<p>Bifilm is one of the main reasons for the reduction of mechanical properties of castings. The present paper proposes a novel idea of controlling bifilm by the modification of the alloy using an element with low melting point and high density. The modification is designed to deactivate bifilm, and reduce the amount of bifilm in the melt. It was found that Bi added into C611 casting aluminum alloy could fill the gap within the bifilm and locally bond the two layers of oxide films together, could disrupt the oxide film allowing the melt to infiltrate into the gap within the bifilm and locally rivet the two layers of oxide films together, leading to the occurrence of bifilm deactivation. Bi addition also facilitated the sedimentation of bifilms, reducing the number of bifilm in the melt. Tensile test experiments showed that the ultimate tensile strength (UTS) and elongation of castings with 1 wt pct Bi were improved by 21.3 and 170 pct, respectively, compared to that of the castings without Bi addition.</p>