Abstract
The compressive creep deformation mechanism of as-cast Mg-8.0Al-1.0Nd-1.0Gd alloy at 180 °C under constant stress of 60 MPa and 90 MPa was novelly analyzed through the distribution characteristics of in-grain misorientation axes (IGMA). Activated slip modes in the creep process was accurately identified and the structure of dislocations is revealed by the weak beam dark-field (WBDF) technology. The intensities of IGMA are concentrated on 011̅0 and 1̅21̅0 axis demonstrates that 0001112̅0(basal slip) and 112̅2112̅3̅ (pyramidal slip) dominate the deformation mechanism. Tensile twins 101̅21̅011 were extensively activated in compression-creep process and the 101̅21̅011 variants with a twinning trace angle close to 90 deg are 1̅012101̅1 and 101̅21̅011 with para-position. The creep mechanism of the alloy crept at 180°C/60 MPa is dominated by grain boundary sliding triggered by the precipitation of β-Mg17Al12, and pipe diffusion-controlled boundary sliding is the dominant creep mechanism of the alloy under 180 °C/90 MPa. In addition, the results reveal that tensile twins induced by dislocation slip contribute to coordinate the grain c-axis deformation, release the stress concentration caused by dislocation accumulation at the grain boundary.
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