Creep Behavior in Pure Magnesium at Room Temperature

Abstract

Grain refinement is an effective technique to increase the ductility of magnesium (Mg) at room temperature: it engenders higher minimum creep rate and large rupture strain of >170% in the sample with grain size (d) of 1.2 µm. Its creep brings about dislocation absorption and nucleation at grain boundaries, enhancing grain boundary sliding with low apparent activation energy of 65 kJ/mol, which is only 70% of that of grain boundary diffusion. Therefore, grain boundary deformation enhances ductility of Mg at the low homologous temperature of about 0.3. However, a sample with d = 6.1 µm shows low fracture strain that is only one-third of that in the fine-grained sample. Creep resistance increases with increasing grain size, meaning that grain refinement leads to good ductility but low creep resistance at room temperature.

Fig. 3 Double logarithmic plot of the applied stress and minimum creep rate of all samples at 297 K. The stress exponent decreases from ca. 10 to ca. 4 with decreasing grain size.