Regulate the microstructure, tensile properties and fatigue crack growth behavior of an Al-Zn-Mg-Cu alloys fabricated by laser powder bed fusion via post-heat treatment

An Al-Zn-Mg-Cu-Si-Zr-Er alloy was fabricated by laser powder bed fusion technology. A unique cellular structure consisting of alpha-Al, Mg2Si, and Al2CuMg phases was observed in both as-printed (AP) and direct aging (DA) alloys. Direct aging treatment at 150 degrees C x 4 h can improve the yield strength and hardness of the alloy, and precipitation strengthening and fine grain strengthening are dominant mechanisms. The strength of the regression re-aging (RRA) heat treated alloy decreased, while the elongation was obviously improved, and the grain boundary was continuous without precipitates free zones. DA could not significantly hinder the fatigue crack growth rate of the as-printed alloy, but the improvement of plasticity, elimination of residual stress, and the effect of precipitates in RRA alloy extend the life of the fatigue crack growth stage, thereby improving the overall fatigue life of the alloy from 1.17 x 105 cycles to 3.93 x 106 cycles.