Effect of Flux Chloride Composition on Microstructure and Coating Properties of Zn-Mg-Al Ternary Alloy Coated Steel Product

In the flux used in the batch galvanizing process, the effect of the component ratio of N1 LC'l to ZnCL· on the microstructure, coating adhesion, and corrosion resistance of Zn-Mg-Al ternary alloy-coated steel is evaluated. Many defects such as cracks and bare spots are formed inside the Zn-Mg-Al coating layer during treatment with the flux composition generally used for Zn coating. Deterioration of the coating property is due to the formation of AlCl_x mixture generated by the reaction of Al element and chloride in the flux. The coatability of the Zn-Mg-Al alloy coating is improved by increasing the content of ZnCl₂ in the flux to reduce the amount of chlorine reacting with Al while maintaining the flux effect and the coating adhesion is improved as the component ratio of NH₄Cl to ZnCl₂ decreases. Zn-Mg-Al alloy-coated steel products treated with the optimized flux composition of N1 LC'HZnC'k show superior corrosion resistance compared to Zn-coated steel products, even with a coating weight of 60 %.