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Description
Hot-dip galvanizing (HDG) Zn coatings represent a low cost and effective way of protecting steel against corrosion. In recent years, Zn coatings containing Mg became a promising next generation of Zn-based coatings due to their superior performance compared to pure Zn coatings in terms of corrosion resistance, formability, weldability and paintability [1].
These properties are strongly influenced by the microstructure which develops during the solidification process of the coating [2-3]. In this regard, computer-aided simulations represent powerful tools for a deep understanding of the microstructure evolution of HDG-Zn coatings as a function of the process conditions.
In this work, we systematically investigate the microstructure, in terms of surface morphology and surface phase fraction, of Zn+1.2%Al+1.2%Mg (ZAM) coating by means of phase-field approach. Our simulations enable understanding how the coating microstructure is influenced by the cooling rate. In particular, we investigate how cooling conditions determine the final eutectic structure and primary phases. First insights into the role of micro-alloy elements (i.e. elements added to the reference Zn+1.2%Al+1.2%Mg composition) on the surface microstructure are also discussed.
[1] Shimizu T., Fukio Y., Yasushi M., et.al., “Corrosion products of hot-dip Zn-6%Al-3%Mg coated steel sheet subjected to atmospheric exposure”, Tetsu-to-Hagané, Vol. 89, pp.166-173 (2003).
[2] Anping D., Baoping L., Yanling L., et.al., “Effect of Mg on the Microstructure and Corrosion Resistance of the Continuously Hot-Dip Galvanizing Zn-Mg Coating”, Materials (Basel), Vol. 10(8), pp. 980 (2017).
[3] Elvins J., Splittle J.A., et.al., “The effect of magnesium additions on the microstructure and cut edge corrosion resistance of zinc aluminium alloy galvanised steel”, Corrosion Science, Vol. 50, pp. 1650-1658 (2008).