基于铝基Al-V中间合金的含V相微观结构演变机理

Application of V minor alloying process in aluminum alloys has been of great concern. However, due to the various forms of V-constituents present in Al-V master alloys and the unstable microstructure of V-containing phases after the alloys being remelted, it is extremely important to answer the fundamental questions about microsturcture evolution of different V-containing phases. In this project, Al-based Al-V master alloys will be prepared as the starting point, and Al-1.6Mg-1.2Si (wt. %) wrought aluminum alloy will be micro-alloying designed by adding 0.15 wt. % V. V-containnig phases themselves will focused on all the time, as a result, studies of the formation and microstructure evolution of V-containnig phases will be carried out in details. By means of melting Al-based Al-V master alloys with temperature rising or dropping, the dependence of the intrinsic characteristic parameters of V-constituents and the key controlling factors can be established quantitatively; Mechanism of nucleation and growth of V-constituents, as well as the phases transformation theories should be improved. Then, the relevance between these theories and the microstructure formation of V-constituents will be established; The dissolution behaviors of V-constituents in the molten liquid of wrought aluminum alloys will be emphatically analyzed, and the microstructure evolution of V-phases from V-constituents and the corresponding influence factors should be characterized quantitatively; Considering the precipitation of V-dispersoids in the process of homogenization treatment of the wrought aluminum alloy, a whole set of microstructure evolution of V-containing phases will be obtained. This work will be expected to reveal the thermodynamic characteristics of the microstructure evolution of V-containing phases. Moreover, the scientific evidences and experimental data will be provided to support the application of V minor addition into the aluminum alloys.

V在铝合金中的微合金化应用已倍受关注。但Al-V中间合金V结晶相种类多样、合金重熔后含V相微观结构多变等特点，使得解答各种含V相微观结构组织遗传演变规律这些根本问题至关重要。本项目拟从铝基Al-V中间合金入手，对Al-1.6Mg-1.2Si(wt%)铝合金进行V微合金化(0.15%)，始终聚焦含V相本身，开展其在各阶段的形成与结构演变规律研究。通过分段升、降温方法熔炼Al-V中间合金，建立V结晶相本征特征参数与其控制因子定量模型；完善V结晶相形核、长大机理与相变理论，重点分析其与V结晶相结构形成的关联性；追踪观察V结晶相在变形铝合金熔体中的溶解行为，定量表征V结晶相向含V相转变的结构演变规律及影响因素；再结合变形铝合金均匀化处理后含V弥散相析出规律，从而建立一整套含V相微观结构演变机理。本项目有望揭示含V相在结构演变过程中的热力学本质，对V在铝合金中的微合金化应用提供新的科学理论依据和数据。

利用钒(V)来微合金化铝合金能有效改善其组织性能，但因V结晶相的多样性，使得含V相本身在铝合金中的微观结构演变规律尚不清晰。本项目利用追根溯源的研究路线，从Al基Al-V中间合金所含的V结晶相本征参数的定量表征入手，确定其形核长大机制及析出控制因子模型，在此基础上聚焦V结晶相本身，追踪观察其在Al-Mg-Si变形铝合金熔体中的溶解行为及结构演变，探寻其控制因子、作用机制和对合金组织影响，揭示其全过程演变的热力学本质。取得了如下重要结果：1）发现了针状Al7V亚稳相及其析出规律，建立了Al8V5、Al3V、Al10V和Al7V相在Al基Al-V中间合金熔炼过程中相互转化的相变模型，明确了熔炼温度是该相变的关键控制因子；2）除了化学成分能够从根本上改变V结晶相的形核与长大规律以外，V结晶相的形核长大与Al-V中间合金的浇铸温度和冷却速率密切相关，直接决定其面积占比、平均尺寸和尺寸波动。极低和极高的凝固冷却速率是控制Al10V相析出和长大的关键控制因子，两者的形核机制截然不同。浇铸温度和凝固冷却速率是Al3V相析出的关键控制因子，通过对这两个参数的耦合调控能够精确控制Al3V相的形核长大与分布状态；3）Al3V相和Al10V相在Al-Mg-Si变形铝合金熔炼过程中可转变为AlFeVSi相和AlVSi相。若产物由Al3V相转变而来，其主要受Al3V相尺寸和分布的共同影响；而如果产物是由Al10V相转变而来，那么Al10V相的尺寸是影响产物种类的决定性因素。AlFeVSi相的形态为片状或尺寸较大的团状，多分布于晶界或与共晶相共存，而分布于晶内的含V相均为尺寸较小的团状AlVSi相。4）Al3V和Al10V相对Al-Mg-Si变形铝合金铸态晶粒的细化效果与其溶解行为密切相关，只有在尺寸较大时，才会对变形铝合金铸态晶粒产生较为明显的细化效果，两者相比Al3V相的细化作用更大。