Research On Alcohol-based Flame Retardant Coating For Magnesium Alloy

Chemical properties of magnesium element is very active, when being liquid, it can easily react with oxygen and nitrogen of the air and water in the mold. As a result, pores and oxide skin appear on the surface of cast magnesium alloy, and the casting surface quality reduces, which had caused great pressure on manufacturers.This paper first study the effect of silicasol, polyvinyl butyral, phenolic resin, attapulgite and fire-resistant aggregate on the physical properties that is rheology, thixotropy, viscosity, suspensibility, density, permeability, strength under ambient and high temperature, as well as the cracking resistance under high temperature. The results show that the strength of the coating with silicasol as binder agent under ambient and high temperature is too low to reach the application requirements, while that with phenolic resin as binder agent has well bonding effect and can be used as a substitute of silicasol. Then we optimize the content of the raw materials, ferric oxide 70%, talc 20%, quartz powder 10%, phenolic resin 4%, attapulgite 3%,polyvinyl butyral 0.25%, Boric Acid 3% and SDS 0.2%.The properties of the developed flame retardant coating and the Italian coating were compared. The density, gas evolution, permeability and suspension property of the developed coating were better than that of the Italian coating, while there is no obvious difference in the strength under ambient-temperature and high-temperature and high temperature cracking resistance of the two coatings. The filling height in the casting of magnesium alloy using the developed flame retardant coating and the Italian coating as retardant coating also were compared, it was found that the filling height of developed flame retardant coating was 15 percent higher than that of the Italian coating, so the developed coating is suitable for the castings of magnesium alloy.Casting experiments show that the developed coating has good flame retardancy and high strength; acute thermal cracking and sand crushing did not happen; the permeability was well and the pour filling was steady; the reverse ejection and missrun phenomena did not appear. Moreover, the ability of resisting sand penetration was well. The coating can be easily split away off. Therefore, the developed coating can meet the actual needs of the casting of magnesium alloy.