Influence of Tool Rotation Speed on Soundness of Water-Cooled Friction Stir Welded Armour Grade Al–Cu Joint

Abstract

Need of AA2519-T87 aluminium alloy in the military application leads to explore the possibility of efficient joining technique. The fusion weldability of Al–Cu alloy is poor because of the formation of residual stress, distortion, and solidification defects. The solid-state welding process, friction stir welding (FSW), can be remedy for the above-said shortcomings which does not have melting and solidification of material. However, the elevated temperature experienced in the thermo-mechanical heat affected zone (TMAZ) and heat-affected zone (HAZ) will coarsen and dissolute Al₂Cu precipitates. The undesired precipitate transformation can be controlled by adopting the in-process water-cooling technique. The material flow behaviour and joint characteristics for the water cooling are different from conventional FSW. To explore the usefulness of water-cooling technique, the joining mechanism and resultant joint characteristics have to be studied. Hence, an attempt is made to investigate the influence of predominant process parameter, tool rotational speed (TRS) on microstructure features and joint soundness. This investigation reports that joint fabricated using lower TRS of 1200 rpm is sound due to the lower extent of Al₂Cu precipitate coarsening and narrowing of weaker TMAZ and HAZ regions.