Effect of Rotational Speed on Mechanical, Microstructure, and Residual Stress Behaviour of AA6061-T6 Alloy Joints through Friction Stir Welding

In the present work, the behaviour of an AA6061-T6 alloy joint through friction stir welding was studied comprehensively under a set of processing parameters so as to establish a better microstructure-strength relationship in the joint. In-depth investigations have been done on intermetallic compounds and their phases using SEM, XRD, optical microscopy, and EDS, and thereby on the mechanical properties of the welded joint through tensile, hardness, and residual stress. The results revealed the evolution of grain boundaries and the existence of second-phase particles such as Mg 2 Si, MgZn 2 , MgCu 2 , and Al 2 CuMg. Moreover, using a rotational speed of 800 rpm results in enhanced hardness, tensile strength, and flexural strength. The highest and lowest tensile strengths of 198 and 171 MPa correspond to 800 and 600 rpm, respectively. The grain size distribution in the weld zone is 76.94, 0.83 and 36.82 µm for 600, 800, and 1000 rpm, respectively. Flexural strength was improved for the 800-rpm case and reached a maximum of 380 MPa. The lowest residual stress was found for an 800-rpm sample with tensile and compressive nature of stresses. Ductile fracture behaviour was obtained for tensile samples obtained at 600 and 800 rpm, whereas in the case of 1000 rpm, brittle fracture behaviour was seen.