Abstract
Grain size and aging state are the two major microstructural factors affecting the mechanical properties of Al alloys. In this study, fatigue tests were conducted on 7075 Al alloy with varying grain sizes and aging states. The results indicate that both grain refinement and over aging (OA) treatment are beneficial for enhancing fatigue performance, with the 7075-Min alloy exhibiting the highest fatigue strength of 265.8MPa in the OA state. For grain size, a quantitative positive linear relationship was found between the reciprocal of the square root of the average grain size and the fatigue strength coefficient. Grain refinement optimizes the fatigue performance by increasing the fatigue strength coefficient. Compared to the under aging (UA) state, OA treatment promotes the growth and coarsening of precipitates at grain boundaries (GBs) and within the interior of grains. This change in precipitate morphology effectively facilitates dislocation cross slip, reducing fatigue damage caused by dislocation blocking. The impact of the precipitation-free zone (PFZ) on fatigue performance is negligible compared to that of the precipitates. This study clarifies the relationship between microstructure and fatigue performance, providing valuable insights for microstructure regulation to optimize the fatigue performance of Al alloys.
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