热轧态5A90铝锂合金细晶板低温超塑性及组织演变

Low Temperature Superplasticity and Microstructure Evolution of Hot Rolled 5A90 Al-Li Fine-grained Sheets

以0.0004~0.05 s^(-1)应变速率拉伸测试了热轧态5A90铝锂合金细晶板在375~475℃温度区间的应力-应变曲线,并建立了Arrhenius本构模型。采用电子背散射衍射(EBSD)观察了不同变形温度、应变和应变速率下的晶粒和晶界分布,分析了5A90细晶板高温变形时的组织演变规律。结果表明,原始5A90热轧板的平均晶粒尺寸仅为1.27μm,在375℃和0.002 s^(-1)下的伸长率高达607.9%,呈现优异的低温超塑性变形能力。当变形温度为375~425℃时,激活能是113.72 kJ/mol,超塑性变形机理为晶界滑移和位错滑移;当变形温度高于450℃时,由于温度效应,晶粒发生异常长大,细晶板超塑性变形能力下降,且变形抗力增加。热轧态5A90细晶板适宜的超塑性变形条件为变形温度375~425℃和应变速率为0.002~0.01 s^(-1)。

The stress-strain curves of the hot rolled 5A90 Al-Li alloy fine-grained sheets at the deformation temperature of 375-475℃were tested by the tensile test with strain rate of 0.0004-0.05 s^(-1),and the Arrhenius constitutive model was established.The grains and distribution of grain boundaries were observed at different deformation temperatures,strains and strain rates by electron back sacttering diffraction(EBSD),and the microstructure evolution of 5A90 fine-grained sheets during high temperature deformation was analyzed.The results show that the average grain size of the original 5A90 hot rolled sheets is only 1.27μm,and the elongation at 375℃and 0.002 s^(-1)is as high as 607.9%,showing excellent low temperature superplastic deformation ability.When the deformation temperature is 375-425℃,the activation energy is 113.72 kJ/mol,the superplastic deformation mechanism is grain boundary slip and dislocation slip;when the deformation temperature is higher than 450℃,due to the temperature effect,the grains grow abnormally,the superplasticity deformation ability of the fine-grained sheets decreases,and the deformation resistance increases.The suitable superplastic deformation condition of hot rolled 5A90 fine-grained sheets is the deformation temperature of 375-425℃and the strain rate of 0.002-0.01 s^(-1).