Effect of T6 heat treatment on microstructure and mechanical properties of large-weight aluminum alloy flywheel housing parts formed by local-loading squeeze casting

In this research, ZL104 aluminum alloy flywheel housing with large wall-thickness difference and complex shape were formed via local-loading squeeze casting. The effects of T6 heat treatment process parameters (solution time and temperature, aging time and temperature) on mechanical properties and microstructure of ZL104 aluminum flywheel housing were studied. The microstructure of the formed parts with heat treatment was analyzed by scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and optical microscope (OM). The mechanical property test results indicated that the improvement of strength was limited with the increase of solution temperature and solution time, but the elongation improved significantly. For solution treatment, the optimum mechanical properties (ultimate tensile strength, yield strength, and elongation were 243 MPa, 133 MPa, and 14%) were obtained at 550 °C/3 h. The strength increased first and then decreased with the increase of aging time. After 8 h/175 °C aging treatment (following by solid solution), the maximum tensile strength and yield strength reached 312 MPa and 251 MPa, respectively. After T6 heat treatment, the morphology of Si spheroidized and coarsened obviously. The Si particles with fine size were formed. Continuous dynamic recrystallization occurred during heat treatment but was not very sufficient.