A comparison of microstructure, texture and formability of direct chill cast versus continuous cast aluminum-magnesium alloys.

摘要

In this dissertation, microstructure and texture evolution of Al-Mg alloys produced by direct chill (DC) cast and continuous cast processes (CC) during thermo-mechanical processing were compared and the differences in formability between DC and CC alloys were identified. At the same time, the underlining mechanisms that cause the difference in structure, texture and formability between DC and CC alloys were analyzed.; The recrystallization temperature of the DC AA5052 hot band was about 55°C lower than that of the CC AA5052 hot band. After complete recrystallization, DC AA5052 hot band possessed a stronger cube component than the CC AA5052 hot band. This result was associated with the particle structures of DC and CC AA5052 hot bands. Two different phase particles, Al6((Mn,Fe) and Mg2Si, existed in the DC and CC AA5052 hot bands. CC AA5052 hot band contained more Mg2Si particles than did the DC AA5052 hot band due to the absence of homogenization of the CC material before hot rolling. Mg2Si particles were easily dissolved at high treatment temperatures. After preheating at 454°C for 4 hours, the particle density in the preheated CC AA5052 hot band is closer to that in DC AA5052 alloy due to the dissolution of the Mg2Si particles. Therefore, the differences on recrystallization behaviors of the 80% cold rolled materials decreased, if the DC and CC materials were preheated at 454°C for 4 hours before cold rolling. If the as-received DC and CC AA5052 hot bands were directly cold rolled to 80% reduction, the cold rolled CC AA5052 alloy had a higher recrystallization temperature and a weaker cube recrystallization texture than the cold rolled DC AA5052 alloy.; There still existed differences in texture evolution during cold rolling and isothermal annealing between DC and CC AA5052 and AA5182 materials, although the preheat treatment decreased the differences in particle structures and recrystallization temperature between DC and CC materials. Texture evolution during cold rolling and isothermal annealing was quantitatively analyzed by Johnson-Mehl-Avrami-Kolmogorov (JMAK) type equations, which allow the precise prediction of texture of cold rolled and annealed aluminum sheets.; CC materials show good mechanical isotropy, while DC materials possess superior bendability and stretchability at O-temper condition.