Good appearance and defect free friction stir welded joints of aluminium alloy to copper were obtained in a narrow range of welding conditions. The weld nugget (WN) consisted mainly of Cu(Al) solid solution, Al and several intermetallic compounds (IMCs), including CuAl₂, CuAl, Cu₉Al₄ and Cu₃Al although the maximum peak temperature measured in the weld was 422°C. Intercalation was a typical structure distributed widely in the WN and consisted of many parallel alternate lamellae. At the WN/Cu interface, the intercalations were characterised by flat or bended feature and composed of CuAl+Cu₉Al₄, Al+CuAl₂+Cu(Al) and Cu(Al) laminae. The formation mechanisms for these intercalation structures and IMCs were attributed to the intense stirring action of the tool pin and the short circuit diffusion caused by extreme deformation respectively. The fracture surface exhibited some IMCs, including Cu₉Al₄ and CuAl₂, which should be responsible for the limited tensile strength. The hardness profiles were consistent with the variation in the structures within the WN, and lower tool rotation rate resulted in higher peak hardness.

A thermoplastic ABS and an aluminium alloy 6061-T6 were joined using friction lap welding (FLW). The joint characteristics were evaluated to investigate the effects of 6061-T6 surface and the welding parameters on the joint properties. ABS and 6061-T6 were joined via an interfacial MgO layer. The voids generated by thermal decomposition would affect the strength of the joint. Owing to the small temperature range between the melting point and the thermal decomposition point of ABS, controlling the welding temperature is the key to the success of the 6061-T6/ABS FLW process. The relationship between the 6061-T6 surface after welding and the adhesion properties of ABS and 6061-T6 under different processing parameters was investigated.