The Role of Tool Design in Influencing the Mechanism for the Formation of Friction Stir Welds in Aluminum Alloy 7020

Abstract

Design of the required tool is a key and important parameter in the technique of friction stir welding (FSW). This is so because tool design does exert a close control over the quality of the weld. In an attempt to optimize tool design and its selection, it is essential and desirable to understand the mechanisms governing the formation of the weld. In this research study, few experiments were conducted to systematically analyze the intrinsic mechanisms governing the formation of the weld and to effectively utilize the analysis to establish a logical basis for design of the tool. For this purpose, the experiments were conducted using different geometries of the shoulder and pin of the rotating tool in such a way that only tool geometry had an intrinsic influence on formation of the weld. The results revealed that for a particular diameter of the pin there is an optimum diameter of the shoulder. Below this optimum shoulder diameter, the weld does not form while above the optimum diameter the overall symmetry of the weld is lost. Based on experimental results, a mechanism for the formation of friction stir weld is proposed. A synergism of the experimental results with the proposed mechanism is helpful in establishing the set of welding parameters for a given material.

Keywords:

• Defect formation
• Interface formation
• Material flow
• Shoulder to pin ratio
• Solid-state welding

ACKNOWLEDGMENTS

The authors thank Defense Research Development Organization, Indian Space Research Organization (unit: LPSC), and Indian Institute of Science (Unit: STC) for providing financial support that made this exhaustive research endeavor possible. The authors extend most sincere thanks, appreciation, and gratitude to the anonymous peer reviewer for their many useful comments, corrections, and suggestions.