The influence of different lap configurations and preheating process on the macro-/microstructures and mechanical properties of friction stir spot welding welds with both similar and dissimilar materials (6061-T6 aluminium alloy and AZ31B magnesium alloy) was investigated. The results showed that the different lap configurations resulted in different macro-/microstructures and mechanical properties of welds. Defect free welds and intermetallic compound containing welds were obtained in configurations of similar (Mg/Mg and Al/Al) and dissimilar (Mg/Al and Al/Mg) respectively. The welds with similar materials had the highest tensile shear strengths, followed by the Mg/Al welds; the Al/Mg welds had the lowest strength. The preheating process improved the tensile shear strengths of Mg/Mg, Al/Al and Mg/Al welds and reduced that of Al/Mg welds respectively.
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