Abstract: The Portevin-Le Chatelier (PLC) effect, arising from dynamic strain aging (DSA), manifests as serrated flow during plastic deformation. While extensively studied in conventionally manufactured (CM) aluminum alloys, its behavior in additively manufactured (AM) counterparts remains poorly understood. In this work, the effects of temperature (T), strain rate (ε), and microstructure (grain morphologies and precipitates) on the PLC behavior of a representative laser powder bed fused (LPBF) Al-Mg-Sc-Zr alloy are investigated. The PLC behavior exhibits strong dependence on T and ε, occurring only within an intermediate deformation window. A distinct strain-dependent transition of serration types is highlighted—from type B within the Lüders plateau to type A or mixed (A + B) at higher strains—which has rarely been observed in CM alloys. While further investigation is required, this transition is mainly attributed to evolving strain partitioning between coarse columnar and ultrafine equiaxed grains in the LPBF-induced bimodal structure. Direct aging reveals that dense Al₃(Sc, Zr) precipitates suppress the PLC effect by reducing strain partitioning and consuming vacancies, whereas grain coarsening after over-aging eliminates the Lüders plateau. This work highlights the critical role of microstructural heterogeneity in governing DSA-mediated flow instabilities in AM Al alloys.

Key words: Laser powder bed fusion, Portevin-Le Chatelier behavior, Strain rate, Al-Mg-Sc-Zr alloy, Bimodal grain structure