Papers by Author: Bong Sun You

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 CeCl3-containing fluxes on RE element loss, the high temperature mechanical properties, microstructure and corrosion properties of magnesium alloy containing RE have been studied. The results showed that a certain amount of CeCl3 in purification fluxes restrained the reaction between the Ce element and fluxes to decrease the loss of Ce in alloys. With the flux containing 9% CeCl3, the loss rate of alloy element Ce can be reduced from 26.9% to 3.4%, and the σb and δ of the alloys at 150°C counld be improved from 160.9MPa and 6.2% to 176.5MPa and 7.9% compared with that of conventional MgCl2-containing flux , respectively. Besides, the coarse β phase and rod-like RE phase were refined effectively by CeCl3-containing fluxes.

Abstract: AZ31 magnesium plates with 1mm in thickness were fabricated by casting and subsequent hot rolling process. Both wheel-band continuous casting (modified Properzi) and horizontal continuous casting (HCC) machine were designed and employed to produce AZ31 alloy plates. The plates with 5x50mm in size produced by modified Properzi process exhibited good surface qualities that were sustained during following rolling process. Surface qualities of HCC plates with 120x30mm in size were very sensitive depending on the processing parameters. Homogenization treatment or surface machining before rolling was effective to get good thin plate. By means of rolling process, microstructures were refined effectively to the size of 7~10µm.

Abstract: In this study the effects of Ca addition on the rollability, microstructures and tensile properties of AZ31 alloy were evaluated. In Ca containing alloys, reduction ratio and preheating temperature are the most important variables to make good sheet without any crack. The number and length of side crack increased with increasing Ca content. With increasing the reduction ratio per pass and decreasing the preheating temperature, crack initiates easily at the side. The dendritic grains were changed to fine equiaxed grains through hot rolling by dynamic recrystallization. The Al2Ca precipitates which were segregated to grain boundaries during solidification were rearranged parallel to the rolling direction. The tensile properties of hot-rolled AZ31-xCa sheets were decreased slightly by addition of Ca.

Abstract: The initial coarse grain size of 400㎛ of a as-cast AZ31 alloy was refined to 130㎛ by carbon addition method. The microstructural evolution, recrystallization, edge cracking phenomena of the coarse grained AZ31 alloy during hot rolling were investigated and compared with those of grain refined AZ31 alloy.

Abstract: The liquid oxidation behavior of Mg-Ca base alloys containing Be has been presented in this paper. The ignition temperature test and microbalance measurement indicated that the oxide film formed at elevated temperature was protective, resulting in the improved oxidation resistance and ignition-proof properties. A Ca-rich zone was found at the very near surface of oxide layer. With Be addition the oxide layer became dense and compact, which was impermeable for the rapid diffusion of oxygen and magnesium through the oxide layer. It was concluded that the formation of BeO in the oxide layer suppressed the continuous growth of the oxide layer.