Abstract: A process for producing an aluminum alloy-made forged scroll part includes a step of casting an aluminum alloy material into a round bar having a diameter of 130 mm or less, the aluminum alloy material comprising 8.0-12.5 mass % of Si, 1.0-5.0 mass % of Cu and 0.2-1.3 mass % of Mg; a step of cutting the aluminum alloy round bar into a stock material for forging; a step of subjecting the stock material to upsetting at an upsetting ratio of 20-70% to form a pre-shaped product that is a workpiece; and a forging step of applying pressure onto the workpiece with a punch at a temperature of 300-450° C. to form a scroll wrap in a direction of the punch pressure, and wherein the forging step includes a single step in which a forged scroll part is press-formed while a back pressure smaller than the punch pressure is applied to an end of the scroll wrap in a direction opposite to the punch pressure direction.

Abstract: A forged scroll part is made from an aluminum alloy material, in which harmful primary Si crystals are not formed and variation in wrap height between scrolls is low. The alloy material includes 8.0-12.5 mass % of) Si, 1.0-5.0 mass % of Cu and 0.2-1.3 mass % of Mg, and if necessary, 2.0 mass % or less of Ni and/or 0.5 masse or less of one or more species selected from among Sr, Ca, Na and Sb. A process for producing the forged scroll pa includes casing the aluminum alloy material through continuous casting into a round bar material having a diameter of 130 mm or less and subsequently subjecting the material to upsetting and hot forging with back pressure to produce a forged scroll part containing Si particles having a size of less than 15 &mgr;m and a mean size of 3 &mgr;m or less.