Flat friction stir spot welding of AZ31B magnesium alloy using double side adjustable tools: microstructure and mechanical properties

A flat friction stir spot welding (FSSW) using double side adjustable tools has been developed to join magnesium alloy plates, through which sound joints bearing high mechanical performance and good surface appearance without keyhole have been successfully obtained. In this flat FSSW method, failure behaviour can only happen in the plate thickness direction due to the significantly enlarged bonded width. Sound joints can be obtained at low rotation speed; consequently, the average grain size in the tip area of the unbonded interface can be significantly decreased and the corresponding texture becomes random, giving rise to superior joint properties.