In this study, ceramic coatings were grown on the surface of as-cast aluminum alloys via plasma electrolytic oxidation (PEO). The effect of the Si- and Ca-alloying elements in aluminum on the growth process, morphology, composition, mechanical, and corrosion properties of the PEO coatings was investigated. Uniform coatings with a minimum number of defects were formed on the surfaces of Al–Ca alloys. Increasing the Si content in Al led to an increase in the bulk and surface porosity of the coatings. The α-Al₂O₃ phase mainly formed in the coatings synthesized on pure Al and Al–Ca alloys, while an increased amount of Si in Al alloys hindered the formation of the α-Al₂O₃ phase. The coatings had a microhardness of 660–1180 HV_, which was 20–30 times higher than that of the original as-cast alloy. Moreover, the coating on the Al–Ca alloys had the highest peak hardness, which was probably caused by the formation of a greater amount of the α-Al₂O₃ phase. Electrochemical studies in 3.5% NaCl have shown that PEO coatings reduce the corrosion current density. Of all PEO-treated alloys, Al and Al1Ca have the lowest corrosion current density and hence the highest corrosion resistance due to the composition and uniformity of the coating.

The development of fundamental knowledge that allows making proper correlation among the chemical composition, structure and properties of non-ferrous alloys is a priority task for the metallurgy of nonferrous metals and alloys, as this knowledge makes the main contribution to the development of this subject and is a powerful tool for expanding the areas of their application. A variant of the establishment of regularities in metal science is the study of phase equilibria, transformations in the temperature range and compositions of metallic systems. In the scientific literature there is a lot of information on the results of studies of two- and three-component alloys in order to construct equilibrium phase diagrams. However, the non-equilibrium crystallization of alloys, and thus, the non-equilibrium phase diagrams are of greater practical interest from the point of view of industrial production. Taking into account that the compositions of industrial alloys, as a rule, are multi-component, it can be stated that there is no reliable information on multi-component systems in the literature. Industry is interested in the possibility of using alloys with low cost, however, with high performance properties, which is possible in the case of using chemical elements of technical purity, industrial waste or scrap for their preparation. First of all, it concerns aluminum alloys, as the volume of their consumption is the highest among alloys of non-ferrous metals. In addition, the number of applications made of these alloys is continuously growing. The purpose of this paper is to perform a comparative analysis of the non-equilibrium phase diagrams of aluminum-based alloys with an increased content of impurities in comparison with their equilibrium counterparts known from the published scientific literature. In the process of work, equilibrium and non-equilibrium phase diagrams of aluminum with basic alloying elements and the most frequent harmful impurities are constructed. This work was supported by Task No. 11.2072.2017 / 4.6 for the implementation of the project on the theme “Development of technology for obtaining deformed semi-finished products from alumo-matrix eutectic composites reinforced with L12 nanoparticles without hardening”.

Increasing demand for industrial applications of aluminum alloys achieved a new aspect; nowadays the demand for corrosion-resistant alloys largely exceeds the one for other high-strength, wear-resistant and heat-resistant aluminum alloys. Moreover, the relatively low-cost of casting technology provides an increased share of demand for foundry corrosion-resistant alloys in comparison with the deformable ones. Another advantage of foundry Al alloys is their excellent recyclability. However, recycling of scrap metals causes an increase in the content of impurity elements. In this study, the influence of individual and combined addition of impurity elements, such as Si, Fe, Cu, Zn, Pb, Sn, Ni and Mn, on the casting properties of corrosion-resistant Al – Mg alloy with the Mg content ranging between 4–8% was investigated. While the microstructure of the alloys in as-cast state was characterized using optical and scanning electron microscopes, the fractured surfaces of tensile test specimens were investigated using the latter microscope. The results of the experimental investigations of the effect of the main impurities on casting properties, such as fluidity, hot cracking, shrinkage and pre-shrinkage expansion of Al – Mg based alloys have been systematically summarized. It has been found that among various impurity elements, Si, Fe and Cu can exert much greater influence on fluidity and hot tearing. All these elements tended to improve fluidity; however, it occurred at the expense of a considerable reduction in hot tearing of Al – Mg alloys. The casting properties of die castings, castings obtained under pressure and die castings after hot isostatic pressing (HIP) have been studied and compared with each other and it has been found that isostatic pressing causes reduction of porosity in alloys, but slightly affects the mechanical properties. Casting with excess gas pressure (P = 0.7 atm) exerted almost no apparent influence on density (porosity) of the castings from various alloys. In general, the increased content of impurities has an insignificant effect on the casting properties of Al – Mg based alloys, so it is concluded that low-grade (secondary or recycled) aluminum can be used in the fabrication of corrosion-resistant applications. The work was carried out with support of grant # РНФ 14-19-00632-П.

The use of science-intensive technologies allows industrial enterprises to become competitive in both the domestic and foreign markets. In Russia, a large amount of enterprises of various branches of the economy operate using the non-ferrous metals and alloys, in particular Al based alloys. In recent years, there has been a steady increase in the number of such enterprises. To ensure the uniqueness of alloy properties, high-purity aluminum is mainly used to prepare Al based alloys, which causes the production cost to increase. However, the high-purity aluminum in such alloys can be replaced by a technical one; hence, the economic profit for the production of Al alloys becomes obvious and multifold. The research works conducted in this direction in the past have resulted in the development of various kinds of new alloys, heat treatment routes and micro-alloying techniques. However, the detailed information regarding the effect of high-pressure die casting on the microstructure and properties of aluminum alloys with high impurity levels is lacking in the literature. Considering the needs of the industry for new scientific solutions aimed at quality assurance and cost reduction of products, this work investigates the influence of injection molding and isostatic pressing on the structure and properties of aluminum alloys with a high content of impurities. New solutions are proposed for the use of traditional aluminum alloy castings produced by injection molding technique. Scientific solutions to increase the properties of alloys as a result of injection molding and the application of isostatic pressing are presented. The technologies investigated in this study can allow increasing the density of castings and reducing their porosity, hence, providing an additional increase in the mechanical properties of alloys with a high content of impurities.The work was carried out in accordance with the plan of research works of the Department of Metallurgy of Non-Ferrous Metals of NUST “MISiS” and within the framework of the tasks for the international NETCENG project in the post-project period.