DEVELOPMENT OF HOP-DIP ALUMINIZATION PROCESS SUBSEQUENT FOR CERAMIC COATING FORMATION BY MICRO-ARC OXIDATION

Micro Arc Oxidation (MAO) is a leading protective coating technology for aluminum, magnesium and titanium converting the surface into a hard and dense ceramic layer with outstanding resistance to corrosion and wear. The resulting ceramic coatings are formed with best mechanical, dielectric, anti-corrosive and hot-resistant properties.

To apply MAO on steel-made products, certain aluminum layer with homogeneous thickness should be applied onto steel to allow subsequent transformation into alumina. For better adhesion of the formed ceramic layer, certain thin Al-Fe intermetallic layer should be formed. In the case of absence of such intermetallic layer, the mentioned adhesion will be low. In the opposite case of too thick intermetallic layer, its brittleness will be an origin of the future layer`s failure.

Special hot-dip aluminization process for subsequent MAO was developed. It allows to control a thickness of the formed aluminum and intermetallic layers according to the requirements of MAO. The research presents development of hot-dip aluminization process for low-carbon steel St37. Aluminized (up to 200 microns thick) as well as intermetallic Fe-Al (a few tens of microns thick) layers have been obtained through variation of aluminum melt temperature (ranged from 700 to 900 ^oC), dip time (ranged from 1s to 5 min) and steel-surface preparation (cleaning methods, roughness and temperature) and then were oxidized by MAO process and characterized by SEM, GDA, microhardness and salt-spray testing. The obtained results were discussed and optimized.