Al alloy cast impeller for compressor and process for producing same

A method for producing an impeller for compressors, the impeller being formed as an Al alloy casting, comprising a boss part, a plurality of blade parts, and a disc part, and having a 0.2% proof stress value of 260 MPa or more at 200° C., the method comprising:

• preparing a 720 to 780° C. Al alloy molten metal that contains Cu:
• 1.4 to 3.2 mass %, Mg:
• 1.0 to 2.0 mass %, Ni:
• 0.5 to 2.0 mass %, Fe:
• 0.5 to 2.0 mass %, and Ti:
• 0.01 to 0.35 mass %, the balance of Al and unavoidable impurities;
• pressure casting the Al alloy casting comprising:
• pressure injecting the Al alloy molten metal resulting from said preparing into a product shape space configured from a plaster mold having a plaster mold temperature of 200 to 350° C.,
• disposing a chill plate in contact with a disc surface of the Al alloy molten metal, and
• controlling a chill temperature of the chill plate to complete solidification first in the disc part, then the blade parts, and then the boss part, and to achieve a secondary dendrite arm distribution in which said maximum secondary dendrite arm spacing of the disc part is less than said maximum secondary dendrite arm spacing of the blade parts, and the maximum secondary dendrite arm spacing of the blade parts is less than the maximum secondary dendrite arm spacing of the boss part, said chill temperature being controlled to be greater than or equal to 110° C. and less than or equal to 250° C., the plaster mold temperature and the chill temperature satisfying the relationship chill temperature (° C.)<(plaster mold temperature−50) (° C.);
• after said pressure casting, a solution treatment step of subjecting the Al alloy casting to a solution treatment;
• and
• an aging treatment step of subjecting the Al alloy casting to an aging treatment after the solution treatment.