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

实验研究了含1.80%Li(6.65%Li)至3.33%Li(11.8%Li)的4种Al-Li合金的过饱和固溶体分解现象和相的粗化行为。Al-Li二元合金的分解过程如下：α-&gt；均相有序--gt；有序域--gt；Delta‘delta.均相有序结构和有序相都是亚稳定相的前驱相，且所含Li少于化学计量比成分25mol%Li。β‘相对提高Al-Li合金的机械强度最为有效。并对三角洲相的粗化行为进行了定量分析。在透射电子显微镜的暗场图像中，清晰地观察到了三角洲的析出物。用图像分析系统测定了平均半径、粒度分布、标准差和偏斜度。三角洲相的粗化符合深井…。更多地研究了所有合金的r3-t定律(r：平均半径，t：时效时间)。粗化速率常数k随体积分数的增加和温度的升高而增大。Delta‘/基质界面能的导出值为-0.2J/m2。在本研究范围内，Delta’颗粒大小分布(PSD)对老化时间没有很强的依赖性。然而，随着三角洲相体积分数的增加，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三角洲相的实验结果，但考虑到颗粒间的相遇效应的LSEM理论较好地解释了粗化速率常数和PSD。发现添加少量元素Zr能形成细小的复合粒子，并能有效地改善力学性能。所得结果可用于控制和预测Al-Li合金的析出组织，改善合金的性能。较少

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