Study Of Balance Optimization Of Damping Capacity And Mechanical Properties For Mg-Cu-Mn Alloys

With the rapid development of modern industry and transportation, the vibration and noise pollution caused by which has become more and more serious. Not only military industry but also civil industry, has an urgent demands of lightweight, energy saving and control of vibration and noise. The application of low density and high specific strength metallic materials can effectively lighten the structural weight and achieve the goal of lightweight, energy saving. The high damping metallic materials become valuable in suppressing mechanical vibration and attenuating wave propagation for the control of noise and the stabilization of structures. Mg not only is the lightest commercial metallic material but also has the best damping capacity among various metallic materials. Therefore, it can meet the emergent demands of lightweight, energy saving and control of vibration and noise in modern industry.However, according to the dislocation damping mechanism of Mg, in order to obtain high damping, the dislocations must be relatively free to move. Material strengthening traditionally involves controlled creation of internal defects and boundaries to obstruct dislocation motions. Thus, to a certain extent, Mg strengthening and damping are conflicting goals. Therefore, the balance optimization between mechanical and damping capacity of Mg has become a critical problem in present study. It necessary to note that the damping capacity of sintered Mg-Cu-Mn alloy even exceeds that of pure Mg and the rapture strength of which attains 290MPa, but those performance of which are unstable and the prepare process is complicated. The conventional melted Mg-Cu-Mn alloy also exhibits excellent damping but poor strength.Based on the above problem, first, in this paper, the Y and Zn was added into CM31 (Mg-3%Cu-1%Mn) alloy to improve its damping capacity and mechanical properties initially and the effects of on of Mg-Cu-Mn alloys were studied. The results show that the addition of Y and Zn improves YTS values but decreases the UTS and elongation values of as-cast alloys. The improvement of YTS is attributed to the grain refinement strengthening of Y and Zn, and to the solid solution strengthening of Zn. The reduction of UTS and elongation are caused by the precipitation of a compound phase along the grain boundary. The damping capacity of as-cast alloy 2 increased significantly at the high strain amplitude stage and surpassed that of CM31, and even approached that of Mg. This phenomenon is believed to be related to the formation of long and parallel dislocation configurations, and to the interactions between these dislocations and plastic second-phase particles.Second, hot extrusion was performed to further enhance the mechanical properties of as-cast Mg-Cu-Mn alloys. The results show that extrusion significantly improved the mechanical properties but dramatically decreased the damping capacity of as-cast alloys. The significant improvement of mechanical properties can be ascribed to follows: a. refinement strengthening caused by dynamic recrystallization; b. work hardening caused by dislocation tangles; c. dispersion strengthening caused by the crushed and dispersive distributed compound phases. The dramatical decrement of damping capacity is attributed to the shortening of mean distance of dislocation between hard pining points, which is caused by dynamic recrystallization, work hardening and dispersive distribution of compound phases.Third, the repeat bending deformation was performed to improve the damping capacity of as-extruded Mg-Cu-Mn alloys by introducing straight dislocation configuration. The results show that the straight dislocation configuration is truly introduced by repeat bending deformation and the damping capacity of as-extruded is subsequently improved and the damping capacity increases with the increment of bending deformation strain.Finally, heat-treatment was applied to improve the damping capacity of as-extruded Mg-Cu-Mn alloys. The results show that the damping capacity of as-extruded Mg-Cu-Mn alloys increased in the initial stage of heat-treatment but decreased in the later stage. The recovery and recrystallization can account for this variation. Combining G-L theory and kinetic formula of recovery and recrystallization, the author analysis and discuss the variation of damping capacity of as-extruded Mg-Cu-Mn alloys during heat-treatment from a kinetic viewpoint. Besides, the fitting curves exhibit the theory calculation can well fit the experiment results.