Enhancing the shear strength and oxidation resistance of aluminum-chromium phosphate heat-dissipating coatings by the introduction of a micro arc oxidation transition layer

Herein, aluminum-chromium phosphate (ACP) heat-dissipating coatings were prepared on titanium alloys with micro-arc oxidation (MAO) transition layers by a slurry method. The effects of the MAO transition layers on the phase structure, surface morphology, elemental composition, shear strength, spectral emissivity and oxidation resistance of the ACP coatings were investigated. The results showed that the introduction of the MAO transition layer had no obvious effect on the phase composition and surface morphology of the ACP coating. In addition, a MAO layer with Al and P (MAO(AP)) increased the shear strength of the ACP coatings to 6.9 MPa after curing at 200 °C, which was 117% higher than that of the ACP coating, and the shear strength could be further increased to 11.3 MPa by calcination at 700 °C. The weight gain of the samples with the ACP/MAO(AP) coating was only 0.27 mg/cm² after exposure to air at 700 °C for 200 h, which was 48% lower than that of the samples with only the ACP coating. In addition, the spectral emissivity of the ACP/MAO(AP) coating was consistent with that of the ACP coating. Thus, the introduction of the MAO(AP) layer is effective to improve the shear strength and oxidation resistance of the ACP heat-dissipating coating.