The presence of oxide films is detrimental to the properties of aluminum alloy castings. In addition to acting as a defect in their own right, oxide films also promote microporosity formation by facilitating pore nucleation. In this work the microporosity formation phenomena under different oxide formation levels (oxide film levels) were studied in directionally east A356 samples. The emphasis is placed on the large pore size distribution, which is crucial for the fatigue performance of the castings. To achieve different oxide film levels, the A356 samples were cast under two pouring conditions: direct pouring and high-surface-area pouring. Porous disc filtration analysis (PoDFA) was used to assess the melt cleanliness and identify the inclusions in the castings. The porosity volume fraction and size distribution were measured by the 3-D X-ray micro-tomography (XMT) analysis. By fitting the experimental results with a comprehensive pore formation model, an estimate of the pore nucleation population has been made.
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