Effect of heat treatment and extrusion processing on the microstructure and mechanical properties of spray formed 7055 alloy

The effect of extrusion and heat treatment processes on the microstructure and mechanical properties of the spray formed 7055 alloy were systematically studied by three-dimensional X-ray microscope, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atom probe tomography and tensile testing. It was found that the main second-phases in the as-deposited 7055 alloy include θ (Al 2 Cu) and Mg(Zn,Al,Cu) 2 phases with similar structure to the ƞ (MgZn 2 ) phase dissolved with Al and Cu. The Al 2 Cu particles embedded in Mg(Zn,Al,Cu) 2 phase are widely distributed on the grain boundaries. Compared with the as-cast 7055 alloy, the S (Al 2 CuMg) phase and T (Al 2 Mg 3 Zn 3 ) phases were not detected in the as-deposited alloy due to the change of solidification paths caused by rapid solidification. The microporosity caused by spray forming is always observed in the as-deposited alloy, these micro-pores can be effectively eliminated by the extrusion processing. Meanwhile, compared with extrusion directly after preheating at 420 °C/24 h, additional high temperature two-stage homogenization treatment before extrusion can reduce the adverse effect of S (Al 2 CuMg) phase and promote the precipitation of high density of Al 3 Zr dispersoids, which significantly increases the recrystallization resistance and improve the mechanical properties of the alloy. • The as-deposited 7055 alloy exhibits different primary second phases compared with cast 7055 alloy. • Microporosity caused by spray forming can be can effectively eliminated by extrusion process. • Homogenization combined with extrusion can effectively reduce the adverse effect of S phase.