LZ91镁锂合金超塑性能及负角度盒形件超塑成形

发布时间：2018-07-08 11:31

本文选题：镁锂合金 + 超塑性　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：随着航天工业中对优质轻合金的要求越来越高,镁合金成为迅速崛起的新型工程材料。镁锂合金在结构金属材料中是最轻的,被称为超轻镁合金。镁锂合金具有高比强度、高弹性模量,良好的阻尼减震性、电磁屏蔽性等优点。镁合金在超塑性状态具有大延伸、变形抗力低、良好的成形性能等优势,这些特点拓宽了镁合金超塑成形在工业中的应用。本文以LZ91镁锂合金的超塑成形为背景,对其超塑性能、微观组织演变、成形工艺进行了研究。通过LZ91镁锂合金的高温拉伸实验,得到材料变形的最佳超塑成形温度及应变速率。以真应力-真应变拉伸曲线为基础,计算应变速率敏感性指数m值,构造合金的热变形本构方程。对高温拉伸后的晶粒组织及不同应变速率下合金中的位错演变进行了研究。通过拉伸实验数据,利用MSC.MARC有限元模拟软件对负角度盒形件的不同成形工艺方案进行模拟,根据模拟结果优化成形工艺参数,并在此基础上实现了LZ91镁锂合金负角度盒形件的超塑成形。LZ91镁锂合金的高温拉伸实验表明,材料的最佳超塑成形温度为300oC,应变速率是5×10-4s-1,此时合金的延伸率为812.6%。在250oC下材料的应变速率敏感性指数m值为0.65,说明材料的超塑性能良好;通过回归分析获得材料的热变形本构方程。对高温拉伸变形后试样标距部位的晶粒组织进行观察后可得,超塑拉伸后,晶粒大小随着应变速率的降低和温度的升高而不断长大;对不同应变下镁锂合金内部的位错像进行观察发现,拉伸过程中位错增殖速度很慢,密度很低,较低的位错密度不足以发生动态再结晶。两者共同作用造成应变硬化现象。使用MSC.MARC有限元模拟软件对LZ91镁锂合金负角度盒形件的不同成形工艺方案进行模拟,最终选择固体粉末介质胀形方案。通过讨论摩擦力对成形零件厚度分布的影响,从而优化成形工艺。最后模拟计算得到零件成形时的压力-时间曲线。根据以上实验结果,在250oC的条件下采用分瓣模具超塑成形出负角度盒形件。
[Abstract]:With the requirement of high quality light alloy in aerospace industry, magnesium alloy has become a new type of engineering material. Magnesium-lithium alloys are the lightest in structural metal materials and are called super-light magnesium alloys. Mg-Li alloy has the advantages of high specific strength, high elastic modulus, good damping and damping, electromagnetic shielding and so on. Magnesium alloy has the advantages of large extension, low deformation resistance and good formability in superplastic state. These characteristics broaden the application of superplastic forming of magnesium alloy in industry. The superplastic properties, microstructure evolution and forming process of LZ91 Mg-Li alloy were studied in this paper. The optimum superplastic forming temperature and strain rate of LZ91 magnesium-lithium alloy were obtained by high temperature tensile test. Based on the true stress-strain tensile curve, the strain rate sensitivity exponent m is calculated and the constitutive equation of hot deformation of the alloy is constructed. The grain structure after high temperature tensile and dislocation evolution in alloys at different strain rates were studied. By using the tensile test data and the finite element simulation software MSC.MARC, the different forming process schemes of the negative angle box parts are simulated, and the forming process parameters are optimized according to the simulation results. On this basis, the superplastic forming of LZ91 magnesium-lithium alloy with negative angle box. The high temperature tensile test of LZ91 magnesium-lithium alloy shows that the optimum superplastic forming temperature is 300oC, the strain rate is 5 脳 10-4s-1, and the elongation of the alloy is 812.6. The strain rate sensitivity index m of the material is 0.65 at 250oC, which indicates that the superplastic property of the material is good, and the constitutive equation of thermal deformation of the material is obtained by regression analysis. After high temperature tensile deformation, the grain size increases with the decrease of strain rate and the increase of temperature. The dislocation images of magnesium-lithium alloy under different strain were observed. It was found that the dislocation proliferation rate was very slow and the density was very low during the tensile process, and the low dislocation density was not sufficient for dynamic recrystallization. The joint action of the two causes strain hardening. The different forming processes of LZ91 magnesium-lithium alloy negative angle box parts were simulated by using MSC.MARC finite element simulation software. Finally, the medium bulging scheme of solid powder was selected. By discussing the influence of friction force on thickness distribution of forming parts, the forming process is optimized. Finally, the pressure-time curve is obtained by simulation. According to the above experimental results, the negative angle box was formed by using the split die superplastic at 250oC.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG306

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