本文選題：Ti/Al異種合金 + 電子束熔釬焊�。� 參考：《南京理工大學(xué)》2017年碩士論文

【摘要】：鋁鋰合金和鈦合金在航空、航天工業(yè)有著廣泛的應(yīng)用,由于近年來制造業(yè)都在追求結(jié)構(gòu)輕型化、結(jié)構(gòu)功能一體化和低成本設(shè)計(jì)與制造,所以鋁鋰合金和鈦合金的復(fù)合結(jié)構(gòu)具有巨大的應(yīng)用前景,但是由于鈦、鋁的物理化學(xué)性質(zhì)相差較大,而且二者化學(xué)反應(yīng)極容易形成脆性金屬間化合物,所以這就給Ti/Al的焊接造成了一定的困難。本試驗(yàn)采用了電子束熔釬焊接方法,利用電子束的高深寬比、能量的精確可控性得到了可靠地Ti/Al異種合金焊接接頭,該方法有效地控制了過渡層的組成。設(shè)計(jì)焊接接頭設(shè)計(jì)試驗(yàn)、焊接參數(shù)的調(diào)整試驗(yàn)、偏束量的調(diào)整試驗(yàn)和焊縫根部強(qiáng)化焊試驗(yàn)等對(duì)照組試驗(yàn)進(jìn)行工藝優(yōu)化,分析了各組對(duì)焊縫成形規(guī)律的影響。并對(duì)某些對(duì)照組采用金相顯微鏡、掃描電鏡(SEM)及附帶的能譜分析儀(EDS)、X射線衍射儀(XRD)研究微觀組織分布、元素分布規(guī)律和物相組成,最后采用靜載拉伸試驗(yàn)和顯微硬度測(cè)試對(duì)不同接頭進(jìn)行了力學(xué)性能評(píng)價(jià)。鋁鋰合金熔焊部分主要分為母材、熱影響區(qū)、細(xì)晶區(qū)、柱狀晶區(qū)、等軸晶區(qū),在焊接過程中接頭軟化導(dǎo)致了焊縫強(qiáng)度降低。熔釬焊界面金屬間化合物主要有棒狀、鋸齒狀和胞狀三種生長(zhǎng)形態(tài),生長(zhǎng)情況受偏束量和界面位置決定,其中棒狀金屬間化合物對(duì)界面結(jié)合強(qiáng)度有增強(qiáng),胞狀結(jié)合強(qiáng)度最差。由線掃描可以發(fā)現(xiàn),偏束量越大界面反應(yīng)層越薄,同一焊縫從上至下反應(yīng)層越來越薄。結(jié)合線掃描和區(qū)域掃描結(jié)果發(fā)現(xiàn)單相的棒狀和鋸齒狀金屬間化合物原子比例不穩(wěn)定,所以做出了反位缺陷的猜想。通過焊縫物相分析發(fā)現(xiàn),不同偏束距離的物相組成有部分差異,這跟界面反應(yīng)溫度有關(guān),界面溫度決定物相的轉(zhuǎn)換是否徹底。經(jīng)過工藝優(yōu)化的焊接接頭物相由TiAl3、Ti5Al11、TiAl、Ti3Al四種相組成,其中棒狀、鋸齒狀和胞狀金屬間化合物組織的大部分是TiAl3,而這些組織的根部連續(xù)過渡層則存在Ti5Al11、TiAl、Ti3Al等金屬間化合物。對(duì)工藝優(yōu)化后的焊接接頭通過靜載拉伸試驗(yàn)拉伸強(qiáng)度可以達(dá)到260MPa。焊縫的拉伸斷面可以分為韌性斷裂面和脆性斷裂面,韌性斷裂面出現(xiàn)大量的韌窩和第二相粒子,脆性斷裂面呈現(xiàn)解理刻面。斷裂過程是由焊縫中下部區(qū)域開始出現(xiàn)斷裂縫隙,隨著延伸長(zhǎng)度的變化,斷裂面擴(kuò)張最終韌性區(qū)域斷裂。對(duì)于斷口不同區(qū)域組織構(gòu)成,脆性斷裂部分主要是TiAl3,而韌性斷裂部分主要是鋁鋰合金組織。
[Abstract]:Al-Li alloy and titanium alloy have been widely used in aviation and aerospace industry. In recent years, the manufacturing industry has been pursuing structural lightweight, structural and functional integration and low-cost design and manufacture. Therefore, the composite structure of Al-Li alloy and titanium alloy has a great application prospect, but the physical and chemical properties of Ti and Al differ greatly, and the chemical reactions between them are easy to form brittle intermetallic compounds. So this caused some difficulties for the welding of Ti / Al. In this experiment, the welding method of electron beam fusion brazing is adopted. The high aspect ratio of electron beam and the precise controllability of energy are used to obtain the reliable Ti / Al dissimilar alloy welding joint. The composition of transition layer is effectively controlled by this method. Design welding joint design test, welding parameter adjustment test, offset beam adjustment test and weld root reinforcement welding test were optimized. The influence of each group on weld forming law was analyzed. The microstructure, element distribution and phase composition of some control groups were studied by metallographic microscope, scanning electron microscope (SEM) and EDS X-ray diffractometer (XRD). Finally, mechanical properties of different joints were evaluated by static load tensile test and microhardness test. The melting and welding parts of Al-Li alloy are mainly divided into base metal, heat-affected zone, fine-grained zone, columnar zone and equiaxed zone. During the welding process, the joint softening results in the decrease of weld strength. The intermetallic compounds in the fusion-brazing interface are mainly rod-shaped, sawtooth and cellular, and the growth is determined by the amount of skew beam and the position of the interface, among which the intermetallic compounds of rod-shaped intermetallics enhance the interfacial bonding strength, and the cellular bonding strength is the worst. It is found from the line scanning that the reaction layer of the interface is thinner with the increase of the skew beam amount, and the reaction layer of the same weld is thinner from top to bottom. In combination with the results of line scanning and region scanning it is found that the atomic ratio of single-phase rod-like and sawtooth intermetallic compounds is unstable so the conjecture of counterposition defects is made. It is found that there are some differences in phase composition between different beam distances, which is related to the interfacial reaction temperature, and the interfacial temperature determines whether the phase transition is complete or not. The phase of the welded joints optimized by the process is composed of four phases: TiAl _ 3C _ 3C _ 5AL _ (11) Al _ (11) Ti _ (3AL) Al _ (3AL), among which the rod-shaped, sawtooth and cellular intermetallics are mostly TiAl3, and the intermetallic compounds such as Ti5Al11TiAlTiAlTi3Al exist in the continuous transition layer at the root of these structures. The tensile strength of the welded joint can reach 260 MPA by static load tensile test. The tensile section of the weld can be divided into ductile fracture surface and brittle fracture surface. A large number of dimples and second phase particles appear on the ductile fracture surface and the brittle fracture surface presents cleavage surface. The fracture process begins with the crack in the middle and lower part of the weld, and with the change of the extension length, the fracture of the fracture surface expands to the final ductile zone. The brittle fracture is mainly TiAl3 and the ductile fracture is Al-Li alloy.
【學(xué)位授予單位】：南京理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG457.1

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