Effect of stirring on the silicon morphological evolution in hypoeutectic Al-Si alloys

Semi-Solid Metal, SSM, Processing is a relatively new technology to fabricate near or net-shaped casting products. In contrast to conventional casting routes, i.e. starting material is fully liquid, casting begins with the mushy alloy. For SSM processing of Al-Si alloys, there are two important microstructural features to influence the properties of the finished products. These are the size, shape and volume fraction of the primary alpha-Al phase and the morphology of silicon within the eutectic regions. It is well known that the irregular growth mode of eutectic Si can be modified by addition of modifiers such as strontium or sodium. In this paper, it will be shown that during SSM processing of Al-Si alloys; melt stirring not only alters the morphology of alpha-Al phase to rosette or globule shape, but also refines the eutectic silicon.