Mg-4Sm-2Zn-0.5Zr合金热变形行为及其挤压工艺与组织性能研究

发布时间：2018-02-27 11:45

本文关键词： Mg-4Sm-2Zn-0.5Zr合金本构模型热加工图热挤压显微组织力学性能　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：镁合金以其低密度、高比强度和其他优良特性被广泛应用在航空航天、汽车及电子等领域。随着科学技术和国防建设的提高,对于高性能轻质镁合金的需求也越来越大。一方面,稀土元素对镁合金强化效果显著,但成本问题始终制约稀土镁合金的应用发展;另一方面,变形镁合金表现出优于铸造镁合金的力学性能。为满足对低成本耐热镁合金的强烈需求,本文自主开发出Mg-4Sm-2Zn-0.5Zr新型合金,并研究其热变形行为,为制定该合金的热加工工艺提供理论指导。本文以自主开发的Mg-4Sm-2Zn-0.5Zr合金为研究对象,以Gleeble等温压缩实验为基础,研究了该合金热变形过程的本构模型和热加工图,基于热加工图探讨了合金的热挤压工艺,并进行了组织分析和力学性能测试。主要研究内容如下:(1)通过等温压缩实验绘制出Mg-4Sm-2Zn-0.5Zr合金在温度350-450°C、应变速率0.001-1s-1变形条件下的真应力应变曲线,发现流变应力随着温度上升或应变速率降低而减小。根据实验数据,首先构建了该合金峰值应变条件下的Arrhenius本构方程,然后通过对材料参数的拟合,建立了一般应变条件下的应变补偿型Arrhenius本构方程。通过本构方程的预测应力值与实验应力值对比,表明本构方程的有效性。(2)基于Matlab软件平台,以应变速率、温度和应变作为输入,以流变应力作为输出,通过设置合理的BP神经网络参数,创建Mg-4Sm-2Zn-0.5Zr合金的流变应力本构关系模型,然后用遗传算法和粒子群算法优化BP神经网络的权值和阀值,建立了合金本构关系的GA-BP模型和PSO-BP模型。(3)建立了该合金基于神经网络模型和Muthy失稳准则的热加工图。综合应变对于热加工图的影响,建立起该合金的三维加工图。根据加工图中功率耗散因子和失稳区的分布,同时结合合金热W'缩过程的微观组织分析,确定了合金的最佳工艺参数。(4)以加工图给出的最佳温度与应变速率为目标,通过对不同初始温度与挤压速度的挤压过程进行数值模拟,获得最佳挤压工艺参数。另外,对挤压态合金进行微观组织分析和力学性能测试,并与铸态合金进行对比。
[Abstract]:Magnesium alloys are widely used in aerospace, automotive and electronic fields because of their low density, high specific strength and other excellent properties. On the one hand, the effect of rare earth elements on magnesium alloy strengthening is remarkable, but the cost problem has always restricted the development of rare earth magnesium alloy application, on the other hand, The mechanical properties of wrought magnesium alloys are superior to those of cast magnesium alloys. In order to meet the strong demand for low cost heat-resistant magnesium alloys, a new type of Mg-4Sm-2Zn-0.5Zr alloy was developed and its hot deformation behavior was studied. In order to provide theoretical guidance for drawing up the hot working process of the alloy, the constitutive model and hot working diagram of the alloy during hot deformation were studied on the basis of the Gleeble isothermal compression experiment and the self-developed Mg-4Sm-2Zn-0.5Zr alloy. Based on the hot working diagram, the hot extrusion process of the alloy is discussed. The microstructure and mechanical properties of Mg-4Sm-2Zn-0.5Zr alloy were analyzed and tested. The main contents are as follows: (1) the true stress-strain curve of Mg-4Sm-2Zn-0.5Zr alloy at 350-450 掳C, strain rate 0.001-1s-1 was drawn by isothermal compression experiment. It is found that the flow stress decreases with the increase of temperature or the decrease of strain rate. According to the experimental data, the Arrhenius constitutive equation under the peak strain condition of the alloy is first constructed, and then the fitting of the material parameters is carried out. The strain compensated Arrhenius constitutive equation under the general strain condition is established. By comparing the predicted stress value of the constitutive equation with the experimental stress value, it is shown that the constitutive equation is effective and based on the Matlab software platform. Temperature and strain are taken as input and rheological stress is taken as output. By setting reasonable parameters of BP neural network, the constitutive model of rheological stress of Mg-4Sm-2Zn-0.5Zr alloy is established. Then genetic algorithm and particle swarm optimization algorithm are used to optimize the weight and threshold of BP neural network. The GA-BP model and PSO-BP model of the constitutive relation of the alloy are established. The hot working diagram of the alloy based on the neural network model and the Muthy instability criterion is established. The influence of the comprehensive strain on the hot working diagram is obtained. According to the distribution of the power dissipation factor and the instability zone in the machining diagram, the microstructure of the hot W' shrinkage process of the alloy was analyzed. The optimum processing parameters of the alloy are determined. The optimum temperature and strain rate given in the machining diagram are taken as the goal. The optimum extrusion process parameters are obtained by numerical simulation of the extrusion process at different initial temperatures and extrusion speeds. The microstructure and mechanical properties of the extruded alloy were analyzed and compared with the as-cast alloy.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22;TG379

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