ISSN 2305-6894

The structure and protective properties of IFHANAL conversion coatings on aluminum alloys

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, Moscow, 119071 Russian Federation

Abstract: The chemical oxidation in a chromate-free IFHANAL converting solution leads to the formation of conversion coatings with different thicknesses on aluminum (1010) and its alloys (5154, 6063, 2024, 7075). According to the data of polarization measurements in chloride solutions, the thickness of the coatings under study is not a determining factor in their protective ability. A significant increase in the protective properties of the coatings obtained is observed upon filling of the coatings in a solution of IFKhAN-25 corrosion inhibitor. This effect of coating filling is associated with changes in their structure during the hydration of surface oxides. According to X-ray phase analysis data, the conversion coating on 1010 aluminum alloy in its initial state consists of amorphous aluminum oxide phases. Filling of the coating in distilled water and in a solution of corrosion inhibitor equally changes the phase state of the surface oxide. The level of oxide crystallization increases in both cases, but the effect of the inhibitor on the process of oxide hydration is not observed. Perhaps, the crystallization of the oxide promotes adsorption of the inhibitor and increases the protective properties of the filled coating. Filling of conversion coatings on the Al–Mg alloys studied also modifies the phase state of surface oxides, making them less amorphous. The corrosion inhibitor in filling solutions is directly involved in the process of oxide hydration in conversion coatings on Al–Mg alloys, contributing to the strengthening of their protective properties. During the filling of more complex hetero-oxide structures in Al–Mg–Cu(Zn) alloys, the corrosion inhibitor adsorption makes a prevalent contribution to the increase in protective properties.

Keywords: aluminium alloys, conversion coatings, X-ray phase analysis, filling of coatings, corrosion inhibitor

Int. J. Corros. Scale Inhib., , 4, 673-682 PDF (991 K)
doi: 10.17675/2305-6894-2018-7-4-13

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