Plastic deformation behavior and operative slip systems in Mg17Al12 single crystals

This is the first report on the experimental clarification of the operative deformation mode in the Mg17Al12, which is an important strengthening phase in conventional Mg alloys such as AZ91. The plastic deformation behavior of Mg17Al12 single crystals was examined, and it is found that {101}<111> slip is the predominant operative deformation mode. Moreover, it is clarified that its operation behavior exhibits a strong orientation dependence. Slip on {101} is clearly observed for a loading orientation close to <001>, but the slip traces become faint as the loading orientation moves away from <001>. Plastic deformation is only possible at and above 300 °C with a high yield stress greater than 300 MPa. The yield stress monotonically decreases as the temperature increases for all investigated loading orientations. The stress-strain curve exhibits a significant decrease in the flow stress just after yielding, indicating that the nucleation of dislocations is difficult owing to the complicated crystal structure. The yield stress varies with the loading orientation, but the difference becomes small above 400 °C, accompanied by the disappearance of slip traces. These experimental results imply that the mechanism controlling the deformation varies from dislocation glide to others such as dislocation-climb-controlled deformation at high temperatures.