Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. FSW is considered to be the most significant development in metal joining in a decade. Here the paper involves the friction stir welding for two materials such as Aluminium alloy (6061) and high strength and low alloy steel, aluminium alloy (6061) has good corrosion resistance and good walkability. High strength low alloy steel has high strength and toughness, due to better properties of these materials it can be taken into consideration for welding process. Then the materials are welded under various process parameters, the welding strength for different process parameters are noted .then better parameters is chosen for further welding process. During friction stir welding heat distribution will occur, Due to heat distribution some of the failure will occur so that it can get analysed through ANSYS software for selecting better welding condition. During this process various tests has been made such as tensile test, Hardness test and SEM test for obtaining better mechanical properties.