Microstructure analysis and interfacial wave formation mechanism research of Mg/Al dissimilar metal laser impact welding in a vacuum environment

Abstract

Laser impact welding (LIW) joints for the center exists springback region, resulting in a small effective welding area seriously affects the LIW joints performance problems. This paper for the first time put forward the vacuum environment LIW process, to carry out the vacuum environment of the two dissimilar lightweight metal magnesium/aluminum (Mg/Al) LIW. Results of the research showed that no springback occurred in the welded area. In order to reveal the vacuum environment LIW mechanism, the surface and cross-section morphological characteristics, weld interface microstructure, interface waveform element content and mechanical properties of laser impact welded Mg/Al dissimilar metals were investigated by optical microscope (OM), scanning electron microscope (SEM), electron backscattering diffraction (EBSD), energy spectrometry (EDS), and the universal testing machine. Studies have shown that the experimental success rate in the vacuum environment is much higher than that in the atmospheric environment, and the vacuum environment eliminates the springback cracking defect phenomenon generated in the center of the welded joints, which greatly increases the effective welding area of the weld. The number of Mg grain refinement in the interface region of the vacuum environment welding is more, and the bonding force of the two-plate welding is increased. Significant orientation differences, severe plastic deformation and high strain at the weld interface are one of the reasons for the successful LIW. Mg/Al welding samples produced elemental diffusion phenomenon, no obvious melting phenomenon, which is conducive to improving the welding quality. Tensile strength of the welded samples in the vacuum environment was higher than that in the atmospheric environment. Using the SPH-Lagrange coupling method, numerical simulations were carried out to study the trends shear stress, pressure, velocity, temperature and equivalent plastic strain distribution at the weld interface under vacuum environment, which revealed the interface wave formation mechanism in the center of laser impact welded joints with no springback cracking phenomenon. Vacuum laser impact welding opens up a new technology pathway for LIW of Mg/Al welded joints without springback in the center, which plays an important role in improving Mg/Al welding performance.