Microstructure Evolution Of LPSO Phase And The Corresponding Damping Capacities And Mechanical Properties In Mg-Zn-Y Alloys

With the rapid development of modern industry and transportation, the vibration and noise pollution caused by which has become more and more serious. Magnesium(Mg) alloys with low density and high damping properties may potentially help meet increasing demands for vibration and noise control in modern industries. However, the strength and damping seem to be a contradiction in Magnesium, so that the practical high damping- high strength Magnesium alloys were hardly obtained in the abstract. Previous research shows that the LPSO phase clearly exerts positive effects in balancing the damping capacities and mechanical properties of Mg alloys. Thereby, it may introduce a new method to produce magnesium alloys with high damp ing capacity and high strength.Therefore, in the current study, Mg-Zn-Y was used to obtain dual phase alloy and LPSO phase alloy by controlling Y/Zn atom ratio. It can study the relationship between LPSO phase with the damping capacities and mechanical property in Mg-Zn- Y alloys. Study showns that the existence of LPSO structure improves the hardness and strength, but decreases the plasticity. Appropriate LPSO phase content is is advantageous to the damping of alloys, but the alloys with too much LPSO phase shows a low damping performance. The alloys with about 48% or 64% LPSO phase shows the best damping in a high or low strain region. The Mg86Zn6Y8(at.%) alloy casted by directional solidification is almost composed of LPSO phase, shows a lower damping capacity than that of pure magnesium. It proves that the existence of LPSO structure can improves both the damping and strength, but it is not because of the separate LPSO phase.In this part, the effects of heat treatment on the morphology of long-period stacking ordered(LPSO) phase, the corresponding damping capacities and mechanical properties of Mg95.34Zn2Y2.66(at.%) dual phase alloys are investigated. The block, lamellar, and rod-shaped LPSO phases can be obtained through different heat treatment processes. Th LPSO phase in as-cast Mg–Y–Zn alloys is 18 R stacking sequence, and it transform into 14 H stacking sequence after heat treatment. The rod-shaped LPSO phase is respectively obtained in the matrix after annealing at 540 °C for 4 h. The lattice distortion energy, heat treatment temperature and time are the main factors in the transformation of rod-shaped LPSO phase. Lamellar phases are respectively obtained in the matrix after annealing at 400 °C for 10 h. The transformation of lamellar LPSO phase is affected by solution atoms in matrix. Meanwhile, it reveals that the block and lamellar LPSO phases are more conducive to the strength of the alloy, the appearance of the rod-shaped LPSO phase increase damping capacities notably while maintain a high yield strength.Therefore, microstructure evolution of long-period stacking ordered phase in the process of deformation and the corresponding damping capacities and mechanical properties are investigated. It shows that extrusion deformation improves the strength, but severe decreases the damping capacity. After annealing at 540 °C for 4 h, there are a large number of rod-shaped LPSO phases in the Mg93Zn3Y4(at.%) and Mg95.34Zn2Y2.66(at.%), and both rod-shaped LPSO phases and lamellar LPSO phase in Mg97.67Zn1Y1.33(at.%) alloys. After rolling, the Mg-Zn-Y alloys with rod-shaped LPSO phases show better damping and strength, especially in the high deformation stage. The appearance of the rod-shaped LPSO phase is in favour of mechanical and damping in rolled magnesium al oy.Then, this paper studied the effect of Mn on the damping mechanism in Mg and Mg-Zn- Y alloys. This study shows that Mg-Mn alloys exhibit high strain-dependent damping values that are attributed to the dislocation that connects to the dispersed α-Mn. However, excessive α-Mn creates an obstacle dislocation effect, which leads to the decrease in damping capacities because of the tangled dislocations. In Mg-Zn- Y-Mn alloys, Mn comes with fine grains and dispersion strengthening, it can improve strength while maintain damping capacities. During heat treatment, rod-shaped LPSO phases can be divided into small block phase that due to Mn particles, which significant increase plastic of alloys. Combination of heat treatment and Mn element, it can improve the alloy plasticity, strength and damping at the same time, show the win-win situation of damping capacities and mechanical properties.Finally, a new high damping Mg-Zn-Y alloys was designed based on the above research and two kinds of damping and mechanical equilibrium optimal regulation model, the rod model and framework model is put forward. Study shows the rod model is more advantageous to the alloy’s mechanical properties, and frame type model is easier to obtain high damping. At last, it present an improvement measures for obtaining the high damping-high strength magnesium al oy.