ABSTRACT
Studies were made of the effects of various intermetallic (Fe-Al, Ni–Al, Cu-Al) phases in the aluminium matrix on the corrosion resistance of aluminised carbon steel in NaCl solutions.
Intermetallic phases were characterised by X-Ray microdiffractometry. Surface quantitative analysis (XPS) was also used to assess the surface composition of specimens before exposure.
Electrochemical (polarisation and electrode impedance measurements) as well as free corrosion tests were carried out in aqueous aerated solutions at pH 6.5 and with dissolved oxygen content of 6.5 ppm The exposure times ranged from 2 to 360 hours. Passive films formed on metallic surfaces were characterised using the XPS technique. The corrosion morphology was assessed by optical microscopy.
It was found that: (1) intermetallic phases in the aluminium matrix enhance both general and localised corrosion processes, and (2) intermetallic phases (mainly copper) hinder the film self-repairing property, thus preventing the formation of a homogeneous passive film and thereby stimulating localised corrosion.
