Cerium citrate as ecologically friendly corrosion inhibitor for AA7075 alloy

• Published in: Materials and corrosion Vol. 73; no. 6; pp. 950 - 960
• Main Authors: Marunkić, Dunja, Pejić, Jovanka, Jegdić, Bore, Marinković, Aleksandar, Radojković, Bojana
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-06-2022
• Subjects: aluminium alloy; Aluminum base alloys; Cerium; Ce‐citrate; Chemical precipitation; Corrosion; Corrosion effects; Corrosion inhibitors; Corrosion mechanisms; Corrosion resistance; Corrosion resistant alloys; Corrosion tests; EIS; Electrical resistivity; Electrochemical impedance spectroscopy; High resistance; Intermetallic compounds; Low concentrations; Pitting (corrosion); SEM/EDS; Sodium chloride; Solid solutions; Uniform attack (corrosion)
• ISSN: 0947-5117; 1521-4176
• DOI: 10.1002/maco.202112900

The corrosion behaviour of high‐strength AA7075 aluminium alloy in NaCl solution, without and in the presence of environmentally friendly corrosion inhibitors (Ce‐chloride and Ce‐citrate) in low concentrations (<0.5 mM), was analysed. The degree of precipitation of the solid solution of AA7075 alloy was determined by measuring the electrical conductivity, while the surface morphology and appearance of intermetallic compounds before and after corrosion testing were analysed by SEM/EDS method. The general corrosion resistance of the tested alloy in NaCl solution and the degree of the inhibitory effect of the corrosion inhibitors were determined on the basis of electrochemical impedance spectroscopy and polarization measurements, while resistance to pit formation on the bases of Epit. AA7075 alloy showed high resistance to general corrosion in the presence of both tested inhibitors, while resistance to pit formation was significantly higher in the presence of Ce‐citrate (concentration 0.5 mM). Also, Ce‐citrate present in NaCl solution at lower concentrations provides satisfactory resistance of AA7075 alloy to general and pitting corrosion. A mechanism of protective action of Ce‐citrate inhibitor has been proposed.
It has been shown that the resistance of AA7075 alloy to pit formation in the presence of Ce‐citrate is far higher than in the presence of Ce‐chloride. Ce‐citrate shows a high inhibitory effect even at lower concentrations of 0.5 mM. In the presence of Ce‐citrate, a complex is formed between the cerium cation and the carboxyl groups of the citrate anion. The formed complex creates an inhibitory film of high corrosion resistance.