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

Abstract

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

KEYWORDS:

• Magnesium–lithium alloys
• Refill Friction Stir Spot Welding
• refill FSSW
• microstructure
• solid-state spot welding

Acknowledgements

The authors would like to acknowledge the technical assistance, helpful discussion and advice received from Mr Zhijun Li, Mr Chunsheng Sha and Mr Songbin Li.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Scientific and Innovative Action Plan of Shanghai (grant number 18190730800). The first author was sponsored by Shanghai Rising-star Program (grant number 20QB1402700).