Abstract: The present study focuses on the influence of a 5-pass overlapped friction stir lap welding of AA6061-T6 on the mitigation of defects and its simultaneous effect on microstructure and mechanical properties. Tool pin overlapping percentage of 0%, 25%, 50% and 75% was employed, from which it was observed that defects significantly reduced at higher overlapping. Fine equiaxed grains were observed across all the nugget zones in both top, and bottom regions were developed due to simultaneous overlapped passes; the grain size of which varied from 8.5 µm to 3.5 µm. The grains became finer, which increased of overlapping percentage. The microhardness of the processed zone was significantly reduced during overlapping that varied from a range of 43 HV0.1 to 49 HV0.1 as compared to base metal which was interpreted due to changes in grain size and secondary precipitate distribution during overlapping. A maximum ultimate tensile strength of 230 MPa was achieved at 50% overlapping, whereas minimum ultimate tensile strength of 160 MPa was achieved at 0% overlapping. Fractography of fracture surface showed a ductile failure at 50% that showed a number of dimples of varying shapes and sizes.

Abstract: The current investigation is a preliminary approach proposing the feasibility of a modified joint configuration namely double-butt-lap (DBL) in the field of friction stir welding (FSW). The main scope of adopting this kind of joint configuration is to essentially eliminate the irregularities in material flow and defects (root gap, kissing bond) that are observed while joining by using the commonly followed simple square butt joint configuration (SSB) technique. Two different geometries of the joint configuration are fabricated on 6 mm thick AA6061-T6 plates. FSW is carried out at a parametric combination of 1100 rpm, 75 mm/min and 1.5° tilt angle. The comparison of the macrographs of DBL with SSB reveals a quite distinct cross-sectional macrostructure of DBL from SSB in terms of material flow in the nugget zone (NZ). Sharp material flow lines without any macro defects are observed in the case of DBL 2. Mechanical test analysis reveals remarkable enhancement in the mechanical properties of some joint configuration of DBL over SSB. The current research work may act as a foundation for future research work in the utility of such configurations in the diverse field of FSW.