Water jet peening is a surface modification technique which can introduce compressive residual stresses beneath the surface of the engineering components. In this paper, the effects of water jet peening process, in the absence of abrasive materials on residual stresses, surface roughness, and fatigue life of the aluminium alloy 7020 samples were numerically and experimentally investigated. Therefore, two nozzles with respective exit angles of 0° (round nozzle) and 20° (orifice nozzle) were used and residual stresses were measured through centre-hole drilling technique. Furthermore, fatigue tests were performed on the water peened samples. Results indicated that in contrast to the horizontal speed of the nozzle, pressure of source and stand-off distance exerted a profound influence on the magnitude of residual stresses and surface roughness. Moreover, in cases which the pressure of the source exceeded a certain limit, fatigue life of the workpiece declined due to the surface crack formations.
