In general, arc fusion processes are economical and flexible. They are well established for joining conventional aluminium alloys, but there are particular problems which must be considered when joining aluminium based MMCs. Molten MMCs are viscous, and therefore mixing with conventional filler alloys is difficult. During solidification, in certain instances, a solidifying interface will reject reinforcing particles giving rise to heavily reinforced and unreinforced regions in a weld. The degree of particle clumping is also a function of particle size, cooling rate and gravitational effects and particle/matrix combinations. A final consideration is the reaction in Al/SiC MMCs between the aluminium matrix and silicon carbide reinforcing particles: