The effect of raw material fabrication process on microstructural characteristics in reheating process for semi-solid forming

In this paper, the reheating process in the A356 alloy, by electromagnetic stirring (EMS) and extrusion, is discussed. The EMS method is used mainly to manufacture raw materials of a globular microstructure. If relevant reheating is carried out, products with excellent mechanical properties can be manufactured by EMS. However, the cost of raw material for EMS is very high. Contrarily, extruded material has a fine dendrite microstructure and has rarely been assumed to be suitable for the semi-solid forming process. It was found in this study that the microstructure of extruded material could be globularized and applied to the semi-solid forming process only with the relevant reheating parameters. This applicability was estimated by investigating, through image analysis properties such as the solid fraction, the mean equivalent diameter and roundness under various reheating conditions. Under the same reheating conditions, the microstructure of the material by EMS and that of the material by extrusion was compared. Also, the variation of the globular morphology and the coarsening of the primary α-Al phase were investigated according to the final isothermal holding time in the reheating process using a billet diameter 4 in.