MICROSTRUCTURE EVOLUTION AND STATIC RECRYSTALLIZATION BEHAVIOR OF HOT-ROLLED Mg-1Zn AND Mg-1Y ALLOYS DURING ISOTHERMAL ANNEALING
GANG Jianwei1,SHI Binqing2, CHEN Rongshi2, KE Wei2
1. Northeast Light Alloy Limited Liability Company, Harbin 150060
2. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016
Cite this article:
GANG Jianwei,SHI Binqing, CHEN Rongshi, KE Wei. MICROSTRUCTURE EVOLUTION AND STATIC RECRYSTALLIZATION BEHAVIOR OF HOT-ROLLED Mg-1Zn AND Mg-1Y ALLOYS DURING ISOTHERMAL ANNEALING. Acta Metall Sin, 2012, 48(5): 526-533.
Abstract Wrought Mg alloys alloyed with rare elements (RE) addition were deemed to be one of the most promising Mg alloys in industrial application, due to the formation of weakened texture and refined microstructure. Generally, the wrought Mg alloys with RE addition after normal thermal-mechanical processing possessed incompletely recrystallized microstructure, so it was necessary to research the subsequent annealing treatment for controlling the microstructure. Unfortunately, the corresponding investigations on the mentioned above were still limited. In this study, hot-rolled Mg-1.02Zn and Mg-0.76Y (mass fraction, %) alloys were selected to investigate the microstructure evolution, static recrystallization behavior and grain growth kinetics under different annealing treatments. The microstructure examination showed that hot-rolled Mg-1Zn alloy was composed of shear bands and twins with the occurrence of dynamic recrystallization; whereas only twins were observed in the hot-rolled Mg-1Y alloy, no shear bands and recrystallization were detected. That should be attributed to the difference in the deformation modes during rolling processing. After isothermal annealing for the two alloys, recrystallization occurred in some remaining twins, whereas no recrystallization took place in others. EBSD analysis revealed that low angle grain boundaries or orientation differences were observed in the remaining twins with recrystallization, suggesting that recrystallization should be associated with the levels of stored deformation energy. The process of static recrystallization and grain growth kinetics were described by the JMAK model and grain growth model, respectively. The process of static recrystallization for the Mg-1Zn alloy was mainly dominated by the process of nucleation; while that for the Mg-1Y alloy was both controlled by the process of nucleation and growth, resulting in finer grain size. Moreover, the results showed that the Avrami exponent of recrystallization n≈1 deviated from the expected value in theory n=4, which could be due to the non-random recrystallization sites in the deformed alloys. Lower value in the grain growth exponent n' was obtained for Mg-1Y alloy than that for Mg-1Zn alloy, which may be ascribed to the stronger dragging effect of the solute Y element on the grain boundaries than that of solute Zn element.
