Effect of micro-nano structure on residual stress in A356 alloy

The residual stress generated in aluminum alloys after solution treatment can significantly reduce their dimensional stability and fatigue life. common methods for mitigating residual stresses often lead to some deterioration of mechanical performance. This study primarily utilizes grain refinement to regulate the micro-nano structure, aiming to achieve an optimal balance between mechanical performance and residual stress mitigation. The results demonstrate that grain refinement significantly reduces residual stress. Compared to the non-refined A356 alloy which exhibited high residual stress after solution treatment, the addition of 0.5 % Al-Ti-B reduced the residual stress by 73 MPa. Furthermore, after various aging durations, the residual stress of the A356 alloy with 0.5 % Al-Ti-B addition was consistently lower compared to the alloy without such addition. The grain-refined A356 alloy also maintained excellent mechanical properties, achieving a tensile strength of 282 MPa and an elongation of 8.9 %. TEM analysis revealed that thermal aging prompted the precipitation of numerous Mg 2 Si phases in the A356 matrix, significantly reducing dislocation density and lattice distortion. Grain refinement decreased dislocation density at grain boundaries and promoted a finer, more dispersed distribution of precipitates, which reduced uneven thermal expansion and alleviated stress concentration. Thus, grain refinement not only markedly reduces residual stress but also preserves outstanding mechanical properties.