Refill Friction Stir Spot Welding (Refill FSSW) of magnesium lithium alloys: effects of air and argon cooling

Magnesium-lithium alloys are among the lightest commercially-available structural alloys. However, reactive nature of Mg and Li makes fusion welding this family very difficult, if not impossible. The solid-state joining processes considered suitable alternatives since can be carried out at temperatures well below melting these Refill Friction Stir Spot Welding (Refill FSSW) 2.2 mm thick Mg-Li plates, using air argon as cooling gas, was investigated. Initial examinations revealed formation adherent oxides-based residues on tool shoulder. microstructural examination air-cooled samples showed presence oxide inclusions within weldment. As expected, argon-cooled process reduced additionally resulted in flat smooth welded surfaces. Nevertheless, somehow unexpectedly, had no noticeable effect shear strength or microhardness joints.