Grain refinement of Mg-Al alloys by optimization of process parameters based on three-dimensional finite element modeling of roll casting

To study the influence of roll casting process parameters on temperature and thermal-stress fields for the AZ31 magnesium alloy sheets, three-dimensional geometric and 3D finite element models for roll casting were established based on the symmetry of roll casting by ANSYS software. Meshing method and smart-sizing algorithm were used to divide finite element mesh in ANSYS software. A series of researches on the temperature and stress distributions during solidification process with different process parameters were done by 3D finite element method. The temperatures of both the liquid-solid two-phase zone and liquid phase zone were elevated with increasing pouring temperature. With the heat transfer coefficient increasing, the two-phase region for liquid-solid becomes smaller. With the pouring temperature increasing and the increase of casting speed, the length of two-phase zone rises. The optimized of process parameters (casting speed 2 m/min, pouring temperature 640 °C and heat transfer coefficient 15 kW/(m2·°C) with the water pouring at roller exit was used to produce magnesium alloy AZ31 sheet, and equiaxed grains with the average grain size of 50 μm were achieved after roll casting. The simulation results give better understanding of the temperature variation in phase transformation zone and the formation mechanism of hot cracks in plates during roll casting and help to design the optimized process parameters of roll casting for Mg alloy.