Testing the Environment-Induced Cracking (EIC) Sensitivity of High-Strength 7xxx Series Al-Zn-Mg-Cu Aluminum Alloys
N. J. Henry Holroyd, Ryan T. Euesden, Matthew E. Curd, Juhi Srivastava, Timothy L. Burnett, John J. Lewandowski, Geoffrey M. ScamansABSTRACT
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.