Heat-Treatment-Induced Deformation Shift in LPBF-Fabricated Heterogeneous Microstructured Al–Zn–Mg–Cu Alloys

This study investigated the effect of T6 heat treatment on the tensile properties and deformation behavior of heterogeneous microstructured Al–Zn–Mg–Cu alloys fabricated by laser powder bed fusion. In the as-built state, pronounced microstructural heterogeneity, including non-uniform precipitate distributions and solute segregation concentrated in the coarse columnar grain (CCG) regions, promoted strain localization within the fine equiaxed grain (FEG) regions. This architectural imbalance produced a high ratio of hetero-deformation-induced (HDI) stress to overall flow stress. T6 heat treatment induced solute homogenization and more uniform precipitation across the matrix, together with grain growth that largely eliminated the distinct ultrafine equiaxed grain zones. These changes caused a clear hardness reversal between the FEG and CCG regions, shifting strain localization toward the CCG regions. Consequently, although the absolute magnitude of HDI stress increased with the higher flow stress, its relative contribution decreased because of the homogenized architecture. Despite reduced uniform elongation caused by early necking, overall tensile ductility improved substantially through suppression of premature intergranular cracking in the FEG regions, clarifying the relationship between microstructural evolution and deformation behavior.