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Improvement of the Functional Characteristics of Coatings Obtained By the Method of Hard Anodizing of Aluminum Alloys

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We analyzed the ways of improvement of the functional properties of coatings on aluminum alloys obtained by the method of hard anodizing. It is shown that the protective properties of hard anodic coating are closely related to its porosity. In the course of pulsed anodizing, as a result of the efficient heat dissipation (removal) for a low current density, the diameter of pores decreases as compared with the process running under direct current, whereas their number remains invariable. This results in a higher wear resistance and a more uniform hardness profile over the thickness of the coating. It was established that, for too low current densities, the dissolution of oxides prevails over their formation. The hardness and wear resistance of the coating are deteriorated. It is shown that the most important mechanical property of the anodic coating is its wear resistance but not hardness. The most common electrolytes used for aluminum anodizing are aqueous solutions of sulfuric acid, as well as electrolytes based on sulfuric and oxalic acids. Various additives to electrolytes (e.g., glycolic acid and glycerol) are applied to reduce the dissolution of oxides. The use of ozone-air mixtures for the bubbling of electrolytes in the course of anodizing of aluminum alloys increases the thickness of oxide coatings by 30%. As the concentration of ozone increases, the microhardness of the coating becomes higher and the degree of wear of anodized specimens decreases. It is shown that the thickness and hardness of the oxide film can be increased by the preliminary heat treatment of cast aluminum alloy and the use of electrolytes with aluminum sulfate promoting the formation of a large number of fine Al2O3 crystals in the film and increasing hardness.

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Authors and Affiliations

  1. Karpenko Physicomechanical Institute, National Academy of Sciences of Ukraine, Lviv, Ukraine

    М. М. Student, I. М. Pohrelyuk, H. V. Chumalo & V. M. Hvozdetskyi

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  1. М. М. Student
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  2. I. М. Pohrelyuk
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  3. H. V. Chumalo
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  4. V. M. Hvozdetskyi
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Correspondence to H. V. Chumalo.

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Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 56, No. 6, pp. 87–95, November–December, 2020.

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Student, М.М., Pohrelyuk, I.М., Chumalo, H.V. et al. Improvement of the Functional Characteristics of Coatings Obtained By the Method of Hard Anodizing of Aluminum Alloys. Mater Sci 56, 820–829 (2021). https://doi.org/10.1007/s11003-021-00500-x

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