Failure Analysis Of Aluminum Ingot Mould And Research On Its Coating

Aluminum as a non-ferrous metal material of modern industry has been favored in the fields of automobile industry,house decoration,food packaging,aerospace,because of its excellent properties such as low density,high strength,abundant reserves,etc.With the rapid economic and social development,China has become the world's largest aluminum consumer and aluminum producer.In the process of casting and producing metal aluminum ingots,the working environment of the metal mold(aluminum ingot mold for short)in which molten aluminum is poured is severe.Aluminum ingot molds need to withstand the temperature gradient of 10?700?and the erosion and corrosion of high-temperature molten aluminum in a short period of time.It is easy to cause damage during long-term service,leading to increased production costs,reduced production efficiency and even major safety accidents.In this thesis,we research and preparation of phosphate-based composite coatings to improve the service life of aluminum ingot molds,by analyzing the damage reasons and mechanism of failed aluminum ingot molds.It is easy to use non-metallic materials with low thermal conductivity to protect the metal mold.Coating life is the difficulty and key that affects its application in actual production.In order to solve this key problem,this article adopts the following technical route:use copper oxide transition layer to adjust the thermal expansion coefficient gap and adhesion strength between the protective coating and the mold substrate,and add fused magnesia to the protective coating to increase its thermal expansion coefficient and improve it.Adhesion to the mold substrate,adding alumina fiber to the coating to improve its thermal shock performance.Under the framework of this technical route,the relevant process parameters were studied and optimized,and the following conclusions were obtained:(1)There is obvious oxidation and decarburization on the inner surface of the failed aluminum ingot mold,which leads to a decrease in the yield strength and hardness of the cavity surface.Thermal fatigue damage is formed under the action of thermal stress,and further erosion and corrosion by molten metal are caused.The main reason for mold failure.(2)The prepared copper oxide transition layer can enhance the compatibility of the protective coating with the mold substrate.When the composition ratio of the transition coating is:10.0 wt.%silicon carbide,50.0 wt.%copper oxide,and 30.0wt.%Phosphoric acid,5.0 wt.%magnesium oxide,5.0 wt.%aluminum dihydrogen phosphate;when the thickness is 20?m,the transition layer forms a good chemical bond between the mold substrate and the protective coating.(3)Incorporating fused magnesia can reduce the elastic modulus of the protective coating,increase the thermal expansion coefficient,enhance the adhesion strength and thermal shock resistance,when the coating composition ratio is:33.4wt.%fused magnesia,44.0 When wt.%aluminum dihydrogen phosphate,13.3 wt.%silicon carbide,13.3 wt.%?-Al₂O₃,the thermal shock resistance is increased by 525%,and the adhesion strength is increased by two levels;alumina fiber is added at this ratio Prevent the expansion of micro-cracks in the coating and reduce the elastic modulus of the coating to improve the thermal shock performance of the coating.When the alumina fiber is added at 1.6%,the number of thermal shock resistance(700?)of the coating is 44 Secondly,the thermal shock resistance is increased by76%,and the overall performance is better than similar coatings.