On the structure and chemical composition of chromium based conversion coatings on aluminium: a TOF SIMS study

Abstract

Cr based conversion coatings were studied by means of time-of-flight secondary ion mass spectrometry as a function of treatment time. It was shown that a duplex layer structure is present at any conversion time. During the coating development, the top layer, which is mainly composed of chromium phosphate, thickens while Al, F and AlO species are encapsulated in the inorganic coating. In order to minimize the influence of surface roughness, different substrates with smooth surfaces were converted and measured under identical conditions. It was shown that the duplex structure was not affected by the metallurgy of the different starting materials.