The Correlation of Stir Zone Texture Development with Base Metal Texture and Tool-Induced Deformation in Friction Stir P
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TRODUCTION
FRICTION stir welding/processing (FSW/FSP) has rapidly become an important process for joining or processing of various alloys,[1,2] especially aluminum alloys.[3,4] Despite a widespread use of FSW process in various industries, the details of microstructure evolutions and texture development during this process remain still a challenging issue. In this process, a non-consumable rotating tool is plunged into the workpiece causing to raise temperature as a result of heat generation through the friction between the tool and the workpiece as well as the tool-induced deformation adiabatic heat.[5] It results in softening the surrounding material, which enables the material flow around the rotating tool.[6,7] Due to the concurrent processes of severe plastic deformation and recovery at M. SARKARI KHORRAMI, Ph.D. Graduate, M. KAZEMINEZHAD, and A.H. KOKABI, Professors, are with the Department of Materials Science and Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran. Contact e-mail: [email protected] Y. MIYASHITA, Associate Professor, is with the Department of Mechanical Engineering, Nagaoka University of Technology, Kamitomioka 1603-1, Nagaoka, Niigata 940-2188, Japan. Manuscript submitted March 12, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
the elevated temperature, microstructural evolutions and texture development associated with dynamic recrystallization would be responsible for the formation of equiaxed fine grains in the stir zone.[8] In face-centered cubic (FCC) metals, the stacking fault energy possesses a strong influence on the recovery/recrystallization processes and on the texture evolution likewise. For aluminum alloys, the relatively large stacking fault energy results in the development and the persistence of deformation textures throughout the stir zone.[9] However, considering a complicated deformation field applied by the rotating tool and the existence of steep strain and temperature gradients in the stir zone,[10] a definitive argument over this issue has not been propounded. Some researchers have attempted to confirm that the predominant mode of deformation during FSW of aluminum alloys, particularly in the regions surrounding the tool, is simple shear[11–14] as that observed in high-temperature torsion.[15] Previous studies indicated that a texture reflecting the shear deformation introduced by the tool shoulder may be observed primarily just near the top surface where the influence of the shoulder is most pronounced. However, the deformation field resulting from the pin is more effective in other regions.[9] Although the previous investigations examined the texture evolution during FSW, there is a
lack of understanding regarding the correlation between the developed texture and the deformation field in the vicinity of the rotating FSW tool. In addition, the previous works were focused on the texture development during FSP/FSW of annealed or commonly deformed aluminum alloys. But, the texture development during FSP/FSW of severely deformed aluminum has not been survey
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