Preparation and Performance of Micro-Arc Oxidation Coatings for Corrosion Protection of LaFe 11.6 Si 1.4 Alloy.

The microstructure, corrosion resistance, and phase-transition process of micro-arc oxidation (MAO) coatings prepared on LaFe 11.6 Si 1.4 alloy surfaces in different electrolyte systems were systematically investigated. Research has demonstrated that various electrolyte systems do not alter the main components of the coatings. However, the synergistic action of Na 2 CO 3 and Na 2 B 4 O 7 more effectively modulated the ionization and chemical reactions of the MAO process and accelerated the formation of α -Al 2 O 3 . Moreover, the addition of Na 2 CO 3 and Na 2 B 4 O 7 improved the micromorphology of the coating, resulting in a uniform coating thickness and good bonding with the LaFe 11.6 Si 1.4 substrate. The dynamic potential polarization analysis was performed in a three-electrode system consisting of a LaFe 11.6 Si 1.4 working electrode, a saturated calomel reference electrode, and a platinum auxiliary electrode. The results showed that the self-corrosion potential of the LaFe 11.6 Si 1.4 alloy without surface treatment was -0.68 V, with a current density of 8.96 × 10 -6 A/cm 2 . In contrast, the presence of a micro-arc electrolytic oxidation coating significantly improved the corrosion resistance of the LaFe 11.6 Si 1.4 substrate, where the minimum corrosion current density was 1.32 × 10 -7 A/cm 2 and the corrosion potential was -0.50 V. Similarly, after optimizing the MAO electrolyte with Na 2 CO 3 and Na 2 B 4 O 7 , the corrosion resistance of the material further improved. Simultaneously, the effect of the coatings on the order of the phase transition, latent heat, and temperature is negligible. Therefore, micro-arc oxidation technology based on the in situ growth coating of the material surface effectively improves the working life and stability of La(Fe, Si) 13 materials in the refrigeration cycle, which is an excellent alternative as a protection technology to promote the practical process of magnetic refrigeration technology.