Effect of non-isothermal retrogression and re-ageing on through-thickness homogeneity of microstructure and properties of Al-8Zn-2Mg-2Cu alloy thick plate

Abstract

In order to improve the through-thickness homogeneity and properties of aviation aluminum alloy thick plate. The effect of heating-cooling retrogression and re-ageing on the performance of Al-8Zn-2Mg-2Cu alloy thick plate was investigated by hardness tests, electrical conductivity tests and transmission electron microscopy (TEM) observation. Results revealed that, during retrogression heating, the fine pre-precipitates in surface layer dissolve more and the undissolved η′or η phases are more coarsened than that of center layer. During slow cooling after retrogression, precipitates continue coarsening but with a lower rate and the secondary precipitation occurs in both layers. Finer precipitates resulting from the secondary precipitation are more in surface. However, the coarsening and secondary precipitation behaviors are restrained in both layers under quick cooling condition. The electrical conductivity and through-thickness homogeneity of precipitates increases while the hardness decreases with cooling rate decreasing. After the optimized non-isothermal retrogression and re-ageing (NRRA) including air-cooling retrogression, the through-thickness homogeneity which is evaluated by integrated retrogression effects has been improved to 94%. The tensile strength, fracture toughness and exfoliation corrosion grade of Al-8Zn-2Mg-2Cu alloy plate is 619 MPa, 24.7 MPa·m^1/2 and EB, respectively, which indicates that the non-isothermal retrogression and re-aging (NRRA) could improve the mechanical properties and corrosion resistance with higher through-thickness homogeneity.

Keywords

non-isothermal ageing / retrogression and re-ageing / Al-8Zn-2Mg-2Cu alloy / thick plate, homogeneity

References

[1] ZindaniD, MaityS R, BhowmikS. Decision making tools for optimal material selection: A review [J]. Journal of Central South, 2020, 27: 629-673

[2] KrishnanunniS, GuptaR K, AjithkumarG, et al.. Investigation on effect of optimized RRA in strength and SCC resistance for aluminium alloy AA7010 [J]. Materials Today: Proceedings, 2020, 27: 2385-2389

[3] FengD, ZhangX M, LiuS D, et al.. Non-isothermal “retrogression and re-ageing” treatment schedule for AA7055 thick plate [J]. Materials & Design, 2014, 60: 208-217

[4] WangY, CaoL, WuX, et al.. Effect of retrogression treatments on microstructure, hardness and corrosion behaviors of aluminum alloy 7085 [J]. Journal of Alloys and Compounds, 2020, 814: 152264

[5] RenJ, WangR, PengC, et al.. Effect of repetitious retrogression and re-aging treatment on the microstructure, strength and corrosion behavior of powder hot-extruded 7055 Al alloy [J]. Materials Characterization, 2020, 162110190

[6] ZhaoH, GaultB, PongeD, et al.. Reversion and re-aging of a peak aged Al-Zn-Mg-Cu alloy [J]. Scripta Materialia, 2020, 188269-273

[7] FENG Di, ZHANG Xin-ming, CHEN Hong-mei, et al. Effect of non-isothermal retrogression and re-ageing on microstructure and properties of Al-8Zn-2Mg-2Cu alloy thick plate [J]. Acta Metallurgica Sinica, 2018(1): 100–108. DOI:https://doi.org/10.11900/0412.1961.2017.00203.

[8] WeiS, FengY, ZhangH, et al.. Influence of aging on microstructure, properties and stress corrosion cracking of 7136 aluminum alloy [J]. Journal of Central South, 2021, 28: 2687-2700

[9] AzarniyaA, TaheriA K, TaheriK K. Recent advances in ageing of 7xxx series aluminum alloys: A physical metallurgy perspective [J]. Journal of Alloys and Compounds, 2019, 781: 945-983

[10] STALEY J. Method and process of non-isothermal aging for aluminum alloys: US20070267113 [P]. 2007-11-22.

[11] LiuX, ZhangD, WangC, et al.. Effect of grain boundary precipitation on corrosion of heating-aging treated Al-4.47Zn-2.13Mg-1.20Cu alloy [J]. Journal of Materials Research and Technology, 2020, 9(3): 5815-5826

[12] JiangD, LiuY, LiangS, et al.. The effects of non-isothermal aging on the strength and corrosion behavior of AlZnMgCu alloy [J]. Journal of Alloys and Compounds, 2016, 681: 57-65

[13] LiuY, LiangS, JiangD. Influence of repetitious non-isothermal aging on microstructure and strength of Al-Zn-Mg-Cu alloy [J]. Journal of Alloys and Compounds, 2016, 689: 632-640

[14] PengX, GuoQ, LiangX, et al.. Mechanical properties, corrosion behavior and microstructures of a non-isothermal ageing treated Al-Zn-Mg-Cu alloy [J]. Materials Science and Engineering A, 2017, 688: 146-154

[15] LI Ji-chen, FENG Di, XIA Wei-sheng, et al. The non-isothermal double ageing behaviour of 7055 aluminum alloy [J]. Acta Metallurgica Sinica, 2020(11): 1495–1506. DOI: https://doi.org/10.11900/0412.1961.2020.00039.

[16] LiJ C, FengD, XiaW, et al.. Effect of non-isothermal ageing on microstructure and properties of 7B50 aluminum alloy [J]. Acta Metallurgica Sinica, 2020, 56: 1255-1264

[17] FengD, ZhangX M, LiuS D, et al.. The effect of pre-ageing temperature and retrogression heating rate on the microstructure and properties of AA7055 [J]. Materials Science and Engineering A, 2013, 588: 34-42

[18] WangT, YangL, TangZ, et al.. Effect of aging treatment on microstructure, mechanical and corrosion properties of 7055 aluminum alloy prepared using powder by-product [J]. Materials Science and Engineering A, 2021, 822141606

[19] WangY, LiuM, XiaoW, et al.. Effects of multi-stage aging treatments on the precipitation behavior and properties of 7136 aluminum alloy [J]. Journal of Alloys and Compounds, 2020, 814152256

[20] NicolasM, DeschampsA. Characterisation and modelling of precipitate evolution in an Al-Zn-Mg alloy during non-isothermal heat treatments [J]. Acta Materialia, 2003, 51(20): 6077-6094

[21] FengD, ZhangX, LiuS, et al.. Non-isothermal retrogression kinetics for grain boundary precipitate of 7A55 aluminum alloy [J]. Transactions of Nonferrous Metals Society of China, 2014, 24(7): 2122-2129