PURPOSE: To make it possible to aim at making a rotor casing, a rotor, etc. light weight while they have a highely wear-resistant capability, by integrally forming each of them with the use of a hyper-eutectic Al-Si alloy of highly wear-resistant die-casting material in a method of die-casting.

CONSTITUTION: A rotor casing 1, a rotor 2 and a vane 3 are each integrally formed with the use of a hyper-eutectic Al-Si alloy of highly wear-resistant die- casting material in a method of die-casting. The hyper-eutectic Al-Si alloy of highly wear-resistant die-casting material is composed of Cu of 4.0 to 5.0wt%, Si of 13.5 to 20.0wt%, Fe of less than 1.3wt%, additives of less than 0.5wt% Mg and less than 0.5wt% Ni with containing impurities, and the balance of Al. Since the alloy is a hyper-eutectic Al-Si alloy, primary crystals having a Vickers hardness of around 1320 are precipitated and distributed, and therefore, the alloy is lightweight and has an excellent wear-resistant capability.