The invention provides a high-
toughness heat-resistant Mg-Gd-
Y alloy suitable for gravity
casting and a preparation method thereof. The
alloy comprises the following chemical components of, in percentage by
mass, 4.0%-10.0% of RE, 2.0%-6.0% of Zn, 0.5%-1.2% of Al, 0.1%-0.3% of Mn, 0.01-0.08% of M and the balance Mg, wherein M is one or two elements Ti and B. The preparation method comprises the following steps of (1), proportioning according to Mg-Gd-
Y alloy components; (2), melting a industrial pure
magnesium ingot; (3), heating to 700 DEG C, melting industrial pure
zinc, Mg-Gd-Mg-Y and Mg-Mnintermediate
alloy; (4), heating to 730 DEG C, adding and melting industrial pure aluminum ingots, Al-Ti, Al-Ti-B and Al-B intermediate
alloy, refining to obtain a
magnesium alloy melt; (5), carryingout gravity
casting; and (6) carrying out secondary
solid solution and
artificial aging treatment. According to the method, after the alloy is subjected to gravity
casting, secondary
solid solution treatment and
artificial aging heat treatment, the tensile strength is 298 Mpa and the elongation percentage is 16% at
room temperature; the high-temperature tensile strength is 216 Mpa and the elongation percentage is 22% at 200 DEG C, and the high-end requirement for lightweight development in the industries of
aerospace, war industry, automobiles and the like is met.