Effect of annealing on the structure, mechanical and electrical properties of Cu/Mg-composite wires

Abstract Cu/Mg-composite rods, inside the Cu-shells of which 1 or 400 Mg-filaments are contained, were obtained by hydroextrusion at room temperature. The structure, microhardness and electrical properties of the obtained composites have been studied both in the as-extruded state and after various heat treatments. It is shown, at heating to 450 °C, that the solid-state reactions between copper and magnesium lead to the formation of the porous Mg-based solid solution and two sub-layers of CuMg2 and Cu2Mg intermetallic phases (thick and thin, respectively) at the interface. As a result of heating to 530 °C, high-strength filaments based on these intermetallic phases are formed in the composites. Annealing at 750 °C completely changes the structure of Cu/Mg-composites. Instead of 400 Mg-filaments, one core is formed, which has an eutectic structure and consists of Cu-based fcc-solid solution with islands of Cu2Mg-phase. It was found that, as a result of these reactions, the microhardness of filaments increases by more than an order of magnitude, while the electrical resistivity of the composite remains almost unchanged. The subsequent deformation further increases the strength of Cu/Mg-composites. A conclusion is made that the method for obtaining high-strength Cu/Mg-composite wires tested in this work is new and promising.