导　　师： 蒋敏

学科专业： 080502

授予学位： 硕士

作　　者： ;

机构地区： 东北大学

摘　　要： 镁合金具有高的比强度、比刚度、优异的减震性能而得到了广泛应用。但镁合金的屈服强度低、延展性以及高温蠕变性能差,制约了镁合金的发展。近年来在镁合金中发现的LPO相在不显著降低塑性的同时大幅提高镁合金的强度,是一种潜在的理想强化相。目前的研究主要集中在LPO镁合金的制备和性能,而缺乏对LPO镁合金的相平衡关系的了解,限制了镁合金的开发和应用。本论文将通过实验方法,系统研究Mg-Cu-Y和Mg-Cu-Gd合金富镁区域的相平衡关系,研究结果将为LPO镁合金成分设计提供切实可靠的理论依据,同时也为镁合金中Cu、Y、Gd合金化提供理论指导。 本研究采用光学显微分析、差热分析、扫描电镜和能谱成分分析、x射线衍射结构分析方法对Mg-Cu-Y合金富Mg区域300、400和450℃的相平衡以及Mg-Cu-Gd合金富Mg区域440℃相平衡进行实验分析和测定,实验结果如下： /(1/)Mg-Cu-Y三元系存在一个三元金属间化合物X,即LPO相,其与/(Mg/)构成相平衡。确定了X相的成分范围为4.33～5.36at./%Cu和5.41～7.15at./%Y。/(Mg/)+X的两相区为一狭窄的成分范围,过量的Y含量析出Mg24Y5相,而过量的Cu含量时,300和400℃析出脆性的Mg2Cu相,450℃以上出现L相。 /(2/) Mg-Cu-Gd三元系同样存在三元金属间化合物x,并与/(Mg/)构成相平衡。x相中Cu和Gd的含量分别为6.90-7.88at./%和6.86～7.36at./%。Mg-Cu-Gd三元系富Mg区存在/(Mg/)+X+Mg5Gd和/(Mg/)+X+Mg2Cu两个三相平衡。 /(3/)结合扫描电镜分析及DSC分析,根据所建立的Mg-Cu-Y三元系400和450℃的相平衡关系,确定Mg-Cu-Y三元系在约442℃发生一个三元包共晶反应,即L+/(Mg/)→X+Mg2Cu。 Magnesium alloy have wide applications due to their high specific strength, specific stiffness and excellent damping characteristic.However, the low yield strength, ductility and poor elevated temperature creep limit the development of magnesium alloys. Recently it has been found that an LPO phase increases the strength effectively without destroying the ductility. Since then, more attentions have been paid to the preparation and performances of the LPO magnesium alloy, however, the works on the phase equilibria of the LPO magnesium alloys are scarce. In this work, the phase relationships in the Mg-rich region of the Mg-Cu-Y and Mg-Cu-Gd alloys have been studied by experiments. The results will provide reliable date for alloy design of the LPO magnesium alloys. Different experimental techniques including optical optical microscope, scanning electronic microscope, energy-dispersive X-ray analysis and X-ray diffraction analysis have been done to the Mg-rich region of the Mg-Cu-Y alloys at300、400and450℃,and to the Mg-Cu-Gd alloys at440℃. The experimental results are as follows: /(1/) A ternary intermetallic compound X phase, which is the LPO phase, has been found to be stable in the Mg-Cu-Y system. The X phase gets equilibrium with /(Mg/) phase, with a composition range of4.33～5.36at./%Cu and5.41-7.15at./%Y. The two-phase region of /(Mg/)+X is narrow, and at a higher Y content, Mg24Y5phase precipitates, while at a higher Cu content, the brittle Mg2Cu phase precipitates at300and400℃, and at a higher temperatures above450℃, the liquid phase occurs. /(2/) Similar to the phase relationship in the Mg-Cu-Y system, the X phase is also stable in the Mg-Cu-Gd system, which gets equilibrium with /(Mg/) phase. The X phase has a composition of6.90～7.88at./%Cu and6.86～7.36at./%.Gd. Three-phase equilibria of /(Mg/)+X+Mg5Gd and /(Mg/)+X+Mg2Cu have been detected at lower temperatures. /(3/) With the analysis of scanning electricity microscope and differential scanning calorimetry, and based on the phase

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领　　域： [金属学及工艺] [一般工业技术] [金属学及工艺] [金属学及工艺] [金属学及工艺]