Abstract:  Al-11.5Zn-2.0Mg-1.6Cu alloy was synthesized by spray forming (SF) technique followed by hot extrusion and heat-treatment. Its microstructural evolution was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) in the whole process. The curve of hardness as a function of aging time was obtained at 120 ℃. Test results indicate that the grain morphology is equiaxed and uniform in the central region of the spray-formed billet, but fine and irregular in the bottom and top regions. Both the grain boundary and the intragranular phases are identified as MgZn₂ intermetallics. Hot extrusion promotes the refinement of the microstructure. Grain boundary phase disappears, meanwhile, η-phase (MgZn₂) and Al₃Zr particles precipitate from the matrix after extrusion. The alloy reaches its maximum hardness after being aged at 120 ℃ for 14 h, associated with a massive precipitation of intermediate η′-phase (MgZn) in the matrix.

Key words:   Al-Zn-Mg-Cu alloy; spray forming; microstructure; hot extrusion; aging