Abstract: Apparatus for casting of low-density metals, such as magnesium alloys, into an air-permeable mold includes a housing forming a substantially airtight chamber in which is disposed a mold assembly including a mold secured between top and bottom plates by encircling bands or straps. A bottom-discharge reservoir vessel for molten metal is disposed above the mold, the vessel outlet communicating with the mold inlet through a coupling against which the mold assembly is resiliently urged by bias springs to insure an airtight coupling. A valve is selectively operable for opening and closing the vessel outlet and closure apparatus cooperates with the vessel for providing a substantially airtight closure thereof. A pressure control system is coupled to the vessel and the chamber for establishing a pressure differential therebetween which cooperates with gravity to urge the molten metal from the vessel into the mold when the valve is open.