Microstructure and Residual Stress Distributions Under the Influence of Welding Speed in Friction Stir Welded 2024 Alumi
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INTRODUCTION
FRICTION stir welding (FSW) technology requires a meticulous understanding of the process and consequent mechanical properties of the welds in order to be used in the production of high-performance components, especially in aerospace, where damage tolerance design is extensively used in aircraft construction and mandatory for large civil aircraft.[1] The effects of welding parameters such as rotational and traverse speed, tool geometry, and tool tilt angle were widely investigated in order to obtain high-quality welds in terms of microstructure, hardness, and joint strength. Among these parameters, tool rotational and traverse speed strongly influence the thermal cycle and are the two most important welding parameters.[2–4] Dubourg et al.[5] showed that how the welding conditions and the weld properties would be affected by the process parameters. Rotational speed has been recognized as one of the most significant process parameters. Radisavljevic et al.[4] studied the influence of rotational speed and feed rate (R/v ratio) on the formation and mechanical properties of FSW joints. Peel et al.[6] have investigated the influence of traverse speed on the weld residual stress in aluminum AA5083 DANIAL GHAHREMANI MOGHADAM and REZA MASOUDI NEJAD, Ph.D. Candidates, and KHALIL FARHANGDOOST, Associate Professor, are with The Mechanical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran. Contact e-mail: [email protected] Manuscript submitted November 29, 2015. Article published online March 1, 2016. 2048—VOLUME 47B, JUNE 2016
using X-ray diffraction. Synchrotron residual stress analyses indicate that the weld zone is in tension in both the longitudinal (parallel to tool traverse) and transverse (perpendicular to tool traverse) directions. The peak of the longitudinal stresses increased with the traverse speed. Fratini et al.[7] derived the residual stress profiles for aluminum alloys 6082-T6, 7075-T6, and 2024-T4 with the hole-drilling technique. The results have shown that unlike traditional welding processes, the residual stresses are negative in the surface of the examined zone, and increased with depth until values of about 100 to 150 MPa that occur at a depth of about 0.5 to 1.0 mm. Xu et al.[8] measured the residual stresses on the top and bottom surfaces of the butt-jointed FSW using the hole-drilling strain-gage method. Zhang et al.[9] presented a new method to accurately determine both the macroscopic and microscopic (including elastic mismatch, thermal misfit, and plastic misfit) residual stresses in metal matrix composite welds via neutron diffraction. The results showed that raising the rotational speed had a small influence on the total residual stress, whereas the L component (along the welding direction) of the total residual stress increased and the N component (along the plate thickness) decreased. The numerous studies have been accomplished to estimate the residual stresses in mechanical components.[10,11] Numerical models have also been widely used to predict seve
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