Study On Process, Microstructure And Properties Of Plasma Sprayed Ceramic Coating On AZ91D Magnesium Alloy

The preparation of Al2O3(A),Al2O3-13% TiO2,Al2O3-20% TiO2 and transition Al2O3-20% TiO2 coatings on magnesium alloy AZ91D by plasma spraying is studied in this paper, and the coating's thickness,micro-hardness,bond strength and anti-thermal shock property have also been tested. The phase structure,morphology and composition of coatings are investigated by SEM,EDS and XRD, the wear property of coatings are compared with magnesium alloy AZ91D. according to the results in the corrosion experiment , calculate the corrosion rate, analyze the corrosion features.For the spraying gun speed of 200mm/s, the powder feed rate of 25g/min, orthogonal experimental design method was used to study the influence of arc current, primary gas flow and spraying distance on the properties of coatings. The results indicate that spraying distance is the most influential factor for microstructure and properties of the coating, the optimized spray parameters are: arc current of 700A, primary gas flow rate of 60psi, spraying distance of 90mm.The coatings are characteristic of lamellar microstructure with porosities, micro-cracks and un-melted particles. The adhesion between coating and substrate is mechanical bond. The addition of TiO2 results in better integrity of AT13 and AT20 coatings than that of Al2O3. Al2O3 coating consists ofγ- Al2O3 andα- Al2O3. AT20 coating consists ofγ- Al2O3,α- Al2O3 and Al2TiO5.The micro-hardness of Al2O3 was the highest during these coatings, it was 864.89HV. Under the condition of 250℃and 300℃heating and water quenching, the coatings demonstrated all high anti-thermal shock property .bonding coating played the positive role between the substrate and the ceramic coating. The coating's bonding strength with bond coat were higher than coatings'without bond coat. The AT20 coating's bonding strength was the highest. The wear test revealed that the wear resistance of AT13 coating was better than other coatings. The predominant wear mechanism of coatings is spalling fatigue wear and adhesive wear. The primary corrosion of coatings were uniform corrosion, which took place on the coating surface. The corrosion resistance was better than AZ91D magnesium alloy.