By increasing the content of RE, th

By increasing the content of RE, the AE44 alloy was developed targeting at applications at higher temperatures. This alloy has been used tomake engine cradle of GM Corvette [55]. Rzychon et al. [50]observed neither change in the fraction of Al11RE3 nor the formation of Mg17Al12 in the die-cast AE44 alloy after annealing at 175 °C for 3000 h. Thus, even at 200 °C, the alloy still showed a low secondary creep rate _ ε as 5.72 × 10−10 s−1 under 60 MPa, and only 0.13% of creep strain after 120 h. Furthermore, replacement of Ce-rich mischmetal with either La [47] and/or Nd [56] was found to further improve the creep properties of the die-cast AE alloys. Higher thermal stability of Al11La3 and Al11Nd3 than that of Al11RE3 (majority is Al11Ce3) was considered to be responsible for the improved creep resistance. Furthermore, the combined effect of REs and Ca (or Sr) on creep properties were also investigated [57–61]. Dargusch et al. [57]reportedthat1wt % addition of Sr to die-cast AE42 alloy led to the improvement of creep strength and yield strength with decrease in ductility at high tempera tures. Companion paper by Dargusch et al. [58] observed an additional thermally stable phase, Mg8Al4Sr, which reinforced the grain boundaries and also reduced the supersaturation of Al solute in theMgmatrix. In addition, combined additions of Ca and Sr to AE41 alloy [59, 60]exhibited even better compressive creep resistance due to the further reduction in volume fraction of the Mg17Al12 phase, which promoted the hindering effect of Al-RE, Al-Ca and Al-Sr intermetallic compounds to dislocation climb and grain boundary sliding. But, the reverse effect of addition of Ca on creep resistance of AE44 alloy was observed by a most recent work [61]. The authors suggested that the shrink of (Mg, Al)2Ca phase lattice and denuded zones near grain boundaries contributed to the deteriorated creep resistance of the alloy.More recently, Mn addition was found to be effective in increasing the creep resistance of the AE alloys through strengthening theMgmatrix. Generally, it's considered that small Mn addition has negligible influence on mechanical properties, but it may improve the corrosion resistance. Increasing the Mn addition to 0.3–0.5 wt% was reported to significantly impede creep deformation of a die-cast AE43 alloy at 150°C and 175 °C, as shown in Fig. 3 [62]. As increasing the Mn addition level from 0 to 0.3 wt%, the creep strain was significantly reduced at the test conditions. But further additions to 0.5 wt% showed very marginal effect. The minimum creep rate of the alloy was decreased by at least three orders of magnitude at both 150 °C/90 MPa and 175 °C/75 MPa when 0.5 wt% Mn was added. Zhu and co-workers [62]suggested that the dynamic precipitation of nano-scaled Al-Mn particles contributed to the noticeable strengthening effect,which overwhelmed the softening effect from Mg17Al12 precipitates. This result indicates an alternative approach to develop newcreep-resistantMg-Al alloys by of fering the possibility of strengtheningMg matrix by precipitation hardening, which previously is not an available option to HPDCMg-Al alloys due to their weak ageing responses.