Microstructural evolution and mechanical properties of Al-xZn-2.6Mg alloy

Al-xZn-2.6Mg (x=6.8, 7.1, 7.4) alloys were designed based on the 7A62 aluminum alloy. The effects of Zn content on the microstructure and mechanical properties of as-cast, hot-rolled and solution-aged alloys were investigated, and their aging precipitation behavior was also analyzed. The results show that with the increase of Zn content from 6.8% to 7.4%, the content and size of secondary phase in the as-cast alloy increased, and its distribution tended to be mesh-like. The average grain size of the hot-rolled alloys decreased from 20.8 μm to 9.9 μm, and the average misorientation difference of grain boundaries and the proportion of the large angle grain boundaries increased gradually. After solution and aging treatment, the volume fraction of η′-MgZn₂ phase precipitated in the alloy was significantly increased, but its size was basically constant. The mechanical properties of 7.4% Zn alloy were the best, with the yield strength, tensile strength, and elongation reaching 570.9, 616.8 MPa and 9.7%, respectively, due to the joint action of fine grain strengthening, solid solution strengthening and precipitation strengthening.