Bifilms are known to be one of the most important defects in casting of aluminium alloys. The size of bifilms can vary from micron to millimetres and there are three major types of oxides structures that aluminium can form: amorphous, gamma and alpha alumina. Depending on the alloying elements such as Mg or Sr, the oxide structure can transform into a spinel type morphology. In this work, artificial bifilms were formed and their healing mechanism were determined. Al-12Si and Al-7Si alloys were used and 100, 200 and 300 ppm Sr was added. Experiments were carried out at 700, 750 and 800oC for 60 hours and every 12th hour, a sample was collected. TGA, XPS and SEM analysis were used to characterise the oxide structure. Change in Si morphology and porosity formation was investigated with regard to the oxide structures of the bifilms.