1. Introduction
It is known that the presence of corrosion pits is the main reason
for degradation in fatigue performance of high strength precipitationhardened
aluminium alloys such as 7075-T6, commonly used in
aerospace industry. Such materials are usually exposed to the natural
environment during the operation. Even the low level of pitting
corrosion resulting from salt-water spray and/or salt fog on aluminium
structures is the precursor to corrosion fatigue degradation [1,2].
There are a number of studies on mechanism of pitting formation and
their effects on fatigue strength [1–6]. A study [6] carried out on 7075-
T6 alloy showed that, depending on the severity of pitting, the
reduction in fatigue strength could reach approximately 60%, based on
a fatigue life of 107 cycles. Surface treatments are widely used to
improve corrosion resistance of machine components. Anodic oxidation,
which is an electrochemical process to form stable oxide films on
the surface of metals, is one of the most unique and widely used
methods to improve surface performance such as corrosion and wear
resistance. The oxide film is composed of a compact inner layer and a
porous outer layer [7–9]. By selecting appropriate anodizing conditions,
the porous films can be tailored to suit particular applications.
However, the anodic coatings have a detrimental effect on the fatigue
performance. Since the oxide coating is brittle compared to the
aluminium substrate, it easily cracks under cyclic stress. Another
important parameter is the internal tensile stress. Rateick et al. [10]