基于修正流变应力的2050铝锂合金统一本构方程和热加工图

Constitutive modeling and processing maps of 2050 Al-Li alloy based on corrected flow stress

通过热压缩模拟实验研究热轧态2050铝锂合金在340~500℃、0.001~10 s^(−1)下的高温塑性变形行为,分析了热压缩过程中的外摩擦和温度变化对合金流变应力的影响,并且对测量得到的流变应力进行了修正。基于修正流变应力构建了热轧态2050铝锂合金的流变应力统一本构方程,包括应变修正Arrhenius模型和Hensel-Spittel模型,同时还绘制了合金在不同应变量下的热加工图,并通过金相显微镜观察了不同变形条件热压缩试样的晶粒形貌。结果表明:外摩擦会导致流变应力测量值高于理想值,而绝热温升造成的温度变化会导致流变硬化或软化,使得流变应力改变。统一本构方程模型在拟合区间内都具有较高的拟合性,应变修正Arrhenius模型在稳态流变阶段的拟合程度较高,Hensel-Spittel模型能描述合金在整个热变形过程的流变应力变化。通过热加工图可以发现热轧态2050铝锂合金最佳的加工范围是温度420~500℃、应变速率0.001~0.003 s^(−1)区域。流变失稳区为温度350~480℃、应变速率3.16~10 s^(−1)和温度340~360℃、应变速率0.1~3.16 s^(−1)两个区域。合金在稳定区主要发生动态回复和动态再结晶,而在失稳区主要发生局部流变。

The hot deformation behavior of hot-rolled 2050 Al-Li alloy at 340−500℃and 0.001−10 s^(−1) was studied by hot compression simulation experiment.The effects of friction and temperature variation on the flow stress of the alloy during the hot compression process were analyzed,and the true stress−strain curves were corrected.Based on the corrected curves,the constitutive equation of the hot-rolled 2050 Al-Li alloy was constructed,including the strain modified Arrhenius model and Hensel-Spittel model.At the same time,the processing maps of the alloy under different true strains were established.The microstructure of the hot compressed samples was observed by the optical microscope.The results show that the friction will cause the measured value of true stress to be higher than the actual stress value,and the temperature change caused by adiabatic heat will cause flow softening and decrease the true stress.The two types of constitutive equation models both fit well in the fitting interval.The strain-compensated Arrhenius model has a higher degree of mathematical fitting in the steady-state.The Hensel-Spittel model can describe the entire hot deformation process of the alloy.It can be found from the processing maps that the best processing range for the hot-rolled 2050 Al-Li alloy is within the region that the temperature ranges from 420℃to 500℃and the strain rate ranges from 0.001 s^(−1) to 0.003 s^(−1).The instability areas locate on two regions,there are region of temperature 350−480℃,strain rate 3.16−10 s^(−1) and region of temperature 340−360℃,strain rate 0.1−3.16 s^(−1).The alloy mainly undergoes dynamic recovery and dynamic recrystallization in the stable area,while the flow localization mainly occurs in the instability area.