To satisfactorily join insert fittings and to remarkably reduce the occurrence of troubles, such as insufficient strength and pressure leakage due to fall-off.

This alloy has a composition consisting of, by weight ratio, 0.4-1.2% titanium, 6.0-10.0% silicon, 0.2-0.6% magnesium, and the balance aluminum with inevitable impurities or consisting of 0.4-1.2% titanium, 9.6-12.0% silicon, 1.5-3.5% copper, and the balance aluminum with inevitable impurities. Insert fittings are integrally cast-in by using this alloy.