Tool rotational speed impact on temperature variations, mechanical properties and microstructure of friction stir welding of dissimilar high-strength aluminium alloys

Temperature variations during friction stir welding result from the heat generated by the frictional action of a rotating tool on the workpiece. This temperature distribution affects the mechanical behaviour and ultimately the quality of welds produced. The study of the correlations between process parameter, temperature, mechanical properties and microstructure has become imperative in order to promote welds devoid of defects and possessing sound mechanical properties and to establish a temperature feedback control for effective components designs for industrial applications. This work studied the impact of tool rotational speed on temperature profile, mechanical behaviour and microstructure of friction stir welding of dissimilar aluminium alloy 6101-T6 and 7075-T651. Processing parameters of three different rotational speeds with values 1250 rpm, 1550 rpm and 1850 rpm and a constant travel speed of 50 mm/min were employed. The temperature profile was measured with one end of thermocouple wires embedded in the plates and the other end connected to a data capturing software device. The temperature profile indicates that the temperature rises with time and is higher at the retreating sides than at the advancing side of the weld. The tensile test results show that the ultimate tensile strength decreases as the temperature increases. Microstructural observations of weld zone revealed non-uniformity in material flow. However, more material penetration into each other occurred more at 1550 rpm.