Prediction of temperature at weldline in air and immersed friction stir welding and its experimental validation

In immersed friction stir welding (FSW), the workpiece is completely immersed in the water environment during welding. The thermal modelling of immersed FSW is carried out using a three-dimensional heat transfer model. Friction stir welding experiments on aluminium AA8011 are carried out to find the temperature distributions in a workpiece in air and immersed state. K-type thermocouples are used to measure the temperature histories at different locations on the workpiece during FSW. A regression analysis is used to forecast the temperatures at the weldline experimentally. The temperature distribution at the weldline is also calculated using numerical simulation. The temperature distribution obtained using this experiment is in good agreement with the temperature distribution obtained using numerical simulation. The result indicates that peak temperature distribution area is significantly narrow, and thermal history showed that temperature rise and fall after FSW is sharp due to higher cooling rate in the presence of water. A comparison is also made between the temperature obtained in air and immersed FSW. It is also observed that the joint tensile strength of immersed FSW is higher than that of air FSW welded joint.