National University of Science and Technology MISIS, Moscow, Russia

A. G. Rakoch, Professor at the Department of Steel Metallurgy, New Production Technologies and Metal Protection, Doctor of Chemical Sciences, Professor, e-mail: rakoch@mail.ru

D. P. Catenda, Postgraduate Student at the Department of Steel Metallurgy, New Production Technologies and Metal Protection

RIFAR JSC, Gai, Russia

A. A. Lobach, Innovation Director, Candidate of Technical Sciences

Tsentr Sertifikatsii LLC, Moscow, Russia
E. P. Monakhova, Principal Specialist in Corrosion Protection,Candidate of Technical Sciences, e-mail: evmo444@ya.ru

This paper examines and compares the electrochemical and corrosion behaviour of silumins AK12M2 and AK12pch. It was found that despite a greater number of intermetallic compounds in the AK12M2 alloy than in the AK12pch alloy, the rate of their corrosion in a weakly alkaline (pH 8.3) aqueous solution in contact with air at a temperature of 90 ^оC is almost the same. The latter is due to diffusion control of the cathodic process, which is accompanied by oxygen depolarization. At the same time, at room temperature and with all the other conditions being the same, the corrosion rate of the AK12M2 alloy is higher than that of the AK12pch alloy, which is caused by a higher concentration of intermetallic compounds (cathodes) and a low rate of oxygen diffusion to the cathode areas compared with that at 90 ^оC. Under anodic polarization, the working electrodes are practically not polarizable, and the corrosion process is accompanied by simultaneous transition of both trivalent and monovalent aluminium cations into the solution. With almost no polarization of anodic processes, this makes the free corrosion potentials independent from changes in the electrolyte temperature. It was established that after deoxygenation of this solution to 0.05 mg/l at room temperature and at 90 ^оC, the silumins have high corrosion resistance. In this case, the corrosion process is mainly accompanied by hydrogen depolarization as the result of a shift in the free corrosion potential of silumins to negative values. The high corrosion resistance of the AK12M2 and AK12pch alloys in a deoxygenated, weakly alkaline aqueous solution is due to their being in a passive state. Consequently, under these conditions, radiators made of the AK12M2 alloy by injection molding, despite the large number of intermetallic compounds in them, will have a long and trouble-free service life in heating systems.

1. Balaban-Irmenin Yu. V., Lipovskikh V. M., Rubashov A. M. Protecting water heating pipelines from internal corrosion. Moscow : Novosti teplosnabzheniya, 2008. 288 p.
2. Rodionova I. G., Feoktistova M. V., Baklanova O. N., Amezhnov A. V. et al. Influence of the chemical composition and microstructural parameters on the corrosion resistance of carbon and low-alloy steels. Metallurg. 2017. No. 9. pp. 57–62.
3. Rodionova I. G., Amezhnov A. V., Zaytsev A. I., Mogutnov B. M. et al. Corrosion resistance of non-alloy and low-alloy steels in neutral aqueous media. Moscow : Metallurgizdat, 2021. 388 p.
4. GOST 1583–93. Aluminium casting alloys. Specifications. 29 p.
5. Timelli G., De Mori A., Haghayeghi R. Effect of pressure cycles and thermal conditions on the reliability of a high-pressure diecast Al alloy heating radiator. Engineering Failure Analysis. 2019. Vol. 105. pp. 276–288.
6. Timelli G., De Mori A., Haghayeghi R. Reliability of a high-pressure die cast Al alloy radiator. Engineering Failure Analysis. 2019. Vol. 105. pp. 87–97.
7. Grid code of the Russian Federation. Moscow : SPO ORGRES, 2003.
8. Monakhova E. P., Rakoch A. G., Lobach A. A., Catenda D. P., Al-Habib K. M. Effect of the phase composition of AK12M2 and AK12pch silumins on the corrosion and electrochemical behaviour in weakly alkaline aqueous solution. Part 1. Thermodynamic calculation of the phase composition of silumins. Tsvetnye Metally. 2024. No. 1. pp. 65–69.
9. Tomashov N. D., Chernova G. P. Theory of corrosion and corrosion-resistant structural alloys. Moscow : Metallurgiya, 1986. 360 p.
10. Sinyavskiy V. S., Valkov V. D., Kalinin V. D. Corrosion and protection of aluminium alloys. Moscow : Metallurgiya, 1986. 368 p.
11. Sinyavskiy V. S. Development of pitting corrosion in aluminium alloys and how it is related to stress corrosion. Zashchita metallov. 2001. Vol. 37, No. 5. pp. 521–530.
12. Volkova O. V., Dub A.V.B., Rakoch A. G., Gladkova A. A., Samoshina M. E. Comparing castings of experimental alloys Al6Ca, Al1Fe, Al6Ca1Fe with those of commercial alloy AK12M2 in terms of their proneness to pitting corrosion. Korroziya i zashchita metallov. 2017. No. 5. pp. 75–81.
13. Zhuk N. P. A course in metal corrosion and protection. Moscow : Metallurgiya, 1976. 472 p.
14. Revie R. W., Uhlig H. H. Corrosion and corrosion control. Canada : A John Wiley & Sons Inc. Publication, 2008. 513 p.
15. Whitman W. G., Russell R. P. The natural water corrosion of steel in contact with copper. Industrial & Engineering Chemistry Research. 1924. Vol. 16, No. 3. pp. 276–279.
16. Rakoch A. G., Lobach A. A., Monakhova E. P., Begnarskii V. V. et al. Electrochemical and corrosion behavior of AK12M2 alloy in a model solution used in heating systems. International Journal of Corrosion and Scale Inhibition. 2022. Vol. 11, No. 3. pp. 1115–1130.
17. Tomashov N. D., Chernova G. P. Passivity and corrosion protection of metals. Moscow : Nauka, 1965. 208 p.