新型高强铝合金的热变形行为及组织演变

Hot Deformation Behavior and Microstructure Evolution of a New High Strength Aluminum Alloy

摘要:

采用高温压缩实验研究了新型Al-Zn-Mg-Cu高强铝合金在温度300~450 ℃、应变速率0.001~10 s-1和压缩变形程度30%~80%范围内的热变形行为和组织演变。分析了该合金在实验参数范围内变形的应力-应变曲线特征。动力学分析获得该合金热变形的应力指数和激活能分别为4.97和150.07 kJ/mol, 表明合金的热变形主要受扩散所控制。金相组织观察发现，随着变形温度的升高或应变速率的降低，变形组织晶内析出相逐渐溶入基体组织，晶内组织逐渐趋于均匀；同时粗大的晶粒沿变形方向拉长，晶界难溶相的碎化和弥散化程度增大。TEM和EBSD (electron back-scattered diffraction) 组织分析表明，该合金在高温压缩变形过程中组织演变主要是亚晶的形成和完善的过程，热变形组织演变机理为动态回复和大应变几何动态再结晶

Abstract:

Hot deformation behavior and microstructure evolution of a new high strength Al-Zn-Mg-Cu alloy were studied in a temperatures range of 300~450 oC, a strain rates range of 0.001~10 s-1, and a reductions range of 30%~80% by high-temperature compression tests. Characteristics of stress-strain curves were investigated. Kinetics analyses indicate that the stress exponent and hot deformation activation energy are 4.97 and 150.07 kJ/mol, respectively, suggesting that deformation would be controlled by diffusion mainly. Microstructure observation by OM shows that precipitates in the deformed grain dissolve into the matrix and microstructure in the deformed grain become homogeneous gradually at higher temperatures or lower strain rates, while the prior coarse grains elongate along the deformation direction, and coarse un-dissolved phases at grain boundaries become smaller and more dispersive at the same time. The results of TEM and EBSD show that microstructure evolution during hot deformation of the alloy is characterized by generation and formation of sub-grains, and mechanisms of microstructure evolution during hot deformation is dynamic recovery and geometric dynamic recrystallization at large reductions.