An aluminum-silicon lost foam casting alloy having reduced microporosity and a method for casting the same is herein disclosed. A preferred lost foam cast alloy consists essentially of 6 to 12% by weight silicon and preferably 9.0 to 9.5% by weight silicon, 0.035-0.30% strontium, 0.40% maximum iron, 0.45% maximum copper, 0.49% maximum manganese, 0.60% maximum magnesium, 3.0% maximum zinc, and the balance aluminum. Most preferably, the lost foam alloy is free from iron, titanium and boron. However, such elements may exist at trace levels. Most preferably, the alloy is lost foam cast with the process that applies at least 10 atmospheres of pressure during solidification. However, the range may be 5 to 60 atmospheres. The strontium addition is greater than 0.005% by weight and most preferably greater than 0.05% by weight. In accordance with the present disclosure, alloys having substantially decreased tensile liquid failure defects and substantially decreased surface puncture defects in comparison to conventional lost foam cast aluminum silicon alloys are obtained. Further, hydrogen porosity formation is substantially completely suppressed and surface porosity defects are substantially decreased in comparison to conventional lost foam silicon alloys when casting lost foam cast alloys in accordance with the claims of the instant disclosure. The instant disclosure further discloses aluminum silicon alloys that may be utilized in both the lost foam with pressure and the die casting processes.