Retrogression and re-aging 7B50 Al alloy plates based on examining the through-thickness microstructures and mechanical properties

HOU Long-gang; ZHAO Feng; ZHUANG Lin-zhong; ZHANG Ji-shan

doi:10.13374/j.issn2095-9389.2017.03.016

Volume 39 Issue 3

Mar. 2017

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Article Navigation > Chinese Journal of Engineering > 2017 > 39(3): 432-442

HOU Long-gang, ZHAO Feng, ZHUANG Lin-zhong, ZHANG Ji-shan. Retrogression and re-aging 7B50 Al alloy plates based on examining the through-thickness microstructures and mechanical properties[J]. Chinese Journal of Engineering, 2017, 39(3): 432-442. doi: 10.13374/j.issn2095-9389.2017.03.016

Citation:

HOU Long-gang, ZHAO Feng, ZHUANG Lin-zhong, ZHANG Ji-shan. Retrogression and re-aging 7B50 Al alloy plates based on examining the through-thickness microstructures and mechanical properties[J]. Chinese Journal of Engineering, 2017, 39(3): 432-442. doi: 10.13374/j.issn2095-9389.2017.03.016

Citation:

HOU Long-gang, ZHAO Feng, ZHUANG Lin-zhong, ZHANG Ji-shan. Retrogression and re-aging 7B50 Al alloy plates based on examining the through-thickness microstructures and mechanical properties[J]. Chinese Journal of Engineering, 2017, 39(3): 432-442. doi: 10.13374/j.issn2095-9389.2017.03.016

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Retrogression and re-aging 7B50 Al alloy plates based on examining the through-thickness microstructures and mechanical properties

doi: 10.13374/j.issn2095-9389.2017.03.016

1) State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
2) Shandong Nanshan Aluminium Co. Ltd., Longkou 265706, China

Received Date: 2016-05-12

Abstract

Abstract

For enhancing the corrosion resistance of the T6-aged high-strength Al alloys with higher strength, retrogression and reaging (RRA) treatments were used to optimize the morphologies, sizes, distribution of precipitates, especially grain boundary precipitates (GBPs). The effects of different retrogression treatments on the microstructures and mechanical properties were studied so as to gain suitable RRA process for 7B50 Al alloy plates. It is found that increasing the retrogression temperature or time will promote the coarsening of transgranular and intergranular precipitates in the center and surface layers of 7B50 Al alloy plates as well as the precipitation of stable η-MgZn₂ phase, which will decrease the strength and raise the conductivity. The retrogression temperature will greatly affect the strength and conductivity. The continuously distributed GBPs induced by T6 aging become discontinuous after RRA treatment, accompanying with slightly increasing sizes of transgranular precipitates. Based on the strength and conductivity of the center and surface layers, 165℃/6 h is the suitable retrogression process for 7B50 Al alloy plates. However, the severe deformation of the surface grains compared to that of the central grains caused by hot rolling leads to a higher content of subgrains or substructures in the surficial grains, which promotes the surface layer to quickly reach the peak aging, and the subsequent retrogression treatment results in much more stable η phase in the surface layer. The formation of stable η phase as well as the coarsening or growth of transgranular precipitates could be mainly responsible for the strength difference between the surface and center layers. Although there are some differences about the grain structures between the surface and center layers after quenching/RRA treatments with some local subgrain growth, the positive impact of RRA treatment to the strength is apparently unable to compare with the obvious strength reduction caused by early precipitation of stable η phase in the surface layer. Thus, the RRA treatment cannot relieve the property difference between the center and surface layers of 7B50 Al alloy plates, but it can make the strength and conductivity of the center and surface layers to concurrently meet some working requirements.
- aluminum alloy,
- retrogression,
- re-aging,
- microstructure,
- properties,
- precipitation

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References(25)

References

[1]	Staley J T, Liu J, Hunt W H Jr, et al. Aluminum alloys for aerostructures. Adv Mater Processes, 1997, 152(4):17
[2]	Heinz A, Haszler A, Keidel C, et al. Recent development in aluminium alloys for aerospace applications. Mater Sci Eng A, 2000, 280(1):102
[3]	Williams J C, Jr Starke E A. Progress in structural materials for aerospace systems. Acta Mater, 2003, 51(19):5775
[5]	Spiedel M O. Stress corrosion cracking of aluminum alloys. Metall Trans A, 1975, 6:631
[6]	Osaki S, Itoh D, Nakai M. SCC properties of 7050 series aluminum alloys in T6 and RRA tempers. Jpn Inst Light Met, 2001, 51(4):222
[7]	Ramgopal T, Gouma P I, Frankel G S. Role of grain-boundary precipitates and solute depleted zone on the intergranular corrosion of aluminum alloy 7150. Corrosion, 2002, 58(8):687
[8]	Puiggali M, Zienlinski A, Olive J M, et al. Effect of microstructure on stress corrosion cracking of an Al-Zn-Mg-Cu alloy. Corros Sci, 1998, 40(4):805
[9]	Cina B M. Reducing the Susceptibility of Alloys, Particularly Aluminium Alloys, to Stress Corrosion Cracking:US Patent, 3856584. 1974-12-24
[10]	Kanno M, Araki I, Cui Q. Precipitation behaviour of 7000 alloys during retrogression and reaging treatment. Mater Sci Technol, 1994, 10:599
[11]	Park J K. Influence of retrogression and reaging treatments on the strength and stress corrosion resistance of aluminium alloy 7075-T6. Mater Sci Eng A, 1988, 103(2):223
[12]	Robinson J S, Tanner D A, Whelan S D. Retrogression, reaging and residual stresses in 7010 forgings. Fatigue Fract Eng Mater Struct, 1999, 22(1) 51
[13]	Viana F, Pinto A M P, Santos H M C, et al. Retrogression and re-ageing of 7075 aluminium alloy:microstructural characterization. J Mater Process Technol, 1999, 92-93:54
[14]	Marlaud T, Deschamps A, Bley F, et al. Evolution of precipitate microstructures during the retrogression and re-ageing heat treatment of an Al-Zn-Mg-Cu alloy. Acta Mater, 2010, 58(14):4814
[15]	Li G F, Zhang X M, Li P H, et al. Effects of retrogression heating rate on microstructures and mechanical properties of aluminum alloy 7050. Trans Nonferrous Met Soc China, 2010, 20(6):935
[17]	Ma C Q, Hou L G, Zhang J S, et al. Experimental and numerical investigations of the plastic deformation during multi-pass asymmetric and symmetric rolling of high-strength aluminum alloys. Mater Sci Forum, 2014, 794-796:1157
[18]	Tsai T C, Chuang T H. Relationship between electrical conductivity and stress corrosion cracking susceptibility of Al 7075 and Al 7475 alloys. Corrosion, 1996, 52(6):414
[19]	Dumont D, Deschamps A, Brechet Y. On the relationship between microstructure, strength and toughness in AA7050 aluminum alloy. Mater Sci Eng A, 2003, 356(1):326
[20]	Sha G, Cerezo A. Early-stage precipitation in Al-Zn-Mg-Cu alloy (7050). Acta Mater, 2004, 52(15):4503
[22]	Song R. G, Dietzel W, Zhang B J, et al. Stress corrosion cracking and hydrogen embrittlement of an Al-Zn-Mg-Cu Alloy. Acta Mater, 2004, 52(16):4727
[23]	Meng Q C, Fan X G, Ren S Y, et al. Comparison of microstructure and corrosion properties of Al-Zn-Mg-Cu alloys 7150 and 7010. Trans Nonferrous Met Soc China, 2006, 16(A3):s1356
[25]	Huo W T, Hou L G, Lang Y J, et al. Improved thermo-mechanical processing for effective grain refinement of high-strength AA 7050 Al alloy. Mater Sci Eng A, 2015, 626:86
[26]	El-Baradie Z M, El-Sayed M. Effect of double thermomechanical treatments on the properties of 7075 Al alloy. J Mater Process Technol, 1996, 62(1):76
[27]	Berg L K, Gjønnes J, Hansen V, et al. GP-zones in Al-Zn-Mg alloys and their role in artificial aging. Acta Mater, 2001, 49(17):3443
[28]	Buha J, Lumley R N, Crosky A G. Secondary ageing in an aluminium alloy 7050. Mater Sci Eng A, 2008, 492(1):1
[29]	Kumar M, Poletti C, Degischer H P. Precipitation kinetics in warm forming of AW-7020 alloy. Mater Sci Eng A, 2013, 561:362