| ZAlSil2Cu2Mgl alloy is widely used in industry for its good fluidity and low thermal crack tendency during casting process. However, its application in more fields is limited for its low hardness, wear-and corrosion-resistance. But, the advances in suface treatment technology, such as micro-arc oxidation, offer promising hope for its application in more fields in future. The ceramic coatings in-suit can be formed on the surface of ZAlSil2Cu2Mgl alloy by microarc oxidation technology. In the previous researches, silicate as an essential component of electrolyte is used more. At the mean time, microarc oxidation process carried drastically out at high current densities induced by the excessive sodium ions from silicate and sodium hydroxide, that has many direct adverse effects on the formation of microarc oxidation caotings and its properties. For this purpose, in this work, an new electrolyte system is composed of potassium hydroxide, instead of sodium hydrate, and silica sol, instead of sodium silicate. The ceramic coatings were prepared on the surfaces of ZAlSil2Cu2Mgl alloy and the fomation and characteristics of the coatings investigated by eddy current thickness gauge, SEM, and XRD. Besides, the characteristics of ceramic coatings obtained in the KOH-mSi02-nH20electrolyte systerm were compared with in NaOH-Na2SiO3system and in NaOH-mSiO2·nH2O system.The results show that the thickness of ceramic coatings increaed with the increase of concent of KOH in the electroltes (KOH3.45-4.25g/L+mSiO2-nH2O2.0g/L+Na2EDTA2.0g/L) and the maxium of the thickness reached even200.1μm. Howerver, the thickness of ceramic coatings decreased while the concent of KOH in the electrolyte in excess of4.05g/L. A ceramic coating with smooth surface and186.7μm thickness was obtaied in the electrolyte contained3.85g/L KOH.Similarly, the thickness of ceramic coatings increaed gruadually and later decreased with the increase of concent of silica sol in the electroltes (KOH3.85g/L+mSiO2-nH2O1.0-3.0g/L+Na2EDTA2.0g/L) and the maxium of the thickness reached ca186.7μm. The results indicate that the ceramic coatings with smooth surface and low wear mass loss were mainly composed of mullite, α-Al2O3, γ-Al2O3, and χ-Al2O3phases.It was not found that the forward voltages varing from380V to440V effect observably on the thickness, surface morphology, and phase composition of ceramic coatings. However, the thickness of ceramic coatings decreased slightly and later increaed with the variation of reverse voltage from60V to120V in the microarc oxidation process. The amount of micro-cracks in the coatings decreased and the surfaces of coatings were obtained. The ceramic coating with thickness of223.7μm was formed at140V reverse voltage.The thickness of ceramic coatings decreased gradually from245.2μm to101.9μm while the power frequency varing from50Hz to200Hz and, meanwhile, the ceramic coatings with more smooth surfaces and lower wear mass loss were obtained.It is also found that the process of microarc oxidation carried not drastically out in the electrolyte system composed of potassium hydroxide, instead of sodium hydrate. The ceramic films possess an appropriate thickness, smooth surface, and high wear-resistance. |
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