Understanding damage accumulation upon AA7075-T651 used in airframes from a microstructural point of view

Corrosion and corrosion fatigue of aircraft components remains a critical issue for the service readiness of aging aircraft. The favorable mechanical properties of AA7075-T651 arise as a result of a heterogeneous microstructure that compromises the corrosion resistance of the alloy, ultimately resulting in localized corrosion. Understanding the factors that govern extent, rate and morphology of damage accumulation is essential in developing models to predict corrosion and corrosion fatigue resistance. The electrochemical properties of AA7075-T651 have recently been investigated on a phase-by-phase basis. As a result, quantitative microstructural characterization of AA7075-T651 takes on a critical importance in the understanding of corrosion damage accumulation, based on localized chemistry (and hence electrochemistry) of the alloy. This work presents results of a study using analytical microscopy (SEM, TEM, STEM, EDXS, EBKP) to reveal what phases, intermetallics and particles constitute AA7075-T651; allowing characterization and discrimination on a chemical basis. Knowledge of the type of localized chemistry that exists may be coupled with electrochemical results and used to typify damage accumulation processes on the nano and microscale.