Relative porosity in aluminium and in aluminium alloys

Pores are readily formed in aluminium alloy castings. Density and porosity area fraction are often used quantitatively to evaluate the quality of aluminium alloy castings. This study used the relative porosity, the ratio (d_c - d_r)/d_c, where d_c is the density of the chilled sample and d_r is the density of the reduced-pressure test sample, to evaluate the quality of aluminium and Al-6Si and Al-13Si alloys. The bursting of degassing bubbles on the free surface of the melt brought debris of oxide particles into the melt, which were eventually trapped in the castings after pouring. These particles were accompanied with air pockets and/or engulfed by bubbles, resulting in pores shown on the sections of poured castings.