The invention relates to the field of
magnesium alloy of
metal materials, and concretely relates to a
casting magnesium alloy containing Zn, Al, Cu and Mn with high strength and
toughness. The
casting magnesium alloy comprises the following components in percentage by weight: 6.0-8.0% of Zn, 0.5-1.5% of Al, 0.5-1.0% of Cu, 0.3-0.7% of Mn and the balance of Mg and inevitable
impurity elements, wherein the content of the
impurity elements is less than 0.01%. A preparation method of the
casting magnesium alloy comprises the steps of:
smelting Mg at the temperature of 740-760 DEG C by using an iron
crucible; after pure magnesium is completely smelted, sequentially adding preheated pure
metal Zn, Al, Cu and Mg-10wt.% and Mg intermediate alloy for alloying, wherein mixed CO2 and SF6 are used as protective gases in the pure magnesium
smelting and alloying processes; stirring, slagging off, standing for 15-20 minutes, adjusting the temperature of an alloy fusant to 700-720 DEG C, and casting into an
ingot; and carrying out
solution treatment on the alloy for 24-64 hours at 350-400 DEG C,
quenching by
warm water at 40-60 DEG C, then preageing for 8-24 hours at 50-70 DEG C, and finally preageing for 2-6 hours at 150-200 DEG C to obtain the casting
magnesium alloy with high strength and
toughness. In
room temperature extension tests of the casting
magnesium alloy, the yield strength is not less than 205MPa, the tensile strength is not less than 305MPa, the elongation rate is not less than 10%, and the casting magnesium alloy has excellent comprehensive
mechanical property.