Preparation And Mechanism Of Mg-Based Alloys With High Damping And Mechanical Properties

The mechanical vibration,which is more or less involved in many industry processes and production practices,can inevitably affect operation efficiency and precision of equipments.The brittle cracks of metal parts caused by mechanical vibration can shorten the service life of equipments.Moreover,the noise generated by mechanical vibration can lead to environmental pollution and endanger physical and mental health of front-line operators near equipments.Therefore,the reduction of mechanical vibration and noises has become one of increasingly concerned and urgent problems to be solved in equipment production and process operation.Among many methods to control mechanical vibration and noise,Mg-based alloys have become promising materials for high damping properties,which has attracted extensive attention in domestic and foreign industry and scientific research.As-casted Mg-Zr binary alloys and Mg-0.6Zr-xY(x=1.0-5.0)ternary alloys were prepared by remelting casting method in this study.Meanwhile,as-extruded Mg-based alloys were obtained by extrusion method.The phase characteristics of prepared Mg-based alloys were identified by XRD,SEM and TEM,and the damping and tensile mechanical properties of Mg-based alloys were studied by dynamic mechanical analyzer in a type of Q800 and universal testing machine.The influence of alloying element addition,forming mode as casting or extrusion,strain s,temperature T,vibration frequencies f and heating rate v on the damping properties of Mg-Zr binary alloys and Mg-0.6Zr-xY ternary alloys was investigated.In addition,the relationship of microstructure,damping and tensile mechanical properties of prepared Mg-based alloys was explored to provide valuable scientific information for the promotion of Mg-based alloy materials with high damping and tensile mechanical properties.The main summary remarks can be obtained as follows:Based on the observation of microstructure of prepared Mg-based alloys,as-casted and as-extruded Mg-Zr binary alloys and Mg-0.6Zr-xY ternary alloys were composed of the equiaxed ?-Mg grains in uniform sizes.In addition,?-Zr phases were found in Mg-Zr binary alloys and Mg-0.6Zr-xY ternary alloys while Mg24Y5 phases existed in Mg-0.6Zr-xY ternary alloys.The addition of alloying element Zr or Y can effectively refine the grain size of prepared Mg-based alloys.Nevertheless,the refinement effect of Zr or Y addition decreases with the increase of[Zr]or[Y].As to the prepared as-extruded Mg-based alloys,the increase of extrusion ratio Re or the decrease of extrusion temperature Te can refine the grain size.According to the experimental results of damping properties of as-casted and as-extruded Mg-Zr binary alloys and Mg-0.6Zr-xY ternary alloys,the two-segment characteristics of both ?-tan? curves and T-tan? curves of prepared Mg-based alloys can be observed.Damping properties tan? of Mg-0.6Zr-xY ternary alloys are smaller than that of Mg-Zr binary alloys due to the addition of alloying element Y resulting in the deterioration of damping properties tan?.Moreover,the damping properties tan ? of as-casted and as-extruded Mg-0.6Zr-xY ternary alloys display a decreasing tendency with the increase of Y addition from 1.0 mass%to 5.0 mass%on condition that strain ? is greater than the inflection stain ?cr at ambient temperature Tam.The damping properties expressed by internal friction tan? of prepared Mg-Zr binary alloys can be effectively promoted by increasing either heating rate v or strain ? under the condition of changing temperature T.Increasing vibration frequency f can effectively decrease the damping properties of as-cast and as-extruded Mg-Zr binary alloys and Mg-0.6Zr-xY ternary alloys on condition that temperature T is greater than the inflection temperature Tcr,which can be proved by the relationship between the damping properties tan ? of actual viscoelastic body and vibration frequency f as tan?=Q-1=1/(??)m=1/(2?f?)m.However,increasing vibration frequency f has little effect on the T—tan? curves for prepared Mg-based alloys under the condition of f>5.0 Hz.The inflection temperature Tcr of T—tan? curves for prepared Mg-based alloys increases with the increasing vibration frequency f.However,growth rate decreases as vibration frequency f increases.The decreasing order of damping properties tan? for prepared Mg-based alloys by changing extrusion ratio R,or extrusion temperature Te under the condition of T>Tcr can be obtained as tan?=17>tan?Re=30>tan?=67 and tan ?Te?=380?>tan?Te=410?>tan?Te?440?.The effect of strain ? on damping properties tan? for the as-casted and as-extruded Mg-Zr binary alloys and Mg-0.6Zr-xY ternary alloys can be ideally explained by dislocation pinning theory or the Granato-Lucke model.Further more,the influence of temperature T on damping properties tan? for the prepared Mg-based alloys complies with the grain boundary sliding theory.Increasing[Y]from 1.0 to 4.0 mass%can obviously promote both yield strength RP0.2 and ultimate tensile strength Rm of as-casted Mg-0.6Zr-xY ternary alloys,however further increasing[Y]from 4.0 to 5.0 mass%cannot result in an evidently increasing tendency for RP0.2 and Rm.The elongation A of as-casted Mg-0.6Zr-xY ternary alloys increases of adding[Y]from 1.0 to 3.0 mass%,but decreases with[Y]from 3.0 to 4.0 mass%.However,the measured results of yield strength R,0.2 and ultimate tensile strength Rm are different for as-extruded Mg-0.6Zr-xY ternary alloys that increasing[Y]from 1.0 to 5.0 mass%leads to an increasing tendency of RP0.2 and Rm.The effect of[Y]on RP0.2 and Rm of as-casted and as-extruded Mg-0.6Zr-xY ternary alloys can be well explained by the grain boundary strengthening and solid solution strengthening mechanisms.The similar measured results of elongation A for as-extruded Mg-0.6Zr-xY ternary alloys can be obtained by[Y]=3.0 mass%as a criterion.Both yield strength RP0.2 and ultimate tensile strength Rm of as-extruded Mg-0.6Zr binary alloys can be slightly promoted by increasing extrusion ratio Re from 17 to 67 under the condition of extrusion temperature Te=440 ?,however increasing extrusion temperature Te from 380 ?to 440 ? cannot affect the RP0.2 and Rm of as-extruded Mg-0.6Zr binary alloys at extrusion ratio Re=30,which may be due to the higher extrusion temperature Te380 0C.The effect of increasing extrusion ratio Re from 17 to 67 on Rp0.2 and Rm of as-extruded Mg-0.6Zr-xY ternary alloys is not significant,while the influence of extrusion temperature T.from 380 ?to 440 ?C on RP0.2 has a negative tendency but on Rm has no clear regularity.The optimal Zr content of the as-cast Mg-Zr binary alloys with better performance of damping properties tan? is recommended to be 0.6 mass%in a range of Zr content from 0.6 to 5.0 mass%under the condition that temperature T is less than inflection temperature Tcr.Nevertheless,the optimal Zr content is recommended to be 2.5 mass%at T>Tcr,,for better damping properties tan? of as-cast Mg-Zr binary alloys.Meanwhile,the optimal Y content of the as-cast and as-extruded Mg-0.6Zr-xY ternary alloys with greater damping properties tan? is recommended to be 1.0 mass%and 4.0 mass%in a range of Y content from 1.0 to 5.0 mass%at T<Tcr and T>Tcr,respectively.