【作者】 卫爱丽；

【导师】 梁伟；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2010， 博士

【摘要】 高铝锌基合金(ZA)是近几十年来国内外应用十分广泛的一种有色金属材料,它具有良好的铸造性能、力学性能、抗磨损性能和低廉的制造成本等优点。高铝锌基合金是绿色合金,其熔炼耗能比铜低得多。工业上用其部分替代青铜、黄铜和巴氏合金等制造减摩、耐磨零件。在应用过程中发现ZA合金在中低速重载连续工作时,因温升造成强度和耐磨性下降,难以满足工况的高温要求,限制了它的应用。为了进一步提高锌铝合金的高温性能,本文较为系统地研究了稀土元素对高铝锌基合金的组织和常温、高温(100℃和180℃)力学性能的影响,对扩大其应用范围有较大意义。综合国内外研究现状,本文选用Zn-25Al-5Mg-2.5Si合金为研究对象,通过加入不同含量的稀土元素Gd、Y、Nd和Dy,制备出Zn-25Al-5Mg-2.5Si-xRE合金。利用金相显微镜、扫描电镜、能谱仪和X射线衍射等多种现代分析手段,研究了四种稀土元素对Zn-25Al-5Mg-2.5Si合金的微观组织、生成相形态及分布的影响,测试了合金的常温和高温力学性能,分别得出了各稀土元素的最佳加入量。对合金的微观组织观察表明:适量稀土元素Gd、Y、Nd和Dy能够明显细化Zn-25Al-5Mg-2.5Si合金的铸态组织,改善组织的形貌。稀土能在合金中形成具有较高硬度和热稳定性的颗粒状或块状高熔点化合物,这些高熔点化合物弥散分布于基体组织中。当Gd和Nd的添加量为0.8wt%、Y的添加量为0.4wt%、Dy的添加量为1.2wt%时,合金的细化效果最好。对合金相组成的XRD分析结果表明:稀土加入Zn-25Al-5Mg-2.5Si合金后,优先与Al形成Al-RE化合物,多余的稀土与Zn形成Zn-RE化合物。Gd加入Zn-25Al-5Mg-2.5Si合金中形成的稀土相是Al3Gd、GdZn12;Y加入合金中形成的稀土相是Al3Y、Y2Zn17;Nd加入合金中形成的稀土相是Al2Nd、NdZn2;Dy加入合金中形成的稀土相是AlDy、DyZn。合金的力学性能测试结果表明:加入适量的RE能提高Zn-25Al-5Mg-2.5Si合金的硬度和室温、高温拉伸强度,并能改善合金的塑性。力学性能随RE的增加基本上呈先升后降的趋势。当Gd和Nd的添加量为0.8wt%、Y的添加量为0.4wt%、Dy的添加量为1.2wt%时,合金的强度达到最大值。分析认为,稀土元素Gd、Y、Nd和Dy主要是通过细晶强化和析出强化的共同作用提高了合金的室温和高温强度,改善了合金的塑性。比较四种稀土元素对合金的组织与性能的影响规律,结果表明Dy的加入对合金组织细化和力学性能改善最为有效,其余依次是Gd、Nd和Y。对合金拉伸断口的SEM形貌分析表明:未加稀土的Zn-25Al-5Mg-2.5Si合金的断裂形式为脆性断裂。随着稀土的加入和温度的升高,合金的拉伸断口组织中韧窝数量增多,合金的塑性得到提高。当稀土加入量过大,形成的稀土化合物相在基体中或晶界上团聚时,合金的断口类型又由韧性断裂转变为脆性断裂。我国有色金属资源和稀土资源非常丰富,因此本文把稀土加入到有色合金中提高其性能,扩展其应用范围,对资源利用和经济发展有着重要的意义。更多还原

【Abstract】 Zinc alloys containing higher aluminum (ZA alloys) are one of the widely used non-ferrous materials in recent decades because of their many advantages such as good casting and mechanical properties, excellent wear-resisting performance and lower manufacturing cost. Meanwhile, ZA alloys are environmentally friendly because the melting energy consumption for the alloys is much lower than for the copper alloys. ZA alloys have been used to substitute for some traditional alloys such as brass, bronze and babbitt metals to prepare some wear-resistant and anti-friction components.However, their application is partly restricted because of their strength and wear-resistance declining with increase of temperature when they are overloaded or under continuously working. In order to further improve the properties of ZA alloys at high temperature, this paper investigated the effects of rare earth(RE) elements on the microstructure and the strength at room temperature and high temperature (100℃and 180℃), which is significant for extending their application fields. Zn-25Al-5Mg-2.5Si-xRE alloys were prepared by adding different content of rare earth elements Gd, Y, Nd and Dy to Zn-25Al-5Mg-2.5Si alloys. Metallurgical microscopy, scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction were employed to investigate the effect of different rare earth elements on the microstructure, morphology and distribution of the phases of the Zn-25Al-5Mg-2.5Si-xRE alloys. Mechanical properties at room temperature and high temperature were tested and the optimum contents of rare earth elements were obtained.It was showed from the microstructure of the alloys that the additions of the appropriate amount of rare earth elements Gd, Y, Nd and Dy were capable of refining the as-casting microstructure and improving their morphology. Granular and massive compounds with higher melting point, hardness and stability were formed in the alloys as a result of the addition of rare earth elements. The compounds were dispersively distributed in the boundary and intracrystalline of the alloys. When 0.8wt% Gd or 0.8wt% Nd or 0.4wt% Y or 1.2wt% Dy was added to the alloy, the optimized grains refining effect on the alloys was obtained.XRD was used to analyze the phases composition in the alloys. The results showed that Al-RE compounds were preferentially formed as rare earth elements were added and then the redundant rare earth elements interacted with Zn to form Zn-RE compounds. Rare earth phases Al3Gd and GdZn12 were formed when Gd was introduced into Zn-25Al-5Mg-2.5Si alloy. Similarly, rare earth phases Al3Y and Y2Zn17, Al2Nd and NdZn2, AlDy and DyZn were also formed because of the addition of Y, Nd and Dy, respectively.It was revealed from the testing results of the mechanical properties of Zn-25Al-5Mg-2.5Si alloys adding RE that the higher hardness, tensile strength and plasticity at high temperature were achieved. The mechanical properties increased with increase of RE at first and then decreased later. When 0.8wt% Gd or 0.8wt% Nd or 0.4wt% Y or 1.2wt% Dy was added to the alloy, the maximum tensile strength was obtained.It is suggested that strength and hardness at the room temperature and high temperature increased and the plasticity of alloys were improved by adding rare earth elements Gd, Y, Nd and Dy mainly through the combined action of grain refining and precipitation strengthening.The comparison of the effect of four rare-earth elements on microstructure and properties of alloys showed that Dy was the most effective in alloy microstructure refinement and properties improvement, Gd, Nd and Y followed.SEM was used to characterize the fracture morphology of the alloys. It was showed that the fracture mode of the alloys without rare earth elements was brittle-fracture. With the increase of RE and the rise of temperature, the quantity of dimple fracture was increased, resulting in the improvement of plasticity of the alloys. However, when rare earth phases agglomerated in the matrix or grain boundary with adding excessive RE, plasticity of the alloys decreased.In this paper, the properties of non-ferrous alloys were remarkably improved with the addition of earth elements, which will extend the application fields of non-ferrous alloys and is significant for the economic development and resource utilization.更多还原