Performance Of The Coated Belt For High-speed Continuous Casting And Rolling Aluminum Slab

Currently, the aluminum industry of China is facing the problems of high energy consumption, low yield, low profits, high-end products production difficulties, ect. In order to solve these aforementioned problems, Yichuan Power Group has imported Hazelett aluminum continuous casting and rolling production line. Although the production line has been put into production, problems such as short coated belt life, sticky aluminum, inadequate performance stability, uneven heat transfer, the use of belt completely dependent on imports still existed. Since the strip is the mold of aluminum High-speed Continuous Casting and Rolling, it has a significant impact on the quality of the strip. What’s more, coated belt is also one of the key factors that constraints the development of Chinese aluminum horizontal continuous casting and hot-rolled technology.In this paper, magnesia partially stabilized zirconia (MSZ) coating and yttria partially stabilized zirconia (YSZ) coating on low-carbon steel substrate are prepared by the existing domestic plasma spraying equipment，based on the method to prepare metal-based ceramic coating. According to the performance requirements of the steel belt used on High-speed Continuous Casting and Rolling aluminum, the properties of ceramic coatings, such as the resistance to liquid aluminum corrosion, high temperature wettability, morphology and surface roughness, thermal diffusivity, normal temperature wear resistance, high temperature wear resistance, resistance to bending fatigue and thermal fatigue of MSZ and YSZ coatings have been studied. Compared to the property of the coated belt used on Hazelett continuous casting and rolling aluminum, the following conclusions are achieved:①Both the MSZ and YSZ coatings prepared in this paper do not react with aluminum liquid, which show stable chemical properties. These two coatings are non-wetting with liquid aluminum at high temperatures, and the YSZ coating shows better property as compared to that of MSZ coating; The surface roughness of MSZ, YSZ and Hazelett coatings is10um,9um and7um, respectively. Within a certain range, the larger roughness is beneficial to enhance the non-wetting property between liquid aluminum and non-wetting coatings;②In the temperature range of400oC to600oC, the thermal diffusivity of MSZ, YSZ and Hazelett coatings is0.067-0.0967cm2/s,0.057-0.0794cm2/s,0.0565-0.0919cm2/s, respectively. Through analyzing the thermal insulation ability of the YSZ coating with the thickness of50um by the ANSYS software. It can be included that in the range of550oC to700oC, the heat-insulating temperature of YSZ coatings is beyond120oC, which will protect the underlying belt from heat stress and consequent distortion effectively.③At room temperature, the average stability friction coefficient of MSZ, YSZ and Hazelett coatings is0.29,0.15and0.26, respectively. Moreover, YSZ coating shows better property as compared to that of MSZ and Hazelett coatings. At the temperature of600oC, the average stability friction coefficient of MSZ, YSZ and Hazelett coatings is0.37,0.23and0.34, respectively. Additionally, after60-minutes high temperature friction, MSZ coating becomes a complete failure. And the base of the MSZ coating has been exposed. The bonded layer of YSZ coating also produces a certain degree of wear. For Hazelett coating, the bonded layer has a great degree of wear and serious surface furrows. The mainly wear forms of the coatings at high temperature are slice peeling and furrows, which are attributed to high temperature cycle stress and grindings’ adhesion;④None of MSZ, YSZ or Hazelett coating occurs apparent failure in the bending fatigue test, but crack initiation and propagation is found. The incompletely melted particles and pore structure on MSZ and YSZ coatings surfaces have prevented the expansion of cracks effectively, which endow them with a better performance to resist bending fatigue. The surface of Hazelett coating is smooth, which leads to the crack extending seriously and part of the region or even occurring slice peeling.⑤The average thermal fatigue failure life is58times for MSZ coating,62times for YSZ coating, whereas30times for Hazelett coating. For MSZ coating, the thermal fatigue failure is ascribed to the weak bond of the ceramic layer. For YSZ and Hazelett coatings, the thermal fatigue failure is primarily caused by thermal expansion coefficient mismatch between the coatings and the thermally grown oxide.