Patent attributes
An aluminum silicon die cast alloy having a very low iron content and relatively high strontium content that prevents soldering to dies into die casting process. The alloys of the present invention also have a modified eutectic silicon and modified iron morphology, when iron is present, resulting in low microporosity and high impact properties. The alloy comprises 6-22% by weight silicon, 0.05 to 0.20% by weight strontium and the balance aluminum. Preferably, the alloy of the present invention contains in weight percent: 6-20% silicon, 0.05-0.10% strontium, 0.40% maximum iron and most preferably 0.20% maximum iron, 4.5% maximum copper, 0.50% maximum manganese, 0.60% maximum magnesium, 3.0% maximum zinc, balance aluminum. On cooling from the solution temperature, the strontium serves to modify the eutectic silicon structure as well as create an iron phase morphology change if iron is present, facilitating feeding through the aluminum interdendritic matrix. This, in turn, creates a finished die cast product with extremely low levels of microporosity defects. The strontium content also appears to create a non-wetting monolayer of strontium atoms on the surface of a molten casting, preventing die soldering, even at very low iron contents. The alloy may be used to cast any type of object and is particularly suited for casting outboard marine propellers, driveshaft housings, gear case housings, Gimbel rings and engine blocks.
