To provide a high-strength aluminum alloy casting having excellent mechanical properties and a spiral scroll formed by die-casting the alloy and also to provide methods for manufacturing them.

In the high-strength aluminum alloy casting, 0.1 to 0.3 wt.% of Ag is added to an aluminum alloy having a composition consisting of, by weight, 7.5 to 11.5% Si, 3.8 to 4.8% Cu, 0.45 to 0.65% Mg, 0.4 to 0.7% Fe, 0.35 to 0.45% Mn, ≤0.2% inevitable impurities and the balance Al. The aluminum-alloy spiral scroll casting which is die-cast from the above alloy is subjected, after released from a mold, to solution heat treatment where heating is applied at 495 to 505°C for 2 to 6 hrs, to hardening treatment and further to aging treatment where heating is applied at 160 to 220°C for 2 to 6 hrs.