Phosphating
Phosphating is a process in which a firmly adhering layer of sparingly soluble metal phosphates is formed on iron or zinc surfaces. This layer serves as a base for paints and as a lubricant in cold forming.
Physical-Chemical Mechanism of Action
Phosphating occurs through the reaction of iron or zinc with a phosphate solution at elevated temperature. This forms metal phosphates that create a dense, firmly adhering layer on the surface.
Metallurgical Relevance & Risks in Welding
The phosphated surface can decompose or deform at high temperature in the weld zone. This can lead to porosity, cracking, and poor paint adhesion. It is important to remove or protect the phosphated surface before welding.
Workshop Practice & Action Instructions
Before welding the metal, the phosphated surface should be thoroughly cleaned. This can be done by chemical cleaning agents or mechanical methods such as grinding. Ensure no residues of the phosphate solution remain, as they could be reactivated at elevated temperature and affect the weld.