低合金化对Al-Bi难混溶合金液相分离行为与摩擦磨损性能的关联作用机理

Immiscible alloy is characterized by a miscibility gap in the liquid state, which induces macro-segregation in solid state and limits its application. But due to the good self-lubricating property, Cu-Pb and Al-Pb were first used as bearing alloys. At present, bearings containing lead are gradually not accepted due to the polluting and toxic character of lead. Hence, Al-Bi immiscible alloy as a potential lead-free self-lubricating alloy is now getting more and more attention. To develop a new type Al-Bi alloy with good friction and wear properties, minor alloying is expected to be an effective way. But, for immiscible alloy, additional alloying elements distinctly change the miscibility gap of binary immiscible alloy, and consequently influence the liquid phase separation behavior and the subsequent solidification microstructure, which finally influence the friction-wear properties of alloy. Hence, to disclose the above influence of additional alloying elements is the prerequisite of minor alloying for immiscible alloy. Aiming to support the development of new self-lubricating immiscible alloy through minor alloying, the research on associated effect of minor alloying on liquid phase separation behavior and friction-wear properties of immiscible Al-Bi alloy is proposed in this project. Firstly, the influence of additional alloying elements on evolution of second phase in miscibility gap, as well as the trapping of second phase in matrix phase on advancing solidification front will be studied, in order to disclose the influence of additional alloying elements on the size and distribution of second phase in solidified microstructure. Secondly, the influence of additional alloying elements on friction and wear properties of Al-Bi alloy will be studied taking account of the couple effect of distribution of second phase and the micro hardness of the double phase in alloy.

难混溶合金因具有液相分离特性极易偏析而难于制备与应用，但因具有优异的自润滑特性，Cu-Pb和Al-Pb系难混溶合金轴瓦材料首先得到了应用。目前，因Pb的污染和危害性，探索新型无铅Al-Bi基难混溶合金自润滑材料又受到了关注。低合金化是提高合金性能的常用方法，但对于难混溶合金，因液相分离区间的存在，低合金化对合金的液相分离行为以及随后的凝固组织表现出复杂的影响，同时关联的影响了合金的摩擦磨损性能，探索这些影响的机理成为难混溶合金低合金化设计的前提。本项目以Al-Bi体系为基础，研究不同低合金化元素对难混溶合金第二相在不混溶区间内的演变以及凝固前沿基体相生长截留第二相的影响机制，以揭示低合金化对合金组织中第二相分布的影响机理；耦合低合金化元素对第二相分布以及两相显微硬度的双重作用，研究低合金化对难混溶合金摩擦磨损性能的影响机理，旨在为难混溶合金自润滑材料的多元低合金化提供理论依据和技术支持。

为研究低合金化对Al-Bi基难混溶合金凝固行为与摩擦磨损性能的关联作用机理，以探索制备无铅轴瓦，本项目开展了相关研究，主要成果概述如下：研究了Sn、Si、Cu低合金化元素以及元素复合对Al92Bi8合金凝固组织、力学性能、摩擦磨损性能的关联作用机理。研究发现，Sn具有明显细化Al92Bi8 合金中富Bi相的作用。该作用的机理是Sn降低了合金的不混溶区间宽度以及富Al和富Bi间的界面张力。Sn相以Al + LBi↔(Sn) +(Bi)三元共晶形式析出，并分布在富Bi相内。研究表明Sn在Bi相中的分布并没明显强化富Bi相，但是Sn对合金整体的硬度和强度有轻微的提高作用，该提高作用主要是归因于Sn对富Bi相的细化作用。研究表明Si和Cu对富Bi相有明显的粗化作用。在Al92Bi8合金中，Si主要是通过LAl ↔ LBi + (Al) + (Si) 三元偏晶反应产生针状Si相分布的Al基体中，对Al基体以及合金具有明显的强化作用。痕量的Si分布在富Bi相中不明显提高其硬度。含1wt%Cu的Al92Bi8合金中并没出现三元偏晶，Cu主要是固溶在Al基体中，部分在降温过程中以θAl2Cu相脱溶析出，从而对Al基体和合金起到明显的强化作用。.在对Al92Bi8合金进行多元低合金化时，Sn、Si、Cu在合金中能够分别发挥其各自的作用，在通过Si和Cu明显提高合金性能的前提下，通过增加Sn的添加量可以消除Si和Cu加剧Bi相偏析的作用而进一步提高合金的性能，如多元复合设计的(Al0.92Bi0.08)95Sn3Si1Cu1合金。.进一步研究了合金的摩擦磨损性能，研究表明，Sn、Si、Cu元素在不改变Al92Bi8合金摩擦系数的前提下，能够提高合金的耐磨性，元素对合金耐磨性提高的幅度与其对合金的强化效果成对应关系。.研究结果的主要意义：明确了低合金化元素对难混溶合金第二相分布和两相力学性能的双重作用，以及该作用对难混溶合金摩擦磨损性能的影响机理，为难混溶合金自润滑材料的多元低合金化提供了理论依据和技术支持。