Surface Characterization by Confocal Raman Spectroscopy: Phase Differentiation of Zn–Mg Alloys on Industrial Substrates

Abstract As part of a substrate characterization, plant-specific zinc–magnesium (ZM) alloyed steel substrates were investigated. The substrates differ in their manufacturing specifications, which influences the formation and composition of the ZM layers in the near-surface region. The structural and chemical characterization of the sample surfaces were performed using confocal Raman spectroscopy and scanning electron microscopy (SEM) with integrated energy-dispersive x-ray spectroscopy (EDX). The ZM substrates exhibit a heterogeneous and sample-dependent phase distribution. Different Zn- and Mg-rich phases could be clearly distinguished optically, allowing for the identification of areas of advanced corrosion. A comparative approach revealed pronounced qualitative differences in the relative proportions of individual phases between the various substrates. Phase-specific oxides were identified spectroscopically. A significant shift of the characteristic band in the region around 200 cm −1 by ± 20 cm −1 was observed, which can be qualitatively attributed to an increased or decreased magnesium content in the phase and the resulting formation of Mg-rich oxides. Near-surface phase formation was strongly influenced by the alloy composition, the cooling rate, and the layer thickness. Wavenumber shifts showed that increased Mg and Al contents favored the formation of ternary phases, decreased cooling rates led to Mg enrichment of the surface, and smaller layer thicknesses resulted in thinner, more amorphous oxide layers.