Effect of interfacial microstructure on lap shear strength of friction stir spot weld of aluminium alloy to magnesium alloy

In the present study, an attempt was made to join two dissimilar light metal alloys which are becoming increasingly familiar in the automotive industry, i.e. AA5083 aluminium alloy and AZ31 magnesium alloy, by the friction stir spot welding process. Lap welds were produced with various welding parameters, and interfacial microstructures and lap shear strengths of these welds were examined. Friction stir spot welding produced defect-free welds, even though a thick interfacial layer composed mainly of intermetallic compounds was present. The thickness of the interfacial layer did not appear to affect the lap shear strength of the weld, whereas the distribution of intermetallic compounds in the interfacial layer did so. Microstructural factors of the interface governing the lap shear strength of the weld were examined.