A fracture model of corrosion fatigue crack propagation of aluminum alloys based on the material elements fracture ahead of a crack tip

In this study, attempts were made to extend the concept of material elements fracture ahead of a crack tip during fatigue crack propagation (FCP) to corrosion fatigue crack propagation (CFCP) of aluminum alloys in a corrosive environment. Considering the effect of corrosion damage on the material elements, anodic dissolution and hydrogen embrittlement, a corrosion-blunting-fracture model for CFCP was developed. The expression for the CFCP rate, (da/dN)cf = Bcf(ΔK − ΔKthcf)2, which reveals the correlation between the CFCP rate and stress intensity factor range, the CFCP threshold, loading frequency, anodic dissolution rate and hydrogen embrittlement of the material elements, is thus derived. The test results and analysis of the CFCP rates of LY12CZ and LC4CS aluminum alloys show that the expression for the CFCP rate gives a good fit to the test results of the CFCP rates in a 3.5% NaCl environment at loading frequency 10 Hz and stress ratios from 0.1 to 0.7. The analysis results of other aluminum alloys 7075-T7651 and 7049-T73 obtained by the CFCP rate expression are in good agreement with the test results of the CFCP rates in a 3.5% NaCl environment at loading frequencies from 0.1 to 10  Hz and a constant stress ratio.