Bonding and microstructure evolution in electromagnetic pulse welding of hardenable Al alloys

Abstract

Electromagnetic pulse welding (EMPW) is a promising solid-state joining process, offering fast and strong bonding with no heat affected zone. Despite the growing interest in this process, there is little understanding of the dynamic phenomena that lead to bonding and microstructural changes during EMPW of key engineering materials such as age-hardenable aluminium alloys. This study combines experiments with numerical modelling of plastic deformation to provide an insight to these phenomena in joining of a high-strength aluminium alloy in the T4 and T6 temper conditions. Initially, bonding criteria are postulated in view of the calculated plastic strain at the interface of the T4 sample. These criteria are then used for the prediction of the extent of bonded interfaces for different sets of materials and process parameters. The predictions are shown to be in quantitative agreement with the experimental results for the T6 sample. The corresponding microstructural studies show that bonding is associated with remarkable microstructural changes in the samples, including dissolution of precipitates, formation of high-angle boundaries, and recrystallisation, especially near the bonded interfaces. Moreover, the results of post-weld heat treatments and mechanical testing demonstrate that the impact-induced deformation in EMPW can also influence subsequent precipitations, hence result in improved properties of the entire sample, in a way not achievable by conventional age hardening treatments.