This paper presents results of joining of AA5754 and DP800 based on the friction stir welding process. Joints were produced by the tool made of H13 tool steel which was allowed to penetrate through the aluminium sheet until reaching the surface of steel sheet without penetrating into it. This approach is an economic and robust way to operate the dissimilar welding process without excessive tool cost. Bonding was achieved by interfacial diffusion reactions between aluminium and iron with a formation of intermetallic compounds. The formation of brittle intermetallic compounds at the interface between the materials was studied. Three intermetallic phases were found at the interface including Al13Fe4, Al5Fe2 and Fe3Zn10. A range of process parameters was identified with a thickness of the intermetallic layers around 2 mu m. Shear fracture failure mode was observed under overlap loading. The mechanisms of formation of the joints and factors controlling the strength were discussed.

In this study, lap joints between AA5754 and DP1000 ultra-high strength steels were producedby friction stir welding. In order to investigate the roles of zinc on intermetallic phase formation and joint properties, steel substrates were used, two being galvanised coated and one uncoated. Joint performance has been evaluated in term of maximum tensile shear loading. The effects ofthe process parameter, translational speed; chemical compositions; and intermetallic phase formationon the mechanical properties have been investigated. The results show that joints witha galvanised layer exhibit higher strength as compared to the non-coated steel. A thicker galvanisedlayer promotes the presence of zinc in the aluminium matrix, resulting in better jointproperties. The level of zinc contents in the aluminium matrix depends on process temperature and material circulation characteristics. Two stable Al-rich intermetallic phases, Al5Fe2 and Al13Fe4, were detected at the interface regardless of the coating conditions.