The microstructural evolution at the fracture surface in response to very-high-cycle fatigue (VHCF) under stress ratios (R) of −1 and 0.5 in an AlSi10Mg alloy produced by Laser Powder Bed Fusion was investigated. The results show that appreciable growth of the Si precipitates at the cellular network boundaries in the as-built microstructure was observed under R = −1. Moreover, significant amorphization of the initial crystalline Si precipitates occurred in the vicinity of the fracture surface under this condition. A layer of fine Al grains was developed in the “fish-eye” region of the fracture surface. These microstructural responses are rationalized by the generation of lattice defects including dislocations and sub-grain boundaries during cyclic pressing of crack surfaces under R = −1, which mediates the Si solute diffusion and re-precipitation in the alloy as well as the amorphization of initial Si crystalline precipitation. In contrast, far fewer dislocations were observed near the crack surfaces under R = 0.5, which is attributed to the absence of cyclic pressing of crack surfaces and severe plastic deformation in this scenario. This work provides insights into the stress ratio dependence of the microstructural evolution in the fatigued Al alloys. The obtained knowledge is useful for future understanding of the fatigue failure in Al alloys produced by additive manufacturing.

研究了通过激光粉末床熔合生产的 AlSi10Mg 合金在应力比 (R) 为 -1 和 0.5 下响应超高周疲劳 (VHCF) 的断裂表面的微观结构演变。结果表明，在 R = -1 的情况下，在竣工微观结构中的蜂窝网络边界处观察到 Si 析出物的明显生长。此外，在该条件下，在断面附近发生了显着的初始结晶Si析出物的非晶化。在断面的“鱼眼”区域形成了一层细小的铝晶粒。这些微观结构响应通过在 R = -1 下循环压制裂纹表面期间产生晶格缺陷（包括位错和亚晶界）来合理化，它介导了合金中的硅溶质扩散和再沉淀，以及初始硅结晶沉淀的非晶化。相比之下，在 R = 0.5 时，在裂纹表面附近观察到的位错要少得多，这归因于在这种情况下没有裂纹表面的循环挤压和严重的塑性变形。这项工作提供了对疲劳铝合金中微观结构演变的应力比依赖性的见解。所获得的知识有助于未来了解增材制造生产的铝合金的疲劳失效。这归因于在这种情况下没有裂纹表面的循环挤压和严重的塑性变形。这项工作提供了对疲劳铝合金中微观结构演变的应力比依赖性的见解。所获得的知识有助于未来了解增材制造生产的铝合金的疲劳失效。这归因于在这种情况下没有裂纹表面的循环挤压和严重的塑性变形。这项工作提供了对疲劳铝合金中微观结构演变的应力比依赖性的见解。所获得的知识有助于未来了解增材制造生产的铝合金的疲劳失效。