Homogenisation of chemical composition and microstructure in laser filler wire welding of AA 6009 aluminium alloy by in situ electric current stirring

Owing to the rapid cooling rates, the deposited and base metals could be mixed incompletely during laser welding of Al alloys in most cases. The objective of this research is to explore a possible method to promote the mixing of materials inside the molten pool by making use of the magnetofluid dynamic effect of electric current. Full penetration CO2 laser welding of 3 mm thick alloy 6009 sheets was performed with an external electric current simultaneously into the weld pool via a filler wire. It is found that the deposited metal is mainly concentrated on the upper part of the weld fusion zone, and the weld zone microstructure is non-uniform without the electric current addition. With the application of an electric current, the weld fusion zone geometry is reshaped, and the chemical composition and microstructure of the weld metal are homogenised. The mechanism is found to be electromagnetic force stirring of the molten pool.