【作者】 万迪庆；

【导师】 杨根仓；

【作者基本信息】 西北工业大学 ， 材料加工工程， 2006， 硕士

【摘要】 镁合金是工业应用中最轻的结构金属材料之一,具有较高的强度,其比钢度与铝合金相当。镁合金具有优异的工艺性能、较好的耐腐蚀性能、良好的导热、减振及电磁屏蔽性和可回收性,被认为目前最具发展前途的金属材料。然而,镁合金的不足之处是室温强度不高和高温强度偏低。因此,开发新型高强度镁合金已成为镁合金研究中的重点。 准晶具有特殊的物理-化学性能。其中准晶的高硬度使其特别适合于作为韧性基体材料中的强化相,如果使一定尺度准晶颗粒均匀分布在镁基体中,则有可能制备出准晶增强高强度镁合金材料,从而拓展了镁合金的应用领域。 Mg-Zn-Y三元合金中准晶形成能力较强,而且通过普通铸造方法就可得到大体积分数稳定准晶,这为准晶增强镁基合金的开发提供了途径。 本论文主要内容包括Mg-Zn-Y三元合金中稳定准晶的制备、鉴定,以及采用熔体混溶法制备准晶增强镁合金。本文的主要研究结果如下: 1、X射线衍射和透射电镜分析结果表明铸态Mg-Zn-Y系合金中存在稳定的二十面体准晶。其成分近似为Mg₂₉Zn₆₃Y₈。 2、Mg₃₀Zn₆₀Y₁₀三元合金凝固过程中准晶相是由初生相和液相发生包晶反应生成的。初生相近似成分为Mg_16.32Zn_70.60Y_13.08,其形成温度为723℃,生成准晶相的包晶反应温度为648℃。 3、Mg-Zn-Y系合金铸态组织中准晶相呈现花瓣状或多边形形貌,此外准晶相花瓣形貌存在多样性,从扫描电镜图片中可以观察到6瓣,5瓣状花瓣。决定准晶相生长形貌的决定因素是其特殊的准周期结构。 4、合金成分和冷却速率显著影响准晶相生长形貌。当准晶合金凝固过程中形成的低温相越多（主要为Mg₃Zn₇相）,凝固时间越长时,准晶相长时间熟化使准晶花瓣端部分叉和花瓣脱落,脱落准晶游离到低温相中最后在界面能的作用下形成多边形状。 5、采用熔体混溶法向AZ91合金引入Mg-Zn-Y准晶合金后其混溶组织发生了较大变化。主要组成相有α-Mg,Mg₂Zn,Al₃Zn₄Y₃相。混溶后合金铸态抗拉强度最大达到228MPa,比铸态AZ91强度性能明显提高。更多还原

【Abstract】 Magnesium alloy is one of the lightest materials among the industry application alloys. Magnesium alloys have good strength , particularly, which specific strength are nearly equal to that of aluminium alloys .With good processing property , corrosion resistance,well heat conductivity, damping and electromagnetsim shield properties ,Magnesium alloys are wildly considered to be the advanced industry alloy in future.However , the disadvantage of magnesium alloys are low room temperature strength and poor elevated temperature strength, thus, many workers at present have focused on development of high strength magnesium alloys .Quasicrystal has high hardness and the Young’s modulus. Since it has been discovered at 1984, it keeps constantly relation with the alloy strength. If distributing stable quasicrystal particles with appropriate dimension homogeneously in magnesium matrix ,high-strength magnesium alloy can be produced.The stable icosahedral quasicrystal in Mg-Zn-Y system alloy was fist discovered by Luo in 1993 .Later, the researcher found that the quasicrystal has good potential formative ability and it can be formed at a wide component range at a large volume fraction in Mg-Zn-Y system alloy. This alloy system provide a bright way for producing quasicrystal -strengthed magnesium alloys.In the present thesis,the preparation of Mg-Zn-Y quasicrystal,mopholgy evolution,microstructures analysis and structure examination were completed and a high strengthen magnesium alloy strengthened by quasicrystal particles was produced by melt-mixing method. The research results of the paper are as follow:1. The stable icosahedral quasicrystal was successfully prepared in Mg-Zn-Y system alloy by traditional cast method. The quasicrystal was identificated by X ray diffraction and TEM technology to be stable Icosahedral quasicrystal .The quasicrystal composition is calculated to be Mg₂9Zn₆3Y₈ by EDX.2. The solidification process of Mg₃0Zn₆0Y₁0 alloy ,quasicrystal forms by peritectic reaction at 647℃ ,the primary phase composition is7o.6oYi3.o8,which forms about at 723 °C.3. Icosahedral phase has special quasi-structure ,so its growth morphology is different from the common crystal phase. In Mg-Zn-Y system alloy, the morphology of quasicrystal is liable to be petal-like. The six-branches, five-braches, and polygon-like quasicrystal are all observed in the solidification microstructure of Mg-Zn-Y system alloy.4. Alloy composition and cooling rate are major actors depending on the patterns of icosahedral quasicrystal morphology.The more content of low-temperature phases,such as Mg3Zn7 phase, and the slower cooling rate ,the much more easily changing the petal-like to polygon-like morphology by interface energy.5. Through the melt-mixing method ,the main phases in final mixing alloy are a-Mg, Mg2Zn, AI3Z114Y3 which have changed dramatically compared to masteralloys. The tensile test shows that the mixing alloy has ab 200 MPa ,which is higherthan AZ91 alloy . The quasicrystal-strengthed mechanics is attributed to good interface action force between quasicrystal / matrix and dislocation movement hindered by quasicrystal.更多还原