Effect of Tool Pin Profiles on Joint Characteristics of Under Water Friction STIR Welded AA2519-T87 Aluminium Alloy

AA2519-T87 is an age hardenable aluminium alloy used in the fabrication of light combat vehicles in the military application. Fusion welding of this aluminium alloy results in solidification related problems like porosity, hot cracking, etc. In order to overcome such problems, friction stir welding (FSW) process is used to join this material. The thermal cycle experienced by the thermo mechanical affected zone (TMAZ) and heat affected zone (HAZ) is causing grain coarsening and precipitates dissolution and resulting in poor joint properties. To get rid of this problem, under water friction stir welding (UWFSW) process can be adopted. However, the material flow during friction stirring will be entirely different in FSW and UWFSW. Hence an investigation is undertaken to study the effect of tool pin profiles on stir zone characteristics and the resultant tensile properties of the joints fabricated by UWFSW. Four different pin profiles, namely, straight cylindrical (STC), taper cylindrical (TAC), straight threaded cylindrical (STC), and taper threaded cylindrical (TTC) were used to fabricate the joints. From this investigation, it is found that the joint made by taper threaded pin profiled tool exhibited higher tensile properties and this may be attributed to the grain boundary strengthening and narrowing of lower hardness distribution region (LHDR).