Resumen
Coatings with a thickness of about 100 µm were obtained by microarc oxidation of technically pure aluminum and aluminum alloyed with copper and zinc in an alkaline silicate electrolyte at a current density of ~20 A/dm2. The results of studying the surface morphology, phase composition, and hardness of MAO coatings are presented. The change parameters were the electrolyte composition and the concentration of alloying (Cu and Zn) elements. This study was carried out because the currently available data are not enough to understand the nature of the influence of the chemical composition of the aluminum alloy and electrolysis conditions (in particular, electrolyte composition) on the mechanism and kinetics of ??a transformation. Without understanding this, a directed change in the structural state and properties of MAO coatings becomes impossible. As a result of the studies, it was found that during microarc oxidation of aluminum alloys in an alkaline electrolyte with the addition of liquid glass (Na2SiO3) of various concentrations, the strengthened layer consists of oxides a-A12O3, ?-A12O3 and mullite 3Al2O3·2SiO2. The data of x-ray diffraction analysis of the coatings indicate the crystal structure of the coatings. It was established that aluminum alloying with copper and zinc significantly affects the phase composition of the coating, changing the quantitative ratio of the phases in a nonlinear manner. The highest content of the a-A12O3 phase (up to 60 vol. %) is achieved by Cu doping. The highest hardness of MAO coatings is achieved using an electrolyte with a composition of 1 g/l KOH and 6 g/l Na2SiO3 in aluminum alloys with a copper content of more than 3 %, and zinc ? 2?3 %. It is established that the mechanism of formation of the phase composition should be associated with stabilization and destabilization of the ?-A12O3 phase. Therefore, to achieve high hardness, it is necessary to choose those alloying elements that affect the destabilization of ?-A12O3, which ensures the formation of the a-A12O3 phase (corundum). In this regard, it was revealed that Cu2+ cations contribute to the destabilization of the ?-?12?3 phase, and Zn2+ cations lead to stabilization of the ?-?12?3 phase at a Zn content >3 %