热轧Mg-1Zn和Mg-1Y合金退火组织演变及静态再结晶行为

对比研究了高温轧制制备的Mg-1.02Zn及Mg-0.76Y(质量分数,%)合金在不同温度退火条件下的组织演变及静态再结晶和晶粒长大动力学行为.结果表明,Mg-1Zn合金的轧制组织以剪切带和孪晶为主,在剪切带和孪晶内伴随着动态再结晶;而Mg-1Y合金的轧制组织中只有孪晶,未观察到剪切带和再结晶发生.退火过程中,Mg-1Zn合金静态再结晶过程主要受控于形核过程,而Mg-1Y合金则既受控于形核过程又受控于长大过程.利用经典的JMAK模型和长大模型分别描述了2种合金热轧制后的静态再结晶和晶粒长大动力学过程,结果表明,静态再结晶过程的Avrami因子n值与理想预测值偏离可能来自于再结晶的不均匀形核.固溶稀土Y原子比Zn原子对晶界移动的拖曳作用更强,导致Mg-1Y合金比Mg-1Zn合金晶粒长大因子n’更高.

MICROSTRUCTURE EVOLUTION AND STATIC RECRYSTALLIZATION BEHAVIOR OF HOT-ROLLED Mg-1Zn AND Mg-1Y ALLOYS DURING ISOTHERMAL ANNEALING

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 thermalmechanical 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-IY 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-lZn 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≈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-lZn 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.