AlCuMg合金析出相微结构与工艺及性能的关系研究

发布时间：2018-06-06 23:13

本文选题：AlCuMg合金 + 析出相　；参考：《湖南大学》2015年博士论文

【摘要】：Al-Cu-Mg合金是航天航空用主要结构材料之一,其强化的主要原因在于A1基体中形成的强化析出相。为了提高Al-Cu-Mg合金的综合力学性能,即较高的强度和较高的韧性,就要获得相应形态的析出相。因此,认识析出相的结构、种类、形貌、尺寸、分布、析出相与位错、不同种类析出相之间的相互联系,以及析出相形态随时效条件的演化规律等析出相的形态特征,就成了调控合金性能的重要途径。近年来,国内外学者对此已经作了大量的工作和报道,并得到了很大进展,但仍然存在一些问题有待阐明和澄清。针对该领域存在的一些典型科学问题,本论文通过调节热处理工艺,采用不同的性能表征手段,和先进的原子分辨率透射电镜(TEM)和扫描透射电镜(STEM)技术,结合第一原理计算技术,对目标Al-Cu-Mg合金的工艺、性能和微观组织结构,以及它们间的本征关系,展开了系统的实验研究和细致的分析、理解研究,获得了一些有意义的结果。论文获得的主要结果如下：(1)从对AA2024合金180℃单级时效析出规律的观察表明,合金中主要有两种系列的强化析出相,即S相和GPB区,以及它们的亚稳前驱体。其中S相是一种板条状相,它的基本位向关系为[100]s//[100]Al, [010]s//[021]Al, [001]s//[012]Al。本文实验观察表明,S相可环绕100s轴作出小角度调整旋转,以达到应变能降低的状态。在其转动过程会伴随晶格常数,形貌和界面的变化。S相的转动现象与时效条件有关,时效时间越长,温度越高,越容易观察到转动的s相,且转动与否与析出相尺寸无关。由于转动S相通常需要较高的时效温度或较长的时效时间才能形成,且常常尺寸过大而对合金的硬度贡献有限。此外,S相既可以独立形核,也可以在第二相界面处形核,后者形核的S相形貌像比同条件下独立形核的S相多为柱状。(2)在较高的温度下或较低温度但较长时间的时效时间内,GPB区作为另外一种主要析出相,可以与S相同时形成,也可以围绕S相伴随着其进一步长大而慢慢形成,在长时间时效以后又会消失。GPB区为一维针状晶体,在其横截面内无周期结构。(3)在180℃时效初期可在合金中观察到大量的第二相和位错缺陷。其中第二相与A1基体的界面可为S相提供形核质点。同时,过去人们将在时效早期的铝合金中形成的位错缺陷认为是“位错圈”,本文通过对合金中位错的一系列TEM衍衬像分析,得出AA2024合金中形成的位错实为蜷线位错,它的形成与S相(早期的)和Al基体界面匹配性差以及溶质原子偏聚有关。(4)不同温度、不同时间时效样品的TEM观察结果表明,S相的形核和生长具有很强的各向异性和受温度影响的特征,同时伴随低维相转变。因为S相具有正交的晶体学结构,导致其生长具有各向异性特征。但特别的是,由于S相的厚度生长需要经过其前驱相GPS2-Ⅱ才能实现,又因为在较高温度(180℃)下,GPS2-Ⅱ沿宽度方向的生长被在其两端快速形成的GPB单元阻挡,所以高温下S相的平均宽长比要明显小于其低温下的平均宽长比。同时,我们的研究还显示尽管GPB单元和S相能成一个GPB-S或GPB-GPS2-Ⅱ复合体,但GPB区并不能直接转变成S相,反之也一样。(5)在理解合金单级时效硬化规律的基础上,为提高合金的强度和韧性,本文探讨了多级时效(T614和T616时效)对合金的性能和显微组织影响规律。研究表明,相对于T6处理,T614和T616增加了一个中断时效,在这个过程中合金中不能析出更多的强化相(S相和GPB区)。与T6条件相比,T614可使合金获得较好的韧性,源于合金中形成了原子团簇。而在接下来的再时效过程中合金中也没有更多S相形核,原有的S相又发生明显粗化,导致T616峰值时效相比T6状态峰值时效的性能下降。
[Abstract]:Al-Cu-Mg alloy is one of the main structural materials for aerospace and aerospace. The main reason for its strengthening is the enhanced precipitate formed in the A1 matrix. In order to improve the comprehensive mechanical properties of the Al-Cu-Mg alloy, that is, higher strength and higher toughness, the corresponding precipitates should be obtained. Therefore, the structure, type, morphology and size of the precipitated phase are recognized. The distribution, the interrelation between phase and dislocation, the interrelation between different kinds of precipitates and the morphological characteristics of precipitates in the precipitation phase state with the evolution of aging conditions have become an important way to regulate the properties of the alloys. In recent years, a great deal of work and reports have been made by domestic and foreign scholars, and great progress has been made, but it still exists. Some problems need to be clarified and clarified. In view of some typical scientific problems in this field, this paper uses the heat treatment process, the use of different performance characterization methods, advanced atomic resolution transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) technology, combined with the first principle calculation technology, the process of the target Al-Cu-Mg alloy. The results are as follows: (1) the main results of the paper are as follows: (1) from the observation of the precipitation rule of the single stage aging of AA2024 alloy at 180 C, there are two kinds of intensification analysis in the alloy. The phase, that is, the S and GPB regions, and their metastable precursors, the S phase is a slate phase, and its basic relationship is [100]s//[100]Al, [010]s//[021]Al, and [001]s//[012]Al., in this paper, the experimental observation shows that the S phase can make a small angle adjustment around the 100s axis to achieve a state of strain energy reduction. In its rotation process it will be accompanied. The rotation of.S phase, the change of lattice constant, morphology and interface, is related to the aging condition. The longer the aging time is, the higher the temperature is, the more easily the rotating S phase is observed, and the rotation is independent of the size of the precipitated phase. As the rotation of the S phase usually requires a higher aging temperature or a longer aging time, the size is too large and the opposite is often used. The hardness contribution of gold is limited. In addition, the S phase can both be independent of nucleation and can nucleate at the second phase interface. The S phase appearance of the latter is more columnar than the S phase of the independent nucleation under the same condition. (2) the GPB region is the same as another major precipitate at a higher temperature or lower temperature but a longer time of aging, which can be the same as S. The formation can also be formed around the S phase with its further growth. After a long time aging, the.GPB region will disappear as a one-dimensional needle like crystal, and there is no periodic structure in its cross section. (3) a large number of secondary phases and dislocation defects can be observed in the alloy at the initial age of 180 C. The interface between the second phase and the A1 matrix can be a S phase At the same time, the dislocation defects formed in the aluminum alloy in the early age of aging are considered as "dislocation circles". By analyzing a series of TEM contrast images in the dislocations in the alloy, it is concluded that the dislocation formed in the AA2024 alloy is actually a curled line dislocation, and its formation is poor in matching the interface between the S phase (early) and the Al matrix as well. (4) the results of TEM observation at different temperatures and different time aging samples show that the nucleation and growth of the S phase have strong anisotropy and temperature influence, and are accompanied by the low phase transition. Because the S phase has an orthogonal crystallographic structure, it leads to the anisotropy of its growth, but in particular, because of S The growth of the phase thickness needs to be achieved through its precursor GPS2- II, and because at a higher temperature (180 C), the growth of GPS2- II along the width is blocked by the GPB unit which is rapidly formed at both ends, so the average width to length ratio of the S phase at high temperature is significantly smaller than the average width ratio under the low temperature. Meanwhile, our study also shows that although GP is in spite of GP The B unit and the S phase can be a GPB-S or GPB-GPS2- II complex, but the GPB region can not be directly transformed into S phase, and the opposite is the same. (5) in order to improve the strength and toughness of the alloy, the influence of the multistage aging (T614 and T616 time effect) on the properties and microstructure of the alloy was investigated. Compared with the T6 treatment, T614 and T616 increase an interruption aging, and in this process the alloys cannot precipitate more intensities (S and GPB). Compared with T6 conditions, T614 can make the alloy get better toughness, derived from the atomic cluster in the alloy, and there is no more S phase in the alloy during the re aging process. The original S phase is obviously coarsened, resulting in a decrease in the peak age effect of T616 compared with the T6 peak aging.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG146.21

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