Microstructure, mechanical and electrochemical studies of dissimilar friction stir welded aluminium alloys

In the present investigation, the influence of tool rotational speed (900, 1100, 1300, and 1500 rpm) on microstructure, mechanical characteristics, and corrosion behavior of friction stir welding (FSW) of dissimilar Al5083-6061 alloys was studied. Optical and scanning electron microscopes were used to study the microstructural features. The grain size measured at the stir zone (SZ) decreased considerably in contrast with the base materials (BM) but increased with tool rotational speed. The mixing degrees of two materials at the SZ are enhanced by increasing rotational speeds. The mechanical properties, such as hardness and tensile properties, were studied using Vicker's hardness tester and universal testing machine. The hardness of the weld joints is inferior to that of the base metal, and uniform hardness distribution and the highest average hardness in SZ were obtained at 1100 rpm. The higher strength and elongation of 202 MPa and 5.2%, respectively, were achieved at 1100 rpm, with joint efficiency of 65%, due to optimum heat input, and the lowest tensile strength and elongation of 156 MPa and 3.2%, respectively, were obtained at 1300 rpm with a joint efficiency of 50% due to excess heat input. It is curious to note that an increase in tensile elongation accompanies the enhancement of weld strength. The fracture occurred at the retreating side of the heat-affected zone as it is the weakest zone in the FSWed joint. Different corrosion tests, such as immersion, open circuit potential, and Tafel polarization tests, were carried out using an electrochemical workstation. The corrosion findings showed that the corrosion resistance of the samples increased after the welding, and the highest corrosion resistance was obtained at 1100 rpm.