Compressor impeller cast from al alloy and method for producing same

Abstract

The present invention provides: a compressor impeller that cast from an aluminum alloy, has superior production characteristics, and exhibits stable high-temperature strength when used at temperatures around 200° C.; and a method for producing same. The compressor impeller that is cast from an Al alloy is provided with a boss section, a plurality of vane sections and a disc section; the boss section, the plurality of vane sections and the disc section excluding the end section comprise an Al alloy comprising a predetermined metal composition; and at the end section of the disc section, there are at least 10,000/mm 2 of intermetallic compounds having a circle-equivalent diameter of 1-6 μm, and there are no greater than 500/mm 2 of intermetallic compounds having a circle-equivalent diameter exceeding 6 μm.

1 . A compressor impeller cast from an Al alloy, comprising:
 a boss section;   a plurality of vane sections; and   a disc section,   wherein the boss section, the plurality of vane sections, and the disc section excluding an end section comprise an Al alloy comprising 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 %, Ti: 0.01 to 0.35 mass %, and B: 0.002 to 0.070 mass % and a balance of Al and unavoidable impurities,   wherein the end section of the disc section comprises an Al alloy comprising 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 %, Ti: 0.005 to 0.175 mass %, and B: 0.001 to 0.035 mass % and a balance of Al and unavoidable impurities, and   wherein at least 10000/mm 2  of intermetallic compounds having a circle-equivalent diameter of 1 to 6 μm, and no greater than 500/mm 2  of intermetallic compounds having a circle-equivalent diameter exceeding 6 μm exist in the end section of the disc section.   
     
     
         2 . The compressor impeller cast from the Al alloy according to  claim 1 ,
 wherein the compressor impeller is for use in large-scale applications including ships, and   wherein the boss section has a height of 200 to 80 mm, the disc section has a diameter of 300 to 100 mm and the vane sections have a height of 180 to 60 mm with 30 to 10 vanes measuring 4.0 to 0.4 mm in thickness at a vane tip.   
     
     
         3 . The compressor impeller cast from the Al alloy according to  claim 1 ,
 wherein the compressor impeller is for use in small-scale applications including automobiles, and   wherein the boss section has a height of 100 to 20 mm, the disc section has a diameter of 120 to 25 mm, and the vane sections have a height of 90 to 5 mm with 20 to 4 vanes measuring 3.0 to 0.1 mm in thickness at a vane tip.   
     
     
         4 . A method for producing a compressor impeller cast from an Al alloy, comprising:
 a molten metal preparation step of preparing a 720 to 780° C. Al alloy molten metal comprising 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 a balance of Al and unavoidable impurities, and adding a refining agent to the Al alloy molten metal to incorporate Ti: 0.01 to 0.35 mass % and B: 0.002 to 0.070 mass % in an alloy composition of the Al alloy molten metal;   a casting step of casting an Al alloy casting by pressure casting whereby the Al alloy molten metal prepared is injected through a molten metal inlet into a space having a product shape configured from a plaster mold having the molten metal inlet at the bottom of the plaster mold, and a 100 to 250° C. chill disposed on a surface that contacts with an impeller disc surface, the space being formed by disposing the plaster mold and the chill so that the chill is at upper position and the plaster mold is at below position, and an inflow rate at the molten metal inlet into the space being 0.12 to 1.00 m/s;   a solution treatment step of solution treating by subjecting the Al alloy casting to a solution treatment; and   an aging treatment step of aging treating by subjecting the Al alloy casting to aging after the solution treatment.   
     
     
         5 . The method for producing the compressor impeller cast from the Al alloy according to  claim 4 , wherein
 an end section of an disc section of the compressor impeller has a cooling rate of 0.1 to 200° C./s in the casting step.   
     
     
         6 . The method for producing the compressor impeller cast from the Al alloy according to  claim 4 ,
 wherein the Al alloy casting is heat treated for 2 hours or more at a temperature 5 to 25° C. below a solidus temperature of the Al alloy in the solution treatment step, and   wherein the Al alloy casting after the solution treatment step is subjected to a heat treatment at 180 to 230° C. for 3 to 30 hours in the aging treatment step.   
     
     
         7 . The method for producing the compressor impeller cast from the Al alloy according to  claim 5 ,
 wherein the Al alloy casting is heat treated for 2 hours or more at a temperature 5 to 25° C. below a solidus temperature of the Al alloy in the solution treatment step, and   wherein the Al alloy casting after the solution treatment step is subjected to a heat treatment at 180 to 230° C. for 3 to 30 hours in the aging treatment step.