Microstructures and Mechanical Properties of A356 Alloy and A6061 Alloy through Rheo, Upsetting, Thixo, Forming Process, and T6 Heat Treatment

The thixo process has the benefit of producing a semi-solid material in which fine primary α-Al grains are uniformly distributed. However, it also has the disadvantage of a costly raw material billet. In this study, a semi-solid slurry was prepared from the rheo process by cooling and electromagnetic stirring, and then a billet for the thixo process was manufactured through an upsetting process with semi-solid slurry. Then, the billet was reheated (thixo process) to make a semi-solid state, and then a final sample was manufactured through a forming process. In both A356 and A6061 materials, the equivalent diameter of the primary α-Al grains became smaller and the roundness became close to one throughout rheo, upsetting, thixo, and forming processes. Due to the refinement and spheroidizing effect of the primary α-Al grains, the tensile strength was improved by each process, and the elongation was slightly decreased. However, after T6 heat treatment, the tensile strength of A356 was decreased, but the elongation was greatly improved. In the case of A6061, on the other hand, the tensile strength was significantly improved, and its elongation decreased after T6 heat treatment.