Hyper-plasticity Mechanism Of Electromagnetic Expanding Forming For Aluminum Alloy Tubes

The electromagnetic forming process was a high-velocity manufacturing technique.Compared with the machining process of quasi-static loading,some kinds of metals showed far higher ductility in the electromagnetic forming process which was deemed to hyper-plasticity.At present,researchers had different opinions in terms of the mechanism of hyper-plasticity.This article studied the stages of deformation,localization,the formation of localized band and fracture of 6063-T6 aluminum alloy in the electromagnetic forming process by the electromagnetic expansion experiment and the finite element simulation.Then the influence of the inertial effect and geometry size was evaluated through an analysis of the forming ability of 6063-T6 aluminum alloy under different strain rates.The main contents and results include:(1)As the results of experiments show that the nominal strain at the initiation of nonunformed deformation do not have evident change in the process of dynamic loading when compared with the process of quasi-static loading.But the strain at the onset of localized instability increases a lot;the hyper-plasticity is mainly caused by the inertial effect and geometry size during the high speed expanding formation.(2)As the results of simulation show,the inertial effect influences the feature size of localized bands which is irrelevant to the geometry size of specimen.(3)Due to the transformation of localization pattern from shear to tension,the average hoop strain at the onset of localization and the formation of localized band and fracture tend to increase firstly and then decrease with the increasing of the aspect ratio of the specimen which show the shape of hump;the average hoop strain at the onset of localization increases as the aspect ratio of the specimen increases when the pattern is shear failure,but the average hoop strain at the onset of localization decreases as the aspect ratio of the specimen increases when the pattern is tensile failure.(4)The strain at the onset of localization is determined to be forming limit in the forming process by the principle of strain rate development.Then the forming limit diagram of 6063-T6 aluminum alloy is drawn out under different strain rates.