D. Mendeleev University of Chemical Technology of Russia, Chair of Innovation Materials and Corrosion Protection, Moscow, Russia:

A. A. Abrashov, Associate Professor, Candidate of Engineering Sciences, e-mail: abr-aleksey@yandex.ru
N. S. Grigoryan, Associate Professor, Candidate of Сhemical Sciences, e-mail: ngrig108@mail.ru
M. A. Simonova, Student, e-mail: simonovamas11@rambler.ru
N. A. Asnis, Leading Engineer, Candidate of Engineering Sciences, e-mail: asnis@mail.ru

Magnesium alloys come short of corrosion resistance due to high negative values of their standard potentials. Lacquer coating is one of the most poplar methods to prevent corrosion of magnesium alloy products. As adhesion layers under lacquer coating before coloring of magnesium and its alloys, chromate coatings are widely applied. The major drawback of chromatizing solutions is their high toxicity resulting from hexavalent chromium compound involved. In recent years, as an alternative to chromate layers on magnesium and its allows, nanosize conversion titanium- and (or) zirconium-containing adhesive coatings made of solutions of hexafluoro zirconic and hexafluoro titanic acids are widely used in international practice. The solution composed of hexafluoro zirconic (H₂ZrF₆), hexafluoro titanic (H₂TiF₆) and tartaric (C₄H₆O₆) acids is developed. The corrosion tests show that protective properties of new coatings meet the requirements imposed on adhesive layers to underlay lacquer coatings: the invasion depth of corrosion from the notch groove is within 2 mm after 100 h of curing in the salt-spray chamber. It is found that lacquer coating with the developed adhesive underlayer posesses higher adhesion strength as compared with chromate coatings.

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13. ASTM D4541–17. Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers.
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