一、绪言 Al—Zn—Mg系合金通过时效硬化处理可以得到高强度,且焊接性能优良,因此,被作为结构材料广泛应用。但该合金在含有氯离子的环境中容易产生应力腐蚀裂纹(SCC),因而,使用时必须考虑使用环境。在此之前,关于Al—Zn—Mg合金的SCC有很多研究,对各种影响因素已很明了。也就是说,通过时效处理,在显示出最高强度即所谓的峰值时效状态,SCC敏感性极高,与此相反,在过时效状态, I. INTRODUCTION Al-Zn-Mg series alloys have been widely used as structural materials due to their high strength and excellent weldability by age hardening treatment. However, this alloy is susceptible to stress corrosion cracking (SCC) in environments containing chloride ions. Therefore, the environment must be taken into account when it is used. Prior to this, there have been many studies on the SCC of Al-Zn-Mg alloys, and it has become clear to various influencing factors. That is to say, by aging treatment, SCC is extremely sensitive in showing the highest intensity, the so-called peak aging state, whereas in the overage state,