The uniformity of the zinc coating affects the product's corrosion resistance and service life; therefore, it should be included in standards for testing and evaluation. Coating uniformity can be assessed using the uniformity coefficient (η) or by the average coating thickness (H) and standard deviation (S). Necessary measures should be taken during the hot-dip galvanizing process to improve the uniformity of the zinc coating.
The quality of a zinc coating can be evaluated based on the weight of the zinc deposited on the substrate, the adhesion between the coating and the substrate, and the uniformity of the coating. Coating uniformity is a critical quality indicator; in general service conditions, corrosion typically initiates at the thinnest points of the zinc layer and spreads outward, leading to rusting and wire breakage, which ultimately compromises the service life. While standards clearly specify requirements for coating weight and adhesion, specifications regarding uniformity vary; in the 1970s, ISO standards and those of various countries generally mandated the use of the copper sulfate test for this purpose.
