Chemical Conversion Coating
The chemical conversion coating forms through a controlled reaction of the metal surface with a solution. It improves adhesion and provides temporary corrosion protection.
Physico-Chemical Mechanism
The chemical conversion coating forms when the metal surface contacts a specific solution catalyst. This process can be caused, for example, by electrolysis or a chemical reaction between the metal and the solution. The metal reacts with the chemicals in the solution to form a new layer that adheres to the surface.
Metallurgical Relevance & Risks in Welding
The chemical conversion coating improves the adhesion of adhesives and paints to the metal surface. It protects against short-term corrosion, which is especially helpful in humid or salty environments. However, it can also cause problems if it is too thick or not completely removed before welding. An overly thick layer can impair the permeability of the metal structure and lead to cracks or distortion.
Workshop Practice & Procedures
Before welding the metal, the chemical conversion coating must be carefully removed. This can be done by cleaning with a fine abrasive or a chemical cleaning solution. The temperature and time of the welding processes should be chosen so that the conversion coating does not re-form. For certain metals and welding processes, it is important to use a special cleaning or preparation solution to ensure optimal adhesion and corrosion protection.