Testing the Environment-Induced Cracking (EIC) Sensitivity of High-Strength 7xxx Series Al-Zn-Mg-Cu Aluminum Alloys

ABSTRACT The information provided by today’s standardized test methods used to assess the environment-induced cracking (EIC) sensitivity of high-strength 7xxx series Al-Zn-Mg-Cu alloys fails to provide the quantitative data needed for engineering design and service-lifetime prediction. Current EIC test output is qualitative in nature and is based on historical comparisons. The environmental test conditions and initial alloy surface conditions used are not related/relevant to those anticipated during commercial use. The reported in-service EIC issues for the current latest generation of Al-Zn-Mg-Cu alloys repeat the 1960’s experience of “unexpected” major service failure issues for AA7079-T651 components. There is a critical need for EIC test methods that consistently differentiate EIC susceptibilities for relatively resistant alloy tempers in a reasonable time frame that are directly relatable to service performance. A novel test method is proposed to quantitatively assess an alloy’s inherent EIC sensitivity.