Mechanical properties and their microstructure evaluation in the thixoforming process of semi-solid aluminum alloys

Semi-solid forming technology has some advantages over conventional forming processes such as die casting, squeeze casting, and hot/cold forging. Thixoforging technology can produce non-dendritic alloys for the semi-solid forming of complex-shaped parts in metal alloys. In this study, the filling behavior and various defects of products were observed, and microstructures and mechanical properties were investigated along with parameters such as pressure and die temperature. Thixoforging experiments were performed at fs=55%. The punch speed was Vd=200 mm/s. Die temperature was changed in steps to Td=400, 350, 300, and 250°C. The applied pressure was changed to P=100 and 150 MPa. The porosity, which is an internal defect, was observed, particularly at lower die temperatures. To distribute uniformly the regions of solid- and liquid-phase around the specimen on forming, it is necessary to increase the punch speed and optimize the gate design. Furthermore, a dense microstructure was found at lower die temperature and higher applied pressure. In a tensile test, it was observed that the higher the applied pressure, the higher the ultimate strength, yield strength, and elongation. In a hardness test, it was observed that the hardness decreased gradually from the center to the periphery of the specimen.