| The purpose of this thesis is to solve the problem that the strength and the anti-exfoliation property can not meet the requirements at the same time for the domestic production of the plates of the high-strength 7475 aluminum alloy. It is studied the high-strength 7475 aluminum alloy, the homogenization of the semi-continuous cast ingot, the solution of the hot rolled plate and the ageing treatment of the pre-strained plate for the domestic production by means of tensile test, conductance measurement, exfoliation test, metallographic microscopy, scanning electron microscopy, transmission electron microscopy and microzone energy spectrum analysis, which provide the foundation for establishing the proper heat treatment in the process of the plates of the high-purity 7475 aluminum alloy. The results are as follows:(1) The low melting point product which begins to melt at 478℃in the semi-continuous cast ingot of the alloy dissolve into the matrix at 465℃for 12 h,while it transforms partly to S phase(Al2CuMg) with melting point about 489℃. The low melting piont product could dissolve entirely into the matrix at 465℃for 48 h or by multi-stage homogenization. Much residual phase(S-type phase) was found in the microstructure of the cast ingot after industrial homogenization.(2) The property of the alloy was influenced a little by heating its cast ingot to 485℃and holding for 10 h in furnace following its first homogenization at 465℃for 24 hours. Following that two-stage homogenization, the third-stage homogenization was preceded by heating to 500℃slowly and holding for 2 h, so that the grain size of the alloy was not influenced very much, but its strength increased a little and its conductivity decreased a little. The proper homogenization treatment was 465℃×24h↗(3h)→485℃×10h↗(3h)→500℃×2h.(3) A small amount of the low melting point product which began to melt at 478℃and much product with melting point about 489℃were still found in 15mm hot-rolled plate made from the cast ingot by industrial conventional homogenization treatment, so the original solution temperature of the hot-rolled plate was required to be below 470℃; low melting piont product existed in 18mm-thick hot-rolled plates, which started melting at 489℃. The alloy would be overburnt when the solution treatment temperature reached 489℃.(4)When 15mm and 18mm thick hot-rolled plates solutioned at 470℃from 0.5h to 4h, the strength could be increased significantly at the first hour, but the mechanical properties could hardly be affected for further more holding time. When the solution time extended to five hours, the only residual phase that did not dissolve into matrix was Fe-containing crystalline phase, the grain recrystallization of plate is not full, and the microstructure still showed on the characteristics of fiber. There was no detrimental effect on the mechanical properties of the alloys when firstly heating to the solution temperature andcooling in air, then doing the second conventional solution treatment, and multi-stage high-temperature solution. The proper solution treatment was 470℃×1h～2h.(5) The property of the pre-strained plate with thickness of 18mm was not sensitive to the temperature and time of first-stage ageing, but it was very sensitive to the temperature and time of second-stage ageing, so the second-stage ageing treatment should be controlled strictly. The second-stage ageing time should be 12～16h when the second-stage ageing temperature was 163℃～160℃following the first step ageing at 107℃for 7h. When the temperature of second-stage ageing was 160℃, the corresponding aging time should be 16 hours, so that the exfoliation degree could be lower than EB. The proper ageing treatment was 107℃×12h+ 163℃×12h.
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