Orientation Analysis within α Dendrite for Crept Mg–Al–Mn Alloy

Misorientation distribution within α-Mg dendrite grains was analyzed for the Mg–5.42 mass%Al–0.28 mass%Mn (AM50) alloy creep-ruptured at 448 K under a stress of 70 MPa using SEM/EBSD analysis. The AM50 alloy produced by die-casting consists of fine grains with approximately 10 µm and coarse grains with 30–40 µm. The misorientation angle within α-Mg dendrite grains is less than 2 degrees for the as die-cast specimen, while sub-boundaries can be clearly identified for the creep-ruptured specimen. The formation/evolution of dislocation substructure is emphasized for the coarse grains, compared with the fine grains. It was demonstrated that misorientation mapping is effective to elucidate the dislocation substructure developed during creep deformation for magnesium alloys with the hexagonal close-packed (HCP) crystal structure.