3A21铝合金筒形件旋压织构的演化规律研究

发布时间：2018-02-26 08:30

本文关键词： 筒形件多道次单向及交叉旋压 3A21铝合金晶体塑性变形织构　出处：《哈尔滨工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：筒形件旋压是典型的局部加载成形工艺,具有省料、成形性能好、工装简单等优点,是制造大型薄壁无缝筒形件的有效方法,已广泛用于航天、航空、兵器、舰船和机械等工业领域。由于旋压变形过程非常复杂,影响因素众多,到目前为止,大量的旋压技术研究工作仍定位于零件成形,旋压缺陷和几何精度控制等方面,零件力学性能控制方面考虑得较少。晶体学织构能对金属材料力学性能产生重大影响,织构也就成为控制材料力学性能的重要手段之一。强力旋压过程中金属产生剧烈的塑性流动,形成特定变形织构,从而影响到旋压件的力学性能。本文将以经过退火处理的挤压无缝3A21铝合金管材,进行多道次单向及交叉旋压实验,并进行筒形件的力学性能和旋压织构研究;采用ABAQUS对筒形件旋压过程进行相应的有限元模拟,并利用用户材料子程序VUMAT提取旋压筒形件的变形历史,然后再通过UMAT实现率相关的晶体塑性本构关系,建立多晶体模型,通过拟合简单压缩应力应变曲线确定室温3A21铝合金的滑移系剪切变形参数,将提取的变形梯度历史并加载到多晶体模型上,基于晶体塑性理论,实现室温3A21铝合金筒形件多道次不同方式旋压变形织构的模拟。进行模拟织构与实测织构的比较。进行多道次旋压实验后,观察旋压件微观组织的演化:多道次旋压过程中少量第二相始终弥散分布在晶界处,其含量不影响晶体学织构的统计。当旋压到第2道次后,晶粒在ND方向近似于均匀分布,晶粒沿RD方向和TD方向等比例拉长。从第4道次到低8道次,晶粒主要沿着RD方向伸长形成长条状的晶粒,沿TD方向也存在一定的拉长,随着晶粒的细化形成纤维状;从力学性能变化规律来看,对于交叉旋压,旋压件环向压缩屈服强度要高于轴向压缩屈服强度,旋压件环向抗拉强度与轴向抗拉强度并没有产生太大的差距,环向抗拉强度略高于轴向抗拉强度。可知交叉旋压相对于单向旋压,有效调控了晶粒取向,提高了筒形件变形抗力。通过对3A21铝合金筒形件多道次单向与交叉旋压变形三维有限元模拟,分析筒形件旋压后的外表面和轴截面的应力应变分布,发现筒形件旋压由于局部加载和变形周期性叠加的特点,筒形件旋压变形使材料承受方向不断变化的拉伸、压缩和剪切的复合变形。对比多道次旋压有限元模拟获得的模拟织构与实测织构,分析旋压晶粒取向演化规律:变形开始时,单向与交叉旋压的晶体取向形成明显{110}112织构,随着减薄率的增加,晶粒取向逐渐靠近难变形相位,到第4、6、8道次,金属取向不再是单一的织构,而是逐渐形成{110}112、{112}111、{123}634等类型的织构。我们还发现,在同一变形量下,材料的织构类型近似等同,单向旋压的织构分布较交叉旋压相对弥散,相对交叉旋压强度较低,因此交叉旋压具有较好的调控晶粒取向的作用,提高了筒形件变形抗力。
[Abstract]:Cylinder spinning is a typical local loading forming process, which has the advantages of saving material, good formability, simple tooling and so on. It is an effective method for manufacturing large thin-walled seamless cylindrical parts. It has been widely used in aerospace, aviation and weapons. As the process of spinning deformation is very complex and there are many influencing factors, up to now, a lot of research work on spinning technology is still focused on parts forming, spinning defects and geometric precision control, etc. The control of mechanical properties of parts is less considered. The crystallographic texture can have a significant effect on the mechanical properties of metal materials. Texture has become one of the most important means to control the mechanical properties of materials. In order to affect the mechanical properties of spinning parts, this paper will carry out multi-pass unidirectional and cross-spinning experiments with annealed seamless 3A21 aluminum alloy tubes, and study the mechanical properties and spinning texture of cylindrical parts. The ABAQUS is used to simulate the spinning process of the cylinder, and the deformation history of the spinning cylinder is extracted by the user material subroutine VUMAT, and then the polycrystalline model is established by using the constitutive relation of crystal plasticity related to the realization rate of UMAT. The slip system shear deformation parameters of room temperature 3A21 aluminum alloy were determined by fitting the simple compression stress-strain curve. The extracted deformation gradient history was loaded into the polycrystalline model and based on the theory of crystal plasticity. The simulation of multi-pass deformation texture of room temperature 3A21 aluminum alloy cylinder is realized. The comparison between the simulated texture and the measured texture is carried out. After the multi-pass spinning experiment, The microstructure evolution of spinning parts is observed: a small amount of second phase is distributed at grain boundaries throughout the multi-pass spinning process, and its content does not affect the statistics of crystallographic texture. When spinning to the second pass, the grain distribution is approximately uniform in ND direction. From the 4th pass to the low 8 pass, the grains are mainly elongated along the Rd direction and elongated along the TD direction, forming fibrous with the refinement of the grains. According to the law of mechanical properties, for cross spinning, the yield strength of annular compression is higher than that of axial compression, and there is not much difference between the annular tensile strength and axial tensile strength. The circumferential tensile strength is slightly higher than the axial tensile strength. The deformation resistance of the cylindrical part is improved. The stress and strain distribution of the outer surface and axial section of the cylindrical part after spinning is analyzed by simulating the multi-pass unidirectional and cross-spinning deformation of the 3A21 aluminum alloy tube by three dimensional finite element method. It is found that due to the characteristic of local loading and periodic superposition of deformation, the spinning deformation of the cylindrical part makes the material endure the continuously changing tensile direction. Compression and shear composite deformation. Compared with the simulated texture obtained by multi-pass spinning finite element simulation and the measured texture, the evolution law of spinning grain orientation was analyzed: at the beginning of deformation, the crystal orientation of unidirectional and cross-spinning formed obvious {110} 112 texture. With the increase of thinning rate, the grain orientation is closer to the difficult deformation phase. At the 4th pass, the metal orientation is no longer a single texture, but gradually forms {110} 112, {112} 111, {123} 634 and other types of texture. We also find that under the same deformation amount, the grain orientation is not only a single texture, but also forms a texture of {110} 112, {112} 111, {123} 634 and so on. The texture type of the material is approximately the same, and the texture distribution of unidirectional spinning is relatively dispersed and the relative cross spinning strength is lower than that of cross spinning. Therefore, cross spinning has a better effect on regulating grain orientation and improving the deformation resistance of cylindrical parts.
【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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