Metallurgy and mechanical performance of AZ31 magnesium alloy friction spot welds

► Metallurgical and geometric stress concentrators are identified in cross-section. ► Hook morphology and thermal input exhibit a strong influence over joint strength. ► Plastic flow originates around the recrystallized zone where tensile stresses are higher. ► Crack may propagate through or totally around the welded zone under shear loading. ► Fracture surfaces indicate extensive plastic deformation under shear.