To produce a scroll having excellent durability (fatugue strength) by cooling the cast scroll made of Al alloy after a producing process high in temp. and then subjecting it to aging treatment.
The Al alloy is subjected to die casting or molten metal casting to mold into the shape of a scroll. Next, the Al alloy is cooled from the high temp. producing state and is subjected to aging treatment. Or, the Al alloy is cooled from the high temp. state, thereafter, its temp. is raised and hold to a solution treating temp., and is quenched at ≥90°C to be subjected to aging treatment. As the Al alloy, an Al-Si alloy contg. 8 to 13% Si as the main alloy components, particularly, an Al-Si-Cu alloy contg. 1 to 4% Cu and 0.5 to 1.5% Mg in addition to Si is preferably used. In the Al-Si alloy, it is possible that, after casting, the alloy is air-cooled to an ordinary temp. and is then subjected to aging treatment, but, after the casting, it is quenched into hot water of ≥70°C from the high temp. state of ≥500°C and is the subjected to aging treatment, by which its fatigue resistance can further be improved.
HAYASHI HIROTAKE
KATAOKA YOSHINORI
