A critical discussion on influence of loading frequency on fatigue crack propagation behavior for extruded Mg–Al–Zn alloys

Effect of loading frequency on the fatigue crack propagation (FCP) rate and mechanism of extruded Mg–Al–Zn alloys is discussed. The results demonstrate that the FCP rate of AZ80 and AZ61 alloys increases with reducing frequency. The frequency has a more significant influence on FCP rate of the AZ80 alloy than that of the AZ61 alloy. This scenario may be attributed to the thickness of the oxide films on the fracture surfaces, strain rate and the microstructure. A model based on the Langmuir and BET equation is established to predict the thickness of the oxidation films on the fracture surfaces.

► The FCP rate increased with a reduction in frequency for both AZ80 and AZ61 materials.
► The influential degree of frequency on FCP rate for the AZ80 alloy was more significant than the AZ61 alloy.
► A model for prediction of the thickness of the oxide film was established.
► The effect of frequency on strain rates is discussed.