The invention relates to a plaster
casting method for a large-sized complex thin-walled
magnesium alloy part. The method comprises the following steps of
coating the surface of an assembled form with a
coating in situ, and arranging shapeless cold iron on a hot spot part, wherein a mixture for manufacturing the shapeless cold iron comprises the following components in percentage by
mass: 1.25 percent of phenolic resin, 0.4 percent of toluenesulfonic acid, 1 to 1.5 percent of
boric acid, 2 percent of
bentonite and the balance of 70 to 140-mesh
chromite sand; pouring a
casting in an adjustable
pressure casting device, arranging a plaster mold poured by the form at the
casting position of the adjustable
pressure casting device, filling a tank with dry air or a CO2
atmosphere with SF6 content of 0.1 to 1.0 percent, and performing
vacuum casting and pressurized solidification, wherein the casting temperature is 710 to 750 DEG C, vacuum degree for primary
mold filling is minus 0.6Mpa to minus 0.8Mpa, and the solidification pressure is 0.020 to 0.025Mpa. According to the method, oxidization can be prevented, the
mold filling capability can be improved, shrinkage cavities and shrinkage porosities in the casting are reduced, and the obtained
magnesium alloy casting is higher in density.