Influence of annealing temperature on ζ-CrZn₁₃ formation in electrodeposited Zn–Cr coatings

Abstract

Electrоdeposited Zn-Cr alloy coatings, containing 3.6, 5.4 and 9.4 mass % Cr were analysed by DSC and XRD. X-ray diffraction patterns of the samples show that when they are annealed to selected temperatures before and after the heat flow peaks of the DSC curve, there is an irreversible transition in all three alloys from η-(Zn, Cr) to ζ-CrZn 13 phase. With increasing Cr content, the start of the transition is shifted to higher temperatures (from 180 to 250°С). The η-(Zn) phase is predominant in the annealed alloy with the lowest content of Cr. In the case of the alloy with the highest Cr content, typical XRD lines of Cr appear along with those of the ζ-CrZn 13 phase. The Zn-Cr coating containing 5.4 mass % Cr transforms almost completely into ζ-CrZn 13 phase with insignificant traces of residual initial η-(Zn, Cr) phase.