Coarsening Mechanism of Ordered Precipitates in the Concentrated Al-Li Alloys and their Properties

实验研究了Li含量为1.80 ~ 3.33%（6.65mol%Li）的四种Al-Li合金的过饱和固溶体分解现象和δ '相的粗化行为。Al-Li二元合金的分解过程为：α →均匀有序→有序畴→ δ ′ δ。均匀有序结构和有序畴都是亚稳δ ′相的前驱体，其Li含量低于化学计量比25mol%Li。δ '相对提高Al-Li合金的力学强度最为有效。定量分析了δ相的粗化行为。在TEM暗场图像中清楚地观察到δ '沉淀。使用图像分析系统确定平均半径、粒度分布、标准偏差和偏度。δ相的粗化是根据已知的 ...更多信息 wn r^3 - t定律（r：平均半径，t：时效时间）。粗化速率常数k随delta体积分数和温度的增加而增加。δ ′/基体界面的界面能为-0.2 J/m^2。在本研究范围内，δ ′颗粒尺寸分布（PSD）对老化时间没有很强的依赖性。随着δ相体积分数的增加，PSD变得更加对称.尽管任何一种颗粒粗化理论都不能完全解释δ相的实验结果，但考虑颗粒间碰撞效应的LSEM理论很好地解释了粗化速率常数和PSD。微量添加元素Zr能有效地提高复合材料的力学性能。所得结果对控制和预测Al-Li合金的析出相组织，提高合金的性能具有重要意义。少

Decomposition phenomena of supersaturated solid solution and coarsening behavior of the delta' phase were experimentally investigated for four Al-Li alloys containing 1.80 mass%Li (6.65 mol%Li) up to 3.33 mass%Li (11.8mol%Li). The decomposition of the Al-Li binary alloy was found to take place as follows :alpha -> homogeneous ordering -> ordered domain -> delta' deltaBoth the homogeneous ordering structures and ordered domains were precursors to the metastable delta' phase and contained less Li than that of the stoichiometric composition, 25mol%Li. The delta' phase was most effective to increase the mechanical strength of Al-Li alloys. The coarsening behavior of the delta' phase was also quantitatively analyzed. The delta' precipitates were clearly observed in the TEM dark field images. The mean radius, particle size distribution, standard deviation and skewness were determined using an image analysis system. The coarsening of the delta' phase took place in accordance with the well-kno … More wn r^3 - t law (r : mean radius, t : aging time) for all alloys investigated. The coarsening rate constant, k, increased with increasing delta' volume fraction and temperature. The derived value of the interfacial energy for the delta'/matrix interface was - 0.2 J/m^2.The delta' particle size distribution (PSD) was found to have no strong dependence on aging time within the present investigation. The PSD, however, became more symmetrical with increasing volume fraction of the delta' phase. Although any of the particle-coarsening theories did not fully explain the experimentally obtained results for the delta' phase, the LSEM theory taking into account the encounter effect between particles explains weel the coarsening rate constant and PSDs. The small additional element Zr was found to produce fine composite particles and was effective to improve the mechanical properties. The obtained results are applicable to control and predict the precipitate microstructures and improve the properties of Al-Li alloys. Less