Heat transfer and material flow modelling of friction stir welding of dissimilar materials: Al 6061-AZ31

Dissimilar welds are widely used in automotive, aerospace and ship building industries to get advantages of selective properties of different materials. Friction stir welding (FSW) is a solid state welding process, suitable method for joining of two dissimilar materials because of its major advantages such as weld strength, free from porosity and other defects which occurs due to liquefaction of metals, and pollution free. FSW of Al alloy and Mg alloy is used in automotive, aerospace and ship building industries due to its high strength and mass reduction properties. Joining of Al and Mg alloy is very difficult using conventional fusion welding due to formation of large amount of intermetallic compounds and this difficulty can be reduced by using FSW. FSW needs optimum process parameters for dissimilar welding. Therefore heat transfer and material flow modelling of friction stir welding of dissimilar material is developed.



The model is developed by solving mass, momentum and energy balance equations in three dimensional domain using finite volume method. To make the model reliable for dissimilar material joining, thermo-physical properties such as specific heat and thermal conductivity of the base materials and mixed zone are experimentally determine as function of temperature. Specific heat capacity and thermal conductivity of welded materials are experimentally measured for dissimilar weld Al6061-T6 and AZ31 Mg alloy by using differential scanning calorimetry (DSC) and laser flash analysis (LFA) respectively. The effect of different tool geometry and process parameters are used to show the variation in temperature field, material flow velocity and torque.