Joule-heating-dominated mechanical softening and dynamic recovery of 6061-T651 aluminum alloy under electric current

Electrically assisted forming (EAF) introduces electric current to induce Joule heating and the electroplasticity effect, thereby reducing the deformation resistance while improving the plastic deformation capability of materials. This provides a promising route for the high-precision forming of high-strength aluminum alloys. In this study, the electrically assisted tension (EAT) behavior of 6061-T651 aluminum alloy under different current densities was systematically investigated, with particular emphasis on the correlation among Joule heating, local strain evolution, microstructural evolution, and fracture behavior. The results show that the Joule heating effect was significantly enhanced with increasing current density, leading to a nonlinear increase in the peak temperature of the specimen. Meanwhile, both the flow stress and ultimate tensile strength (UTS) were markedly reduced. The elongation first increased and then decreased with increasing current density, reaching its maximum value at 250 A/mm². Digital image correlation (DIC) results revealed that the applied electric current promoted strain localization in the central region of the gauge section. Fractographic analysis showed that EAT gradually changed the fracture behavior of 6061-T651 aluminum alloy from quasi-cleavage features to ductile fracture. Electron backscatter diffraction (EBSD) results demonstrated that the applied electric current weakened the tensile deformation texture. Transmission electron microscopy (TEM) observations further revealed that the electric current facilitated dislocation depinning, rearrangement, local recovery, and the dissolution or refinement of Mg–Si precipitates. Overall, the improved formability of 6061-T651 aluminum alloy during EAT cannot be attributed solely to thermal softening, but results from the combined effects of Joule heating and electron-dislocation interaction.