Effect of Al/Mg Ratio on the Microstructure and Phase Distribution of Zn-Al-Mg Coatings

Abstract

In contrast with studies such as those on the effect of a single elemental variable on Zn-Al-Mg coatings, Mg/Al is considered a variable parameter for evaluating the microstructure of Zn-Al-Mg coatings in this work, and the combined effect of the two elements is also taken into account. The Mg/Al ratios in the continuous hot-dip plating of low-alumina Zn-Al-Mg coatings were 0.63, 0.75, 1.00, 1.25, and 1.63. respectively, and the microstructures of the different coatings were observed using scanning electron microscopy (SEM). The surface elemental distributions of the coatings were analyzed with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis to understand the phase distributions of the coatings, which mainly consisted of a zinc monomeric phase, a binary eutectic phase (Zn/MgZn2), and a ternary eutectic phase (Zn/Al/MgZn2). Statistical calculations of the phase distributions in colored SEM images were performed using ImageJ-win64 software, comparative analysis of the solidification simulation results was carried out with thermodynamic simulation software (PANDAT-2023), and evaluation of the corrosion resistance of the platings was performed using macroscopic cyclic immersion corrosion experiments. The results show that with the increase in the Mg/Al ratio, the binary eutectic phase in the coatings gradually increased, the variation trend of the ternary eutectic phase was not obvious, and the corrosion resistance of the coatings gradually improved.

Contributions to a More Realistic Characterization of Corrosion Processes on Cut Edges of Coated Metals Using Scanning Microelectrochemical Techniques, Illustrated by the Case of ZnAlMg-Galvanized Steel with Different Coating Densities

“…These elements lead to the formation of different metallurgical products in the galvanized layer, as well as more compact and stable corrosion products [13,14]. Improved corrosion resistance compared with conventional hot dip galvanized steel is observed when Al is added in 5% (Galfan) or 55% (Galvalume) to the molten bath, and such enhancement has been overcome by the more recent incorporation of Mg [15][16][17][18]. The search for an optimized addition of both elements has yielded excellent anticorrosion performance for coatings containing Al and Mg at around 3% weight, which is appropriate for coatings applied in the automotive industry [19][20][21].…”