On the corrosion, electrochemistry and microstructure of Al-Cu-Li alloy AA2050 as a function of ageing

The corrosion and microstructure of the Al-Cu-Li alloy AA2050 were investigated as a function of artificial ageing. The work herein seeks to provide a consolidated overview of the corrosion of AA2050, in particular the influence of T1 (Al2CuLi) precipitates on the observed behaviour. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were performed to characterise the microstructural evolution of AA2050 during ageing. Accelerated immersion testing revealed that ageing was accompanied by the evolution of three unique stages of resultant corrosion morphologies - which were not correlated with the fine T1 precipitate evolution. Electrochemical testing also revealed that AA2050 showed no discernible metastable pitting from potentiostatic testing. This phenomenon suggests that T1 precipitates may remain too fine to induce localised corrosion in the matrix, and that T1 precipitates in AA2050 are unlikely the controlling factor leading to the evolution of corrosion morphologies observed in AA2050. An elaboration of factors influencing the intergranular corrosion evolution and the role of grain boundary chemistry is also presented.