Laser powder bed fusion of high-strength Sc/Zr-modified Al–Mg alloy: phase selection, microstructural/mechanical heterogeneity, and tensile deformation behavior

Laser powder bed fusion (L-PBF) of Sc/Zr-modified Al-based alloys has recently become a promising method for developing a new generation of high-performance Al alloys. To clarify the modification roles of Sc/Zr elements, an Al–4.66Mg–0.48Mn–0.72Sc–0.33Zr (wt.%) alloy was processed using L-PBF. The effect of the local solidification condition of the molten pool on the precipitation behavior of primary Al₃(Sc,Zr) was analyzed based on time-dependent nucleation theory. It was found that primary Al₃(Sc,Zr) inevitably precipitated at the fusion boundary, while its precipitation could be effectively suppressed in the inner region of the molten pool. This subsequently induced the formation of a heterogeneous α-Al matrix. After direct aging, the heredity of solidification microstructure introduced heterogeneous secondary Al₃(Sc,Zr) precipitates within α-Al matrix. Owing to the inverse relationship between grain boundary strengthening and precipitation strengthening, the direct-aged sample with dual heterogeneous structures exhibited reduced mechanical heterogeneity, resulting in lowered hetero-deformation-induced hardening. The low strain-hardening capability in the direct-aged sample promoted necking instability while inducing a large Lüders elongation, which effectively improved the tensile ductility.