The effects of Al2O3 particles on the microstructure and hardness of cold sprayed Al-Al2O3 composite coating

In this study, Al-Al2O3 composite coating produced by cold spray method on Al-7075-T6 sheet. The pure Al powder is blended with different amount of Al2O3 powder including 25, 50 and 75 wt. %. The feedstock is sprayed on sand blasted substrate using nitrogen gas at a constant temperature of 300 °C, pressure of 30 bar and the stand-off distance of 20 mm. The effect of different values of Al2O3 on the deposition behavior of the Al-Al2O3 powders are investigated. Microstructural characteristics of the coatings are evaluated by scanning electron microscopy, image analysis software, microhardness and X-ray diffraction tests. The results showed that the high velocity of particles leads to the Al2O3 particle breaking during the process. This phenomenon increases the porosity of the coatings Furthermore, the higher value of reinforcement in the initial powder leads to the homogenous distribution of them and the higher coating hardness. The hardness of the Al-75Al2O3 coating is 104 HV, which is increased by 85% compared to pure Al coating. X-ray diffraction test indicated the fine-grained structure, no-oxidation and no phase transformation in the pure and composite coatings.