2019 Volume 60 Issue 4 Pages 503-512
The high-temperature creep mechanism in an extruded Mg alloy comprising an α-Mg matrix and a long-period stacking ordered (LPSO) phase was investigated by theoretical analyses, indentation creep tests, and finite-element (FE) simulations. The creep behaviors of the Mg alloy with the LPSO phase (a dual-ductile-phase alloy), as a potential next-generation lightweight material, were robustly predicted using the characteristic creep parameters, volume fractions, and creep strengths of the two constituent phases. The results of FE analysis showed that highly effective bridging phenomenon may occur at certain geometrical arrangements of the reinforcing phases, where a high reinforcement efficiency close to 1 could be achieved. The experimental results suggested that the creep strength of the dual-ductile-phase alloy closely followed the rule of mixtures and the isostrain rate conditions. The stress exponent n for creep of the dual-ductile-phase alloy was expressed by the harmonic mean weighted by the effective volume fractions of the constituent phases, which strongly depended on the deformation rate. In addition, n consistently fell between the corresponding values for the two constituent phases in the power-law creep region. A similar trend was observed for the deformation rate dependence of the creep activation energy Q, which was expressed by the weighted arithmetic mean value. Thus, the newly derived equations of n and Q were shown to quantitatively capture the mechanical contribution of the reinforcing phase to the creep strength of the overall dual-ductile-phase alloy.
This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 82 (2018) 108–116. In order to more accurately describe the characteristic phenomenon in the dual-phase structure model, a part of Fig. 13 was modified. The Refs. 26), 35), and 39) were also added.