Reduction of Hot Tearing of Cast Semi-Solid 206 Alloys

Among the aluminum alloy family, 206 alloys tend to have the highest mechanical properties, but are often prone to hot tearing. It is known that the addition of silicon can improve fluidity and reduce hot tearing propensity. However, to obtain good mechanical properties during conventional casting processes, the silicon concentration of commercial 206 alloys has to be limited to <= 0.05 wt%. Nevertheless, semi-solid forming offers a unique opportunity which is to increase the silicon content to improve castability without compromising mechanical properties. The aims of the present paper is to report the composition development of modified 206 alloys, study the effect on hot tearing sensitivity from silicon additions with varying copper levels, and evaluate the mechanical properties of a selected 206 alloy containing higher Si. It is found that increasing the silicon content in 206 alloys is beneficial in reducing hot tearing. The high Si 206 alloy variants, produced by the SEED rheocasting process, are considerably less prone to hot tearing and can attain superior mechanical properties.