The corrosion rate of zinc coatings varies depending on the nature of zinc salts (corrosion products) formed on the surface of the zinc coating in various situations. If the zinc salts are not very soluble in the corrosive solution, such as zinc hydroxide, they can protect the underlying zinc layer. Conversely, if the generated zinc salts have high solubility, they cannot or rarely provide protection to the underlying zinc layer, resulting in a faster corrosion rate.
Therefore, the main factors contributing to an increased corrosion rate include: high sulfur content in the air, excessive air humidity, too many solid particles such as dust, frequent thunderstorms, high oxygen content in the aqueous solution on the zinc layer, and a solution pH value between 1 to 6 and 12.5 to 14.5. Impurities in the zinc layer generally have little impact under atmospheric conditions, except in strong acid solutions where they accelerate corrosion of the zinc layer by forming micro-batteries. In strong alkaline solutions, the corrosion rate of the zinc layer will also increase.
