بررسی و مقایسه اثرات عملیات حرارتی RRA، T73 و T6 بر سختی، استحکام کششی و خمشی آلیاژ آلومینیم 7075

نویسندگان

دانشکده مهندسی مواد، دانشگاه صنعتی مالک اشتر اصفهان، شاهین شهر، اصفهان

چکیده

در این مقاله فرایندهای RRA، T73 و T6 با هدف ارتقای خواص مکانیکی آلیاژ آلومینیم 7075 انجام و سختی، استحکام کششی و استحکام خمشی آلیاژ مورد ارزیابی و مقایسه قرار گرفته است. به این منظور محلول­سازی در دمای 530 درجه سانتی­گراد به­مدت 16 ساعت انجام شد. برای عملیات T6، پس از آنیل انحلالی، پیرسازی در دمای 150 درجه سانتی‌گراد به­مدت 24 ساعت صورت گرفت. در فرایند T73 پس از آنیل انحلالی، نمونه در دو مرحله به‌ترتیب در دماهای ‌120 و 180 درجه سانتی­گراد و به­مدت 7 و 20 ساعت پیرسازی شد. عملیات RRA در سه مرحله انجام شد. مرحله اول همانند T6، مرحله دوم عملیات بازگشت در دمای 200 درجه سانتی­گراد به­مدت 20 دقیقه و در مرحله سوم مجدداً پیرسازی همانند T6 انجام شد. بررسی ریز‌ساختار و سطح شکست نمونه­ها توسط میکروسکوپ­های نوری (OM) و الکترونی روبشی (SEM) انجام شد. برای بررسی ترکیب شیمیایی رسوب­ها از طیف‌سنجی با تفکیک انرژی EDS)) استفاده شد. ارزیابی سختی، استحکام کششی و خمشی مطابق با استانداردهای ASTM E384-99 ، ASTM B557-06 و DIN 50121 انجام گرفت. عملیات RRA باعث افزایش استحکام کششی از 466 به 485 مگاپاسکال و سختی از 110 به 165 ویکرز شد. پس از عملیات T6 استحکام کششی از 466 به 505 مگاپاسکال و سختی از 110 به 160 ویکرز افزایش یافت. در فرایند T73 تغییری در استحکام کششی (465 مگاپاسکال) حاصل نشد ولی استحکام تسلیم از 394 به 410 افزایش و سختی از 110 به 84 ویکرز کاهش یافت. استحکام خمشی در فرایندهای T73، RRA و T6 به‏ترتیب از 797 به 844، 920 و 1030 مگاپاسکال افزایش یافت. با انجام فرایند RRA در دما و زمان بهینه سختی، استحکام کششی و استحکام خمشی فرایندهای T6 و T73 بهبود پیدا کرد.

کلیدواژه‌ها


عنوان مقاله [English]

Evaluation and Comparison of the Effects of RRA, T73 and T6 Heat Treatments on Hardness, Tensile and Bending Strengths of 7075 Aluminum Alloy

نویسندگان [English]

  • M. Assadi
  • S.R. Hosseini
Department of Materials Engineering, Malek-Ashtar University of Technology, Shahin Shahr, Iran
چکیده [English]

In the present article, RRA, T73 and T6 heat treatments were carried out to improve mechanical properties of 7075 aluminum alloy and its hardness, tensile and bending strengths were evaluated. For this purpose, solution annealing was performed at 530 ºC for 16 h. For T6 treatment, aging was executed at 150 ºC for 24 h after solution annealing. In T73, aging treatment was done in two stages after solution annealin, at 120 and 180 ºC for 7 and 20 h, respectively. RRA treatment was performed in three stages. The first stage was the same as T6 treatment, the second stage constitutes tempering at 200 ºC for
20 min and in the third stage aging process was repeated like T6 treatment. Evaluation of the microstructures and fractured surfaces were performed with optical microscopes (OM) and scanning electron microscopes (SEM). Energy dispersive spectroscopy (EDS) was used to study the chemical composition of precipitates. Hardness, tensile and bending strength were evaluated according to ASTM E384-11e1, ASTM B557-06 and DIN 50121 standards. RRA treatment increased tensile strength from 466 to 485 MPa and hardness from 110 to 165 Vickers. After T6 treatment, tensile strength increased from 466 to 505 MPa and hardness from 110 to 160 Vickers. In T73 process, the tensile strength remained almost constant (465 MPa) but yield strength increased from 394 to 410 MPa and hardness decreased from 110 to 84 Vickers. The bending strength increased from 797 to 844, 920 and 1030 MPa in T73, RRA and T6 processes, respectively. By applying RRA process in optimized temperature and time, hardness, tensile and bending strengths of 7075 aluminum alloy were enhanced from 5 to 15% compared to that of T6 and T73 processes.

کلیدواژه‌ها [English]

  • Aluminum 7075
  • Solution annealing
  • Aging
  • Tensile strength
  • Bending strength
  • Hardness
1. Rendigs, K.H., “Aluminium Structures Used in Aerospace‌-Status And Prospects”, Materials Science Forum, Vol. 242, pp. 11-24, 1997.
3. Adler, P.N., Delasi, R. and Geschwind, G., “Influence of Microstructure on the Mechanical Properties and Stress Corrosion Susceptibility of 7075 Aluminum Alloys”, Metallurgical and Materials Transactions, Vol. 3, pp. 3191-3200, 1972.
4. John, A., Paton, N.E., Hamilton, C.H. and Mahoney, M.W., “Grain Refinement in 7075 Aluminum by Thermo Mechanical Processing”, Metallurgical Transactions, Vol. 12A , pp. 1267-1276, 1981.
5. Zhao, Y., Liao, X., Valiev, R.Z. and Zhu, Y.T., “Structures and Mechanical Properties of ECAP Processed 7075 Al Alloy upon Natural Aging and T651 Treatment”, Acta Materialia, Vol. 52,
pp. 4589–4599, 2004.
6. Ou, B.L., Yang, J.G. and Wei, M.Y., “Effect of Homogenization and Aging Treatment on Mechanical Properties and Stress-Corrosion Cracking of 7075 Al Alloy”, Metallurgical and Materials Transactions, Vol. 38A, pp. 471-479, 2007.
7. Feng, L.J., Wei, P.Z, Xing, L.C., Qiang, J. Z., Jing, CH. W. and Qiao, V, “Mechanical Properties, Corrosion Behaviors and Microstructures of 7075 Aluminum Alloy with Various Aging Treatments”, Transaction of Nonferrous Metals, Society of China, Vol. 18, pp. 755-762, 2008.
8. Wang, D., Ni, D.R. and Ma, Z.Y., “Effect of Pre-Strain and Two-Step Aging on Microstructure and Stress Corrosion Cracking of 7075 Alloy”, Materials Science and Engineering A, Vol. 494, pp. 360-366, 2008.
9. Panigrahi, S.K. and Jayaganthan, R., “Effect of Ageing on Microstructure and Mechanical Properties of Bulk, Cryorolled and Room Temperature Rolled Al 7075 alloy”, Journal of Alloys and Compounds, Vol. 509, pp. 9609– 9616, 2011.
10. Yilmaz, R.,. Ozyurek, D and Kibar, E., “The Effects of Retrogression Parameters on Hardness and Wear Behaviours of 7075 Aluminum Alloy”, Journal of the Faculty of Engineering and Architecture of Gazi University, Vol. 27, pp. 429-438, 2012.
11. Designation: R209M–02, Aluminum and Aluminum-Alloy Sheet and Plate, Annual Book of ASTM Standards, Available in the Related Materials section (gray pages) of the Annual Book of ASTM Standards, United States, 2002.
12. .Designation: E112-12, Standard Test Methods For Determining Average Grain Size, The Annual Book of ASTM Standards, Section 03 (Metals Test Methods And Analytical Procedures), Volume 03.01 (Metals-Mechanical Testing; Elevated and
Low-Temperature Tests; Metallography), ASTM International, United States, 2012.
14. Designation: B918-01, Standard Practice for Heat Treatment of Wrought Aluminum Alloys, The Annual Book of ASTM Standards, Section 03 (Mechanical Testing_ Elevated and Low-Temperature Tests_ Metallography), Volume 02.02 (Aluminum and Magnesium Alloys), ASTM International, United States, 2003.
15. Designation E384–99, Standard Test Method for Microindentation Hardness of Materials, The Annual Book of ASTM Standards, Section 03 (Mechanical Testing _ Elevated and Low-Temperature Tests_ Metallography), Volume 01.04 (Structural Steel for Bridge, Rolling stock and Ship), ASTM International, United States, 2003.
16. Designation: B557–06, Standard Test Methods for Tension Testing Wrought and Cast Aluminum-
and Magnesium-Alloy Products, The Annual Book
of ASTM Standards, Section 03 (Mechanical Testing_ Elevated and Low-Temperature Tests_ Metallography), Volume 02.02 (Aluminum and Magnesium Alloys), ASTM International, United States, 2004.
17. Designation: E290–97a, Standard Test Methods for Bend Testing of Material for Ductility, The Annual Book of ASTM Standards, Section 03 (Mechanical Testing_ Elevated and Low-Temperature Tests_ Metallography), Volume 03.01 (Metals - Mechanical Testing_ Elevated and Low-Temperature Tests_ Metallography), ASTM International, United States, 2003.
18. Lin, Y.C., Qiang Jiang, Y., Min Chen, X., Xu Wen, D. and Min Zhou, H, “Effect of Creep-Aging on Precipitates of 7075 Aluminum Alloy”, Materials Science and Engineering A588 (2013) 347–356.
19. Lin, Y.C., Qiang Jiang, Y., Cheng Zhang, X., Min Zhou, H., and Deng, J., “Effects of Creep-Aging Processing on the Corrosion Resistance and Mechanical Properties of an Al–Cu–Mg Alloy”, Materials Science and Engineering, Vol. A605,
pp. 192–202, 2014.
20. Starink, M.J. and Li, X.M., “A Model for the Electrical Conductivity of Peak Aged and Overaged Al-Zn-Mg-Cu Alloys”, Metallurgical and Materials Transactions A, Vol. 34A, pp. 899-911, 2003.
21. Mahathaninwong, N., Plookphol, T., Wannasin, J. and Wisutmethangoon, S., “T6 Heat Treatment of Rheocasting 7075 Al Alloy”, Materials Science and Engineering, Vol. A 532, pp. 91–99, 2012.
24. Chandler, H., Heat Treaters Guide Practices and Procedures for Nonferrous Alloys, The ASM Handbook, ASM international, 1996.
26. Magd, E. And Brodmann, M., “Influence of Precipitates on Ductile Fracture of Aluminium Alloy AA7075 at High Strain Rates”, Materials Science and Engineering, Vol. A307, pp. 143–150, 2001.
27. Karaaslan, A., Kaya, I. and Atapek, H., “Effect of Aging Temperature and of Retrogression Treatment Time on the Mivrostructure and Mechanical Properties of Alloy AA 7075”, Metal Science and Heat Treatment, Vol. 49, pp. 443-447, 2007.
28. Hulbert, D., Fuller, C., Mahoney, M. and London, B., “The Mechanical and Thick Section Bending Behaviour of Friction Stir Processed Aluminum Plate”, Scripta Materialia, Vol. 57, pp. 269-272, 2007.
29. Westermann, I., Snilsberg, K., Sharifi, Z., Hopperstad, O., Marthinsen, K. and Holmeda, B., “Three-Point Bending of Heat-Treatable Aluminum Alloys: Influence of Microstructure and Texture on Bendability and Fracture Behavior”, Metallurgical and Materials Transactions A, Vol. 42A, pp. 3386-3398, 2011.

ارتقاء امنیت وب با وف ایرانی