Modification of Mechanical Properties of Al6061 Aluminum Alloy Joint Formed Using Friction Stir Welding by Increasing the Cooling Rate and Application of Vibration

Al6061 alloy is widely used in the industry; so, its welding with reliable methods is of great importance. In the fusion welding of these alloys, imperfections such as cracks, cavities, and segregations of alloy element may occur that necessitates the application of solid state welding processes such as friction stir welding method. In spite of the many advantages of the friction stir welding, several attempts have been made to improve the properties of the resulting joints. In this study, the effect of increasing the cooling rate and the effect of vibration during the process on the microstructure and mechanical properties of Al6061 welds . Also, the simultaneous effect of water and vibration on the mechanical properties of the joints is evaluated The results showed that vibration due to increasing the strain  and water due to increasing the cooling rate reduced the size in the stir zone. Investigations revealed that cooling rate increment decreased the dissolution of Mg2 precipitates significantly. The results of the tensile test showed that the strength of the due to the grain refinement as was applied or when increased. Also, when the vibration and coolant were applied simultaneously, the strength increased dramatically due to significant grain refinement and presence of Mg2 precipitates. On the other hand, with grain refinement, the volume fraction of grain boundaries increases and, thus, the growth of the cracks decreases and correspondingly elongation enhances.