Mechanical properties and microstructure evolution of 2219 aluminum alloy via electromagnetic ring expansion & electromagnetic treatment

Abstract

As an emerging technology to solve the bottleneck of plastic processing of light alloys, electromagnetic forming usually causes a complex mechanical response and microstructure evolution of materials. In this work, based on the electromagnetic ring expansion (EMRE) experiment, the relationship between microstructure evolution and mechanical properties of AA2219-T6 under EMRE with different discharge energies is established. In particular, to reveal the influence of strain and temperature parameters on the output response during the electromagnetic pulse process, a Q235 steel sleeve and an epoxy resin sleeve with different thermal conductivities are applied to constrain the deformation of the ring, respectively, thus the performance under electromagnetic treatment (EMT) are investigated. It is found that, under the threshold discharge energy of 4.23 kJ, the microhardness of the ring via EMT with the steel sleeve is similar to that of AA2219-T6, but increases by 20.9% compared with the ring via EMT with the epoxy sleeve and 17.1% compared with the ring via EMRE. The electromagnetic pulse has no significant effect on the evolution of precipitates in AA2219-T6-EMT (Steel), but the adiabatic temperature rise in AA2219-T6-EMT (Epoxy) caused redissolution of G.P.Ⅱ zones. With the gradual increase of discharge energy under EMRE, the microhardness of AA2219-T6 increases initially and followed by a decrease, while the fracture strain increases continuously. When discharge energy reaches 8.63 kJ, 2219 aluminum alloy has the optimal mechanical properties that, compared with AA2219-T6, the microhardness increased by 14.2% and the fracture strain increased by 18.0%. The dislocation density shows a trend of first increasing and then decreasing with the increase of discharge energy. Combined with the observed phase transformation, it is shown that dislocations generated by EMRE will promote G.P.Ⅱ zones to transform into θ′′ phases, and affected by dislocation density, the transformation effect is most obvious at 8.63 kJ. In addition, the transformation of precipitates greatly increases the probability of hindering the motion of dislocations, which promotes the precipitates to be dispersed, and AA2219-T6 is further strengthened after EMRE. As discharge energy continues to increase, the dislocations begin to annihilate and G.P.Ⅱ zones are redissolved due to the adiabatic temperature rise.