【作者】 李志刚；

【导师】 柳林；

【作者基本信息】 华中科技大学 ， 材料学， 2014， 硕士

【摘要】 铝合金材料以成形性好，比强度高，耐蚀性好等优点在航空航天、汽车工业、兵器工业等应用领域得到广泛应用。而传统冲压成形工艺复杂，产品成形缺陷多。电磁成形技术在近些年来备受关注，主要得益于它本身具有非接触成形，低回弹性，高重复性和提高成形极限特点。电磁成形技术是利用脉冲磁场产生的洛伦兹力，使金属工件进行无机械接触、无模成形。电磁成形是的应变率范围在103s-1到104s-1之间的高速成形技术。高速成形技术通常会产生不同于准静态、低应变率成型技术的变形行为、微结构和织构现象，进而影响材料的性能，因而对电磁成形过程中的变形行为、微结构和织构演变的研究具有重要意义。本论文主要研究了1050A工业纯铝板材在电磁胀形下的微观组织结构和形变织构的演变规律，并考虑电磁胀形下的复杂应变路径和高应变率对微观组织结构和形变织构的演变的影响。论文中采用网格应变法测量了电磁胀形后工件的应变分布，利用背散射电子取向测试技术（EBSD）对工业纯铝的晶粒形貌和变形织构进行的表征，同时结合透射电子显微镜技术对变形后的位错组态进行了表征。论文首先研究了变形织构演变的问题。为了简化研究，采用样品次应变和主应变之间的应变比来反映应变路径的变化，研究发现，成形工件中出现三种不同应力应变状态的典型区域，即近似单轴拉伸区，非双轴等轴区和双轴等轴区。电磁胀形后纯铝板材的整体织构转变路径随着应变比增加时，起始的旋转立方织构首先转向立方织构，然后分化，分别形成戈斯和旋转戈斯织构，最终倾向于稳定在P织构。此外，论文以戈斯织构和旋转戈斯织构为典型代表，用以研究应变路径和高速率应变的对织构演变的影响。之后，论文进一步研究了电磁胀形下纯铝板材塑性变形引起的晶体取向改变过程中局部晶粒取向变化和变形产生的动态回复影响。研究发现随着应变比的增加，应变状态依次经历近似单轴拉伸，非等轴双轴拉伸到近似等轴双轴拉伸，在此过程中局部晶粒的取向分散越来越大，晶粒绕着主应变轴和次应变轴转动的趋势增强。同时论文结合取向因子的估算简化，对滑移系开动情况进行了初步分析。最后研究了高应变率下的温升产生动态回复的问题，动态回复能够在减弱晶体缺陷密度的同时，促进滑移系开动和晶体取向的改变，从而影响变形织构的总体分布强度。更多还原

【Abstract】 Aluminum alloys have been widely used in industrial fields of such as aviation,vehicle and ordnance due to their excellent properties: good formability, high specificstrength and corrosion resistance. However, there are someforming defects andcomplicated processes in the traditional stamp-forming techniques. Electromagneticforming (EMF) has received an increasing attention in recent years for the superiority ofcontact-free forming, low spring-back, high repeatability and enhanced forming limit. Theprinciple of EMF is to use electromagnetic force (i.e., Lorentz force) generated by pulsedmagnetic field to shape metal workpiece without mechanical contact and working medium.EMF is a high velocity deformation process with strain rate ranging from103s-1to104s-1.The high strain rate deformation can give rise to different deformation behaviors andunique microstructures and textures with respect to the conventional quasi-static or lowstrain rate deformation, thus affecting significantly the performance of the formedcomponents. Therefore, it manifests itself for the significance of research on deformationbehaviors and unique microstructures and textures under the electromagnetic forming.The present work mainly focus on the understanding of deformation texture andmicrostructure evolution in pure aluminum sheet after electromagnetic bulging, whileconsidering the influence from complicated strain path and high strain rate. Circle gridsmethod was employed to measure the strain distribution of the deformed workpiece.Electron backscatter diffraction (EBSD) and transmission electron microscope (TEM)technique wereemployedto characterize the morphology of grains and deformation texture,the dislocation configure and microstructure, respectively.With regard to the evolution of deformation texture, concept of strain ratio, i.e. theratio between the minor strain and the major strain, was defined to represent the change ofstrain path for simplicity. Stress-strain states from approximate uniaxial tension,non-equibiaxial tension to equibiaxial tension were experienced in the formedconical-shape workpiece along with the increasing strain ratio. The general textureevolution of the Al sheet under EMF followed that the initial Rotated Cube {001}<110>moved firstly towards Cube {001}<100>, then divided, moved towards Goss {110}<100> and Rotated Goss {110}<110>, which were finally inclined to be stabilized atP{110}<111>. A detail investigation of two texture components, Goss and Rotated Goss,was carried out to examine the effect of strain path and high strain rate on the textureevolution.Furthermore, the orientation change among local grains and the influence of dynamicrecovery was investigated to interpret the general crystal orientation change induced byplastic deformation under electromagnetic bulging. It was found that both the orientationscatter of the local grains and the tendency of rotation around the major strain axis andminor strain axis grew up with the increase of the strain ratio. Meanwhile, the activation ofslip systems was analyzed basing on the elementary estimation of Schmid factors. Finally,the dynamic recovery due to the temperature rise duringhigh strain rate deformation wasdiscussed for its contribution to the decrease in the density of crystal defects andpromotion of the activation of slip system and orientation change, which eventuallyinfluence the general distribution strength of the deformation texture.更多还原