| ZAlSi12Cu2Mg1 alloy is an important engineering material for good casting fluidity, non-thermal crack tendency and low thermal expansion coefficient, etc. But its more wide applications are limited for its low wear, corrosion, and heat resistance as well as short service life. It is strongly expected that the characteristics above can be improved as a compact ceramic coating formed on its surface by means of micro-arc oxidation technique. Up to now, however, there are few researches reported on this field, so it is necessary for this technique to be researched and developed.In this work, ceramic coatings were obtained on the surface of ZAlSi12Cu2Mg1 alloy by multifunction micro-arc oxidation power supply, type WHD-30, by controlling electric parameters. Their thickness and micro-hardness were measured and the phase structure and surface morphology were analyzed by XRD, SEM and TEM.The coatings formed on the surface of ZAlSi12Cu2Mg1 by micro-arc oxidation at 420/110V forward/reverse voltage, 100Hz power frequency, and in the electrolyte composed of Na2SiO3 8.0 g/L, NaOH 2.0 g/L and Na2EDTA 2.0 g/L. The results show that the coatings are mainly composed ofγ?Al2O3,α?Al2O3 and Al 2SiO5 phase. The thickness and the micro-hardness are ca 147μm and HV550.6, respectively. The process of micro-arc oxidation can be divided into two steps, i.e. the oxidation transition and the sinter. In the former, the coating grows outward from the surface of the substrate. The XRD patterns indicate that it is consisted of amorphous alumina. In the later, the sinter reaction of liquid phase occurs between the molten Al2O3 and the precursor and resulted in forming of a ceramic coating composed mainly of crystal alumina. The coating grows toward the inner.It is found that the stability of coatings forming process is significantly improved by adding the additive A in the electrolyte and the noise and ionizable gas in the process are decreased obviously. The electrolyte is still clear until the end of this process. As a result, the electrolyte can be used repeatedly. The XRD analysis showed that the content ofα?Al2O3 phase in film increases as the additive A adding. It indicates the additive A benefits the formation ofα?Al2O3 phase in ceramic film. |
