The microstructure and mechanical properties of dissimilar friction joints between aluminium-based MMC and AISI 304 stainless steel base materials were investigated. The microstructural features which occur in the stainless steel substrate comprise deformation twinning, formation of a fine-grained dislocation substructure in austenite, and plastic deformation. The stainless steel substrate was plastically deformed in the region close to the mid-radius of the dissimilar joint. In a similar manner, 5-10 mu m thick transition layers, comprising regions of locally plasticized MMC-base material, were formed close to the mid-radius location in dissimilar joints. The interlayer formed at the dissimilar joint interface comprised a mixture of oxide (Fe(Al,Cr)(2)O-4 or FeO(AI,Cr)(2)O-3) and FeAl3 intermetallic phases. The notch tensile strength of dissimilar MMC/AISI 304 stainless steel joints increased when the rotational speed increased from 500 r.p.m. to 1000 r.p.m., and at higher rotation speeds, there was no effect on notch tensile strength properties.