Abstract
Impression creep behavior of as-cast Mg-xSi alloys (x = 0.5, 0.8, 1.2 wt.%) was studied under shear modulus-normalized stress values ranging from 0.009 to 0.016 at temperatures between 398 and 491 K. The results showed that creep properties of these alloys are improved with increasing Si content under all the applied loads and temperatures, and Mg-1.2Si alloy has minimum creep rate and thus maximum creep resistance. It was attributed to the higher volume fraction of Mg₂Si, which can reduce grain boundary sliding during the creep test. Stress exponent of all the alloys is between 4.06 and 7.09 in the temperature range of 398 to 447 K. It is changed from the range of 3.96–4.89 to 8.62–12.62 under high-stress values at temperatures between 476 and 491 K. Creep activation energy under shear modulus-normalized stress of 0.010 and 0.012 is close to that of dislocation pipe diffusion of Mg. Under higher stress values at the high temperatures the creep activation energy is equal to that of Mg lattice diffusion. According to the obtained stress exponent values and creep activation energies, pipe-diffusion climb controlled dislocation creep is the dominant mechanism at temperatures between 398 and 447 K, which changes to power-law breakdown (PLB) under high-stress values at 476 and 491 K.

Key words
Mg-Si alloys, impression creep, creep mechanism, microstructure

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