength of the designed alloy was mainly attributed to the precipitation strengthening, sub-structure strengthening, solid solution strengthening and work hardening. Electrical conductivity increased during aging due to the decomposition of supersaturated solid solution. Compared with direct aging treatment, multi-stage thermomechanical treatment with the stepped temperature-reduction further improved the mechanical and electrical properties of the alloy.