Nourian-Avval Ahmad, Fatemi Ali
Department of Mechanical Engineering, University of Memphis, Memphis, TN 38152, USA.
Materials (Basel). 2020 Jul 9;13(14):3068. doi: 10.3390/ma13143068.
Mechanical performance of cast aluminum alloys is strongly affected by the defects formed during solidification. For example, fractography studies of the fatigue specimens have shown that fatigue failure in aluminum castings containing defects is almost always initiated from defects, among which pores are most detrimental. However, elimination of these pores is neither always economically nor technically possible. This work characterizes defects in high pressure die cast aluminum alloy as an illustrative material, but the methods used can be applicable to other types of castings and defects. The defects were evaluated using metallography as well as micro-computed tomography techniques. The variability of defects between the specimens of two sizes as well as different porosity levels are studied statistically. The distributions of defects based on location within the specimens are also analyzed. Moreover, the maximum defect size within the specimens are estimated using extreme value statistics, which can be used as an input to fatigue life prediction models. Extreme value statistics is applied on both 2D and 3D defect data. The accuracy of each approach is verified by comparing the estimated maximum defect size within the specimens with the maximum observed defects on fracture surfaces of fatigue specimens.
铸造铝合金的力学性能会受到凝固过程中形成的缺陷的强烈影响。例如，对疲劳试样的断口分析研究表明，含有缺陷的铝铸件的疲劳失效几乎总是从缺陷处开始，其中气孔的危害最大。然而，消除这些气孔在经济上和技术上都并非总是可行的。这项工作以高压压铸铝合金作为典型材料来表征缺陷，但所使用的方法也可应用于其他类型的铸件和缺陷。采用金相学以及微观计算机断层扫描技术对缺陷进行评估。对两种尺寸以及不同孔隙率水平的试样之间的缺陷变异性进行了统计研究。还分析了基于试样内部位置的缺陷分布。此外，使用极值统计方法估计试样内的最大缺陷尺寸，该尺寸可作为疲劳寿命预测模型的输入。极值统计方法应用于二维和三维缺陷数据。通过将试样内估计的最大缺陷尺寸与疲劳试样断口表面观察到的最大缺陷进行比较，验证了每种方法的准确性。
