【作者】 李冰；

【导师】 花福安；

【作者基本信息】 东北大学 ， 材料加工工程， 2020， 硕士

【摘要】 镁合金作为典型的密排六方(HCP)晶体结构的金属材料,在常规轧制工艺下,会形成较强的基面织构,从而影响镁合金的成形性能。本文以AZ31镁合金为对象,通过实验和模拟方法研究常规轧制(NR)、交叉轧制(CR)、异步轧制(DSR)和交叉异步轧制(CDSR)工艺对材料组织性能、织构演变和成形性能的影响规律,目的是获得组织细小均匀、基面织构较弱、成形性能良好的AZ31轧制板材及相应的轧制工艺。本课题的主要研究内容和研究成果如下:(1)对初始挤压态AZ31镁合金板材微观组织进行表征,利用EBSD测得初始板材的微观织构,沿镁合金板材ED方向做单轴拉伸和平面压缩,沿TD方向做单轴拉伸,测得材料的真应力-应变曲线。利用晶体塑性自洽模型拟合真应力-应变曲线得到镁合金单晶体滑移系的硬化参数。(2)利用自洽模型模拟NR、CR、DSR和CDSR工艺条件下AZ31镁合金的织构演化,结果表明,随着变形量的增加,晶粒的c轴向ND方向偏转,形成典型的基面织构。NR和DSR工艺下的基面织构沿TD方向呈椭圆形分布,CR和CDSR的基面织构沿RD和TD呈圆形的均匀分布,CDSR基面织构偏离ND方向,与RD方向成5°,与TD方向成10°左右分布。由于DSR工艺会产生附加剪切应力使部分晶粒的c轴偏离ND方向,从而减弱基面织构强度。CR和CDSR工艺得到的基面织构分布更加均匀,织构强度较NR和DSR工艺稍有提高。(3)对AZ31镁合金板材进行NR、CR、DSR和CDSR热轧实验,并对轧制后的镁合金进行微观组织观察,结果表明,与NR工艺相比,CR、DSR和CDSR工艺条件下的镁合金板材动态再结晶更加充分,使得镁合金板材的晶粒尺寸得到细化;CR和CDSR工艺条件下的镁合金板材微观组织更加均匀,而DSR工艺条件下的镁合金组织中出现少量的细长晶粒组织,组织均匀性减弱;CR、DSR和CDSR工艺有效降低基面织构强度,降低最为显著的为CDSR工艺。(4)在室温下,对轧后镁合金板材的0°、45°和90°方向进行力学性能进行检测,结果发现,与NR工艺相比,CR、DSR和CDSR工艺对镁合金板材的抗拉强度有一定的提升效果;CR工艺和CDSR工艺对镁合金的塑性应变比起到明显提高作用,并且轧后镁合金板材的各向异性有所降低,其中最为显著的是CDSR工艺,各向异性系数降低到为0.03,使得镁合金在拉深成形过程中形成的“制耳”效应得到显著改善。(5)实验与模拟的结果对比表明,模拟得到的织构类型与实验得到的织构基本一致,尤其是NR和DSR工艺,对于织构强度CR工艺和CDSR工艺表现出一定的差异性,模拟结果显示,本文考虑是由于模拟结果忽略了动态再结晶的影响,并且轧制道次间回炉保温起到一定的退火作用,所以导致模拟与实验结果出现一些偏差。更多还原

【Abstract】 As a typical metal material with dense hexagonal(HCP)crystal structure,magnesium alloy will form a strong basal texture under conventional rolling process,which will affect the forming properties of magnesium alloy.Based on AZ31 magnesium alloy as the object,through experiment and simulation study of normal rolling(NR),cross rolling(CR),different speed rolling(DSR)and cross different speed rolling(CDSR)process on the material microstructure,texture evolution and the influence law of forming performance,the purpose is to obtain fine uniform,weak basal texture,good formability of AZ31 rolled plate and the corresponding rolling technology.The main research content and research results of this subject are as follows:(1)The microstructure of AZ31 magnesium alloy plate in the initial extrusion state was characterized,the microstructure of the initial plate was measured by EBSD,and the true stress-strain curve of the material was measured by uniaxial stretching and plane compression along the ED direction of magnesium alloy plate,and uniaxial stretching along the TD direction.The hardening parameters of single crystal slip system of magnesium alloy were obtained by using the true stress-strain curve fitting with the crystal plasticity self-consistent model.(2)The texture evolution of AZ31 magnesium alloy under NR,CR,DSR and CDSR processing conditions was simulated with a self-consistent model.The texture of the basal plane obtained by NR and DSR processes forms a symmetrical oval distribution along the TD direction,the texture of CR and CDSR presents an approximately circular uniform distribution along the RD direction and TD direction,and the texture of CDSR basal plane deviates from the ND direction,forming a distribution of 5°with the RD direction and about 10° with the TD direction.Due to the additional shear stress generated by DSR process,the c-axis of some grains deviated from the ND direction,thus weakening the texture strength of the substrate.The texture distribution of CR and CDSR was more uniform,but the texture strength was slightly higher than that of NR and DSR.(3)The hot-rolling experiments of NR,CR,DSR and CDSR on AZ31 magnesium alloy plates were carried out,and the microstructure of the rolled magnesium alloy was observed.The results showed that the dynamic recrystallization of the magnesium alloy plates under CR,DSR and CDSR processes was more complete than that under NR processes,and the grain size of the magnesium alloy plates was refined.Under CR and CDSR processes,the microstructure of magnesium alloy plate is more uniform,while under DSR processes,a small amount of thin grain microstructure appears,which weakens the microstructure uniformity.CR,DSR and CDSR processes can effectively reduce the strength of basal texture,and the most significant reduction is CDSR processes.(4)At room temperature,the mechanical properties of rolled magnesium alloy plates were tested in 0°,45° and 90° directions.The results showed that compared with NR process,CR,DSR and CDSR processes could improve the tensile strength of magnesium alloy plates.CR process and CDSR process significantly increased the plastic strain ratio of magnesium alloy,and the anisotropy of magnesium alloy plate decreased after rolling.The most significant is the CDSR process,with the anisotropy coefficient reduced to 0.03,which significantly improved the "ear making" effect of magnesium alloy formed in the drawing process.(5)Experiments compared with the results of simulation show that the simulation to get the texture types of the texture of basic consistent with the experiment,NR and DSR technology,in particular,the texture intensity CR process and CDSR show some differences,simulation results show that the is due to the simulation results,this paper ignores the influence of dynamic recrystallization,and rolling passes between oven heat preservation of annealing effect,so the simulation and experimental results have some deviation.更多还原