Influence of microstructure on corrosion of oil coated thin film Mg-25Al-Zn alloys

• Published in: Transactions of the Institute of Metal Finishing 2013-07, Vol.91 (4), p.182-191
• Main Authors: Leinartas, K, Bražinskienė, D, Miečinskas, P, Staišiūnas, L, Juškėnas, R, Suchodolskis, A, Asadauskas, S J, Grigucevičienė, A
• Format: Article
• Language: English
• Subjects: Alloys; Coatings; Corrosion; Corrosion resistance; Deposition; EIS; Electrochemical impedance spectroscopy; Magnesium aluminium alloy; Magnesium base alloys; Microstructure; Rapeseed oil; Thin film; Thin films; Voltammetry
• ISSN: 0020-2967; 1745-9192
• DOI: 10.1179/0020296713Z.000000000108

Thin films of Mg-25Al-Zn alloy were formed on glass substrates at several temperatures from 6 to 150°C by direct current magnetron sputtering. The microstructure of the deposited thin film coatings was studied by X-ray diffraction and atomic force microscopy. Voltammetric and electrochemical impedance spectroscopy methods were used for evaluation of surface microstructure influence on short term corrosion in borate solutions. Improved corrosion resistance was determined for alloys deposited at lower temperatures. They were characterised by the finest grain size and smaller content of β phase. An accelerating effect of β phase on corrosion was accounted for by formation of microgalvanic couples between it and the Mg matrix. EIS results showed that an increase of β phase content in coatings led to the decrease in hydroxide layer resistance. A similar correlation between the grain size and corrosion performance for electrodes coated with rapeseed oil film was determined. It was concluded that rapeseed oil suppresses microgalvanic corrosion and inhibits β phase corrosion.