Reactive plasma spraying synthesis and characterization of TiB2–TiC–Al2O3/Al composite coatings on a magnesium alloy

• Synthesis of TiB2–TiC–Al2O3/Al composite coatings on Mg alloy by RPS.
• Microstructure and properties of the RPS coatings were characterized.
• The coatings consist of TiB2, TiC, Al2O3 and/or excess Al without by-products.
• The coatings display dense structure and good interfacial bonding with substrate.
• The coatings provide good protection for the Mg alloy against wear and corrosion.

In situ TiB2–TiC–Al2O3/Al composite coatings were successfully synthesized on a magnesium alloy substrate by the technique of reactive plasma spraying from an Al–TiO2–B4C system. Phase composition and microstructure of the coatings were characterized by using X-ray diffraction and scanning electron microscopy, respectively. The coatings were subjected to many property tests of bonding strength, micro-hardness, abrasive wear and electrochemical corrosion. The results indicated that regardless of the Al content in the Al–TiO2–B4C system, the desired phases of TiC, TiB2, Al2O3 and/or excess Al were produced in the coatings with no intermediate phases. The coatings exhibited the typical lamellar structure and bonded strongly to the substrate. Micro-hardness and wear resistance of the coatings decreased with the increase of Al content. However, the increase in Al made the coatings have better corrosion resistance because of the denser structure. The coatings by reactive plasma spraying from the Al–TiO2–B4C system could provide a good combination of protection for the magnesium alloy against both wear and corrosion.