Oxide bifilm defects in aluminum alloy castings

The high oxidation of aluminum alloy would result in abundant oxidation defects. In recent years, bifilm has been increasingly recognized as a source of the metallurgical defects. The crack defects in aluminum alloy casting was investigated in the present work from the viewpoint of bifilm. Computed tomography has been used to image the defects in three dimensions which demonstrated the complexity of the bifilm defect. Detailed energy spectrum analysis showed that the bifilm has different compositions at different thickness. Simulations suggested that the defect is affected by flow field, thus could be eliminated by process optimization. These results would shed new lights on the understanding of the formation of bifilm defects and improve the defects control engineering of castings.