LZ91镁锂合金热变形的本构模型及微观组织演变

Constitutive model and microstructure evolution of LZ91 magnesium lithium alloy during hot deformation

为了研究轧制态LZ91镁锂合金的超塑性变形特征,对其在不同温度(513、553、593和633 K)、不同应变速率(9.06×10^(-4)、4.53×10^(-3)和2.26×10^(-2)s^(-1))下进行了单轴热拉伸试验。结果表明:LZ91合金流变应力曲线呈现典型的动态再结晶特征,峰值应力随变形温度升高(应变速率降低)而降低;在试验温度范围内合金的平均热变形激活能Q=89.74 kJ/mol,在633 K时的应变速率敏感指数m为0.422,说明合金具备超塑性特征,且超塑性变形机制为晶界扩散控制的晶界滑移。轧制态LZ91合金的组织为α-Mg相和β-Li相,且α-Mg相随机分布在β-Li相中,热变形过程中合金产生明显的动态再结晶。

In order to investigate the superplastic deformation characteristics of as rolled LZ91 magnesium lithium alloy,the uniaxial hot tensile test was carried out at different temperatures(513 K,553 K,593 K and 633 K)and different strain rates(9.06×10^(-4) s^(-1),4.53×10^(-3 )s^(-1) and 2.26×10^(-2) s^(-1)).The results show that the flow stress curve of the LZ91 alloy presents typical characteristics of dynamic recrystallization,and the peak stress decreases with the increase of deformation temperature(decrease of strain rate).The average hot deformation activation energy of the alloy is 89.74 kJ/mol in the range of test temperature and the strain rate sensitivity index m is 0.422 at 633 K,which indicates that the alloy has superplastic characteristics and the superplastic deformation mechanism is grain boundary slip controlled by grain boundary diffusion.The microstructure of the as rolled LZ91 alloy is composed ofα-Mg andβ-Li phases,theα-Mg phase is randomly distributed in theβ-Li phase,and the dynamic recrystallization occurs during hot deformation.