Kinetics of corrosion fatigue crack propagation behaviour of Al—Zn—Mg alloy using centre notched specimens

Abstract

Kinetics of corrosion fatigue (CF) crack propagation in an Al—Zn—Mg alloy have been studied as a function of applied potential and temperature in a 3·5 wt-% NaCl solution using centre notched specimens. This study especially concerned the stress corrosion (SC) crack propagation associated with CF crack propagation. CF crack propagation rate increased with increasing applied potential. CF and SC cracks both propagated in a brittle intergranular manner. CF crack propagation was thought to be an enhanced phenomenon of SC crack propagation. By modifying the simple superposition model, synergistic interaction between pure fatigue and environmental effects was taken into consideration in evaluating the CF crack propagation rate. in terms of the SC crack propagation rate. The present experimental data also led to the conclusion that the CF crack propagation rate is simply proportional to (∆Κ)^2·0–2·2, and Boltzmann's factor, where ∆Κ is the stress intensity range. The apparent activation energy for CF crack propagation was found to be ∼ 52 kJ mol⁻¹ at the corrosion potential. The association of CF crack propagation with SC crack propagation supported the conclusion that CF crack growth is controlled by hydrogen embrittlement.