本文選題：鎂銥釹合金 + 時(shí)效處理��； 參考：《吉林大學(xué)》2015年碩士論文

【摘要】：鎂合金以質(zhì)輕、比強(qiáng)度高、耐熱性好和減震性能好等優(yōu)點(diǎn)，成為現(xiàn)代替代鋼鐵、鋁合金和塑料以實(shí)現(xiàn)輕量化的理想材料，被日益廣泛的應(yīng)用在交通工具、“3C”產(chǎn)品和航空航天等領(lǐng)域。但由于高溫蠕變性能差，制約了其發(fā)展應(yīng)用范圍，因此鎂合金的強(qiáng)化及其強(qiáng)化機(jī)理成為鎂合金研究的一個(gè)重要方向。各種稀土被作為合金元素加入到鎂合金中來(lái)改善其常溫高溫性能、耐熱蠕變性等，含有釔和釹元素的WE系列合金是耐熱鎂合金中應(yīng)用最廣泛的合金，如WE54和WE43等，300℃其性能可保持1000h，250℃下能夠長(zhǎng)期工作，在飛機(jī)和賽車(chē)發(fā)動(dòng)機(jī)的汽缸上得到應(yīng)用。最常用的的強(qiáng)化手段是固溶時(shí)效處理，但是，到目前為止，Mg-Y-Nd合金的時(shí)效強(qiáng)化機(jī)制還不太清楚，所以，本課題通過(guò)高溫時(shí)效處理，研究Mg-4Y-3Nd合金不同時(shí)效階段的析出相的析出規(guī)律、析出相的物相轉(zhuǎn)變，從而明確其時(shí)效強(qiáng)化機(jī)制。 研究工作中，采用先金屬模鑄造法再熱擠壓加工制備的Mg-4Y-3Nd合金。并對(duì)其進(jìn)行固溶時(shí)效處理。利用光學(xué)顯微鏡、X射線衍射儀（XRD）、掃描電子顯微鏡（SEM）和能譜儀（SEM-EDS）、透射高分辨（HTEM）、維氏硬度計(jì)研究了不同時(shí)效階段的金相組織、第二相析出規(guī)律、物相結(jié)構(gòu)、時(shí)效硬化，從而明確其時(shí)效強(qiáng)化機(jī)制。 結(jié)果表明：T6態(tài)Mg-4Y-3Nd合金的第二相優(yōu)先在晶界處形核，向晶內(nèi)非連續(xù)析出，隨著時(shí)效時(shí)間的增加，，第二相會(huì)在晶內(nèi)連續(xù)析出，并且第二相在基體組織上呈均勻分布狀態(tài)，不存在鑄態(tài)組織中的連續(xù)樹(shù)枝晶，時(shí)效過(guò)程中，最先析出的第二相細(xì)小，然后體積有稍微長(zhǎng)大，時(shí)效4h后的第二相體積逐漸長(zhǎng)大，直到32h時(shí)有明顯的長(zhǎng)大。物相結(jié)構(gòu)研究表明：T6態(tài)Mg-4Y-3Nd合金的顯微組織由α-Mg固溶體、二元析出相Mg24Y5、Mg2Y、Mg41Nd5和三元析出相Mg14Nd2Y組成。隨著析出相的生成，基體的晶格常數(shù)也隨之變化，同一晶面的2θ減小，晶面間距d增大。 時(shí)效硬度曲線表明：0.5-32h時(shí)效過(guò)程中存在3次時(shí)效硬化峰，包括0.5h時(shí)的一次很快消失的小幅時(shí)效，4h和24h時(shí)兩次明顯的時(shí)效硬化，每個(gè)時(shí)效硬化峰的出現(xiàn)，都表明析出相之間發(fā)生了物相轉(zhuǎn)變，時(shí)效0.5h時(shí)，Mg-Y-Nd合金中主要存在β″相，因?yàn)棣隆逑啻嬖诘臅r(shí)間極短，會(huì)很快轉(zhuǎn)化為β′相，這個(gè)現(xiàn)象表現(xiàn)為時(shí)效1h時(shí)合金的硬度有下降；然后β′相不斷的形成，在時(shí)效4h時(shí)出現(xiàn)一次明顯的時(shí)效硬化現(xiàn)象，時(shí)效8h硬度明顯下降，這是β′相開(kāi)始轉(zhuǎn)變?yōu)棣?相；到時(shí)效24h時(shí)又一次出現(xiàn)明顯的時(shí)效硬化現(xiàn)象，這時(shí)β1相開(kāi)始轉(zhuǎn)化為β相，導(dǎo)致時(shí)效32h出現(xiàn)硬度的明顯下降，在8-32h時(shí)效過(guò)程中存在β′相、β1相和β相共存的現(xiàn)象。
[Abstract]:Magnesium alloy, with the advantages of light quality, high strength, good heat resistance and good damping property, has become an ideal material to replace steel, aluminum alloy and plastic to realize light weight. It is widely used in the fields of transportation, "3C" products and Aeronautics and Astronautics. But because of poor high temperature creep performance, it restricts its development and application, so magnesium is limited. The strengthening and strengthening mechanism of the alloy has become an important direction in the study of magnesium alloys. All kinds of rare earth elements are added to magnesium alloys as alloy elements to improve their temperature and temperature properties at normal temperature, heat resistance, and so on. WE series alloys containing yttrium and neodymium are the most widely used alloys in heat-resistant magnesium alloys, such as WE54 and WE43, and their properties at 300. 1000h can be maintained at 250 C for a long time and can be applied to the cylinder of aircraft and car engine. The most commonly used reinforcement means is solution aging treatment. However, so far, the aging hardening mechanism of Mg-Y-Nd alloys is not very clear. So, this subject has studied different aging stages of Mg-4Y-3Nd alloys by high temperature aging treatment. The precipitation mechanism of precipitates and the phase transformation of precipitates are identified, so as to clarify the mechanism of aging strengthening.
In the research work, the Mg-4Y-3Nd alloy prepared by reheat extrusion of the first metal mold casting method was used. The solid solution and aging treatment was carried out. The optical microscope, X ray diffractometer (XRD), scanning electron microscope (SEM) and energy spectrometer (SEM-EDS), transmission high resolution (HTEM), and Vivtorinox hardness meter were used to study the metallographic structure of different aging stages, second Phase precipitation, phase structure and age hardening can clarify the aging strengthening mechanism.
The results show that the second phase of the T6 state Mg-4Y-3Nd alloy is first nucleated at the grain boundary and discontinuous in the crystal. As the aging time increases, the second phase will continuously precipitate in the crystal, and the second phase is uniformly distributed in the matrix structure, and there is no continuous dendrite in the cast structure. The first precipitate phase is first precipitated during the aging process. The volume is slightly older and the volume of the second phase after aging 4H grows gradually. The phase structure of the T6 state Mg-4Y-3Nd alloy shows that the microstructure of the T6 state Mg-4Y-3Nd alloy is composed of a solid solution of alpha -Mg, Mg24Y5, Mg2Y, Mg41Nd5 and three elements precipitated in the precipitate phase of the alloy. With the formation of the precipitated phase, the lattice lattice of the matrix is constant. The number also varies with the 2 D of the same plane decreasing, and the distance between the crystal faces increases.
The aging hardness curve shows that there are 3 time hardening peaks in the aging process of 0.5-32h, including a small amplitude aging that quickly disappeared at the time of 0.5h, two apparent aging hardening at 4H and 24h, and the occurrence of each hardening peak indicates that the phase transition occurs between the precipitates, and when the time effect 0.5h is the main existence of the beta "phase in the Mg-Y-Nd alloy, because The existence of the beta "phase is very short, and it will quickly transform into beta phase. This phenomenon shows that the hardness of the alloy decreases when the aging 1H is aged; then the phase of the beta phase is constantly formed, and a obvious aging hardening occurs at the aging 4h, and the hardness of the aging 8h decreases obviously. This is the transformation of beta 'phase to beta 1 phase, and another appearance to the aging 24h. The phenomenon of aging hardening occurs when the beta 1 phase begins to be transformed into beta phase, which leads to a significant decrease in the hardness of the aging 32H. In the aging process of 8-32h, there is a phase of beta 'and the coexistence of beta 1 and beta phase.

【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TG146.22;TG166.4

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