Study of the wear resistance of composite coatings modified with h-BN particles on AZ31 magnesium alloy

A low wear resistance is a significant disadvantage of magnesium-based alloys widely used in industry. The results of plasma electrolytic oxidation (PEO) carried out in an aqueous-alkaline phosphate electrolyte with the addition of hexagonal boron nitride (h-BN) powder to obtain coatings with greater wear resistance on the surface of AZ31 magnesium alloy are presented. The PEO method is one of the most promising for surface treatment of magnesium alloys, since oxidation is carried out in alkaline aluminate, silicate or phosphate electrolytes with various functional additives. The addition of nanocrystalline hexagonal h-BN powder in the form of a suspension into the electrolyte volume does not affect the electrical parameters of PEO, and h-BN particles are incorporated into the structure of the formed composite coating, increasing the wear resistance. It is shown that the resulting coatings have a relief typical of PEO with developed morphology and porosity, which change depending on the oxidation time. In this case, the incorporation of h-BN particles into the coating occurs by an inert mechanism, since they do not undergo chemical transformations with the formation of new phases. Composite coatings obtained on the surface of the AZ31 magnesium alloy by the PEO method consist of crystalline phases of MgO and Mg3(PO4)2, regardless of the addition of h-BN particles to the electrolyte. The wear resistance of coatings is 6 – 8 times higher compared to the untreated alloy. The results obtained can be used to produce PEO coatings with increased wear resistance and use them in various sectors of the economy.