Mechanical properties and corrosion behavior of a new RRA-treated Al–Zn–Mg–Cu–Er–Zr alloy

The effect of various retrogression and re-aging (RRA) treatments on mechanical properties and corrosion behavior of a new type Al–Zn–Mg–Cu–Er–Zr alloy was investigated by microhardness testing, tensile testing, intergranular corrosion (IGC) and exfoliation corrosion (EXCO) testing. The results show that the RRA treatment can effectively improve the IGC and EXCO resistance with less strength sacrificing because the grain interior precipitates and the grain boundary precipitates are similar to that of T6 temper and T73 temper. Meanwhile, as the microhardness of the retrogressed alloy reaches the peak value during the retrogression at 170 °C, the corresponding RRA-treated alloy possesses the better strength, but the corrosion resistance is poor in comparison with that of the retrogression at 190 °C. The optimal combination of strength, IGC and EXCO resistance is obtained after retrogression at 180 °C for 60 min. Moreover, for different heat treatment tempers, the corresponding microstructural evolution of the precipitates including Al₃(Er, Zr) particles was also discussed in detail.