MICRO ARC OXIDATION OF HOT-DIP ALUMINIZED STEEL, FOR ENHANCED CORROSION AND WEAR PROTECTION

This work presents a new innovative solution for the corrosion and wear protection of steel. Traditional Micro Arc Oxidation (MAO) technique can be applied to a limited variety of metals, resulting in a surface ceramic layer with enhanced corrosion and wear protection properties. In this work we demonstrate the application of MAO coating to steel. This is allowed by a first process step in which the steel is aluminized, followed by a second process step of oxidation. The aluminization step is done by hot dip method. The process conditions were optimized in order to achieve the best results after the MAO step. The resulting stack has an excellent adhesion between the different layers thanks to the existing intermetallic Fe-Al layer.

The incorporation of the MAO process over the aluminization offers superior corrosion and wear resistance of the coating as compared to standard aluminization of steel. The corrosion resistance was tested by a Salt Spray Test (SST). After 1,000 hours SST, no sign of corrosion was detected in the samples with MAO, while for Aluminized steel without MAO, corrosion was developed after less than 672hr.

The wear resistance was tested by abrasion Taber test. The results of the test are typical for the MAO process: the initial abrasion rate is relatively high, till wearing off of the upper porous technological layer. As the test continues, the abrasion rate is reduced and stabilizes at a low and stable value, typical for the dense and hard functional Alumina layer. The Alumina layer thickness can be increase as required in order to prolong the lifetime of parts under wear conditions.