Boosting crack resistance via MgZn2 phase refinement achieved by tailoring cooling rate in Zn-5Al-1Mg hot-dip galvanized coatings

Ultra-high strength and corrosion-resistant steel wires are critical for long-span suspension bridges. Hot-dip Zn-Al-Mg alloy coatings offer excellent anti-corrosion performance but are prone to cracking after formation, limiting their application. In this study, the alloy composition was designed through thermodynamic calculations, and Zn-5Al-1Mg alloy coatings were prepared via flux-assisted hot-dip galvanizing. The effects of cooling rate on the microstructure and crack resistance of the coatings were examined using in-situ tensile tests, high-throughput nanoindentation tests, and finite element analysis. In-situ tensile results revealed that cracks initially originated in the ternary eutectic regions and propagated along the MgZn 2 phases, with the crack paths influenced by the mechanical property mismatch between adjacent phases. Furthermore, it was revealed by the high-throughput nanoindentation tests that the hard and brittle MgZn 2 phases served as the primary sites for crack initiation. Moderate regulation of cooling rates facilitates the transformation of ternary eutectic phases were transitioned from a continuous network structure to finely dispersed phases, resulting in a significant alteration in crack resistance. The role of cooling rate in regulating microstructural evolution and crack resistance in Zn-Al-Mg coatings is elucidated in this study, and valuable insights are provided for enhancing the reliability of coated cables.