Microstructure and Mechanical Properties of Ultra-fine-Grained Al-Mg-Si Tubes Produced by Parallel Tubular Channel Angul
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PROCESSING and characterization of the ultra-finegrained (UFG) and nanostructured (NS) materials produced using severe plastic deformation (SPD) techniques[1] have received much attention during past two decades due to their enhanced room temperature strength and high-temperature superplastic properties. Many SPD techniques, such as equal channel angular pressing (ECAP),[2–6] high-pressure torsion (HPT),[7] and accumulative roll bonding (ARB),[8,9] were applied for processing of bulk or sheet-shaped UFG materials. These methods are, however, incapable of processing tubular-shaped parts. During the last 5 years, different SPD methods such as accumulative spin bonding (ASB),[10] high-pressure tube twisting (HPTT),[11] and modified ECAP[12] were developed for processing of tubular samples. Recently, two novel SPD methods, i.e., parallel tubular channel angular pressing (PTCAP)[13] and tubular channel angular pressing (TCAP),[14,15] have been proposed by Faraji et al. for a fabrication of UFG and NS material tubes. Among them, the PTCAP process has some G. FARAJI, Assistant Professor, and S. ROOSTAE and A. SEYYED NOSRATI, MSc. Students, are with the School of Mechanical Engineering, College of Engineering, University of Tehran, 11155-4563 Tehran, Iran. Contact e-mail: [email protected] J.Y. KANG, PhD Student, and H.S. KIM, Professor, are with the Department of Materials Science and Engineering, POSTECH, Pohang 790-784, Korea. Manuscript submitted July 19, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
advantages, such as lower process load and better strain homogeneity compared to the TCAP process.[16] The PTCAP process could achieve significant grain refinements and a notable increase in strength of the copper tube after a single PTCAP pass. Processing of UFG AZ91 and NS pure aluminum tubes has been performed using the TCAP process by Faraji et al.[17] and Mesbah et al.[18] Mesbah et al.[18] presented that NS aluminum tubes with high-angle grain boundaries (HAGBs) could be produced using the TCAP process at an equivalent plastic strain of ~8. Despite extensive applications of aluminum and its alloys in various industries, processing of UFG aluminum tubes using the PTCAP process has not been done yet. Precipitation strengthened and age hardening aluminum alloys are some of the most promising candidates for a production of thermally stable high-strength UFG materials. It has been reported that approximately two-thirds of all extrudates are made of aluminum alloys, and 90 pct of them are within the 6xxx series.[19] Furthermore, among many aluminum alloys currently available, the age-hardenable Al-6061 alloy is extensively used in various industrial applications because it provides a good combination of formability and strength. Many reports described the processing of Al-6061 alloy using ECAP,[20–22] HPT,[23,24] and ARB[25–27] processes, in contrast no investigation was made for the processing and characterization of Al-6061 alloy using the PTCAP process. In this study, the multi-pass PTCAP process was applied to pro
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