The high-cycle fatigue, small crack propagation behavior of an A357-T6 cast aluminum alloy is investigated. Laboratory X-ray micro-computed tomography \((\mu {\text {CT}})\) is used to assist in the manufacturing of two flat fatigue specimens containing subsurface shrinkage pores of different sizes (Pore 1 \(\sqrt{A} = 522\,\mu {\text {m}}\) against Pore 2 \(\sqrt{A} = 280\,\mu {\text {m}}\)). Surface crack monitoring is performed by means of optical microscopy and the cracked specimens are analyzed via scanning electron microscopy and electron backscatter diffraction techniques. The subsurface pores tend to induce intergranular crack nucleation, principally when the grain boundaries are oriented perpendicular to the loading direction. Pore 1 induces a fatigue life reduction of 500.000 cycles when compared to Pore 2. The crystallography is able to influence small crack propagation by slightly decelerating the crack growth rates as well as by altering the crack path topography. Tailoring of the crystallography for improved fatigue resistance requires an investigation of the optimal largest defect to grain size ratio.

中文翻译：

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孔径和晶体学对A357-T6铸造铝合金小裂纹HCF行为的影响

研究了A357-T6铸造铝合金的高周疲劳，小裂纹扩展行为。实验室X射线微型计算机断层扫描\（（\ mu {\ text {CT}}）\）用于协助制造两个包含不同尺寸（孔1 \（\ sqrt { A} = 522 \，\ mu {\ text {m}} \）对孔2 \（\ sqrt {A} = 280 \，\ mu {\ text {m}} \））。表面裂纹监测通过光学显微镜进行，并且通过扫描电子显微镜和电子背散射衍射技术。主要是当晶界垂直于加载方向取向时，地下孔隙趋于引起晶间裂纹成核。与孔2相比，孔1引起的疲劳寿命减少了500.000个循环。晶体学能够通过稍微降低裂纹的生长速率以及更改裂纹路径的形貌，来影响小裂纹的扩展。为提高抗疲劳性而进行晶体学的定制需要研究最佳的最大缺陷与晶粒尺寸之比。