Fatigue Crack Growth and Precipitation Characteristics of a High Zn-Containing Al-Zn-Mg-Cu Alloy with Various Typical Aging States

Abstract:

The fatigue crack growth of Al-Zn-Mg-Cu alloy can be adjusted by different aging treatments. In the present work, a high Zn-containing Al-Zn-Mg-Cu alloy was treated by single, double and triple stage aging treatments and typical T6, T79 and T77 states were selected by tensile properties. Fatigue crack growth under these aging states was tested and related fracture morphology and precipitation characteristics were observed. The results showed that fatigue crack growth resistance for the alloy was T6<T79<T77. The corresponding fracture morphology also showed the difference of fatigue striations and the measurement of them provided an additional evidence. The precipitation proved that the alloy with T6 state possessed GPI zone, GPII zone and η' phase while that for T76 state was GPII zone, η' phase and η phase. As for the T77 state, the precipitate types were GPII zone and η' phase. The matrix precipitate for T6 state was smaller and denser than that for T79 and T77 states while that for T77 state possessed a dense distribution than that for T79 state. The measurement of precipitate size distribution also proved it. The grain boundary precipitates for T79 and T77 states were similar, which had a more intermittent distribution than that for T6 state.

• Periodical: Materials Science Forum (Volume 1026)
• Pages: 19-27
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.1026.19
• Online since: April 2021
• Authors: Kai Wen*, Hong Wei Liu
• Keywords: Aging Precipitation, Al-Zn-Mg-Cu Alloy, Fatigue Crack Growth, Zinc Content

References

[1] J. Tang, J. Wang, J. Teng, et al. Effect of Zn content on the dynamic softening of Al–Zn–Mg–Cu alloys during hot compression deformation, Vacuum, 2021, 184: 109941.

DOI: 10.1016/j.vacuum.2020.109941

[2] T. Dursun, C. Soutis. Recent developments in advanced aircraft aluminium alloys, Mater. Des. 2014, 56(4): 862-871.

DOI: 10.1016/j.matdes.2013.12.002

[3] Y. Pan, D. Zhang, H. Liu, et al. Precipitation hardening and intergranular corrosion behavior of novel Al–Mg–Zn(-Cu) alloys, J. Alloy Compd, 2021, 853: 157199.

DOI: 10.1016/j.jallcom.2020.157199

[4] A. Azarniya, A.K. Taheri, K.K. Taheri. Recent advances in ageing of 7xxx series aluminum alloys: a physical metallurgy perspective, J. Alloy Compd, 2018, 781: 945-983.

DOI: 10.1016/j.jallcom.2018.11.286

[5] J.T. Liu, Y.A. Zhang, X.W. Li, et al. Thermodynamic calculation of high zinc-containing Al-Zn-Mg-Cu alloy, Trans. Nonferrous Metals Soc. 2014, 24(5): 1481-1487.

DOI: 10.1016/s1003-6326(14)63216-7

[6] K. Wen, Y. Fan, G. Wang, et al. Aging behavior and fatigue crack growth of high Zn-containing Al-Zn-Mg-Cu alloys with zinc variation, Prog. Nat. Sci. 2017, 27(2): 217-227.

DOI: 10.1016/j.pnsc.2017.02.002

[7] M. Dixit, R. S. Mishra, K. K. Sankaran. Structure–property correlations in Al 7050 and Al 7055 high-strength aluminum alloys, Mater. Sci. Eng. A. 2008, 478: 163-172.

DOI: 10.1016/j.msea.2007.05.116

[8] S. Bai, Z. Liu, Y. Gu, et al. Microstructures and fatigue fracture behavior of an Al–Cu–Mg–Ag alloy with a low Cu/Mg ratio, Mater. Sci. Eng. A. 2011, 530: 473-480.

DOI: 10.1016/j.msea.2011.10.004

[9] M. Nakai, T. Eto. New aspect of development of high strength aluminum alloys for aerospace applications, Mater. Sci. Eng. A. 2000, 285: 62-68.

DOI: 10.1016/s0921-5093(00)00667-5

[10] W. Wen, P. Cai, A. H.W. Ngan, et al. An experimental methodology to quantify the resistance of grain boundaries to fatigue crack growth in an AA2024 T351 Al-Cu Alloy, Mater. Sci. Eng. A. 2016, 666: 288-296.

DOI: 10.1016/j.msea.2016.04.071

[11] L. Lin, Z. Liu, X. Han, et al. Effect of Overaging on Fatigue Crack Propagation and Stress Corrosion Cracking Behaviors of an Al-Zn-Mg-Cu Alloy Thick Plate, J. Mater. Eng. Perform. 2018, 27: 3824-3830.

DOI: 10.1007/s11665-018-3518-0

[12] Y.L. Wang, Q.L. Pan, L.L. Wei, et al. Effect of retrogression and reaging treatment on the microstructure and fatigue crack growth behavior of 7050 aluminum alloy thick plate, Mater. Des. 2014, 55: 857-863.

DOI: 10.1016/j.matdes.2013.09.063

[13] J.C. Li, K.G. Wang. Influence of phase coarsening on fatigue crack growth in precipitate strengthened alloys, Eng. Fract. Mech. 2019, 205: 229-252.

DOI: 10.1016/j.engfracmech.2018.11.029

[14] P. Xia, Z. Liu, S. Bai, et al. Enhanced fatigue crack propagation resistance in a superhigh strength Al–Zn–Mg–Cu alloy by modifying RRA treatment, Mater. Charact. 2016, 118: 438-445.

DOI: 10.1016/j.matchar.2016.06.023

[15] R. Yang, Z. Liu, P. Ying, et al. Multistage-aging process effect on formation of GP zones and mechanical properties in Al–Zn–Mg–Cu alloy, T. Nonferr. Metal. Soc. 2016, 26: 1183-1190.

DOI: 10.1016/s1003-6326(16)64221-8

[16] R. Li, Z. Ren, Y. Wu, et al. Mechanical behaviors and precipitation transformation of the lightweight high-Zn-content Al–Zn–Li–Mg–Cu alloy, Mater. Sci. Eng. A. 2021, 802: 140637.

DOI: 10.1016/j.msea.2020.140637

[17] K. Wen, B. Xiong, Y. Zhang, et al. Over-aging influenced matrix precipitate characteristics improve fatigue crack propagation in a high Zn-containing Al-Zn-Mg-Cu alloy, Mater. Sci. Eng. A. 2018, 716: 42-54.

DOI: 10.1016/j.msea.2018.01.040

[18] K. Wen, B. Xiong, Y. Zhang, et al. Effect of Various Retrogression Regimes on Aging Behavior and Precipitates Characterization of a High Zn‑Containing Al–Zn–Mg–Cu Alloy, Met. Mater. Int. 2018, 24: 537-548.

DOI: 10.1007/s12540-018-0077-8

[19] K. Wen, B. Xiong, W. Ren, et al. Fe-rich particles influenced secondary crack characteristics in an Al-Zn-Mg-Cu alloy extrusion plate with high zinc content, Scripta Mater. 2020, 186: 259-262.

DOI: 10.1016/j.scriptamat.2020.05.045

[20] K. Wen, B. Xiong, Y. Zhang, et al. Single-stage aging behaviour and precipitate evolution in a high Zn-containing Al–9.78Zn–2.02Mg–1.76Cu alloy, Mater. Sci. Tech-Lond. 2018, 34(6): 718-724.

DOI: 10.1080/02670836.2017.1410951

[21] J.D. Verhoeven, Fundamentals of Physical Metallurgy, John Wiley, New York, (1975).