Characterization of the Influence of Tool Pin Profile on Microstructural and Mechanical Properties of Friction Stir Weld
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CTION stir welding (FSW), a solid-state joining technique invented by The Welding Institute in 1991, has numerous applications in many areas such as automotive, aerospace, and shipbuilding industries. FSW has been utilized to weld different alloys such as wrought aluminum alloys,[1,2] Mg,[3,4] and Cu,[5,6] some of which have been classified as practically unweldable by traditional welding methods. This technique utilizes a non-consumable rotating welding tool to generate frictional heat and cause deformation at the welding zone, and thereby affecting the formation of a joint, while the material is in the solid state.[1] An FSW tool, consisting of a shoulder and a pin, is obviously a critical component to the success of the process. The shoulder is the main source of heat generated during the process, the primary constraint to material expulsion and the main driver for material flow around the tool. On the other hand, the pin is the main source for material deformation and the secondary source for heat generation.[7] Consequently, the geometry of both the shoulder and pin is important for the FSW process. Nugget integrity is therefore mainly dependent on a well-designed pin profile.[8] Moreover, pin profile acts a crucial role in material flow and in turn determines the welding speed of the FSW process.[9] JAVAD MARZBANRAD, Associate Professor, and MOSTAFA AKBARI, Ph.D Student, are with the School of Automotive Engineering, Iran University of Science and Technology, Tehran, Iran. Contact e-mail: [email protected] PARVIZ ASADI, Ph.D Student, is with the School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran. SAMAD SAFAEE, M.Sc. Student, is with the School of Mechanical Engineering, Karaj Campus, University of Tehran, Tehran, Iran. Manuscript submitted February 8, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
Recently, some attempts have been made to design FSW tools. Buffa et al.[10] numerically modeled a FSW process with varying pin geometries (cylindrical and conical). They used a lagrangian implicit code, designed for metal forming processes, to model FSW. They adopted the same pin height and fillet radius at the pin– shoulder interface for all the pin geometries, while considering different values of the bottom pin diameters. Elangovan and coworkers[9,11] studied the effect of tool pin profiles on microstructure and mechanical properties of FSPed AA6061 aluminum alloy. They investigated the formation of FSP zone macroscopically and evaluated tensile properties of the joints. Their results show that the square tool pin profile produces mechanically sound and metallurgically defect-free welds compared to other tool pin profiles. Khodaverdizadeh et al.[12] studied the effect of tool pin profile on microstructure and mechanical properties of friction stir-welded pure copper joints. They employed two different pin profiles (square and threaded cylindrical) to fabricate the welds. Their results showed that square pin profile produces finer recrystallized grain structure and higher mechanical proper
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