Friction Stir Spot Welding of Aluminum and Magnesium Alloy Sheets

This paper demonstrates the application of a displacement controlled friction stir spot welding machine in joining 1.5 mm sheets of Al 5754 aluminum and AM60 base materials. Higher fracture loads during overlap shear testing were produced when the projected bonded area immediately adjacent to the keyhole periphery and the energy input during FSW spot welding increased. Partial pull-out of the stir zone occurred in high energy input FSW spot welds with fracture initiating from unbonded regions located on either side of the welded joint.

FSW welding tools contaminated with magnesium had a markedly detrimental effect on the mechanical properties of Al 5754 spot welds. Mg-contamination decreased the energy input and the dimensions of the projected bonded area, and produced regions immediately adjacent to the keyhole periphery in Al 5754 spot welds, which contained brittle intermingled lamellae.