Improved forming capability of 7075 aluminum alloy using electrically assisted electromagnetic forming

Abstract

7075 aluminum alloy has high strength but its formability is poor at room temperature. To improve its plastic deformation capability, a new forming method, electrically assisted electromagnetic forming (EAEMF), is introduced and investigated. Our results indicate that the major and minor strain (i.e. the forming limits) of the material following EAEMF increases by 42.3% and 40.0%, respectively, compared to (conventional) electromagnetic forming (EMF). The respective increase thanks to the new method is even higher (by 76.4% and 83.9%) compared to quasi-static (QS) deformation. Furthermore, the yield strength and tensile strength of the material are reduced by 3.6% and 2.6%, compared with conventional EMF, while the elongation can be increased by 21.6% using EAEMF. The texture and microstructure of the alloy were investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that both grain size and texture strength decrease after EAEMF, while the brass and S textures become more dominant. The dislocation density of the material used for EAEMF is low, and directional alignment of dislocations occurs. This is related to the impulse current promoting the dislocation motion. In addition, Joule heating (by the electric current) enables a dynamic recovery during the deformation process, which reduces both the flow stress and the effect of work hardening. However, it also increases elongation. • The technology of electrically-assisted electromagnetic forming(EAEMF) is proposed for the first time, which is used to break through the limitation of EMF. • EAEMF process can improve the forming limit and energy efficiency. • Under the action of pulse current, the dislocation density decreases, and a part of dislocations show directional arrangement. • The pulse current did not change the types of texture, but changed the volume fraction of different textures.