Abstract
Friction stir welding (FSW) is one of the most prominent methods of joining aluminum alloys. The tool pin profile, force, rotational speed, and transverse speed play a vital role for heat generation and homogeneous mixing of materials during welding. The microstructural and mechanical properties are also varied of the same of weld. There is a wide range of application in FSW of aluminum alloy, i.e., automobiles, aerospace, shipbuilding, and construction. Nowadays, friction stir welding is performed at different environments such as underwater. Moreover, underwater friction stir welding is extensively applied in ship building components and marine structures to enhance the weld joint quality. In this paper, three different types of tool pin profiles, viz. square tapered, conical, cylindrical, are used for welding. The influence of pin profiles in mechanical and macro-structural properties of weld joints is studied. The current work also encompasses the variation of tool pin profiles for welding Al 2024 aluminum alloy in air and underwater. In underwater friction stir welding heat becomes more concentrated under the tool and cooling rates are higher due to water environment which ultimately boost up the mechanical properties of the weld joint. The square tapered pin profile shows higher tensile strength as compared to the other pin profiles. However, hard and brittle precipitates are formed at weld bead due to difference in peak temperature of underwater FSW as compared to air FSW. The macrograph of underwater specimens reveals the absence of heat affected zone that enhances the tensile strength of weld joint.
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