AZ31B镁合金板材热轧变形行为研究

【作者】 蔡志勇；

【导师】 余琨；

【作者基本信息】 中南大学 ， 材料学， 2010， 硕士

【摘要】 本文借助物理模拟和数值模拟技术,采用Gleeble-1500热模拟实验机和MARC有限元分析软件,对AZ31B镁合金热塑性变形行为进行了研究。本文以AZ31B镁合金高温等温压缩变形的真应力一真应变曲线的特征分析为基础,研究了变形温度、变形速度对流变应力的影响规律,建立了AZ31B镁合金流变应力本构方程；利用热力耦合弹塑性有限元法对合金的轧制过程进行了数值模拟分析；并对AZ31B镁合金多道次热轧变形进行了实验模拟。得出以下结论：1.AZ31B镁合金在变形温度为200～500℃、应变速率为0.01～10 s-1范围内变形时的真应力—真应变曲线为动态再结晶型,流变应力随变形温度的升高和变形速率的降低而减小。该合金高温变形时的本构方程为：其中,2.对AZ31B镁合金在热压缩变形过程中的组织演变进行了观察,发现热变形过程的动态再结晶是主要的应变软化机制。AZ31B镁合金在变形温度300℃时开始发生动态再结晶,温度升高或应变速率降低有利于再结晶的加快和再结晶晶粒的长大。3.二维有限元模拟研究结果表明：AZ31B镁合金板材从表面到心部,在一定厚度范围内出现明显的温度梯度；在整个轧制过程中AZ31B板材内部节点的温度变化缓慢,而板材表面节点的温度变化较为剧烈。轧制完成后,表面温度最低点为400℃,心部温度为460℃左右。轧制变形区内拉、压应力的转折处约为板材厚度的1/4处。最大拉应力分布在板材中心位置,最大压应力分布在板材表面。轧制过程最大应变均发生在板材的次表面,从次表面至板材中心部,塑性应变依次降低,最小等效应变发生在板材中心部芯部。其结果与实验情况吻合较好。4.本文对AZ31B镁合金热轧过程进行三维模拟,由于研究条件限制,三维轧制过程仅进行了四个道次的有限元模拟。对轧制过程中板材成形规律进行了分析,对板材温度和轧制速度对变形的影响进行模拟。结果表明,适当提高轧制温度可以减轻变形不均匀性并降低温升；提高变形速度使温升加剧。5.在Gleeble-1500热模拟机上,对AZ31B镁合金多道次热轧进行实验模拟。经流变应力分析发现,AZ31B镁合金在多道次热轧变形过程中流变应力表现出加工硬化——应变软化——二次加工硬化的特征。更多还原

【Abstract】 In the dissertation, hot deformation behaviors of AZ31B magnesium alloy have been extensively investigated with physical and numerical simulation techniques.True stress-strain behaviors were investigated by hot compressive testing on Gleeble-1500 thermal simulator at temperature range of 250 to 500℃with strain rate varying from 0.01 to 10 s-1. The relationships between flow stress, strain rate and deformation temperature were analyzed. The coupled thermo-mechanical simulation analysis of rolling for the alloy was done by using elastic-plastic finite element method on the software platform of MSC.MARC. The results are as follows:1. True stress-strain behavior of the alloy at different strain rate and temperature is characteristic as dynamic recrystallization. And the flow stress decreases with the increase of temperature, while increases with the increases with strain rate. The constitutive equation established by Zener-Hollomo parameter method are: Where,2. Microstructure evolution of AZ31B magnesium alloy during hot-compressive deformation was observed. The results show that, dynamic recrystallization was the main strain softening mechanism during hot deformation. Dynamic recrystallization of AZ31B magnesium alloy start at the temperature of 300℃. Increase of temperature or decrease of strain rate is benefits for dynamic recrystallization or coursen of dynamic recrystallization grains.3. There is obvious temperature gradicent from surface to centre of the workpiece within a certain depth. And the surface temperature changes sharply during the rolling process, while the center temperature changes little. After rolling, the surface temperature is 400℃, while the temperature of center is 460℃. Maximum compressive stress and maximum tensile stress occurr in the surface and center in the deforming region. During the rolling process, strain of secondary surface layer is biggest.The equivalent strain gradually decreases from secondary surface to the center, and the smallest equivalent strain occurres in the center. The simulated results show a satisfactory coincidence with the industrial measured data.4. In this dissertation, three-dimensional simulation of rolling for the AZ31B alloy was done by using finite element method. As the study is limited by conditions, three-dimensional rolling processes were simulated only four passes. Forming law of rolling process of AZ31B magnesium alloy was simulated by finite element method.The effect of process parameters, including the deformation temperature and the deformation velocity on the equivalent stress, the equivalent strain, the temperature raise during rolling deformation has been studied by numerical simulation.5. The experiment simulation of multi-pass hot rolling of AZ31B magnesium alloy was done by Gleeble-1500 thermal mechanical simulator. By flow stress analysis, the flow stress of AZ31B magnesium alloy in the multi-pass hot rolling process shows work hardening stage-softening stage-the second work-hardening characteristics.更多还原