AZ31B Magnesium alloy is one of the lightest metallic materials used for structural applications in automobile industries. AA 2014-T6 Aluminum alloys are not possible to be welded by gas welding techniques due to its poor weldability. If this alloy needs to be welded by fusion and resistance welding, it requires special techniques and hence not economical. It is used for truck body and in aircraft structure. Friction stir welding technique is most suitable for welding AA 2014-T6 Aluminum Alloy. AA 6061-T6 Aluminum Alloy possesses excellent mechanical properties in addition to good corrosion resistance due to which this alloy is commonly used for commercial applications like in transportation, construction and in naval vessels manufacturing. Dissimilar materials (AA 2014-T6 and AA 6061-T6) possess good strength, light weight and good corrosion properties and find applications in automobiles, marines, defense and aircraft etc. The present work was carried out to investigate the effect of process parameters (i.e. rotational speed, welding speed, tool material, tool tilt angle and D/d ratio) on mechanical properties of Aluminum alloy 2014-T6, Aluminum alloy 6061-T6 and AZ31B Mg alloy.