Papers by Author: Chang Dong Yim

Abstract: The solidification behavior of AZ31 magnesium alloy plate during horizontal continuous casting (HCC) with constant velocity was analyzed by three-dimensional CFD simulation. At steady state, the temperature profile in the direction of width was slightly inhomogeneous due to wide width compared to thickness. The temperature profile in the direction of thickness was symmetrical although the temperature at lower part was slightly higher than that at upper part. The region of high temperature increased rapidly with increasing the withdrawal speed, and then the finishing point of solidification increased dramatically. The shape of temperature profile was similar regardless of melt temperature but the overall temperature of plate and the finishing point of solidification increased with increasing the melt temperature. The finishing point of solidification decreased reciprocally with the coefficient of heat transfer.

Abstract: The effects of non-flux purification on the mechanical properties, microstructure and fracture pattern of AZ31+xCa magnesium alloys have been studied. The results show that the purification process of ceramic foam filters incorporating gas bubbling process can improve obviously the ultimate tensile strength σb and elongation δ of AZ31 alloy. With 20ppi MgO filter incorporating gas bubbling treatment under Ar flow rate of 2 l/min and temperature of 730°C, the σb and δ of AZ31 can be improved from 144.6MPa and 5.21% to 180.8MPa and 9.06% by 25% and 73.9%, respectively. Addition of 0.13%Ca to magnesium can not only increase the strength but also improve the elongation. With the further increase of more than 0.13% Ca content, the strength and elongation decrease. The experimental results show that under low Ca content, filtration purification process can greatly improve the σb and δ of AZ31+xCa alloy. However, with the increase of Ca content, the filtration effects decrease. The effective sequence of different filters is as follows: 20ppi MgO>20ppi Al2O3>10ppi MgO>10ppi Al2O3.