【作者】 卢庆亮；

【导师】 闵光辉；

【作者基本信息】 山东大学 ， 材料加工工程， 2006， 博士

【摘要】 镁及镁合金作为目前工业应用中最轻的结构材料之一，具有良好的应用前景，然而由于镁合金自身强度较低、抗氧化性能差以及高温抗蠕变性能差等问题，使其作为某些结构件的应用受到限制，为进一步扩大其应用，人们采用了多种方法来提高其综合力学性能。二十面体准晶相（Ⅰ-phase，下同）由于其特殊的结构而具有优异的力学性能，如高强度、高硬度等，将Ⅰ-phase作为一种增强相引入到镁合金中可大大提高镁合金的力学性能，为新型镁合金的开发和实际应用提供了一种新途径。 本文采用常规铸造法制备了含有粗大网状二十面体准晶晶界相和α-Mg两相组织的Mg-Zn-Y合金。研究了合金含量及Zn／Y比对Mg-Zn-Y合金显微组织和力学性能的影响，探讨了热处理工艺对合金中相析出行为及Ⅰ-phase热稳定性。以时效处理后的Mg-Zn-Y合金为研究对象，研究了两种塑性变形工艺（常规热挤压和等径角挤压变形）对合金显微组织和力学性能的影响，并对合金的细化机制、断裂行为和强化机制进行了研究。 研究结果表明，在Y含量为0.3at.％～2.0at.％，Zn含量为1.7at.％～6.0at.％的富镁Mg-Zn-Y合金中，合金的铸态组织及相组成取决于Zn／Y比和Zn含量，Zn／Y比为6时，合金的铸态组织由α-Mg基体和晶界上富镁相与二十面体准晶两相共晶组织组成；在所研究的合金成分范围内，合金中Ⅰ-phase的形成及其体积分数与合金的凝固速度有关，采用快速凝固的方法得到的合金中，由于第二相的形核及长大受到抑制，形成的Ⅰ-phase的体积分数相对于常规铸造工艺下制备的合金中Ⅰ-phase的含量有所减少，同时发现，合金的极限抗拉强度和屈服强度随合金中Ⅰ-phase体积分数的增加而增加，但合金的延伸率略有降低：在400℃、24h的热处理工艺下，Mg₉₅Zn_4.3Y_0.7合金基体上有球形Ⅰ-phase析出，且析出的Ⅰ-phase在随后的时效处理中表现出热稳定性；在190℃不同时效时间下合金基体中的析出相为密排六方结构的MgZn₂相，其析出行为和Mg-Zn二元合金类似。 Mg-Zn-Y合金的热挤压结果表明，通过挤压变形可以显著细化合金的晶粒组织，合金的晶粒大小可由变形前的40～60μm减小到8～15μm，在挤压过程中位于晶界的Ⅰ-phase被破碎并较均匀地分布在基体合金中，随着挤压比的增大，挤压温度的降低，晶粒进一步细化，Ⅰ-phase的弥散程度增加。挤压变形可以显著地提高Mg-Zn-Y合金的强度、硬度和延伸率；随着挤压比的增大，合金的强度、硬度和延伸率均有所增加；在所研究的三种合金中，Mg₉₅Zn_4.3Y₍0.7合金在523K以25：1的挤压比挤压后，具有较高力学性能，其极限抗拉强度为287MPa，屈服强度为203MPa，延伸率为14.1％。 对于经过预挤压后Mg-Zn-Y合金的ECAP变形结果表明，等径角挤压（ECAP）对于预挤压态Mg-Zn-Y合金组织的细化是一个不断加强的过程，1道次ECAP变形后，在一些粗大晶粒之间分布着许多细小的晶粒，随变形道次的增加，原始粗大晶粒消失，形成均匀细小的等轴晶粒，平均晶粒尺寸为1～3μm，更多还原

【Abstract】 Magnesium and magnesium alloy are becoming more and more attractive for many engineering structural applications owing to their low density and high specific strength, especially the significant advantage of easy-recycling. However, the application of most magnesium alloys has been greatly restricted due to their poor strength, oxidation and creep resistance. In order to extend the application of magnesium alloys, many methods have been reported to improve mechanical properties.Icosahedral quasicrystalline phase (I-phase) that has attractive mechanical and physical properties attributed to their unique atomic structure, such as high strength, high hardness at elevated temperature and low friction coefficient has been reported in many alloy systems. Recently, it has been reported that the Mg-Zn-Y alloys containing I-phase as a secondary solidification phase exhibit good mechanical properties at room temperature and elevated temperature, which provide a good method for the development and application of new magnesium alloys.In this paper, several as-cast Mg-Zn-Y bulk alloys, which consist of a coarse eutectic I-phase in the a-Mg matrix, were fabricated by using the conventional casting method of the design of composition. The effect of the alloy content and Zn/Y ratio on the microstructure of Mg-Zn-Y alloys was studied, and the precipitate behavior of the alloy and thermal stability of I-phase was also investigated. Based on the aging-treated sample, the effect of two deformation processing—hot extrusion and equal channel angular pressing(ECAP), on the microstructure and mechanical properties of Mg-Zn-Y alloys were studied. Moreover, the refinement mechanism, fracture behavior and strengthening mechanism were investigated.The results showed that, when the content of Y was from 0.3at.% to 2.0at.% and the content of Zn was from 1.7at.% to 6.0at.%, the as-cast microstructure and the phase constitution of Mg-Zn-Y alloys were determined by the atom ratio of Zn/Y and the content of Zn element. When the atom ration of Zn/Y is 6, the as-cast Mg-Zn-Y alloys were composed of two different types of phases: the primary a-Mg phase and I-phase. The formation capability and the volume fraction of I-phase in Mg-Zn-Y alloys were determined by the solidification rate of alloys. Because the growth of I-phase was restricted by the high solidification rate, the volume fraction of I-phase in更多还原