Pore-microstructure evolution and quantification of strengthening mechanisms contribution in laser powder bed fusion of AlMgScZr alloy

The intrinsic mechanisms linking process parameters, microstructure, and performance for laser powder bed melting (LPBF) formed AlMgScZr alloys remain to be elucidated. A multi-scale linkage framework is established, encompassing the full process chain from volume energy density (VED), to pore defect and microstructure regulation through heat flux parameters, and ultimately to macroscopic performance. The specific contributions of each strengthening mechanism are quantified, validating the effectiveness of the framework. The results show that within VED of 60–80 J/mm3, an optimal balance between pore nucleation, growth, and degassing achieves a relative density of 99%. The nucleation of spherical pore remains unavoidable, affected by heterogeneous catalysis of Al3(Sc,Zr). Grains evolution is synergistically regulated by thermodynamic parameters of solidification, catalytic nucleation of nanoparticles and intense shear stress. Coarse grains refine to 2.10 µm at VED of 97.2 J/mm3, due to fluid-induced strong shear stress and shifting solidification mode toward fine grains. Refinement promotes dislocation recovery, weakening texture intensity. Microhardness peaks within VED of 60–80 J/mm3, owing to the defect suppression, grain regulation, and Al3(Sc,Zr) formation. The theoretically calculated strength agrees well with experiment (501 MPa), with a 3.3% error. These results provide theoretical guidance for high-quality LPBF fabrication of AlMgScZr alloys.