热压缩过程中Al−9Mg−1.1Li−0.5Mn合金的流变应力和动态再结晶行为

摘要

The flow stress behavior of spray-formed Al?9Mg?1.1Li?0.5Mn alloy was studied using thermal simulation tests on a Gleeble?3500 machine over deformation temperature range of 300?450 ℃ and strain rate of 0.01?10 s?1. The microstructural evolution of the alloy during the hot compression process was characterized by transmission electron microscopy (TEM) and electron back scatter diffractometry (EBSD). The results show that the flow stress behavior and microstructural evolution are sensitive to deformation parameters. The peak stress level, steady flow stress, dislocation density and amount of substructures of the alloy increase with decreasing deformation temperature and increasing strain rate. Conversely, the high angle grain boundary area increases, the grain boundary is in serrated shape and the dynamic recrystallization in the alloy occurs. The microstructure of the alloy is fibrous-like and the main softening mechanism is dynamic recovery during steady deformation state. The flow stress behavior can be represented by the Zener?Hollomon parameterZ in the hyperbolic sine equation with the hot deformation activation energy of 184.2538 kJ/mol. The constitutive equation and the hot processing map were established. The hot processing map exhibits that the optimum processing conditions for Al?9Mg?1.1Li?0.5Mn alloy are in deformation temperature range from 380 to 450 ℃ and strain rate range from 0.01 to 0.1 s?1.%采用Gleeble?3500热模拟试验机对喷射成形Al?9Mg?1.1Li?0.5Mn合金挤压坯进行等温热压缩实验,研究该合金在变形温度为300～450℃和应变速率为0.01～10 s?1条件下的流变应力行为,利用透射电镜(TEM)和电子背散射技术(EBSD)表征合金热压缩过程中的显微组织演变.结果表明,变形参数对Al?9Mg?1.1Li?0.5Mn合金热压缩过程中流变应力和组织演变有非常显著的影响,随着变形温度的降低和应变速率的升高,峰值应力和稳态流变应力增加,合金中的位错和亚结构数量增多;反之,随着变形温度的升高和应变速率的降低,大角度晶界面积变大,晶界呈锯齿状,合金发生动态再结晶;合金的组织呈纤维状,合金在稳态变形阶段的主要软化机制为动态回复;可用Zener?Hollomon参数的双曲正弦函数关系来描述合金的流变应力行为,其变形激活能为184.2538 kJ/mol;热加图表明,喷射成形Al?9Mg?1.1Li?0.5Mn合金挤压坯最合适的加工温度范围为380～450℃,最佳应变速率范围为0.01～0.1 s?1.