Study On Expendable Pattern-Shell Molding Hybird Casting Process For Magnesium Alloys

Magnesium widely used in aviation,aerospace,automotive,computer,communications andhome appliances.because it has a series of sdvantages such as low density,high shock resistantperformance,excellent specific strength,good thermal properties,good machinability,fine resist-ance to electromagnetic interference performance and facilitate to reuse. The topics explored theexpendable pattern-shell molding hybrid casting process for magnesium alloy by combineingthe lost foam casting, investment casting and vacuum casting.Study the main aspects of theprocess to obtain the most effective casting parameters.Study the way to improve the the surface quality of EPS mold by dipping coat and pastingcoat.The result show that:the surface texture could be eliminated in a holidtic approach by usingthe dip way with the coating which formed by paraffin and stearic;The coating which compositedby methyl silicone oil,emulsifying and some other components could be used when local areasurface need to be improved surface quality.Ceramic shell were made by the composite process which use mullite with silica sol andsodium silicate respectively. Study the influence of the sintering which added into the coatingand the low-temperature roasting.Result show that:the shell`s strength could be improvedeffectively by30%by adding NaOH and roasting at600℃;The silica sol which containing inface coating could be gelated faster effectinely by adding3%super sbsorbent resin into theaggregate of the shell,that could be saved the shell make time by almost60%.Invented a coating for avoid the reaction between the magnesium alloy and mold shell.Thecoating per-coated on the surface of the EPS mold,and the mold`s surface will form a protectcoating after shell preparation is completed. n this way can prevent the contact between moltenmetal and mold more completely and more stability to inhibiting the oxidation reaction whichlead surface burning.Study the characteristics of the AZ91D magnesium alloy`s filling feature andmicrostructure and mechanical properties that effect by casting process parameters.study foundthat：the negative pressure casting increased the ability of mold filling of molten metal andimproved the mechanical properties of the castings； as the wall thickness of castings becomethicker the microstructure growing more and more coarse and the mechanical propertiesdecreasing more obviously in the same pouring conditions.Ultimately,we can get a magnesium alloy castings with filling completely and smoothsurface and excellent performance by the expendable pattern-shell molding hybrid castingprocess.