Intermetallic compounds in Al 6016/IF-steel friction stir spot welds

The joining of a 1.2 mm thickness Al 6016 to a 2 mm thickness IF-steel has been performed by friction stir spot welding (FSSW). The intermetallic compounds (IMC) have been identified at the interface Al 6016/IF-steel and quantified as a function of the rotational speed and tool penetration. TEM observations indicated the presence of tangles of elliptical intermetallic compounds. FeAl3, Fe2Al5 and FeAl2 were identified depending on welding conditions. The influence of IMC on tensile shear strength has been established. An IMC layer seems necessary to improve the weld strength, but if the layer is too thick, cracks initiate and propagate easily through the hard IMC tangles.