Simultaneous improvement of strength and damping capacity of Mg-Mn alloy by tailoring bimodal grain structure

A high damping capacity and a high strength is paradox in magnesium alloys needed to be addressed immediately. In this work, adding Mn into Mg matrix, and combined with low extruded temperature, alloys with bimodal grain structure that is made up of fine recrystallized grains and coarse unrecrystallized grains were obtained. The fine recrystallized grains are conducive to the activation of grain boundary slip, leading to alloy exhibits good plasticity. A large number of parallel dislocations exist in unrecrystallized grains, due to the dislocation recovery and dynamic recrystallization rate are evidently suppressed at low extruded temperature and the Mn precipitates impede the movement of dislocations, which cause a high work hardening rate in bimodal grain structure. This phenomenon not only brings about a high yield strength, but also improves damping capacity of Mg-Mn alloys at room temperature. Because the unrecrystallized grains initial to recrystallize at high temperature, the P2 internal friction peak rises and moves toward the low temperature. When the extruded temperature is 220 °C, the comprehensive properties of the Mg-1Mn alloy outperform the high-damping Mg-0.6Zr alloy, and the yield strength, plasticity and damping capacity at ε = 1 × 10−3 are 169 MPa, 32.5% and 0.042, respectively. Tailoring bimodal grain structure is an effective strategy to ensure strength, plasticity and damping capacity of the Mg alloy at the same time.