Effects of Trace Zr and La on Microstructure and Properties of Al-Zn-Mg-Cu Alloy

Al-Zn-Mg-Cu alloys without and with the addition of 0.1wt% Zr and 0.2wt% La were prepared, respectively, and then were subjected to homogenizing, solution, and aging treatment. The effects of Zr and La addition on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloys were investigated. The results show that with the addition of 0.1wt% Zr and 0.2wt% La, the nucleation rate of the alloy increased, the microstructure distribution was more uniform and the grains were refined; the as-cast hardness, tensile strength and elongation increased by 13.60%, 25.00%, 21.88% comparing to those of without Zr and La; the fracture mode changed from the intergranular fracture of the alloy without Zr and La to the dimple transgranular fracture, indicating the improvement of the alloy toughness.