Laser in-situ re-melting induced porosity control and fatigue improvement in LPBFed high-strength Sc-containing aluminum alloy

• Laser in-situ re-melting improves the fatigue reliability of LPBF aluminum alloys by controlling porosity, thereby enhancing both mechanical performance and manufacturability. Moreover, it acts as an integrated heat treatment within the LPBF process, simplifying the overall processing route. • Secondary Al 3 Sc precipitates and Mn solid-solution effects enhanced tensile strength. • Fatigue strength improved to 115 MPa at 10 7 cycles by porosity elimination via re-melting. High-strength aluminum alloys are attractive for aerospace but suffer fatigue failure from porosity introduced during laser powder bed fusion (LPBF). In this study, a Sc-containing alloy was fabricated to near-full density, and the effects of enhancement aging (EA) and laser in-situ re-melting (RE) on microstructure, tensile, and high-cycle fatigue (HCF) properties were compared with the as-built (AB) condition. All samples exhibited a bi-modal grain structure of fine equiaxed grains at molten pool boundaries and coarse columnar grains inside the pools. XRD/TEM revealed coherent AlsSc precipitates that refined grains and improved stability. EA achieved the highest tensile strength (574 MPa) due to secondary Al 3 Sc precipitation and Mn-rich solid solution, while RE gave slightly lower strength (545 MPa) but superior fatigue strength (115 MPa at 10 7 cycles). Three-dimensional(3D) μCT showed that irregular pores > 20 μm persisted in AB and EA samples as fatigue crack initiation sites, whereas RE markedly reduced their number and size. Thermal modeling indicated that RE stabilized the molten pool, suppressed keyhole instabilities, and promoted pore elimination. Acting as an integrated heat treatment, laser in-situ re-melting improves fatigue resistance while simplifying the LPBF process.