本文選題：AlCuMg合金 + 析出相�。� 參考：《湖南大學(xué)》2015年博士論文

【摘要】：Al-Cu-Mg合金是航天航空用主要結(jié)構(gòu)材料之一,其強(qiáng)化的主要原因在于A1基體中形成的強(qiáng)化析出相。為了提高Al-Cu-Mg合金的綜合力學(xué)性能,即較高的強(qiáng)度和較高的韌性,就要獲得相應(yīng)形態(tài)的析出相。因此,認(rèn)識(shí)析出相的結(jié)構(gòu)、種類、形貌、尺寸、分布、析出相與位錯(cuò)、不同種類析出相之間的相互聯(lián)系,以及析出相形態(tài)隨時(shí)效條件的演化規(guī)律等析出相的形態(tài)特征,就成了調(diào)控合金性能的重要途徑。近年來(lái),國(guó)內(nèi)外學(xué)者對(duì)此已經(jīng)作了大量的工作和報(bào)道,并得到了很大進(jìn)展,但仍然存在一些問(wèn)題有待闡明和澄清。針對(duì)該領(lǐng)域存在的一些典型科學(xué)問(wèn)題,本論文通過(guò)調(diào)節(jié)熱處理工藝,采用不同的性能表征手段,和先進(jìn)的原子分辨率透射電鏡(TEM)和掃描透射電鏡(STEM)技術(shù),結(jié)合第一原理計(jì)算技術(shù),對(duì)目標(biāo)Al-Cu-Mg合金的工藝、性能和微觀組織結(jié)構(gòu),以及它們間的本征關(guān)系,展開(kāi)了系統(tǒng)的實(shí)驗(yàn)研究和細(xì)致的分析、理解研究,獲得了一些有意義的結(jié)果。論文獲得的主要結(jié)果如下：(1)從對(duì)AA2024合金180℃單級(jí)時(shí)效析出規(guī)律的觀察表明,合金中主要有兩種系列的強(qiáng)化析出相,即S相和GPB區(qū),以及它們的亞穩(wěn)前驅(qū)體。其中S相是一種板條狀相,它的基本位向關(guān)系為[100]s//[100]Al, [010]s//[021]Al, [001]s//[012]Al。本文實(shí)驗(yàn)觀察表明,S相可環(huán)繞100s軸作出小角度調(diào)整旋轉(zhuǎn),以達(dá)到應(yīng)變能降低的狀態(tài)。在其轉(zhuǎn)動(dòng)過(guò)程會(huì)伴隨晶格常數(shù),形貌和界面的變化。S相的轉(zhuǎn)動(dòng)現(xiàn)象與時(shí)效條件有關(guān),時(shí)效時(shí)間越長(zhǎng),溫度越高,越容易觀察到轉(zhuǎn)動(dòng)的s相,且轉(zhuǎn)動(dòng)與否與析出相尺寸無(wú)關(guān)。由于轉(zhuǎn)動(dòng)S相通常需要較高的時(shí)效溫度或較長(zhǎng)的時(shí)效時(shí)間才能形成,且常常尺寸過(guò)大而對(duì)合金的硬度貢獻(xiàn)有限。此外,S相既可以獨(dú)立形核,也可以在第二相界面處形核,后者形核的S相形貌像比同條件下獨(dú)立形核的S相多為柱狀。(2)在較高的溫度下或較低溫度但較長(zhǎng)時(shí)間的時(shí)效時(shí)間內(nèi),GPB區(qū)作為另外一種主要析出相,可以與S相同時(shí)形成,也可以圍繞S相伴隨著其進(jìn)一步長(zhǎng)大而慢慢形成,在長(zhǎng)時(shí)間時(shí)效以后又會(huì)消失。GPB區(qū)為一維針狀晶體,在其橫截面內(nèi)無(wú)周期結(jié)構(gòu)。(3)在180℃時(shí)效初期可在合金中觀察到大量的第二相和位錯(cuò)缺陷。其中第二相與A1基體的界面可為S相提供形核質(zhì)點(diǎn)。同時(shí),過(guò)去人們將在時(shí)效早期的鋁合金中形成的位錯(cuò)缺陷認(rèn)為是“位錯(cuò)圈”,本文通過(guò)對(duì)合金中位錯(cuò)的一系列TEM衍襯像分析,得出AA2024合金中形成的位錯(cuò)實(shí)為蜷線位錯(cuò),它的形成與S相(早期的)和Al基體界面匹配性差以及溶質(zhì)原子偏聚有關(guān)。(4)不同溫度、不同時(shí)間時(shí)效樣品的TEM觀察結(jié)果表明,S相的形核和生長(zhǎng)具有很強(qiáng)的各向異性和受溫度影響的特征,同時(shí)伴隨低維相轉(zhuǎn)變。因?yàn)镾相具有正交的晶體學(xué)結(jié)構(gòu),導(dǎo)致其生長(zhǎng)具有各向異性特征。但特別的是,由于S相的厚度生長(zhǎng)需要經(jīng)過(guò)其前驅(qū)相GPS2-Ⅱ才能實(shí)現(xiàn),又因?yàn)樵谳^高溫度(180℃)下,GPS2-Ⅱ沿寬度方向的生長(zhǎng)被在其兩端快速形成的GPB單元阻擋,所以高溫下S相的平均寬長(zhǎng)比要明顯小于其低溫下的平均寬長(zhǎng)比。同時(shí),我們的研究還顯示盡管GPB單元和S相能成一個(gè)GPB-S或GPB-GPS2-Ⅱ復(fù)合體,但GPB區(qū)并不能直接轉(zhuǎn)變成S相,反之也一樣。(5)在理解合金單級(jí)時(shí)效硬化規(guī)律的基礎(chǔ)上,為提高合金的強(qiáng)度和韌性,本文探討了多級(jí)時(shí)效(T614和T616時(shí)效)對(duì)合金的性能和顯微組織影響規(guī)律。研究表明,相對(duì)于T6處理,T614和T616增加了一個(gè)中斷時(shí)效,在這個(gè)過(guò)程中合金中不能析出更多的強(qiáng)化相(S相和GPB區(qū))。與T6條件相比,T614可使合金獲得較好的韌性,源于合金中形成了原子團(tuán)簇。而在接下來(lái)的再時(shí)效過(guò)程中合金中也沒(méi)有更多S相形核,原有的S相又發(fā)生明顯粗化,導(dǎo)致T616峰值時(shí)效相比T6狀態(tài)峰值時(shí)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.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG146.21

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