Anodizing under conditions of oxygen activation of the inter-electrode gap

Structured alumina is currently used in a wide range of applications. Interest in a surface with a wear-resistant coating motivates creation of methods for high-speed oxidation with an increase in the thickness and hardness of the layer, with obligatory observance of environmental parameters and a decrease in the energy intensity of production. Considering the activity of aluminum towards oxygen, a very important aspect is the search for conditions to increase the natural oxide film to the level of functional significance. The generally accepted scheme of classical anodizing represents a closed system of an electrolytic cell, inside which the elements are activated in the interelectrode gap to the state of ionic excitation under the action of an electric field. The efficiency of interaction depends on the medium’s nature and variability of the volt-ampere parameters. This work proposes a different mechanism for intensifying the process. Oxygen is activated outside the electrolytic cell and in the allotropic state, in the form of ozone, is transmitted into the interelectrode gap. The phase composition, structure, thickness, and microhardness are investigated. The aim of the research is to establish the effect of ozone on the oxidation process.

Binary Additives Enhance Micro Arc Oxidation Coating on 6061Al Alloy with Improved Anti-Corrosion Property

Given the corrosion tendency of the natural oxide film of aluminum alloys, micro arc oxidation (MAO) treatment is used as an efficient and economic method to enhance the corrosion resistance. However, irregular voids, pores, and micro cracks are easily formed during the MAO process, which are harmful to the anti-corrosion property of MAO coatings. In this paper, binary additives of electrolytes, including (NaPO3)6 and H3BO3, were used to obtain MAO coatings with improved thickness and compact microstructures on 6061 aluminum alloys. The as-prepared coatings were investigated using a thickness meter, scanning electron microscope (SEM), X-ray diffractometer (XRD), and electrochemical impedance spectroscope (EIS). The results showed that the coordinated influence of the binary additives could change the discharge behaviors and micro morphologies of the MAO coatings compared to the base silicate electrolyte. A thicker and stronger MAO coating could be achieved, which was mainly composed of Al2O3 phases. The EIS tests revealed that the corrosion current density of the obtained optimal MAO coating decreased by three orders of magnitude from 1.209 × 10−6 A·cm−2 to 2.981 × 10−9 A·cm−2. We believe that the binary additive-enhanced MAO coatings could provide a promising anti-corrosion solution in various applications.