Structure of Electrodeposited Zn–Mn Alloy Coatings

Abstract

Structure of electrodeposited Zn–Mn alloys which are one of the corrosion-resistant zinc alloy coatings suitable for automotive body panels was investigated using X-ray diffraction, SEM and SIMS.
The coatings are composed of fine grains or granular grains which contain fine particles, depending on the Mn content. The coatings have an uniform depth distribution of Mn and Zn.
X-ray diffraction revealed that the coatings have either single or dual alloy phases which are the following phases, namely η phase, Γ phase, ε phase, γ-Mn phase and α-Mn phase, depending on the Mn content. The ε phase and γ-Mn phase as high temperature phases exist when the range of the Mn content is above 20 mass%. Both phases are stable when heated at 170°C. The γ-Mn phase is transformed to the β-Mnphase and the α-Mn phase by heating beyond 250°C, although the e phase is unchanged.