自润滑铝合金中电脉冲耦合活性元素诱发超细弥散软相形成及调控机理

Bi合金化铝硅系合金能大幅改善摩擦特性及尺寸稳定性等，在高性能金属摩擦副材料等方面具有广泛的应用前景，但组织中软相易偏析，电脉冲复合活性元素为偏晶合金凝固工艺提供了新思路。本项目拟开展交流电脉冲下具偏晶特性多元铝合金凝固特征及电效应强化活性元素机理研究，采用同轴双管的连续定向凝固方法，通过小管直径调节对流来探索强制对流等电效应对液相分离和偏晶反应的影响规律，并提出抑制相偏析的电效应条件。基于电脉冲凝固细晶特性，采用不同电极构型浇铸法阐明别相形核与生长对软相的动态调控规律。综合考虑宏/微观流场特征和修正的相场参数，建立电脉冲下液相分离相场模型，揭示电脉冲下多元偏晶合金组织演化机理及控制方法。在此基础上，通过电脉冲耦合活性元素锡调控连续凝固过程制备超细弥散软相，分析耦合强化机理，建立含活性元素含量、电脉冲参量和凝固变量的超细弥散第二相形成临界条件判据，拓展多元偏晶合金凝固组织控制的新途径。

The multicomponent Al-based alloys with Bi element, which can improve friction properties and dimension stability etc., have a great promising application in the friction materials of self-lubricate performance. In order to suppress serious phase segregation due to the liquid-liquid decomposition, the application of alternating electropulsing coupling with active element to multicomponent immiscible alloys, as a novel solidification technology, has been designed. In this project, we are devoted to investigate the solidification behavior of Al-based alloys with Bi addition under alternating electropulsing and related mechanisms. Since intensity of flow field depends on the diameter of corundum tube when the current density is constant, influence of current effects including the forced melt flow etc. on liquid-liquid and liquid-solid phase transformations can be studied by continuous unidirectional solidification using corundum tube with sleeve, based on which the proper conditions for the suppression of phase segregation will be pointed out. On the basis of previous grain refinement under electropulsing, the relevance of crystal nucleation and growth of primary and eutectic phase to the distribution characteristics of minority phase droplets will be revealed by casting with various electrode employing modes. Under the condition of double-scaled melt flow coupling with modified thermodynamic and kinetic data, phase-field simulation of liquid separation will be established. Subsequently, the solidification mechanisms and control method of microstructure in multicomponent immiscible alloys are discussed under electropulsing. The active element Sn will be further added to prepare a well-dispersed microstructure. Based on investigation of the strengthening mechanism of current effects to the role of Sn, we will build a critical conditions criterion for the formation of the dispersed distribution of ultrafine second phase including content of Sn, electropulsing parameters and solidification parameters. This study will open up a new effective way for solidification process of multicomponent immiscible alloys.