Abstract: This paper investigates the effect of different cooling conditions and varied tool rotations upon the weld quality of aluminium samples carried out by friction stir welding (FSW) process. In FSW parameters play an important role like tool design and material, tool rotational speed, welding speed and axial force. The processing is controlled by different parameters, such as tool rotational speed, feed rate and processing medium. Controlling these parameters helps to improve the mechanical and micro structural properties of the samples. Friction stir welding at tool rotation speeds of 600 rpm, 900 rpm and 1200 rpm using two cooling conditions normal water and nitrogen gas was successfully done. This improved the tensile and micro structural properties compared to parent material. Cooling the samples by nitrogen gas was found to decrease the heat input during welding which limits the grain growth during the process. The decrease in heat input resulted in reducing the microscopic voids in the material leading to an increase in micro hardness and improvement of tensile properties. It was found that good machining properties can be achieved at the relatively higher rotational speed when no cooling condition is applied i.e. FSW is done in normal water. The best results out of all the samples were produced by nitrogen gas cooling under tool rotational speed of 1200 rpm as it showed higher tensile strength of 260 MPa, fine grained micro-structure, better micro hardness value of 141 Hv and impact strength 14.6 Nm.

Keywords: Friction stir welding, microstructure, cooling conditions, rotational speeds.