Investigations on the Effect of Sheets Positioning in Advancing & Retreating Side for Dissimilar FSW of DH36 Steel and Aluminum Alloy 6061

Abstract

Joining the different materials such as steel with aluminum makes the unique hybrid structures used in many industries like marine, aero, automobile and railway industries. In this study, the authors were attempted to join the shipbuilding grade steel, i.e., DH36 steel with aluminum alloy 6061 (AA6061) using the friction stir welding (FSW) technique. The effect of the sheets positioning on weld characteristics through energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) was predicted. DH36 steel was fixed at the advancing side (AS) in an experiment: E1 and AA6061 at the AS in an experiment: E2. The microstructural study revealed significant grain refinement and grain elongation in the stir zone (SZ) and thermomechanically affected zone (TMAZ), respectively. EDS analysis proposed the IMCs formation, i.e., Al3Fe and AlFe at IMC layer and Al3Fe inside the SZ of E1, whereas Al2Fe and Al5Fe2 identified at mixed region inside the SZ of E2. The tensile welded samples of E1 fractured at the SZ on the AA6061 side, far from the joint interface. However, the tensile samples of E2 ruptured at the joint interface. The tensile strength of welded joints improved by placing the AA6061 at the retreating side (RS) and DH36 steel at the AS. However, reverse positioning leads to the scattering of steel particles inside the AA6061 matrix, which deteriorated the joint strength due to the formation of cracks and voids. The hardness profiles showed the maximum hardness at the SZ (DH36 steel) and mixed zone in E1 and E2, respectively.