| 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. |
