Study On Mechanical Properties And Damping Capacities Of Mg-Zn-Nd-Cd-Zr Alloy

Magnesium alloys have a great application potential in the aerospace, automotive, electronics, and other industrial fields with the characteristics of low density, high specific strength, excellent anti-vibration capacities, good electromagnetism shield properties, and easy recovery utilization etc, which is known as the most promising metal structure material in the21st century. Pure magnesium possesses extraordinary high damping capacity, but the low tensile strength. Some experimental results have shown that addition of elements, heat treatment and plastic deformation could efficiently improve the strength, and effect on the damping capacity of magnesium alloys. There exist some different views on the damping mechanism of magnesium alloys, especially to the high strength magnesium alloys such as Mg-Zn-Nd-Cd-Zr alloys. The microstructures, the phase constitution of the Mg-Zn-Nd-Cd-Zr magnesium alloy were analyzed by optical microscopy(OM), X-ray diffraction (XRD), scanning electron microscopy(SEM), transmission electron microscopy (TEM). The mechanical properties were tested by tensile test and hardness test. The strain dependent and temperature dependent low frequency damping capacities of these alloys were studied by DMA. The strengthening mechanism and damping behavior of these Mg alloys were revealed comprehensively and systematically.The flow stress behavior of ZK60-2NdlCd alloy was studied using hot simulator. The constitutive equation of flow stress can be expressed as ε=1.579x1011[sinh(0.0123ρ)]5098exp[-160.1×103/(RT)]. The stress-strain curves of ZK60-2Nd1Cd alloys at the strain rate within0.001～1and temperature within300℃-420℃showed a typical dynamic recrystallization characteristic. The hot deformation Was controlled by activation energy.The effect of Cd, Nd, Zn on the microstructures and mechanical properties of ZK60magnesium alloy were studied, and the strengthening mechanisms of Mg-Zn-Nd-Cd-Zr alloy were analysed. Excellent strengthen and plasticity are obtained by solution strengthening, fine grain strengthening, and the second phase strengthening. The tensil yield strengthen is increased and the ultimate tensile strength is decreased of ZK60-2Nd1Cd alloy as-cast owing to the continuous net T phases along the grain boundaries. The ultimate tensile strength and tensile yield strength of ZK60-2Nd1Cd as-extrusion are315MPa and290MPa, and the elongation is16%. The ultimate tensile strength and yield strength of ZK60-2Nd1Cd as-extrusion are315MPa and290MPa, and the elongation is10%, which is owing to additional Nd. The lower the Zn content is, the more decrease of the strength. There are W phases not T phases in the alloy. The ultimate tensile strength and tensile yield strength of ZK60-2.5Nd1Cd alloy are385MPa and320MPa, and the elongation is16%through aging heat-treatment.The effect of Cd, Nd, Zn on the damping capacities of Mg-Zn-Nd-Cd-Zr alloy at room temperature were studied, and the damping mechanisms of Mg-Zn-Nd-Cd-Zr alloy were analysed. At the room temperature, addition atoms of Cd reduced the the mean length of dislocation segments between minor pinns, then the strain-independent damping decreased. T phases or/and W phases exist in the alloy with addition atoms of Nd, and decrease the Zn content, which improve the strain-independent damping.The strain-dependent damping are increased by the increasing of movable dislocation density caused by the decreasing Zn content on certain strain, and the strain-dependent damping of Mg-Zn-Nd-Cd-Zr alloy as-extrusion and as-solution are lower than that of alloy as-cast on the higher strain.The damping capacities of Mg-Zn-Nd-Cd-Zr alloy at high temperature were studied. There are damping peaks of P1and P2in Mg-Zn-Zr alloy, P1induced by the interaction between dislocations and the point defects in the crystal lattice of Mg, and P2caused by the grain boundaries sliding at high temperature. The damping peaks of P1of Mg-Zn-Nd-Cd-Zr alloy are less than that of Mg-Zn-Zr alloy, and the temperature of the P1exist in the higher temperature region with the increase of Zn content. P1peak of the alloys with lower Zn content will be inhibited by solution heat-treatment. There no P2peak in the alloys as-cast, as-sulution, as-extrusion with higher Nd content, and the P1peak will be inhibited by extrusion. Exceeding a certain critical temperature, the high damping values are increasing with the temperature. The higher the Zn content of the alloy is, the higher the temperature damping value is.A new model of a dislocation line pinned by major pins, intermediate strength pins and minor pins was put forward, which could explain the damping flat or the damping maximum values on damping-strain spectrum of the experimental alloys. The intermediate strength pins maybe dislocation, the uneven distribution of the very small amount of point defects, or compounds particle with low melting point.Correlation of mechanical properties and damping properties of Mg-Zn-Nd-Cd-Zr alloy was analysed. The connection models among comprehensive performance index a, the ultimate tensile strength (or tensile yield strength) and damping capacities of alloys as-cast and as-extrusion were builded, respectively.A mathematics model between comprehensive performance index a of Mg-Zn-Nd-Cd-Zr alloy as-cast and the size of grain was builded, the equation can be expressed as α=4639.63-95.42d+0.58d2.