Statistical analysis of micropore size distributions in Al–Si castings evaluated by X-ray computed tomography

In general, micropore size acts as one of the most significant influencing factors on the fatigue strength of aluminium castings. Hence, an in-depth knowledge of the occurrence of micropore sizes and their local distributions in different locations in complexly-shaped lightweight components is of great interest to the casting industry. In this work, the local properties of AlSi8Cu3 and AlSi7Cu0.5Mg cylinder heads and AlSi8Cu3 crankcases were analyzed. Extensive X-ray computed tomography (CT) scans of three specimen positions revealed significant differences in micropore size and distribution. Two CT scan resolutions were selected, with respect to different micropore size populations in the cast components, to enable accurate detection of the microporosity, in addition to an adequate scanning volume, in order to achieve a statistically approved parameter study. Thereby, specimen positions exhibiting smaller mean micropore sizes were scanned at 3 lm/voxel scanning resolution and ones with larger micropore sizes at 8 lm/voxel. A statistical assessment of all of the alloy specifications and specimen positions indicates that the general extreme value and lognormal distribution appropriately describe the micropore size distributions. Finally, an extensive sensitivity study is presented, aimed at examining micropore size characteristics, such as the porosity, sphericity, maximum and mean values and standard deviation, and to investigate their relationships in the investigated cast specimens.