The Preparation And Technologic Study For Mg-alloys Squeeze Casting CoatingAbstrac

Metal mold squeeze casting is an important method to produce Mg-alloys parts, but it has not yet applied to metal mold squeeze casting Mg-alloys coating. In this method the coating spraying is a very critical step, because the coating quality can directly affect the casting surface finish, demoulding, the service life of mould and the yield of the product. In this paper, through comparing the performance characteristics of different raw materials, choose the raw materials that are suitable for Mg-alloys metal type of squeeze casting coating; Besides through three common coating preparation technology, the optimum coating preparation was determined that for coating configuration and performance of the test, compare and analysis; Furthermore through the optimal preparation process to prepare the coatings and to detect the property of suspension, hair gas, surface strength, rheological behavior, leveling, optimized the composition ratio of the coating; Finally through the casting test to verify the coating performance, further optimized the coating ratio and made it better to meet requirement in casting production.The research shows that:(1) the preparation methods of coatings on the properties of coating had a certain influence, including the coating prepared by rolling had the optimal performance and stable performance.(2) Lightweight magnesium oxide could be used as refractory aggregate of squeeze casting of Mg-alloys coatings, talcum powder coating can react with Mg-alloys in high temperature and pressure condition and generate the Mg2 Si and MgO, but talcum powder compound with light magnesium oxide could avoid the happening of the reaction.(3) The amount of linan sodium based bentonite range from 2% to 5%, suspension performance of coatings increased with the increase of bentonite. In light magnesium oxide coating, adding 3% of bentonite and 0.5% CMC could make the suspension rate above 97%.In light magnesium oxide composite coating with talcum powder, adding 3% bentonite and 0.3% xanthan gum, suspension performance of coating could reach above 98%.(4) Binder plays a major role to bonding strength of coating, so the variety and dosage of binder is the main influence factor of coating bond strength and coating strength is affected by various refractory. Light magnesium oxide coating bond strength is low, so it is necessary to improve the binder dosage, the addition of sodium silicate at around 5% in this paper. The Al2(SO4)3 sulfate would happen decomposition reaction under high pressure and the pouring temperature, thus the bonding strength of coating would descend and generate a large amount of gas, so the aluminum sulfate as a kind of inorganic binder is not suitable for magnesium metal mold squeeze casting coating. Experiments show that: the best proportion of metal mold squeeze casting coating for Mg-alloys is light magnesium oxide 100% +linan sodium based bentonite 3%+CMC 0.5%+sodium silicate 5%; Or light magnesium oxide 80%+talcum powder 20%+linan sodium based bentonite 3%+xanthan gum 0.3%+sodium silicate 5%; Or light magnesium oxide 60%+diatomite 40%+linan sodium based bentonite 3%+xanthan gum 0.3%+sodium silicate 5%.