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振动会降低机械设备的加工精度，振动诱发的脆性裂纹等缺陷会降低机械设备的使用寿命，因此减振降噪是机械装备运行中亟需解决的问题之一。研究Mg基合金的高阻尼特性，可望使之成为有应用前景的减振材料。本课题首先采用重熔铸造法制备得到铸造态Mg-Zr二元和Mg-0.6Zr-xY（x=1.0~5.0）三元Mg基合金；其次采用挤压法处理得到上述两种挤压态Mg基合金；在利用XRD、SEM、TEM等物检手段探明Mg基合金物相特征的基础上，采用Q800型动态机械分析仪和万能试验机测试了所制备的Mg基合金的阻尼性能和拉伸力学性能，力图探明合金元素成分、铸造和挤压的成型方式、应变ε、温度T、振动频率f以及升温速率ν等因素对Mg-Zr二元和Mg-0.6Zr-xY三元Mg基合金阻尼性能的影响规律，明晰所制备的Mg基合金的微观组织、阻尼性能和拉伸力学性能的内在联系，为制备和推广具有高阻尼和高强度的Mg基合金材料提供有价值的科学信息，获得的主要结论为：通过微观组织的观察发现，铸造态和挤压态Mg-Zr二元与Mg-0.6Zr-xY三元合金主要由α-Mg晶粒组成，Mg-Zr二元合金中存在α-Zr相，而Mg-0.6Zr-xY三元合金存在α-Zr和Mg24Y5相。添加元素Zr或Y，均能有效细化Mg基合金晶粒；但随着添加量的增大，细化效果减弱。增大挤压比Re或降低挤压温度Te，能够显著细化晶粒。通过阻尼性能tanφ的测试结果表明，铸造态和挤压态Mg-Zr二元与Mg-0.6Zr-xY三元合金的ε–tanφ曲线和T–tanφ曲线均呈两段式的变化趋势。元素Y的添加导致Mg-0.6Zr-xY三元合金的阻尼性能tanφ低于Mg-Zr二元合金的阻尼性能tanφ，且室温Tam条件下当应变ε大于拐点应变εcr，随着[Y]从1.0 mass %到5.0 mass %增加，铸造态和挤压态Mg-0.6Zr-xY三元合金阻尼值tanφ呈递减趋势。提高升温速率ν，或增大应变ε，均可适度提高Mg-Zr二元合金温度T变化条件下的阻尼值tanφ。当温度T大于拐点温度Tcr时，增加振动频率f可减少铸造态和挤压态Mg-Zr二元与Mg-0.6Zr-xY三元合金的阻尼性能tanφ；但当f>5.0 Hz时，单纯提高f对Mg基合金的T–tanφ曲线影响不大，可通过实际粘弹性体的阻尼性能tanφ和振动频率f的关系式tanφ=(ω·τ)–m=(2·π·f·τ)–m证明。随着f的增加，挤压态Mg-Zr二元与Mg-0.6Zr-xY三元合金T–tanφ曲线的Tcr升高，但增长速率降低。当T>Tcr时，挤压态Mg-Zr二元与Mg-0.6Zr-xY三元合金存在tanφRe=17>tanφRe=30>tanφRe=67，以及tanφTe=380°C>tanφTe=410°C>tanφTe=440°C。Granato–Lücke位错钉扎理论良好解释了应变ε对Mg-Zr二元与Mg-0.6Zr-xY三元合金阻尼性能tanφ的影响，而温度T对Mg-Zr二元与Mg-0.6Zr-xY三元Mg基合金阻尼性能tanφ的影响可以用晶界滑移理论进行合理阐释。Y含量从1.0~4.0 mass %增加能提高铸造态Mg-0.6Zr-xY三元合金的屈服强度Rp0.2和极限拉伸强度Rm，而[Y]在4.0~5.0 mass %增加时Rp0.2、Rm无显著增加；伸长率A随[Y]增加呈现先递增后降低的变化关系，拐点[Y]=3.0 mass %。挤压态Mg-0.6Zr-xY三元Mg基合金，[Y]从1.0~5.0 mass %增加时Rp0.2和Rm持续在增加，可通过晶界强化和固溶强化机制来解释。挤压态Mg-0.6Zr-xY三元合金的伸长率A亦随[Y]增加呈现先递增后降低的变化关系，拐点[Y]=3.0 mass %。挤压比Re从17提高到67，能够适度提高挤压态Mg-0.6Zr二元合金的屈服强度Rp0.2和极限拉伸强度Rm；而挤压温度Te从380 °C提高到440 °C，Mg-0.6Zr二元合金的Rp0.2和Rm没有显著性地影响。Re增大对Mg-0.6Zr-xY三元合金的Rp0.2和Rm作用效果不明显，而Te升高对Mg-0.6Zr-xY三元合金的Rp0.2呈递减趋势，但对Rm没有显著影响。Zr含量自0.6~5.0 mass %变化范围内，温度T小于拐点温度Tcr时铸造态Mg-Zr二元合金阻尼性能tanφ较好的Zr含量推荐为0.6 mass %；温度T大于Tcr时的Mg基二元合金阻尼性能tanφ较好的Zr含量推荐为2.5 mass %。Y含量自1.0~5.0 mass %变化范围内，温度T小于Tcr时的铸造态与挤压态Mg-0.6Zr-xY三元合金具有良好的阻尼性能tanφ的成分推荐为[Y]=1.0 mass %；而温度T大于Tcr时的Mg基三元合金阻尼性能tanφ的成分推荐为[Y]=4.0 mass %。;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 ε, temperature T, vibration frequencies f and heating rate ν 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 α-Mg grains in uniform sizes. In addition, α-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 ε–tanφ curves and T–tanφ curves of prepared Mg-based alloys can be observed. Damping properties tanφ 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 tanφ. Moreover, the damping properties tanφ 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 ε is greater than the inflection stain εcr at ambient temperature Tam.The damping properties expressed by internal friction tanφ of prepared Mg-Zr binary alloys can be effectively promoted by increasing either heating rate ν or strain ε 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 tanφ of actual viscoelastic body and vibration frequency f as tanφ=(ω·τ)–m=(2·π·f·τ)–m. However, increasing vibration frequency f has little effect on the T–tanφ curves for prepared Mg-based alloys under the condition of f>5.0 Hz. The inflection temperature Tcr of T–tanφ 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 tanφ for prepared Mg-based alloys by changing extrusion ratio Re or extrusion temperature Te under the condition of T>Tcr can be obtained as tanφRe=17>tanφRe=30>tanφRe=67 and tanφTe=380°C>tanφTe=410°C>tanφTe=440°C.The effect of strain ε on damping properties tanφ 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–Lücke model. Further more, the influence of temperature T on damping properties tanφ 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 Rp0.2 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 °C, however increasing extrusion temperature Te from 380 °C to 440 °C 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 Te≥380 °C. 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 Te from 380 °C 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 tanφ 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 tanφ 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 tanφ 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 TTcr, respectively.
|牛瑞龙. 高阻尼和高力学性能的Mg合金制备及机理研究[D]. 中国科学院大学,2019.|
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