Effect of Two-Step Aging Process on Microstructure and Fracture Toughness of 7085 Aluminum Alloy

Abstract:

In this paper, the effect of two-step aging treatment on microstructure and fracture toughness of 7085 aluminum alloy were investigated by using tear tests to carry out the fracture toughness tests of the alloy and using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to analyze the microstructure. The results showed the main precipitates in the alloy were GP zones and η' phases in the grains after 118°C/6h aging treatment. With further secondary aging treatment, grain boundaries precipitates (GBPs) grew up, and the precipitate-free zone (PFZ) showed up, the increasing proportion of intergranular failure was occurred and the fracture toughness decreased. With further prolonging of the secondary aging treatment time, precipitates in the grains tended to be coarser, the GBPs became discontinuous ,PFZ became wider, and there were decreasing proportion of the intergranular failure and increasing proportion of the transgranular failure showing on the fracture morphologies, the fracture toughness of 7085 aluminum alloy increased.

• Periodical: Materials Science Forum (Volume 852)
• Pages: 149-155
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.852.149
• Online since: April 2016
• Authors: Yang Song, Bai Qing Xiong, Yong An Zhang, Xi Wu Li, Zhi Hui Li, Shu Hui Huang, Hong Wei Yan, Hong Wei Liu
• Keywords: 7085 Aluminum Alloy, Fracture Toughness, Microstructure, Two-Step Aging

References

[1] A Heinz, A Haszler, C Keidel, et al, Recent development in aluminum alloys for aerospace applications, Mater. Sci. Eng. A. 280 (2000) 102-107.

DOI: 10.1016/s0921-5093(99)00674-7

[2] Z Li, B Xiong, Y Zhang, et al, Investigation on strength, toughness and microstructure of an Al-Zn-Mg-Cu alloy pre-stretched thick plate in various aging tempers, Journal of Materials Processing Technology. 209 (2008) 2021-(2027).

DOI: 10.1016/j.jmatprotec.2008.04.052

[3] AMS 4414, Aluminum alloy, hand forgings 7. 5Zn-1. 6Cu-1. 5Mg-0. 12Zr (7085-T7452) solution heat treated, compression stress-relieved, and overaged. (2008).

DOI: 10.4271/ams4414

[4] L John, Advanced aluminum and hybrid aero-structures for future aircraft, Mater Sci Forum. 519/521 (2006) 1233-1238.

[5] T S Srivatsan, Microstructure, tensile properties and fracture behavior of aluminum alloy 7150, Journal of Materials Science. 27 (1992) 4772-4781.

DOI: 10.1007/bf01166019

[6] Z Cvijović, M Vratnica, I Cvijović-Alagić, The influences of multiscale-sized second-phase particles on fracture behavior of overaged 7000 alloys. Procedia Engineering. 1 (2009) 35-38.

DOI: 10.1016/j.proeng.2009.06.010

[7] B Xiong, X Li, Y Zhang, et al, Novel Al-7. 5Zn-1. 65Mg-1. 4Cu-0. 12Zr alloys with high strength high toughness and low quench sensitivity, the Chinese Journal of Nonferrous Metals. 19 (2009) 1539-1547.

[8] D K Xu, N Birbilis, P A Rometsch, Improved solution treatment for an as-rolled Al–Zn–Mg–Cu alloy: Part II. Microstructure and mechanical properties Materials Science and Engineering A. 534 (2012) 244-252.

DOI: 10.1016/j.msea.2011.11.073

[9] P Li, B Xiong, Y Zhang, Quench sensitivity and microstructure character of high strength AA7050, Transactions of Nonferrous Metals Society of China. 22 (2012) 268-274.

DOI: 10.1016/s1003-6326(11)61170-9

[10] M M Sharma, M F Amateau, T J Eden, Hardening mechanisms of spray formed Al-Zn-Mg-Cu alloys with scandium and other elemental additions, Journal of Alloys and Compounds. 416 (2006) 135-142.

DOI: 10.1016/j.jallcom.2005.08.045

[11] ASTM B871-01, Standard test method for tear testing of aluminum alloy products. (2013).

[12] N HAN, X. M Zhang, S. D Liu, et al, Influence of two-step aging on fracture toughness of 7050 aluminum alloy plate, Journal of Central South University (Science and Technology). 42 (2011) 623-628.

[13] D J Chakrabarti, J Liu, R R Sawtell, et al, New generation high strength high damage tolerance 7085 thick alloy product with low quench sensitivity, Materials Forum. 28 (2004) 969-974.

[14] S Gang, A Cerezo, Early-stage precipitation in Al-Zn-Mg-Cu alloy (7050), Acta Materialia. 5 (2004) 4503-4516.

DOI: 10.1016/j.actamat.2004.06.025

[15] R T Shuey, F Barlat, M E Karabin, et al, Experimental and analytical investigations on plane strain toughness for 7085 aluminum alloy, Metallurgical and Materials Transactions A. 40 (2009) 365-376.

DOI: 10.1007/s11661-008-9703-2

[16] Z Cvijović, M Rantinta M Rakin, Micromechanical modelling of fracture toughness in overaged 7000 alloy forgings, Materials Science and Engineering A. 434 (2006) 339-346.

DOI: 10.1016/j.msea.2006.07.018

[17] N Kamp, I Sinclair, M J Starink, Toughness-strength relations in the overaged 7449 Al-based alloy, Metallurgical and Materials Transactions A. 33 (2002) 1125-1136.

DOI: 10.1007/s11661-002-0214-2

[18] D Dumont, A Deschamps, Y Brechet. On the relationship between microstructure, strength and toughness in AA7050aluminumalloy, Materials Science and Engineering A. 356 (2003) 326-336.

DOI: 10.1016/s0921-5093(03)00145-x

[19] J Buha, R N Lumley, A G Crosky, Secondary aging in an aluminum alloy 7050, Materials Science and Engineering A. 492 (2008) 110.

DOI: 10.1016/j.msea.2008.02.039

[20] S Y Chen, K H Chen, G S Peng, et al, Effect of heat treatment on hot deformation behavior and microstructure evolution of 7085 aluminum alloy, Journal of Alloys and Compounds. 537 (2012) 338-345.

DOI: 10.1016/j.jallcom.2012.05.052