Phosphating treatment is a chemical and electrochemical reaction process that is mainly used to form a phosphate conversion film, called a phosphate film, on a metal surface. The main functions of phosphate treatment include.
Author: Anna
Phosphating treatment is a chemical and electrochemical reaction process that is mainly used to form a phosphate conversion film, called a phosphate film, on a metal surface. The main functions of phosphate treatment include.
Provide protection: Phosphate film can prevent the metal from being corroded and extend the service life of the metal.
Improve adhesion: Phosphate film can enhance the adhesion between the coating and the metal substrate, thus improving the corrosion resistance and durability of the coating.
Friction reduction and lubrication: In the metal cold working process, the phosphating film can play the role of friction reduction and lubrication, improve the cold working performance of the material.
The principle of phosphating treatment
The principle of phosphate treatment is to form a phosphate conversion film on the metal surface through chemical and electrochemical reactions. The specific process is as follows:
Immersion in phosphate solution: the workpiece (such as steel, aluminum, zinc parts) immersed in an acidic dilute aqueous solution containing phosphate. The pH value of the solution is 1-3, the relative density of 1.05-1.10.
Chemical reaction: In the solution, iron on the surface of the metal workpiece reacts with other phosphates to form numerous primary cells. In the anodic zone, the iron begins to dissolve into Fe²⁺, while hydrogen is released in the cathodic zone. These reactions lead to an increase in the concentration of Fe²⁺ with HPO₄²- and PO₄³-, and when the concentration is greater than the solubility product of the phosphate, precipitation occurs and a phosphate film is formed.
Application areas of phosphating treatment
Phosphating treatment is widely used in the surface treatment of steel, aluminum, zinc and other metals. It can be used not only as a final finishing layer, but also as an intermediate layer for other coverings. The porous nature of the phosphating film allows sealers, paints, etc. to penetrate into the pores and combine closely with the phosphating film, thus improving adhesion.