Fatigue failure and grain refinement strengthening mechanism of aluminum alloy weld

A comprehensive understanding of fatigue failure and grain refinement strengthening mechanisms in aluminum alloy welds is crucial for improving their fatigue performance. This study proposes a novel macro–micro multiscale modeling method based on realistic microstructures and combines a dislocation-based crystal plasticity finite element model (CPFEM) with continuous fatigue damage theory. Through this approach, the fatigue crack propagation process and grain refinement strengthening mechanisms in laser-welded aluminum alloys are systematically investigated. The results reveal that fatigue crack propagation predominantly involves mixed fracture modes, with transgranular fracture being dominant and intergranular fracture secondary. High-stress regions at crack tips activate slip systems, significantly increasing cumulative slip and dislocation density, driving localized plastic deformation and promoting crack growth. Grain refinement enhances fatigue resistance through synergistic effects of grain boundary strengthening and dislocation strengthening. As grain size decreases, stress concentrations at crack tips are dispersed, broadening high-stress regions and enhancing crack resistance through grain boundary strengthening. Concurrently, grain boundaries hinder dislocation glide, leading to increased dislocation accumulation and interactions, which enhances resistance to crack propagation. Additionally, smaller grains lead to higher stored energy density, increasing energy dissipation and delaying crack growth. These findings provide valuable insights into fatigue failure mechanisms and practical strategies for enhancing the fatigue performance of aluminum alloy welds.