Microstructure evolution and creep behavior of high-pressure die-cast Mg-9Al-1Zn-1Sr alloy

The creep behavior of high-pressure die-cast Mg-9Al-1Zn-1Sr alloy was investigated in detail under temperatures ranging from 130 to 170 degrees C and stresses of 30-80 MPa. The studied alloy exhibited a high stress exponent of 8.4 and low activation energy of 102 kJ/ml. The obtained high stress exponent in studied alloy indicated the breakdown of the conventional power law. For rationalization, a threshold stress was introduced in the analysis, and then the high stress exponent was modified to be 5.2. Simultaneously, taking into account the significant influence of tested temperature on the minimum creep rate, a normalized stress exponent of 5 was achieved via the normalization method. Both methods suggested that the creep deformation of the studied alloy was mainly controlled by the dislocation climb. Moreover, transmission electron microscopy observations revealed that the origin of the threshold stress could be associated with the Orowan strengthening of gamma-Mg17Al12 platelets that dynamically precipitated in Mg matrix during creep. Microstructure analysis results clarified that dislocation climb is the dominant creep mechanism of AZJ911 alloy, while the reticular eutectic Mg17Al12 phase disintegration, dynamical precipitation of y-Mg17Al12, and twinning also influence the creep deformation of AJZ911 alloy.