Localized Dislocation Interactions within Slip Bands and Facet-Like Crack Initiation in Magnesium Alloys

Localization of the plastic strain at slip bands (SBs) is an important feature of cyclic straining and frequently plays a key role in crack initiation connected to the fatigue resistance of metallic materials. However, the mechanism of SB-induced cracking in hexagonal close-packed (hcp) materials have not been revealed so far. Here we studied underlying elastic cyclic deformation and associated dislocation activities within the SBs in a rare earth-containing magnesium (RE-Mg) alloy. The results show that basal slip is the solo deformation mode at grain scale, but gliding of dislocation is still visible near grain boundaries to accommodate localized in the nucleation and growth of damaged zone and move towards the matrix-SB interface, at which the internal cracks initiate and coalesce together forming facet morphology on fracture surface. The contribution of dislocation motion to the formation of damaged zone is believed to retard the development of basal SBs, correspondingly enhancing the fatigue resistance of RE-mg alloys.