Modulation Effects of K2ZrF6 Additive on Microstructure and Heat Resistance of Micro-arc Oxide Coatings Fabricated on LY12 Aluminum Alloy

Zr(OH)(4) particle can be formed and negatively charged in alkaline solution with K2ZrF6 addition. Based on this mechanism, Zr-containing ceramic coatings were fabricated on LY12 aluminum alloy by microarc oxidation (MAO) using K2ZrF6 as a special additive in Na2SiO3-KOH base electrolyte. The modulation effects of K2ZrF6 addition on micro-microstructure, element distribution and phase composition were analyzed by SEM, EDS and XRD, respectively. Heat resistance of MAO coatings formed on LY12 aluminum alloy in different electrolyte was investigated. The results show that the K2ZrF6 addition can increase the micro-arc oxidation rate and significantly alter the structure of MAO coatings. Both the top surface and inner surface of MAO coatings fabricated in Zr-containing electrolyte become relatively smooth. Compared with the coating formed in Zr-free electrolyte, a large amount of Zr element is found in the coating formed in electrolyte with K2ZrF6 addition. Two main phases, gamma-Al2O3 and alpha-Al2O3, are contained in Zr-free coating. In contrast, more amorphous phase is found in Zr-containing coating with reduced amount of crystalline alumina. Experimental results also demonstrate that Zr-containing coating exhibits higher heat resistance.