Numerical Simulation and Experimental Investigation of Microstructure Evolution and Flow Behavior in the Rheological Squeeze Casting Process of A356 Alloy

Abstract

This paper carried out numerical simulations of the entire process of rheological squeeze casting of A356 alloy, evaluated the impact of various combinations of forming process parameters on the temperature field, flow field, and solid-phase fraction of A356 semi-solid slurry, and studied the influence of die temperature (°C) and filling speed (mm/s) on the microstructure formation mechanism of A356 alloy rheological squeeze castings. The research revealed that A356 alloy castings with diverse microstructural features can be achieved by solely controlling the rheological squeeze casting process parameters, without the use of additional heterogeneous nucleating agents or heat treatment. Through combined numerical simulation and experimental results, the optimal rheological squeeze casting process parameters were determined: filling speed of 20 mm/s and mold temperature of 350 °C. It was observed that with the simultaneous increase of mold temperature and filling speed, the average equivalent diameter of the α-Al phase significantly increased from 26.18 μm to 44.27 μm, the uniformity of the eutectic structure distribution was greatly improved, and it was also found that the excessively high filling speed is a critical factor contributing to the coexistence of the script-shaped π-Al₈FeMg₃Si6 phase and the undecomposed the needle-like β-Al₅FeSi phase.