多场作用下纳米准晶与长周期结构相复合增强高强韧镁合金机理研究

In the last decade, magnesium alloys with long-period stacking ordered (LPSO) structures have been developed in the high strength Mg-RE-Zn systems, accordingly attracting progressive interest. However, the formation and strengthening mechanism of LPSO structure phases in Mg-RE-Zn has not been reported which need to make a thorough study. By regulate the segregation of main elements (RE、Zn) and the preferential occupation of supporting elements (Mn、B), we designed a kind of Mg-RE-Zn-Mn-XM alloy using both the first principle method and practical testing. The semi-continuous ingot casting was got by cooperative work of the power ultrasonic vibrating and low-frequent electromagnetic. The high strength and ductilily magnesium alloy composite reinforced with nano quasicrystals and LPSO structure were prepared by extrusion shear deformation of supersonic vibration after heat treatment. The formation, generic changing rule，spatial pattern，the condition integrated with substrate, the impact on the mechanical properties of nano quasicrystals and LPSO structure phases and interaction between them were researched. This study is aimed at revealing the interaction and coordination mechanism of nano quasicrystals and LPSO structure with matrix, and the microcosmic essence of the Mg alloys composite reinforced with them , exploring the behavior and effects on plastic deformation and dynamic recrystallization of alloy, so as to improve its morphotropy and provides the theory basis and new technological approach for prepare the high strength, ductility and heat resisting Mg alloys .

目前的一个重要发现是在高强Mg-RE-Zn合金中发现了长周期结构相，成为业界关注和研究的热点，但其形成机理和对镁合金的强化机制还不清楚，有待深入研究。 运用第一性原理模拟计算与实验研究相结合，在合金凝固过程中有效调控主加RE、Zn元素偏聚方式和辅加Mn、B元素的择优占位，设计出一种Mg-RE-Zn-Mn-XM合金。在功率超声振动与低频电磁场协同作用下获得半连续铸锭，热处理后，经超声振动挤压剪切变形，获得由纳米准晶和长周期结构相复合增强的高强韧耐热镁合金。本项目对纳米准晶和长周期结构相的形成、结构演化规律、在基体中的空间分布模式、与基体结合状态、它们之间的相互作用规律以及对力学性能的影响进行研究，揭示纳米准晶、长周期结构相与基体的相互作用与协调机制以及其复合增强镁合金的微观本质；探索对合金塑性变形和动态再结晶的作用行为，从而提高合金的变形性。为制备高强韧耐热镁合金提供理论依据和技术新途径。

项目通过模拟与实验相结合，利用元素的微合金化与低频旋转磁场的协同作用，在合金凝固过程中有效调控主加RE、Zn元素偏聚方式与辅加Ti、B、Li、TiB2等元素择优合理占位，使初生α-Mg的生长方式由粗大的树枝晶转变为细小等轴树枝晶生长，有效细化合金凝固组织，使合金凝固时的第二相18R与W相的生长模式由共生生长变为离异生长，提高合金的铸态力学性能和可加工性能；发现Ti、B、Li、TiB2具有促进LPSO相形成、抑制W相析出和降低合金拉压不对成性的作用；建立了固溶处理时合金中的W相球化过程模型，通过固溶球化处理，使鱼骨状W相变为球形颗粒状，提高了合金的塑性变形能力；经研究发现18R和W相界面处的动态再结晶是以不连续再结晶机制形核，而在14H扭折带边界处的动态再结晶以连续再结晶机制形核；并揭示出在变形过程中形成的14H的扭折激活了柱面<a>滑移，锥面<a>滑移以及锥面<c+a>滑移。在形变应力的作用下，14H逐渐溶解，使大量Y和Zn原子溶入到再结晶晶粒中，进而导致了一系列更精细的LPSO相及γ'相在再结晶晶粒中的析出成为合金强韧化提升的新诱因和新发现；本项目研究成果的取得，为制备多相复合增强的高强韧镁合金提供理论依据和技术新途径。