Effect of T6 and Re-Aging Heat Treatment on Mechanical Properties of 7055 Aluminum Alloy

Authors: M. Esmailian, M. Shakouri, A. Mottahedi, S. G. Shabestari

Abstract:

Heat treatable aluminum alloys such as 7075 and 7055, because of high strength and low density, are used widely in aircraft industry. For best mechanical properties, T6 heat treatment has recommended for this regards, but this temper treatment is sensitive to corrosion induced and Stress Corrosion Cracking (SCC) damage. For improving this property, the over-aging treatment (T7) applies to this alloy, but it decreases the mechanical properties up to 30 percent. Hence, to increase the mechanical properties, without any remarkable decrease in SCC resistant, Retrogression and Re-Aging (RRA) heat treatment is used. This treatment performs in a relatively short time. In this paper, the RRA heat treatment was applied to 7055 aluminum alloy and then effect of RRA time on the mechanical properties of 7055 has been investigated. The results show that the 40-minute time is suitable time for retrogression of 7055 aluminum alloy and ultimate strength increases up to 625MPa.

Keywords: 7055 Aluminum alloy, Mechanical properties, SCC resistance, Heat Treatment.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1110057

References:

[1] Lorimer GW. In: Russel KC, Aaronson HI, editors. Precipitation in solids. New York, USA: Met. Soc. AIME; 1978. Chapter 3.
[2] Wu, X.J., Raizenne, M.D., Chen, W.R., Poon, C., and W. Walllace, “Thirty Years of Retrogression and Re-Aging”, ICAS 2002 Congress. (2002).
[3] Cina, B. and Gan, R., United States Patent 3856584, December, 1974.
[4] Cina, B. and Ranish, B., Aluminum Industrial Product, Pittsburgh Chapter, American Society for Metals, 1974.
[5] Kanno M, Araki I, Cui Q., "Precipitation behaviour of 7000 alloys during retrogression and reaging treatment", Mater. Sci.Tech. 1994; 10:599.
[6] Park JK, Ardell AJ, "Effect of retrogression and re-aging treatments on the microstructure of Al-7075-T651", Metall Trans A 1984; 15:1531.
[7] Viana, F., Pinto, A.M.P., Santos, H.M.C. and Lopes, A.B., “Retrogression and re-ageing of 7075 aluminum alloy: microstructural characterization”, Materials Processing Technology, 1999, Vol. 92/93, pp. 54-59.
[8] Jiang XJ, Tafto J, Noble B, Holme B, Waterloo G. "Differential scanning calorimetry and electron diffraction investigation on lowtemperature ageing in Al-Zn-Mg alloys", Metall Mater Trans A 2000; 31:339–348.
[9] Park, J.K. and Ardell, A.J. , “Microstructure of the commercial 7075 Al alloy in the T651 and T7 tempers”, Metallurgical Transactions A, 1999, Vol. 14, pp. 1957-65
[10] T. Marlaud, A. Deschamps, F. Bley, W. Lefebvre, B. Baroux, “Evolution of precipitate microstructures during the retrogression and re-ageing heat treatment of an Al–Zn–Mg–Cu alloy”, Acta materialia, 2010, Vol.58, pp. 4814-4826.
[11] Bakker H, Bonzel HP, Bruff CM, Dayananda MA, Gust W, Horvth J, et al. Diffusion in Solid Metals and Alloys. Springer Verlag; 1990.
[12] Marlaud T, Deschamps A, Bley F, Lefebvre W, Baroux B., "Influence of alloy composition and heat treatment on precipitate composition in Al– Zn–Mg–Cu alloys", Acta Mater 2010, Vol.58, pp.248-260.