Corrosion Protection of an Aluminum Alloy with Nontoxic Compound Inhibitors in Chloride Media

• Published in: Corrosion (Houston, Tex.) Vol. 58; no. 10; pp. 826 - 834
• Main Authors: Liu, X.F., Huang, S.J., Gu, H.C.
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.10.2002; NACE
• Subjects: Aluminium; Aluminum; Aluminum alloys; Aluminum base alloys; Aluminum compounds; Applied sciences; Benzimidazoles; Benzothiazole; Chlorides; Chromate; Chromates; Citric acid; Corrosion; Corrosion inhibitors; Corrosion prevention; Electrochemical noise; Electrochemistry; Electrode polarization; Exact sciences and technology; Immersion tests (corrosion); Inhibitors; Metals. Metallurgy; Molybdate; Phosphates; Submerging; Weight loss; Aluminium base alloys; Salt corrosion; Electrochemical noise; Localized corrosion; Corrosion inhibition; Pinhole; Experimental study; Corrosion protection; Sodium chloride; Corrosion inhibitor; Potentiodynamic method; Corrosion; Chlorides
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3287664

ABSTRACTThe 7000 series aluminum alloys are widely used structural materials in the aerospace industry because of their high strength-to-weight ratio and good fracture toughness. Their resistance to corrosion depends upon the rapidly formed stable oxide film. However, in the presence of aggressive anions, such as halide, which can destabilize the passive film over the matrix, aluminum alloys are subject to localized corrosion.1 The microstructural heterogeneity also has an important influence on their resistance to corrosion. Aluminum alloy (AA)7075 (UNS A97075[1]; Al-Zn-Mg-Cu) contains significant amounts of constituent particles such as Al7Cu2Fe and Al2CuMg, 2-4 which are in the form of precipitates, inclusions, and constituent particles. Microflaws in the oxide film exist at particle sites, and potential differences exist between the constituent particles and the matrix. When the material is exposed to an aggressive electrolyte, Al7Cu2Fe particles are more noble than the matrix to enhance matrix dissolution, and Al2CuMg particles act as anodic sites, losing Mg and Al through dissolution in the early stage of corrosion and becoming more cathodic as Cu is left behind. Therefore, these microflaws and the particle-matrix galvanic couples will enhance the development of localized corrosion such as pitting. Because of the existence of many heterogeneous phases at the intergranular zone, pitting corrosion usually develops into intergranular corrosion or exfoliation corrosion on the aluminum alloy, which is accompanied by gas evolution.4 Furthermore, localized corrosion of structural aluminum alloys also induces the occurrence of corrosion fatigue and stress corrosion cracking that can compromise the integrity of the structures. Organic paint containing inhibiting pigment is an important method to protect the structure of aluminum alloys. At present, compounds of chromate 2­ (CrO4 ) are efficient inhibiting pigments for aluminum