In this paper, the tensile properties and stress corrosion resistance of two Al-Zn-Mg-Cu alloys were tested by tensile test and slow stress rate tensile test. The microstructures of the precipitation were observed by transmission electron microscopy, and the proportion and size of the precipitates were measured by ImageJ software. This work revealed that Sc and Zr microalloying will instead reduce the SCC resistance of Al-Zn-Mg-Cu alloys and increase the strength reduction of Al-Zn-Mg-Cu alloys, under certain heat treatment. The area fraction of GBP can be effectively adjusted by the combine of changing quenching agents, step-aging and minor additive of Sc and Zr. With the increase of area fraction of precipitates at the grain boundary, the slow stress corrosion susceptibility decreased first and then increased. This is because when the area fraction exceeds 22.3%, the low stress cracking mechanism will change from hydrogen embrittlement mechanism to anodic dissolution mechanism. The combination of heat treatment and Sc, Zr microalloying enable the area fraction reach approximately 22.3 %, which will make the Al-Zn-Mg-Cu alloys have high strength and low slow stress corrosion susceptibility.

本文通过拉伸试验和慢应力速率拉伸试验对两种Al-Zn-Mg-Cu合金的拉伸性能和耐应力腐蚀性能进行了测试。通过透射电子显微镜观察沉淀的微观结构，并通过ImageJ软件测量沉淀的比例和大小。这项工作表明，在一定的热处理条件下，Sc和Zr微合金化反而会降低Al-Zn-Mg-Cu合金的耐SCC性，并增加Al-Zn-Mg-Cu合金的强度降低。GBP的面积分数可以通过改变淬火剂，逐步老化和添加Sc和Zr的微量添加剂来有效调节。随着晶界析出物面积分数的增加，慢应力腐蚀敏感性先降低后升高。这是因为当面积分数超过22.3％时，低应力开裂机理将从氢脆机理转变为阳极溶解机理。热处理和Sc，Zr微合金化的结合使面积分数达到约22.3％，这将使Al-Zn-Mg-Cu合金具有高强度和低慢应力腐蚀敏感性。