Over the years, research on trivalent chromium passivation (TCP) has expanded into many fields of application, among them as a replacement for conversion coatings containing hexavalent chromium (Cr6), known as chromates. REACH compliant TCP processes have been found to be adequate replacements for chromates, however, implementing them in the highly safety-minded aviation industry, for example, requires fundamental knowledge about the layer composition of these types of conversion coatings. This article outlines the formation of layers in trivalent chromium (Cr3) passivation over the copper-containing aluminum alloy EN-AW 2024.