Study on the optimizing mechanisms of superior comprehensive properties of a hot spray formed Al-Zn-Mg-Cu alloy

In this study, the microstructure of a hot spray formed Al-Zn-Mg-Cu alloy was observed, and the effects of ageing treatment parameters on the precipitation, the mechanical properties and corrosion behavior of the alloy were investigated. The as-deposited Al-Zn-Mg-Cu alloy had a fine equiaxed grain structure with low level of segregation and porosity. After hot extrusion and solution treatment, most of the coarse phases were dissolved, providing a favorable condition for subsequent ageing strengthening. The alloy was subjected to three different ageing treatments: peak-aging, over-aging, and non-isothermal retrogression and re-ageing (NRRA). Results showed that the alloy in peak-ageing condition possessed much better mechanical properties, but poorer corrosion resistance than that in the over-ageing condition. After NRRA treatment, however, great comprehensive performance was achieved for the alloy. In NRRA condition, the optimum combination of the size and number of strengthening phases was responsible for the high mechanical properties, whilst the separated grain boundary precipitates (GBPs) and the higher Cu content of the GBPs contributed to the better corrosion resistance.