This paper examines fatigue crack paths in coarse-grained magnesium alloys. Visualization of the microstructure by etching and continuous crack monitoring with a microscope provide evidence of the crack-grain interaction at different fatigue crack growth regimes. Near-threshold fatigue crack growth promotes the development of rough surfaces by the activation of single slip mechanisms and crack deflection. The R-ratio effect on near-threshold results is discussed in the light of the partial crack-closure model. The role of grain boundaries and grain-to-grain crack deflections on fatigue crack growth rates is discussed.
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