For the two phases of most cast magnesium alloys, cracks mainly occurred in the second phase, in which there were obvious black and white optical characterizations in scanning electron microscope (SEM) images. Quantitative evaluation of the effects of main phase deformation on cracking behavior was carried out based on SEM in-situ observation and the digital image correlation method (DICM). Crack initiation and previous propagation behaviors mainly depended on the plastic deformation of the αMg phase. There were sufficient plastic deformations, or displacement, of the main phase prior to the cracking in the boundary for most cast magnesium alloys. The effect of the applied direction on the micro deformation of all αMg grain boundaries was different. The rotational and inhomogeneous deformation fields in the local position were identified based on SEM in-situ observation and DICM.
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