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임창동,유봉선,서영명 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.4
The effect of the reduction ratio per pass on the microstructural evolution of an AZ31 gravity cast plate during hot rolling was evaluated systematically. {1012} extension twinning was observed in large grains after an earlier rolling pass, but it disappeared upon a subsequent rolling pass due to the reorientation of the grains in an unfavorable direction caused by repetitive rolling. The finer grains were newly formed at the boundaries of the original large grains and twin boundaries by dynamic recrystallization. The grain size distribution was changed from a bimodal distribution upon a small total reduction to a homogeneous distribution upon a large total reduction due to the formation of finer grains that continued at the grain boundaries of large grains by repetitive hot rolling. The size and distribution of the grains were affected not only by the reduction ratio per pass but also by the total reduction (number of rolling passes). The effect of the reduction ratio per pass on the microstructural evolution of an AZ31 gravity cast plate during hot rolling was evaluated systematically. {1012} extension twinning was observed in large grains after an earlier rolling pass, but it disappeared upon a subsequent rolling pass due to the reorientation of the grains in an unfavorable direction caused by repetitive rolling. The finer grains were newly formed at the boundaries of the original large grains and twin boundaries by dynamic recrystallization. The grain size distribution was changed from a bimodal distribution upon a small total reduction to a homogeneous distribution upon a large total reduction due to the formation of finer grains that continued at the grain boundaries of large grains by repetitive hot rolling. The size and distribution of the grains were affected not only by the reduction ratio per pass but also by the total reduction (number of rolling passes).
Ni 첨가량에 따른 중력 주조 Mg-Ni 합금의 수소화 반응 특성의 변화
임창동,유봉선,나영상,배종수,문용민 한국수소및신에너지학회 2004 한국수소 및 신에너지학회논문집 Vol.15 No.3
Magnesium and its alloys have the high potential as hydrogen storage materials because of their highest hydrogen storage capacity, low density and abundant resources. But poor kinetic properties of hydriding and dehydriding and high working temperature have limited their practical applications. In this study, the Mg-Ni binary alloys with different amount of Ni were produced by gravity casting and characterized in order to investigate the relationship between the microstructures and hydriding properties. The maximum hydrogen absorption capacity decreased, but the absorption kinetics increased with Ni content. The difference in the absorption kinetics was resulted from the differences in the sort and shape of primary solid phases and eutectic microstructure.
균질화처리한 AZ31-xCa(x=0~2.0 wt.%) 중력 주조재의 열간압연 특성
임창동,유봉선,김수현,이진수,김완철 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.6
The effects of homogenization on hot rolling properties of gravity cast AZ31-xCa (x=0-2.0 wt.%) alloys were evaluated by examination of surfaces and microstructures of sheets. The side cracking during hot rolling was decreased by homogenization through the elimination of local inhomogeneity and solution of brittle precipitate into matrix. The coarse grains in raw materials were changed to fine grains with the average particle size of 5-10 μm by repeated hot rolling through the dynamic recrystallization. A deformation twinning was more favorably formed in the hot-rolled sheets after homogenization. It is considered that the grains grow and the precipitates are solved into the matrix during homogenization heat treatment, which results in the increased possibility of formation of deformation twinning during hot rolling. (Received March 29, 2004)