Anodic dissolution of a crack tip at AA2024-T351 in 3.5wt% NaCl solution

The anodic dissolution process of a crack tip at 2024-T351 aluminium alloy (AA2024-T351) was determined by means of scanning Kelvin probe (SKP). Wedge-open loading (WOL) specimens were immersed in a 3.5wt% NaCl solution. After various durations of immersion, the Volta potential distributions around the crack were measured by SKP and the surface morphologies were observed by scanning electron microscopy (SEM). It is found that there is a nonuniform distribution of Volta potential around the crack. Before immersion, the Volta potential at crack tip is more negative than that in other regions. However, after immersion, a converse result occurs with the most positive Volta potential measured at the crack tip. SEM observations demonstrate that the noticeable positive shift of Volta potential results from the formation of corrosion products which deposit around the crack tip. Energy-dispersive spectrometry (EDS) analysis shows that the corrosion products are mainly Al oxide and Cu-rich particles. These observations implicate that the applied stress contributes to the preferential anodic dissolution of the crack tip and the redistribution of Cu.