Chromate conversion coatings applied to zinc-plated substrates, commonly referred to as zinc chromate coatings, serve to enhance the corrosion resistance and adhesion properties of the zinc-plated surface. The process typically involves electroplating the substrate with a layer of zinc, creating a sacrificial barrier against corrosion. Subsequently, a chromate conversion coating is applied to the zinc-plated surface. This involves treating the material with a chromate solution, often containing hexavalent chromium compounds. The chromate reacts with the zinc, forming a protective and complex film on the surface.
The resulting zinc chromate coating offers improved resistance against corrosion in diverse environmental conditions. Additionally, it facilitates strong adhesion for subsequent coatings, such as primers or paints, contributing to the overall durability of the treated material. The color of the coating can vary, with common options including clear, yellow, and olive drab. Despite its effectiveness, concerns related to the environmental and health impacts of hexavalent chromium have led to the development and adoption of alternative coatings, such as those based on trivalent chromium or non-chromium formulations, aligning with evolving regulatory standards and sustainability goals.