Effect of Cr content on microstructure and properties of aged Cu-Cr-P alloys

The role of Cr in affecting the precipitates and the properties of aged Cu-Cr-P alloys was investigated and discussed. The results show that there are mainly three sizes of Cr phase in aged Cu-Cr-P alloys, among them, the nano-sized Cr phase plays an important role in the strength of Cu-Cr-P alloys. The strengthening effect of Cr phase (less than 5 nm) with FCC structure completely coherent with the matrix is calculated to be about 200 MPa on the basis of dislocation cut-through mechanism. The strengthening effect of Cr phase (10-20 nm) with BCC structure incoherent with the matrix is calculated to be about 100 MPa on the basis of the Orowan dislocation bypass mechanism. The increase of Cr content changes the number and size of nano-sized Cr phase, which causes the mechanical properties of the Cu-Cr-P alloys to increase first and then decrease. The tensile strength of Cu-0.36Cr-0.01P alloy is 572 MPa and its electrical conductivity is 80% IACS after solid solution treatment at 980 degrees C for 2 h followed by 95% cold rolling and then aging treatment at 450 degrees C for 1 h.