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.