Microstructure and properties of spray-formed high-strength Al-Zn-Mg-Cu alloy containing manganese

An Al-Zn-Mg-Cu alloy containing 2% Mn (mass fraction) was prepared by spray forming method and hot extrusion. The microstructure and mechanical properties of the spray-deposited Al alloy were studied by optical microscopy, scanning electron microscopy, X-ray diffraction, and tensile tests. The results show that the Al alloy has uniformly fine recrystallized grains with an average size of 8μm after hot extrusion and solid solution treatment. MnAl6 particles were precipitated at grain boundaries during the spray forming process, most of the MnAl6 particles were plastically deformed to some extent along the direction of extrusion during the hot extrusion process, and some large MnAl6 particles were fragged. The effect of solution treatment on the size of MnAl6 particles is negligible but the spheroidization of rod-like/plate-like particles occurred at the corner of these particles. The spheroidization of MnAl6 particles is benefit to the decrease of stress or strain concentration which would induce microcracks. When aged at 120℃ for 24 h, the tensile strength of the Al alloy was increased up to 775 MPa with an elongation of 4.3%, and the fracture surface consisted mainly of dimples with a size lower than 500 nm.