Highly improved creep resistance of hot-extruded Mg-0.9Mn-0.5Ce alloy by conventional forging

Abstract

The insufficient creep resistance seriously restricts the practical application of Mg alloys, which needs to be preferentially resolved. In this work, the conventional forging was adopted to highly improve the creep resistance of an extruded Mg-0.9Mn-0.5Ce (wt%) alloy, and the corresponding mechanism on the improvement of creep resistance was carefully analyzed. The forging was conducted at 623 K, 673 K and 723 K with the strain rate of 1.0 × 10−3 s−1, 1.0 × 10−2 s−1 and 1.0 × 10−1 s−1 to a true strain of ε = 0.4 along the extrusion direction (ED), and the tensile creep tests were conducted at 423 K along the ED. It was shown that a mixed microstructure with both coarse and fine grains was obtained, and the basal poles tilted from the transverse direction (TD) to the ED after forging. Microstructure characterization revealed that forging barely showed influence on the active dislocation slip systems even the texture obviously changed. They were basal slip and pyramidal <c + a > slip in both as-extruded and as-forged samples, and the highly improved creep resistance was mainly derived from two aspects. On the one hand, the strong dislocation entanglements and obvious dislocations cells introduced by forging and the tough twin boundaries consolidated by precipitates effectively impeded the continuous movements of dislocation and highlighted the creep resistance. On the other hand, the dynamically precipitated Mg12Ce precipitates on dislocation lines and the obvious segregation of Ce elements at grain boundaries decreased the mobility of dislocations and grain boundaries, which also contributed to the improvement of creep resistance.