Friction stir welding with different tool profiles on structure and hardness of dissimilar aluminium alloy AA5083 and AA6061-T6

Abstract

Underwater dissimilar friction stir welding (FSW) of an aluminium alloy AA5083 and AA6061-T6 in butt joint configuration was studied. Underwater FSW is the solid-state joining operation that utilises the non-consumable tool to connect two facing workpieces without melting the workpiece substance in the underwater environment. Defect has been proven to have negative impact on overall welding engagement. It is becoming an area of increasing concern in any type of manufacturing, including welding. The present study continually looked for ways to manufacture the best underwater FSW tool pin profile for specific applications while minimising the different welding defects. The experimental method was to choose 1 sample among underwater FSW and normal FSW fabricated according to the welding process parameter and met the research criteria based on comparable studies. In addition, optical microscopy was employed to observe the microstructures and welding defects of the joints. The effects of the different tools at three profiles of straight, threaded, and tapered cylindrical tools on the structure and hardness of the joint dissimilar aluminium alloy were investigated. The presence of water is an excellent alternative to enhance durability and reduce the various types of welding defects during the welding process changes occurring in underwater FSW and normal FSW. These results have been used to understand the variation in the welding strength and the microhardness obtained in underwater FSW and normal FSW at both different tool pin profiles and values of welding speed. Results have revealed the presence of various types of defects such as groove and tunnel defects in the weld region. Metallurgical macrostructure observation on the underwater FSW and normal FSW samples revealed the presence of welding defects which were groove and tunnel in the stir zone. The tapered cylinder pin profile and 60mm/min welding speed remarkably affected welding textures resulting in a higher hardness value than the other samples. Furthermore, the optimal combination of rotational speed and welding speed can significantly improve the hardness strength of the welded joint. The study indicates that underwater FSW was achieve 77.56 HV, which is supported by the result obtained. This number was 18% greater than the hardness value achievable with the normal FSW, 63.30 HV. For underwater FSW, higher rotational speed and welding speed were suggested to establish sound welded dissimilar joints and achieve better microstructures which could collectively improve the welding strength.