Applicability of unique scarf joint configuration in friction stir welding of AA6061-T6: Analysis of torque, force, microstructure and mechanical properties

Abstract

The present research introduces a unique concept of scarf joint technique in friction stir welding (FSW) of aluminum alloy AA 6061-T6 plates and an investigation on weld quality. A new joint configuration with two distinct scarf angles (75° and 60°) was considered in this study. The various aspects of welding were compared with contemporary simple square butt (SSB) joint configuration. Welding was carried out at a constant tool rotation speed (TRS), tool traverse speed (TTS) and tool tilt angle of 1100 rpm, 2 mm/s and 2°, respectively. The results are analyzed in terms of force and torque distribution, microstructure, macrostructure, and mechanical property perspective for different joint configurations. The study reveals the minimum amount of force and torque at 60° scarf angle joint configuration compared to that of square butt joint configuration. Macro study shows that all the joints were defect-free, and a prominent onion ring was present in the lower portion of the weld nugget (WN). Fine equiaxed grains with a minimum average grain size diameter of 6.82 μm were obtained in the WN of scarf joint configuration (SJC). The maximum ultimate tensile strength (UTS) and maximum average NZ hardness of 267 MPa and 83.82 HV0.1 were obtained in SJC3 at a scarf angle of 60°. It has been observed from the investigation that the joint efficiency increases from 72.5% (SSB) to 86% (SJC3) at a 60° scarf angle. This unique characteristic may lay an impetus on probable joint strength enhancement technique without increasing the production cost.

Keywords

• Friction stir welding
• Joint configuration
• Al alloys
• Force and torque
• Microstructure
• Mechanical property