conversiecoating

A conversiecoating, or conversion coating in English, is a chemical treatment applied to metal surfaces that forms a protective, adherent film by a chemical reaction with the substrate. The coating becomes part of the surface rather than a separate layer, improving corrosion resistance, paint and adhesive adhesion, and sometimes lubricity.

The coating is typically produced by immersion or spraying after a cleaning and degreasing pretreatment. The treated metal is exposed to a bath that reacts with the surface to create a protective oxide or compound layer. The thickness and composition of the coating depend on the metal type, bath chemistry, temperature, and processing time. Conversion coatings are commonly used as a pretreatment before painting or electroplating.

The main types of conversion coatings include chromium-based coatings applied to aluminum, magnesium, zinc, and steel, already widely used for corrosion protection and as a base for dyes and coatings. Due to environmental and health concerns, hexavalent chromium coatings are increasingly restricted, and trivalent chromium and other non-chrome alternatives are being developed. Phosphate conversion coatings, such as zinc phosphate and manganese phosphate, are commonly used on steel and fasteners to improve corrosion resistance and paint adhesion. Non-chrome options, including zirconium- or titanium-based coatings and silicate-based coatings, are available as lower-risk alternatives for certain applications.

Conversions coatings are used across industries, including automotive, aerospace, electronics, and general metal fabrication. They are typically part of a broader surface preparation sequence that may include cleaning, rinsing, and drying, and they often complement subsequent finishes such as primers, paints, or electroplating.

Environmental, safety, and regulatory considerations are important, especially for chromium-based coatings. Waste treatment and handling maintain compliance with relevant standards, and ongoing development seeks to balance performance with regulatory constraints.