Effect of material location and tool rotational speed on microstructure and tensile strength of dissimilar friction stir welded aluminum alloys

The dissimilar welding of cast and wrought aluminum alloys has high potential to expand the usage of economical castings. Friction stir welding (FSW) is an appropriate technique to join dissimilar aluminum alloys. The present work investigates the effect of material location and tool rotational speed on microstructure and tensile strength of dissimilar friction stir welded cast and wrought aluminum alloy AA6061. Eight joints were made using four tool rotational speeds by changing the location of each aluminum alloy in advancing and retreading sides. The results indicated that the material location prior to welding and tool rotational speed significantly influenced the material flow behavior. The material placed in the advancing side occupied the major portion of the weld zone when tool rotational speed was increased. The microstructure of the dissimilar joints exhibited the presence of four zones namely base metal, heat affected zone, thermomechanically affected zone and weld zone. The weld zone revealed two kinds of regions namely unmixed region and mechanically mixed region. The dissimilar joint showed maximum tensile strength when cast aluminum alloy was placed in the advancing side at all tool rotational speeds.