Two-stage homogenizing heat treatment method for ultrahigh strength aluminium alloy cast ingot

The invention discloses a two-stage homogenizing heat treatment method for an ultrahigh strength aluminium alloy cast ingot. The ultrahigh strength aluminium alloy cast ingot comprises the following components in percentage by mass: 8.13% of Zn, 2.36% of Cu, 2.08% of Mg, 0.21% of Sc, 0.12% of Zr, less than or equal to 0.07% of Fe, less than or equal to 0.09% of Si, less than or equal to 0.05% of other single elements, and the balance of Al, wherein the sum of all the other elements is less than or equal to 0.15%. The two-stage homogenizing heat treatment method for the ultrahigh strength aluminium alloy cast ingot comprises the following steps: heating a cast ingot to 315-325 DEG C in a resistance heating furnace for carrying out low temperature pre-precipitation treatment, and performing heat preservation for 4-6 hours; carrying out high temperature treatment on the cast ingot for a long time in a furnace, heating until temperature is 462-467 DEG C, performing heat preservation for 23-25 hours, and carrying out air cooling. The two-stage homogenizing heat treatment method for the ultrahigh strength aluminium alloy cast ingot has the advantages that dimension and distribution of an Al3Sc/Al3Zr precipitated phase in the alloy ingot are effectively regulated on the basis of eliminating segregation and eutectic structures of main alloy elements in the alloy ingot, so that strength of an alloy is greatly improved, and a recrystallization temperature of the alloy is greatly increased.