Evolution of microstructures and mechanical properties in similar and dissimilar friction stir welding of AA5086 and AA6061

► Similar and dissimilar friction stir welding of AA6061 and AA5086 are studied. ► Peak temperature in AA6061/AA6061 joints is the highest. ► Natural aging after FSW significantly alters mechanical properties of SZ and HAZ. ► Finer grain size is achieved in AA6061 side both in similar and dissimilar joints. In this work, thermo-mechanical behavior and microstructural evolution in similar and dissimilar friction stir welding of AA6061-T6 and AA5086-O have been investigated. Firstly, the thermo-mechanical behaviors of materials during similar and dissimilar FSW operations have been predicted using three-dimensional finite element software, ABAQUS, then, the mechanical properties and the developed microstructures within the welded samples have been studied with the aid of experimental observations and model predictions. It is found that different strengthening mechanisms in AA5086 and AA6061 result in complex behaviors in hardness of the welded cross section where the hardness variation in similar AA5086-O joints mainly depends on recrystallization and generation of fine grains in weld nugget, however, the hardness variations in the weld zone of AA6061/AA6061 and AA6061/AA5086 joints are affected by subsequent aging phenomenon. Also, both experimental and predicted data illustrate that the peak temperature in FSW of AA6061/AA6061 is the highest compared to the other joints employing the same welding parameters.