UC Irvine

The influence of a sulphuric acid anodising process on the fatigue behaviour of a 7075-T73 aluminium alloy has been investigated. Single edge circular notch (SECN) fatigue specimens were used enabling localisation of fatigue damage and assisting detection of fatigue crack initiation and growth. Elastic finite element modelling was performed to quantify the stress concentration factor and von Mises equivalent stress distribution of the notched region. A surface replication method in combination with scanning electron microscopy (SEM) was adopted for in-situ monitoring of the fatigue damage. It was shown that the presence of pitting, developed during the anodic coating pre-treatment, adversely affected the fatigue performance. SEM surface examinations after fatigue cycling indicated the presence of micro-cracks, developed at pit sites. Interestingly these sites were not found to be the source of crack initiation when examined post SEM fractographic analysis. Thus, the stress concentration effect of the corrosion pits was found to be predominant leading to a reduction in fatigue life of approximately 60% for the anodic coated versus untreated specimens.