Effect of grain boundary types and aging precipitation in mechanical and fatigue properties of Al–Mg–Si alloy induced by extrusion and rolling processing

This study investigates the recrystallization mechanisms of the Al-Mg-Si alloy during the plastic deformation process (extrusion or rolling) and subsequent solid solution treatment, elucidating the effect of grain boundary types and aging precipitation characteristics on mechanical and fatigue properties. The results demonstrate that extrusion processing primarily generates abundant LAGBs through DRV and DRX mechanisms within original grains, and the extruded samples (ES) retain a high fraction of subgrain boundaries (68.9%) after solid solution treatment, while the rolled samples (RS) develop fully recrystallized structures bounded by HAGBs (with a fraction of 95.9%). Under peak aged condition (180 °C for 12 h), the ES exhibit finer grain boundary precipitates (GBPs) radius (3.7 nm) and narrower precipitate-free zones (PFZs) (15 nm) along LAGBs, enhancing boundary strength and achieving superior yield strength (419 ± 6 MPa) with moderate elongation (13% ± 1.5%), while the RS show coarser GBPs (7.8 nm) and wider PFZs (29 nm) at HAGBs, resulting in lower yield strength (375 ± 3 MPa) but better plasticity (18.5% ± 0.5 %) due to weaker obstruction to dislocation slip. During the fatigue cycling process, HAGBs in the RS facilitate accelerated intergranular crack propagation, while the high-density LAGBs in the ES reduce strength mismatch between grain interiors and boundaries, promoting transgranular propagation. The mixed distribution of LAGBs and HAGBs effectively blunts crack tips, endowing the ES with enhanced fatigue crack growth resistance.