Forged scroll parts and production process thereof

Abstract

An object of the present invention is to provide an aluminum-alloy-made forged scroll part in which harmful primary Si crystals are not formed and variation in wrap height between the scrolls is low. The present invention also provides a process for producing the forged scroll part. An alloy material including Si: 8.0-12.5%; Cu: 1.0-5.0%; Mg: 0.2-1.3%; and if necessary, Ni: 2.0% or less and/or one or more species selected from among Sr, Ca, Na, and Sb: total 0.5% or less, is cast through continuous casting into a round bar material having a diameter of 130 mmφ or less, and subsequently, the material is subjected to upsetting and hot forging with back pressure to produce a forged scroll part containing substantially no Si particles having a size of 15 μm or more, the mean size of Si particles in the forged part being 3 μm or less.

What is claimed is:  
     
         1 . A forged scroll part comprising an aluminum alloy material, comprising Al base material, Si in an amount of 8.0-12.5 mass %, Cu in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass %, wherein the scroll part substantially comprises no Si particles having a size of 15 μm or more, and a mean Si particle size is 3 μm or less.  
     
     
         2 . A forged scroll part comprising from an aluminum alloy material comprising Al base material, Si in an amount of 8.0-12.5 mass %, Cu in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass, and Ni in an amount of 2.0 mass % or less; one or more species selected from the group consisting of Sr, Ca, Na, and Sb in a total amount of 0.5 mass % or less, or a mixture thereof; wherein the scroll part substantially comprises no Si particles having a size of 15 μm or more, and a mean Si particle size is 3 μm or less.  
     
     
         3 . A forged scroll part produced from an aluminum alloy material according to  claim 1  or  2 , wherein the scroll part is subjected to solution heat treatment, quenching, and aging after the scroll part is subjected to forging.  
     
     
         4 . A process for producing an aluminum alloy-made forged scroll part, which comprises a step for casting an aluminum alloy material comprising Al base material, Si in an amount of 8.0-12.5 mass %, Cu in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass into a round bar having a diameter of 130 mmφ or less through continuous casting; a step for cutting the aluminum alloy round bar into a stock material for forging; a step for subjecting the stock material to upsetting at an upsetting ratio of 20-70% to form a work piece; a forging step for applying pressure onto the work piece with a punch at a temperature of 300-450° C. to form a scroll wrap in a direction of punch pressing, wherein the forging step includes a single step in which a forged scroll part is press-formed while a back pressure is applied to the end of the scroll wrap part in a direction opposite to that of a punch pressure.  
     
     
         5 . A process for producing an aluminum alloy-made forged scroll part, which comprises a step for casting an aluminum alloy material Al base material, Si in an amount of 8.0-12.5 mass %, Cu in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass into a round bar having a diameter of 85 mmφ or less through continuous casting; a step for cutting the aluminum alloy round bar into a stock material for forging; a step for subjecting the stock material to upsetting at an upsetting ratio of 20-70% to form a work piece; a forging step for applying pressure onto the work piece with a punch at a temperature of 300-450° C. to form a scroll wrap in a direction of punch pressing, wherein the forging step includes a single step in which a forged scroll part is press-formed while a back pressure is applied to the end of the scroll wrap part in a direction opposite to that of a punch pressure.  
     
     
         6 . A process for producing an aluminum alloy-made forged scroll part according to  claim 4  or  5 , wherein the aluminum alloy material comprises Al base material, Si in an amount of 8.0-12.5 mass %, Cu in an amount of 1.0-5.0 mass % and Mg in an amount of 0.2-1.3 mass, and Ni: 2.0 mass % or less; one or more species selected from the group consisting of Sr, Ca, Na, and Sb in a total amount of 0.5 mass % or less, or a mixture thereof.  
     
     
         7 . A process for producing an aluminum alloy-made forged scroll part according  claim 4  or  5 , further comprising subjecting the round bar to homogenization heat treatment at 480-520° C. for 30 minutes to four hours, to surface peeling or to homogenization heat treatment and surface peeling after the casting.  
     
     
         8 . A process for producing an aluminum alloy-made forged scroll part according to  claim 4  or  5 , wherein work lubrication in which the work piece is coated with graphite film in advance is carried out in combination with die lubrication in which a graphite-containing oily lubricant is applied to a die during forging.  
     
     
         9 . A process for producing an aluminum alloy-made forged scroll part according to  claim 8 , further comprising heating the work piece at 100-500° C. and immersing the work piece into a lubricant solution prepared by mixing and dispersing graphite powder into water to subject the work piece to work lubrication with graphite film.  
     
     
         10 . A process for producing an aluminum alloy-made forged scroll part according to  claim 4  or  5 , further comprising subjecting the scroll part to solution heat treatment, quenching, and aging after forging.  
     
     
         11 . A process for producing an aluminum alloy-made forged scroll part according to  claim 10 , further comprising subjecting the surface of the scroll part to machining.