Effect of temperature and β-phase morphology on the high-stress creep of magnesium-aluminum-rare earth alloys

• Compare creep resistance of AE44-2 and AE44-4 across temperatures. • AE44-2 has superior creep resistance at elevated temperature. • Hall-Petch-like analysis links finer β-phase spacing to higher resistance. • Crystal orientation effect of α-Mg matrix on creep was identified. • Creep mechanism shifts from dislocation glide to GBS with temperature. This study investigates the high-stress creep behavior of AE44-2 and AE44-4 magnesium - aluminum-rare earth (RE) alloys at multiple length scales using a combination of in-situ tensile and nanoindentation creep tests conducted at 25 °C, 100 °C, and 180 °C with the objective of understanding how β-phase influences creep resistance. Tensile creep results reveal that AE44-2 exhibits superior creep resistance compared to AE44–4 at 180 °C. SEM and EBSD analyses show that AE44-2 contains a higher β-phase area fraction and a more continuous lamellar Al 11 RE 3 network, whereas AE44-4 displays a mixed lamellar/particle β-phase morphology with lower connectivity. Indentation creep tests further reveal a strong negative correlation between β-phase spacing and creep displacement. Activation energy and activation volume parameters extracted from nanoindentation data indicate a gradual shift in creep mechanisms, where dislocation glide remains active at lower temperatures, while grain boundary sliding increasingly contributes at elevated temperatures. Importantly, a new orientation-based analysis highlights that although the overall creep displacement appears orientation independent, both the β-phase sensitivity coefficient ( k ) and the baseline creep displacement (δ 0 ) show a pronounced non-monotonic dependence on c-axis misorientation, peaking near orientations favorable to basal slip. These results provide direct mechanistic evidence that the apparent suppression of orientation effects in AE44 alloys arises from the blocking action of the β-phase network. Overall, this work demonstrates the critical interplay between microstructural connectivity and crystallographic orientation in controlling creep deformation, and highlights the superior high-temperature performance of AE44-2 with its cost-effective Ce-La composition.