The anticorrosion mechanism of chrome-free Dacromet coating is similar to that of Dacromet. It is a three-dimensional protective film that integrates physical shielding, cathodic protection, passivation and electrochemical protection. It can provide a lot of protection for the base metal. Good protection.
(1) Physical shielding effect
Due to the overlapping arrangement of flake metal powder in the coating, the binder and other substances are filled in the microscopic voids of the zinc-aluminum powder to reduce the coating voids and form a very effective barrier layer. The path for erosive ions to reach the substrate is tortuous , Difficult, it plays a shielding role of a physical protective layer.
(2) Electrochemical action
Since the zinc-aluminum potential is negative than that of iron, after the zinc-aluminum coating and the steel substrate form a microscopic corrosion primary battery, the scale-like zinc-aluminum powder is corroded first as the anode, providing cathodic protection for the steel substrate.
(3) Passivation
Since aluminum is easily oxidized in the atmosphere, a dense oxide film is formed on the surface, which better hinders the penetration of corrosive media. In addition, the passivator added to the coating can slow down the corrosion of metals such as zinc and aluminum, thereby reducing the corrosion of the substrate. speed.
(4) Self-healing effect
When the coating is damaged, there may be residual passivation agent that oxidizes the exposed zinc and aluminum surfaces to form a passivation film. On the other hand, the deposition of corrosion products forms a covering layer that isolates the corrosion medium and the protected substrate. It is restored The "blocking" function of the coating.