The Influence of Mechanical Stirring on Semi-solid Microstructures of Hypereutectic Al-Si Alloy
Melts are stirred during solidification through the liquidus solidus range on semi solid microstructure of hypereutectic Al 17%Si 4.5%Cu 0.5Mg alloy.The primary Si formed in the melt are gradually changed from elongated platelets to polyhedral shapes.The spheroidicity of primary Si occur by the mechanism of bending and fracture of Si platelets,wear and collision between Si crystals,and coalescene of Si particles.Cooling rate of melt has a significant influence on the size of primary Si particle.With the increasing of cooling rate,average size of primary Si is decreased homogeneously.When cooling rate is 5 ℃/min, the size are 45 μm and there are a small number of sphere like α phases on final microstructure,which is ideal semi sold microstructure considerably.