Friction Stir Weld Strength Evaluation and Mechanical Characteristics Investigation on AA 6082 with Various Tool Shoulders

Abstract

The design of the friction stir welding tool controls the transverse rate at which FSW may be performed and is crucial to material flow. Three main purposes are performed by the tool: (a) heating the work piece; (b) moving material to create the joint; and (c) holding the hot metal under the tool shoulder. Friction between the rotating tool pin and shoulder as well as significant plastic deformation of the work cause heating within the work piece. The purpose of the tool shoulder is to contain the softened, plasticized metal underneath it and to apply heat to the surface of the material being welded by rotating the tool and applying a significant compressive force. One of the key elements of the friction stir welding process is comprehending the temperature generation surrounding the tool shoulder contact. The current study examined how different tool shoulder end features affected the 6082 aluminum alloy\\\'s mechanical characteristics and temperature. Convex tool shoulders provide the highest level of weld quality across all types when compared to other tool shoulders, according to the same criterion we used during the FSW joining procedure of AA6082.In the end, it was determined that the FSW of AA6082 would benefit greatly by tapper cylindrical, concave tool shoulders.

Introduction

Background & Context

Industries such as automotive, aerospace, and mechanical engineering often face challenges in component fabrication due to material incompatibilities and limitations of traditional welding methods. Solid-state joining methods—especially Friction Stir Welding (FSW)—offer solutions by avoiding melting, reducing defects (e.g., porosity and cracking), and enabling the joining of immiscible or difficult-to-weld alloys.

2. FSW Principles

Welding methods fall into:

• Liquid-phase welding (e.g., arc, laser, electron beam)

• Solid-state welding (e.g., FSW, diffusion bonding, explosive welding)

FSW works by generating frictional heat and plastic deformation without melting the base material, leading to refined microstructures and mechanical properties often superior to fusion welding.

3. Applications of FSW

FSW is widely used in structural and non-structural applications, especially for aluminum alloys in:

• Aerospace & automotive parts

• Rocket engines & missile components

• Reactor and turbine parts

• Composite materials & structural assemblies

4. Research Objective

The study examines the effects of various FSW tool shoulder profiles (cylindrical, taper cylindrical, square, concave, and convex) on the weld quality of Aluminum 6082 alloy plates.

5. Experimental Setup

• Material: Aluminum 6082 (a strong, heat-treatable alloy used in aerospace)

• Machine: LML-KODI 40-VMC

• FSW Parameters: Constant axial force (10 KN), rotation speed (1000 RPM), and feed rate (14 mm/min)

• Tools: H-13 steel with different shoulder designs

6. Results and Observations

A. Mechanical Properties

• Hardness: Cylindrical tool gave highest hardness (56 HRB), square gave lowest (42 HRB).

• Tensile Strength: Highest in taper cylindrical (122 N/mm²), lowest in convex (83 N/mm²).

• Root Bend Strength: Highest in concave (190.22 N/mm²), lowest in taper cylindrical (99.64 N/mm²).

B. Angle Distortion

• Least distortion (1.04°) occurred in concave and convex shoulders.

• Cylindrical and square tools showed higher distortion (~1.23°–1.25°).

C. Weld Appearance

• Best weld texture was seen in cylindrical and concave profiles.

• Taper cylindrical had cracks, square had pinholes, and convex showed mild porosity.

Conclusion

Several FSW tool shoulder profiles were compared and the FSW constant process parameter was assessed. In general, the weld quality has also been impacted by the tool shoulder profile. We have utilized square, convex, concave, wedge, and cylindrical tool shoulders for the FSW procedure. 1) According to this study, the concave tool shoulder profile tool executes without cracking and displays a nice weld bead following the FSW process. 2) During the process of welding with a square shoulder tool pin (42HRB), a low hardness value was attained. 3) In contrast to other tool shoulders, the cylindrical tool profile tool shoulder was accomplished with a very fine texture based on the weld appearance. 4) Compared to other tool shoulders, the taper cylindrical tool shoulder produced the highest tensile strength (122 N/mm2). 5) Compared to other shoulders, the concave tool shoulder produced the highest bending strength (190.22 N/mm2). 6) AUTOCAD analysis of the Angle Distortion Plate or Bead Straightness revealed that the maximum deviation was 2.5° in the tool shoulders at the square, taper cylindrical, and cylindrical shapes. The concave and convex tool shoulders showed the least amount of variation (1.04º). 7) Image J software is used to measure penetration depth. After all the plating was completed using different AA6082 tool shoulders, the Square tool shoulder was discovered to have the greatest penetration depth. Among the several types of tool shoulders, the taper cylindrical tool shoulder exhibited the highest tensile strength, whereas the square tool shoulder exhibited the greatest depth of penetration. The lowest angle distortion were achieved concave & convex during the FSW process. The maximum root bend strength obtained at concave tool shoulders compared to other shoulders. It was determined that the FSW of AA6082 would benefit greatly by concave tool shoulders compared to other tool shoulders.

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Copyright

Copyright © 2025 S. RajKumar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.