Investigation of preparation and properties of Al–Zn–Mg–Cu alloy by metal injection moulding

The sintering densification behaviour, heat treatment and mechanical properties of the Al–Zn–Mg–Cu alloys fabricated by metal injection moulding (MIM) were investigated in this study. It is found that the Al–Mg(–Sn), Al–Zn–Mg and Al–Cu liquid phases were formed successively, and then transformed into a homogeneous Al–Zn–Mg–Cu liquid phase during the sintering process, thereby promoting the sintering densification. The results showed that the precipitation sequence of MIM Al–Zn–Mg–Cu alloy was as follows: GP zone →η′ phase →η phase, which was similar to the wrought 7xxx series alloys. After peak aging treatment, the fine GP zone and η′ phase were the dominant strengthening phases, and the MIM Al–Zn–Mg–Cu alloy exhibited the highest tensile strength of 510 MPa. While the precipitates at grain boundaries of MIM aluminium alloys were composed of η phase and semi-continuous Al–Mg–O layer, which was distinctly different from the wrought 7xxx series aluminium alloys. The hard and brittle Al–Mg–O layer facilitated the initiation and propagation of cracks, and thus deteriorated the grain boundary strength. It might be the reason that the tensile strength and elongation of MIM aluminium alloys are normally inferior to their wrought counterpart.