Influence of exfoliation corrosion on tensile properties of a high strength Al-Zn-Mg-Cu alloy

Abstract

The influence of exfoliation corrosion on the tensile properties of a high strength Al-Zn-Mg-Cu alloy was investigated by ambient temperature tensile testing, optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). After exfoliation corrosion immersion, blisters and corrosion pits can be seen on the sheet surface, which lead to loss of materials and notches. A number of intergranular cracks are observed to initiate at the bottom of the corrosion-induced notches and propagate rapidly into the bulk materials during tensile. Consequently, exfoliation corrosion results in significant loss of strength and brittle fracture. EBSD results show that the crack propagation path is primarily along the grain boundaries with misorientation of ∼45°, and coincidence site lattice (CSL) boundaries are slightly more resistant to crack.

Keywords

exfoliation / tensile properties / fracture / grain boundaries / Al-Zn-Mg-Cu alloy

References

[1] LiJ. F., JiaZ. Q., BirbilisN.. Exfoliation corrosion of 7150 Al alloy with various tempers and its electrochemical impedance spectroscopy in EXCO solution [J]. Materials and Corrosion, 2009, 60(6): 407-414

[2] FangH. C., ChenK. H., ChenX.. Effect of Cr, Yb and Zr additions on localized corrosion of Al-Zn-Mg-Cu alloy [J]. Corrosion Science, 2009, 51(12): 2872-2877

[3] MarlaudT., MalkiB., HenonC., DeschampsA.. Relationship between alloy composition, microstructure and exfoliation corrosion in Al-Zn-Mg-Cu alloys [J]. Corrosion Science, 2011, 53: 3139-3149

[4] ChubbJ. P., MoradT. A., HockenhullB. S.. The effect of exfoliation corrosion on the fracture and fatigue of 7178-T6 aluminum [J]. Int J of Fatigue, 1995, 17(1): 49-54

[5] DeshpaandeN. U., GokhaleA. M., DenerD. K.. Relationship between fracture toughness, fracture path, and microstructure of 7050 aluminum alloy: Part 1. Quantitative Characterization [J]. Metallurgical and Materials Transaction A, 1998, 29(4): 1191-1201

[6] YouJ. H., LiuS. D., ZhangX. M.. Influence of quench transfer time on microstructure and mechanical properties of 7055 aluminum alloy [J]. Journal of Central South University of Technology, 2008, 15(2): 153-158

[7] JianH. G., JiangF., WeiL. L., ZhengX. Y.. Crystallographic mechanism for crack propagation in the T7451 Al-Zn-Mg-Cu alloy [J]. Materials Science and Engineering A, 2010, 527: 5879-5882

[8] KimS. H., ErbU., AustK. T.. Grain boundary character distribution and intergranular corrosion behavior in high purity aluminum [J]. Scripta Materilia, 2001, 44: 835-839

[9] RobsonJ. D., PrangnellP. B.. Predicting the recrystallized volume fraction in AA7050 hot rolled plate [J]. Materials Science and Technology, 2002, 18(6): 607-619

[10] LiuS. D., ZhangX. M., ChenM. A.. Influence of aging on quench sensitivity effect of 7055 aluminum alloy [J]. Materials Characterization, 2008, 59(1): 53-60

[11] LiuS. D., LiuW. J., ZhangY., ZhangX. M., DengY. L.. Effect of microstructure on the quench sensitivity of AlZnMgCu alloys [J]. Journal of Alloys and Compounds, 2010, 507(1): 53-61

[12] KellyD. J., RobinsonM. J.. Influence of heat treatment and grain shape on exfoliation corrosion of Al-Li alloy 8090[J]. Corrosion, 1993, 49(10): 787-795

[13] RobinsonM. J., JacksonN. C.. The influence of grain structure and intergranular corrosion rate on exfoliation and stress corrosion cracking of high strength Al-Cu-Mg alloys [J]. Corrosion Science, 1999, 41: 1013-1028

[14] AlexopoulosN. D.. On the corrosion-induced mechanical degradation for different artificial aging conditions of 2024 aluminum alloy [J]. Materials Science and Engineering A, 2009, 520(1/2): 40-48

[15] PetroyiannisP. V., KamoutsiE., KermanidisA. T. E. A.. Evidence on the corrosion-induced hydrogen embrittlement of the 2024 aluminium alloy [J]. Fatigue Fracture Engineering Materials Structure, 2005, 28: 565-574