Comparison of environmentally assisted cracking in high zinc content 7xxx Al alloys imaged by of time-lapse synchrotron computed tomography (CT)

Owing to their high strength capability, 7000 series Aluminium (Al) Zinc (Zn) magnesium (Mg) Copper (Cu) alloys have been the subject of considerable interest and development since their first widespread application in commercial aircraft in the 1950s. Issues with Stress Corrosion Cracking (SCC) were reported early on in their history and considerable development work has since been undertaken to combat this limitation, through the optimisation of compositions and heat treatments, which culminated in the registration of higher Cu containing alloys such as AA7050 and AA7010 in the early 1970s. When deployed in an overaged condition (e.g. T7651, T7451) these materials have good stress corrosion performance and have subsequently exhibited few problems in service.