PURPOSE: To obtain an aluminum alloy casting having little deterioration of mechanical properties, partically excellent toughness even in the condition of slow cooling speed in the thick part as automobile parts of aluminum wheel, suspending device parts, etc.

CONSTITUTION: The high toughness and high aluminum alloy casting having ≥20mm thickness in a part is composed of, by weight, 4-6% SI, 0.2-0.6% Mg, <0.5% Fe, <0.4% Mn and the balance Al with inevitable impurities and 1.2-2.8(%)μMg(%). The casting is executed in the atmosphere exceeding the air atmospheric pressure on the way of solidification and after casting, T6 treatment is applied. Then, the value of strength index {9146/28}3 × tensile strength (N/mm2) + 40 × elongation (%){9147/28} in the mechanical properties is made to be ≥1100.