Joining aluminium alloy and steel together is hard due to different thermomechanical properties of two materials. FSW was introduced to join two different materials in a safer way. The observation of influence of plate thickness difference between AA6061-T6 aluminium alloy and S235JR mild steel plates, plate positioning and plunge depth during FSW on temperature profile has been conducted to address the increasing interest in FSW to join dissimilar plate thicknesses in applications such as tailor welded blanks. Varying plate thickness, plate position and plunge depth from the top of the thickest plate will be used as the study parameters. By using eleven (11) welded samples with different parameters as guide, the experiment was conducted by using conventional milling machine with specialised tool for FSW. Temperature profile results were expressed in line graphs. As in conclusion, higher plate thickness ratio which is obtained when thicker plate divided by thinner plate can lead to lower peak temperature result, thus first objective is achieved. The second objective achieved as results show that joints with backers tend to have higher peak temperature and the last objective achieved when results of deeper plunge depth gave higher peak temperature as the tool shoulder came in contact with thermocouple during the process.
