Characterisation of surface preparation of 2024 aluminium alloy for conversion coating

Abstract

X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and electrochemical potentiodynamic experiments have been used to study the pretreatment of 2024–T3 aluminium alloy before conversion coating. The pretreatment process included vapour degreasing, alkaline cleaning and Cr based acidic deoxidising steps. This type of pretreatment is appropriate for conversion coatings which meet aerospace standards for corrosion resistance and paint adhesion. During alkaline cleaning an oxide containing Mg, Zn, Si, and Fe developed on the surface of the alloy. During deoxidation there was dissolution and etching of both the intermetallics and the basic oxide scale left after the alkaline cleaning. Characterisation by XPS indicated that the surface was coated with a thin Cr containing coating after deoxidation which provided a degree of passivation to the surface as determined by electrochemical measurements.

MST/3372