Role of insert material on process loads during FSW

In FSW, insert materials are often used to both control the loading conditions as well as to trace the nature of materials flow. This current study aims at understanding the role played by inserts materials by using two different materials, copper and tin as inserts. The copper and tin have higher and lower melting points respectively as compared to aluminum. The metal strips are sandwiched between aluminum plates and friction stir welded at two different rotational speeds. The process loads and torque were recorded during the welding and compared with that obtained for normal butt-welding of aluminum sheets. In the case of copper insert, copper gets distributed in the matrix and it is possible to trace the flow of copper inside the aluminum. In the case of tin, it melts during the welding. The molten tin is squeezed out of faying surface and coats tool shoulder. This lowers the friction and which in turn lowers the torque (55%) and the consequent heat generation. The resultant reduction of temperature in the weld leads to higher tangential and normal loads. Compared to the case without insert, the normal loads for FSW processing with tin insert were higher by 2.2 times and tangential loads were higher by 5.5 times.