【作者】 杨林；

【导师】 张忠明；

【作者基本信息】 西安理工大学 ， 材料科学与工程， 2008， 硕士

【摘要】 通过快速凝固（RS）、往复挤压（RE）、单次挤压（EX）工艺制备了Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr（wt%）合金（下简称“快速凝固挤压镁合金”）。利用OM、SEM等方法分析了合金的组织与相组成,测试了合金的室温力学性能及其疲劳性能,分析了合金的疲劳断口形貌,得到以下主要结论:1、与常规凝固合金相比,快速凝固挤压镁合金的组织得到细化,合金中二次相更加均匀的分布于基体中。合金的硬度值HV₅、抗拉强度和延伸率分别为88.0 kg╱mm²,348MPa和20%。2、快速凝固挤压镁合金对应10⁶循环周次时的疲劳极限为159.2MPa,为其抗拉强度的46%,此比值较其它种类镁合金高。3、快速凝固挤压镁合金疲劳源主要在表面形成。表面与近表面处的第二相或夹杂物、缺陷等容易成为疲劳起始的核心,但未发现试样内部的夹杂或第二相成为疲劳核心或显著影响裂纹的传播方向。疲劳裂纹扩展区由小的平面状断面组成,但微观上没有发现疲劳辉纹的存在。瞬断区特征与静载下拉伸断口相似。4、快速凝固挤压镁合金的细小晶粒、Zn、Zr等原子固溶到基体中产生的固溶强化、强化相颗粒的第二相强化等均可有效的提高快速凝固挤压镁合金的抗疲劳强度。更多还原

【Abstract】 The microstructures and phase compositions of Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr（wt%） alloy prepared by rapid solidification and reciprocating extrusion were studied by optical microscope,scanning electronic microscope.Mechanical properties at room temperature of the alloy as well as the fatigue behavior were tested.The fatigue fracture morphologies of the alloy were analyzed.The conclusions are as follows:1.Compared with conventionally solidified Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr alloy,the microstructures of the Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr alloy prepared by rapid solidification and reciprocating extrusion are much finer,and the secondary phases distribute more uniform.The hardness HV₅,tensile strength and elongation of the alloy are 88.0 kgf/mm², 348MPa and 20%,respectively.2.The fatigue limit of the alloy is 159.2MPa with 10⁶ cycles.The ratio of fatigue limit to tensile strength of the alloy is 46%,which is higher than other magnesium alloys.3.The fatigue cracks originate from surface of the alloy generally.Secondary phases, inclusions and defects at surface and subsurface can become the fatigue initiative nucleus easily. It could not be observed that the inclusions or secondary phases in the interior of the fatigue sample become fatigue source or influence the crack direction of propagation obviously. Fatigue crack extended section is composed of small planar cross-sections,whereas fatigue striations were not observed.The character of instant failure section is similar to tensile fracture with dead-load.4.The grains of the alloy is fine.Zn、Zr dissolved in the matrix can strengthen the alloy by solution strengthening.Meanwhile,the alloy is strengthened with secondary phases by dispersion strengthening.As a result,the fatigue resistance of the alloy is improved effectively.更多还原