ON THE INTERPRETATION OF MELT QUALITY ASSESSMENT OF A356 ALUMINUM ALLOY BY THE REDUCED PRESSURE TEST: THE BIFILM INDEX AND ITS PHYSICAL MEANING

The oxide layer on liquid aluminum serves as a protective property to prevent the alloy from further oxidation. However, it has the potential to be a source of porosity when entrained into the bulk of the liquid. For this reason, oxides entrained into aluminum castings have been shown to degrade casting quality. In the current study, the effectiveness of the reduced pressure test in assessing the quality of A356 alloy melts has been investigated under various conditions obtained by changing six different melt parameters. Several metrics, including average pore size, number density of pores, bifilm index, have been used to measure melt quality. Results have shown that the bifilm index provides reliable measurements of melt quality. Moreover, the bifilm index has been found to have a physical meaning, volume fraction of pores, especially when bifilm index is higher than 50 mm.