Effect of post-heat treatment on the microstructure, mechanical, and corrosion properties of laser powder bed fused Al–Zn–Mg–Cu–Si–Zr–Er alloys

Abstract

Three different post-heat treatments, including direct aging (DA), solution heat treatment + precipitate hardening (T6), and retrogression and re-ageing (RRA), were carried out on a Si–Zr–Er modified Al–Zn–Mg–Cu alloy, which is manufactured by laser powder bed fusion (LPBF). The results show that direct aging maintains the cellular structure of the as-printed (AP) alloy, while T6 and RRA promoted the damage and decomposition of the cellular structure. The size of the primary Al3(Er,Zr) phase increased after heat treatment, and secondary Al3(Er,Zr) phases were uniformly distributed in the matrix with a size of 5–20 nm. The Mg2Si phase in the DA alloy was a long strip pattern, but uniformly distributed in the T6 and RRA alloy. The ultimate tensile strength of the AP, DA, T6, and RRA alloys reached 468, 474, 389, and 354 MPa, respectively. The size, shape, and distribution of the Al3(Er,Zr) and Mg2Si phases have a significant impact on their corrosion resistance, with the latter having a stronger effect. To sum up, the strength of the DA alloy is increased, but its corrosion performance is decreased with heat treatment. On the other hand, the strength of the T6 and RRA alloys is somewhat sacrificed, but their plasticity and corrosion resistance are significantly enhanced.