The use of macroscopic modelling of intermetallic phases in aluminium alloys in the study of ferricyanide accelerated chromate conversion coatings

Intermetallic (IM) second phases of FeAl3, Cu2FeAl7, and CuAl2, were coupled to aluminium for the macroscopic study of the deposition of chromate conversion coatings. Characterisation of the coating deposition was done using X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, Auger electron spectroscopy, scanning electron microscopy with X-ray analysis, and Fourier transform infrared spectroscopy. The coatings covering the IM phases were only one-tenth the thickness of the matrix, and contained higher levels of F, Al, and O. Cr, O, Fe, and N, indicative of a chromate conversion coating, were detected over the matrix. Over IM phases, decomposition of [Fe(CN)6]3−/4−, and fluoride ion attack were found to be responsible for reduced rates of deposition.