Effect of α-Al2O3 additive on the microstructure and properties of MAO coatings prepared on low carbon steel

Abstract

Micro-arc oxidation (MAO) can produce metal surface coatings with excellent properties. By using appropriate auxiliary sealing technology, the micro-holes on the surface of the coatings can be reduced and the performance of the MAO coatings can be further improved. In this work, a dense and corrosion-resistant α-Al2O3 ceramic film was prepared by MAO on the surface of boron-containing low carbon steel (10B21). Based on the electrolyte including NaAlO2, NaH2PO4, Na2CO3 and Na2B4O7, we studied the effects of different concentrations of the α-Al2O3 additive (0, 1, 2, 3 and 4 g/L) in the electrolytes on the MAO layers of 10B21 and investigated the mechanisms for the effect of the added α-Al2O3. The results showed that the added α-Al2O3 particles diffused and were adsorbed into the pores in the MAO layer, and as the conversion rate from Al2O3 to the α phase in the layer increased, the pore in the films became smaller. In particular, for the α-Al2O3 concentration of 3 g/L, the lowest hole of 1∼2 μm was obtained. Since the surface of the MAO films prepared by adding α-Al2O3 had an increased higher α-Al2O3 content, excellent electrochemical corrosion performance in a 3.5% NaCl solution was obtained, and the electrochemical self-corrosion current density was 0.2 μA/cm2. After a neutral salt spray test carried out for 7 days, the corrosion rate was 20 g·m−2·d-1, and the corrosion resistance was greatly improved.