Nanoscale heterogeneities dictate corrosion pathways in a high-strength aluminum alloy

Abstract

Micro-segregation and resulting nanoscale microstructural heterogeneities are unavoidable in wrought 7xxx aluminum alloys produced using current casting and thermomechanical processes. This study demonstrates that these nanoscale heterogeneities significantly impact pit growth in an extruded, age-hardened aluminum alloy 7075-T651. The alloy exhibits a complex microstructure with heterogeneously distributed E-Al18Mg3Cr2 dispersoids, which promote the precipitation of coarse ƞ-Mg(ZnAlCu)2 nanoparticles resulting in the formation of solute-depleted regions both within the grain interior and along the grain boundaries in dispersoid-rich areas. These alterations affect resistance to pit growth at the nanoscale, governing the transition of micro-galvanic sites into large pits with potential for crack initiation. This work underscores the necessity for modifying alloy composition and casting processes to develop superior aluminum alloys for critical applications.