Effects of Mg and Cu on microstructures and properties of spray-deposited Al-Zn-Mg-Cu alloys

As important aeronautics and astronautics materials, the Al-Zn-Mg-Cu alloys have been fabricated by spray deposition. The effects of Mg and Cu on the microstructures and mechanical properties were systematically investigated. The S (Al₂MgCu) and θ (Al₂Cu) phases exist in equilibrium solidification conditions, but they were not found in the rapid solidification conditions due to the change of solidification paths and phase components during the spray deposition process. The volume fraction of the secondary phases/precipitates increases with increasing Mg content, which leads to the improvement of yield strength as well as to raise tendency of intergranular fracture. Undissolved phases can be promoted by increasing Cu content in the Mg-rich (∼2.65 wt% Mg) alloys. Furthermore, Cu has weak effects on yield strength but plays a positive role in maintaining the peak strength value of the alloys in overaged condition. The alloy with a medium (Mg+Cu) content shows superior overall properties: the ultimate tensile strength (UTS), yield strength (YS) and elongation can reach values of 812 ± 3 MPa, 780 ± 3 MPa and 7.0 ± 0.7%, respectively.