트윈롤 주조 후 열간압연된 Mg-0.6wt.%Zn-0.6wt.%Ca 합금 판재의 열처리에 따른 결정립 성장 거동

Abstract

This study aims to mitigate the microstructural heterogeneity arising from the manufacture of magne sium alloy plates using the twin roll casting (TRC) process. Homogenization was introduced through hot rolling and heat treatment, followed by confirmation of observed changes in the microstructure. Following the TRC pro cess, the hot rolled 2mm plate exhibited a dendritic cast structure tilted in the roll rotation direction, while central segregation were developed. This nonuniform structure and central segregation disappeared upon heat treat ment, followed by recrystallization to form uniform and fine grains. Abnormal grain growth (AGG) was observed over the course of heat treatment; grains exhibiting AGG occupied up to 75% of the total area after having held the sample at 400°C for 64 h. The formation of coarse grains was also observed during heat treatment at 340°C over a relatively long duration, though the maximum grain size was significantly smaller than that corresponding to the heat treatment at 400°C. AGG in the 400°C heat treatment occurred because of movement of the grain boundary, which had been fixed prior as a result of the grain boundary fixing effect of the precipitation phase. The re-dissolution of the Ca2Mg5Zn5 precipitated phase over the long duration of the high-temperature annealing pro cess caused the surrounding grains to disappear and regrow.