Abstract
The process of friction stir welding (FSW) has been employed primarily for joining aluminum sheets without melting. The present work relates the results of microstructural investigations of the joint produced by friction stir welding of two high strength heat treatable aluminum alloys in a lap joint of a sheet with an extruded profile. The joint microstructure showed a characteristic mixture pattern of the two alloys. It exhibited a more or less regular pattern of elongated stripes on the advancing side and a turbulent pattern on the retreating side of the joint. These stripes maintained the difference in their appearance, hardness values and chemical composition.