Reheating process of cast and wrought aluminum alloys for thixoforging and their globularization mechanism

A thixoforging process has numerous advantages compared to die casting, squeeze casting, and conventional forging. For the thixoforging process, beside a co-existing solidus–liquidus interval, the reheating conditions to obtain a fine globular microstructure are very important. During reheating, the eutectic must be remelted completely in order to obtain good mechanical properties. The solid fraction distribution over temperature, the phase distribution and the morphology of structure are important for the reheatability of SSM. Moreover, the reheating of the billet in the semi-solid state as quickly and homogeneously as possible is one of the most decisive aspect. To obtain the globular microstructure in the cross-section of the billet, the optimal design of the induction coil for variations of alloys and specimen sizes is necessary. Thus in this study, the optimal coil design of A356 (ALTHIX) and Al2024 with d×l=60 mm×90 mm to reduce the temperature gradient of the billet and to obtain a globular microstructure was theoretically proposed, and then the coil was manufactured. The suitability of the coil design will be demonstrated by reheating experiments. The microstructure characteristics were investigated by changing the heating time, the heating temperature, the holding time, and the heating capacity.