Columnar-to-equiaxed grain transition in laser-MIG hybrid welding of aluminum alloy via an external steady magnetic field

Abstract

Oscillating/alternating magnetic fields have been proven to promote columnar-to-equiaxed grain transition (CET) in laser/arc welded joints, whereas the effectiveness of steady magnetic fields remains controversial. This study explored whether CET can be promoted by an external steady magnetic field in laser–MIG hybrid welding of aluminum alloy. Welds were produced at different magnetic flux densities; grain morphology and thermal–fluid flow were analyzed. The results showed that the steady transverse magnetic field interacted with the arc current to generate a backward Lorentz force in the rear molten pool, fracturing columnar dendrite tips and promoting CET. However, Joule heating induced by the magnetic field caused grain coarsening. This study will provide a more underlying understanding of weld grain growth dynamics.