| Al-Zn-Mg series alloys and their welding joint have high strength. After welding, the strength of welding joint can be recovered to that of the base metal only by natural aging. However this series alloys have poor stress corrosion resistance. It is necessary to resolve the conflicting problem between the strength of base metal and welding joint and their stress corrosion cracking in order to develop high-strength and wieldable Al-Zn-Mg series alloy. Developing new heat treatment for base metal and its welding joint is a method to resolve this problem.The effects of high temperature pre-precipitation on the base metal of 7A52 alloy were investigated under different solution and aging temperature. The effects of high temperature pre-precipitation on the stress corrosion properties of the heat affected zone were also studied after welding.The results show:1) The degree of super-saturation can be changed by solution and pre-precipitation; therefore, has a great influence on the age-hardening and tensile properties. The alloy will have higher super saturation after quenching from high temperature, so that the alloy will have higher hardness and strength. But if the solution temperature is too high, the stress corrosion resistance will decrease.2) High temperature pre-precipitation can change the size and distribution of the precipitation phase on the grain boundary or in the grain, so that the stress corrosion resistance can be improved. Two-step aging has a better stress corrosion resistance than natural aging and three-step aging is superior to the single stage aging in stress corrosion resistance.3) The heat affected zone and its heat treatment were investigated after undergoing the high temperature heats recycle. The pre-precipitation treatment has better stress corrosion resistance than that treatment withoutpre-precipitation.
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