The influence of welding parameters such as tool plunge depth, tool travel speed and tool tilt angle on welding temperature during friction stir welding of AA6061-T6 and S275JR mild steel was the focus of this research. Thermocouple placed in the aluminum alloy plate prior to welding was used to measure the temperature during the welding of joints under different set of parameter values. Joint appearance as well as defects occurring on the surface or within the joint was observed. Microhardness profiles were also taken by measuring microhardness values across the cross section of joints. Excessive flash, tunnel defects and insufficient welding were the type of weld defects observed on different joints with different parameters. Defects were attributed to the varied parameter values affecting the heat generation as well as the flow of the plasticized material. Highest temperature was recorded by the joint fabricated using the largest tool plunge depth, owing to the increased downwards pressure. Microhardness profiles were seen to be similar for all the welded joints. A “plateau” of low microhardness value was observed for all joints associated with the thermomechanically affected zone (TMAZ) and heat affected zone (HAZ). A wider plateau was observed for joints welded with higher tool plunge depth due to higher temperature.
