Fracture behaviour of laser-welded 2219-T6 aluminium alloy under pulsed Lorentz force

Abstract

Electromagnetic forming is a high-speed forming technology, using pulsed Lorentz force to make sheet metal deformed. The fracture behaviour of material during electromagnetic forming is a significant scientific issue in the development of this technology. In the current work, experimental methods are used to investigate the properties and microstructure of laser-welded 2219-T6 aluminium alloy and the fracture behaviour of the weld joint under pulsed Lorentz force. The results indicate that the hardness, strength, ductility, impact toughness of the laser-welded joint are all worse than that of the base metal because of the inhomogeneity of the microstructure and the existence of coarse brittle eutectic phases. This leads to the ductile fracture of laser-welded joint at the initial stage, followed by the sparking and partially melting breaking phenomena, under the pulsed Lorentz force. The molten structure is also observed on the fracture surface of the weld joint after electromagnetic tensile test rather than mechanical high-speed tensile test. During the fracture process under pulsed Lorentz force, local short circuits occur at the ductile crack tip of the weld joint due to the eddy current effect, resulting in the melting of the weld metal. The percentage reduction of area and the dimple sizes in the fracture morphology of the specimen under the conditions of high-speed deformation are larger than that under the condition of quasi-static tensile test, indicating the slight improvement in ductility of the laser-welded joint under high-speed deformation due to the inertial effect and the adiabatic temperature rise from the plastic work. Particularly, the above indicators are even larger under electromagnetic tensile test, revealing extra very slight increase in ductility compared with mechanical high-speed tensile test because of the body force and the additional temperature rise resulting from the Joule heat.