| Magnesium alloys have many excellent properties, such as high specific strength, stiffness and well shock absorption, etc. They have many important applications in aviation, aerospace, auto car, electronics and industry. In addition, magnesium alloys also have application prospects in near furture. However, magnesium alloys are highly active, have low melting point and hardness. They usually show poor wear resistance, poor heat resistance and low corrosion resistance for many industrial applications. Therefore, the development of research and application of magnesium alloys is limited. The surface modification can effectively improve the surface properties of various magnesium alloys. Furthermore, improve the corrosion resistance, wear and heat resistance of magnesium alloys. The preparation of thermal barrier coatings (TBCs) on metal substrates by thermal spraying can improve the wear resistance, corrosion resistance, heat resistance of metals, and gain special surface properties. TBCs, typically comprising of 8YSZ (zirconia stabilized by 8wt% yttria) top coat, has large thermal expansion coefficient, low thermal conductivity and good thermal shock resistance. They have been used to improve the thermal efficiency of turbine engine by providing the capability to sustain a significant temperature gradient across the coating. In this paper, TBCs, comprising of 8YSZ top coat, were prepared on MB26 rare-earth magnesium alloy which has high strength and high toughness. The preparation and performance of TBCs were well studied. Finally, a stable TBCs was fabricated on MB26 alloy, which largely improve the corrosion resistance, wear and heat resistance of magnesium alloys.TBCs, comprising of NiCrAlY bond coat and 8YSZ top coat, were prepared on MB26 magnesium alloy by atmospheric plasma spraying (APS). MB26 magnesium alloy substrate was oxidized during APS. Three coatings were prepared by controlling the substrate temperature with different cooling media including cold water, compressed air and natural cooling during deposition. During plasma spraying, the substrate temperature affects the bonding strength between the coating and the substrate. Under the high substrate temperature, the sprayed coatings were spreaded well, but the MB26 magnesium alloy was seriously oxidized. The coating whose substrate was cooled by compressed air during plasma spraying has the highest bond strength and the best thermal shock resistance among these coatings. The coating largely improves corrosion resistance of MB26 magnesium alloy. The wear resistance of MB26 alloy is largely improved after the coating deposition, the wear rate of coating is 90% lower than MB26 alloy. The coating with a top coat thickness of 108μm reduces the substrate temperature for about 80℃.After heat treatment at 200℃and cold press at 40 MPa, Al layer that is prepared on MB26 alloy by arc spraying is compact and metallurgicaly bonded to Mg alloy substrate. The electroless plated Ni layer was well bonded to MB26 alloy and showed well thermal shock resistance with a blasted substrate surface. After the heat treatment at 230℃, the thermal shock resistance of the Ni layer is further improved.TBCs with Al or Ni interlayer were deposited on MB26 alloy. For TBCs with Al interlayer, the micro-crack in Al layer was prone to growth as crack, leading to the fracture failure of coating. Therefore, Al interlayer does not have any improvement to the bond strength and thermal shock resistance of the TBCs. Ni interlayer performs well, and the composited coatings with Ni interlayer have high bond strength and excellent thermal shock resistance. The thermal shock life of this composited coating with Ni interlayer is 20-30 times longer than the duration of the coating without interlayer. In the quenching process, the corrosion of Mg alloy substrate mainly leads to the failure of TBCs with electroless plated Ni interlayer. |
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