The mechanical and microstructural properties of 2024 and 7075 aluminium alloys joined together by friction stir welding were analysed in the present study. The two materials were welded with perpendicular rolling direction and after were tested in tension at room temperature in order to analyse the mechanical response and to observe the differences with the parent materials, the tensile response of the material in longitudinal direction revealed an increase in strength respect to the transverse one. The cyclic fatigue tests were conducted in the axial direction with R = sigma(min)/sigma(max) = 0.1). The microstructure resulting from the FSW process was studied by employing optical and scanning electron microscopy. (c) 2005 Springer Science + Business Media, Inc.