Strengthening mechanism in laser-welded 2219 aluminium alloy under the cooperative effects of aging treatment and pulsed electromagnetic loadings

Electromagnetic (EM) forming is a high-speed forming technology which uses pulsed EM loadings to form metal sheet parts. A particular advantage of pulsed EM loadings is material strengthening. In the present work, a novel process is proposed to strengthen laser-welded 2219 aluminium alloy. EM uniaxial tension is performed to study the strengthening mechanism in laser-welded 2219 aluminium alloy under the cooperative effects of solid solution-double aging (SS-DA) treatment and pulsed EM loadings. The results indicate that the strength, hardness, and plasticity of the laser-welded joints after SS-DA treatment dramatically improved in comparison to that of as welded joints. This is due to the elimination of brittle eutectic phases and precipitation of dispersive G.P.(II) zones, as well as precipitation hardening which dominates the strengthening mechanism. However, under the cooperative effects of SS-DA treatment and pulsed EM loadings, the strength and hardness of the weld joints increase, but the plasticity decreases as the discharge energy increases. The strength and hardness of the laser welded joints are improved not only because of the appearance of dislocations but also because of the substantial transformative growth of G.P.(II) zones with a bilayer structure to a thick theta phase with a multilayer structure which is in close proximity to the dislocations. This demonstrates the combined strengthening mechanism of the strain and intensified precipitation hardening. The significant growth of the precipitates mainly results from the concentration of the solute Cu atoms and the internal energy rise under the effect of the pulsed EM loadings.