本文選題：鈦合金薄板 + 激光焊接　； 參考：《江蘇大學(xué)》2017年碩士論文

【摘要】：針對鈦合金薄板背反射激光焊接現(xiàn)有研究存在的問題,本文以1.5mm厚TC4鈦合金薄板為對象,圍繞“鈦合金薄板低閾值背反射激光焊接數(shù)值分析與特性”這一主題,開展相關(guān)理論及應(yīng)用基礎(chǔ)研究。研究中,通過對背反射激光焊接過程溫度場和應(yīng)力場數(shù)值模擬與分析的研究,闡明背反射激光焊接過程溫度場和應(yīng)力場的變化及其分布規(guī)律,進(jìn)而為揭示背反射激光焊接成形機(jī)理奠定理論基礎(chǔ);同時,通過鈦合金薄板背反射激光焊接成形工藝特性和組織性能特性的研究,驗(yàn)證這一高效低閾值激光焊接新方法對厚度相對于現(xiàn)有研究增大了約1倍的較厚薄板的適應(yīng)性,從而為進(jìn)一步拓展其應(yīng)用提供技術(shù)支撐和應(yīng)用基礎(chǔ)。研究過程中采用“理論分析與實(shí)驗(yàn)研究相結(jié)合、數(shù)值模擬和試驗(yàn)優(yōu)化并重”的研究方法,所開展的研究工作和取得的主要成果如下。(1)鈦合金薄板背反射激光焊接過程的溫度場數(shù)值模擬與分析的研究。以經(jīng)實(shí)驗(yàn)驗(yàn)證的0.8mm厚鈦合金薄板背反射激光焊接過程的“雙熱源”溫度場模型為基礎(chǔ),通過設(shè)定1.5mm的板厚、1400W的功率和850mm/min的掃描速度建立新的溫度場模型,對1.5mm厚鈦合金薄板背反射激光焊接過程的溫度場進(jìn)行了數(shù)值模擬與分析。研究表明:此模型能夠較好地模擬背反射激光焊接成形過程中的溫度場分布情況,薄板正面和背面均在很短時間內(nèi)形成了類似“淚滴狀”的穩(wěn)定溫度場,熱源前端等溫線密集、溫度梯度大,后端等溫線相對稀疏、溫度梯度相對較小。熔池逐漸從V形過渡到X形的溫度場時程變化,較好地描述了背反射激光焊接過程中所形成的背面輔助能場對工件背面進(jìn)行二次加熱的物理過程;同時,隨著功率的增大或者掃描速度的降低,熔池熔寬和熔深逐漸增大,溫度梯度與功率呈正比,與速度呈反比規(guī)律。(2)鈦合金薄板背反射激光焊接過程應(yīng)力場的數(shù)值模擬與分析研究。以溫度場為基礎(chǔ),采用間接耦合法對鈦合金薄板背反射激光焊接過程的應(yīng)力場進(jìn)行了數(shù)值模擬與分析。研究表明:鈦合金薄板背反射激光焊接過程中,隨著焊接時間的延長其熱應(yīng)力隨之增大;而在其冷卻過程中,鈦合金薄板的應(yīng)力值分布在兩端位置處最大,表現(xiàn)出比較明顯的邊界效應(yīng)。同時,常規(guī)激光焊即無反射墊板狀態(tài)下,焊縫橫切面上表面殘余應(yīng)力整體大于下表面且殘余應(yīng)力分布區(qū)域較寬;而背反射激光焊的焊縫橫切面上表面與下表面的殘余應(yīng)力曲線重合度較高,上下表面殘余應(yīng)力分布也基本相當(dāng)。此外,不同線能量下,背反射激光焊接鈦合金薄板的縱向殘余應(yīng)力變化很小,這表明線能量對其焊接殘余應(yīng)力影響的敏感度較低。(3)鈦合金薄板背反射激光焊接成形工藝特性研究。以接頭焊縫的背寬比、堆高和變形角這三個指標(biāo)對成形性進(jìn)行定性和定量的表征,進(jìn)而探究激光工藝參數(shù)對背反射低閾值激光焊接接頭成形性的影響及其規(guī)律。研究表明:在本文實(shí)驗(yàn)條件下,焊接正背面均呈現(xiàn)亮藍(lán)色或金黃色,焊接宏觀形貌較好,焊縫形貌均呈現(xiàn)典型的X形焊縫;激光工藝參數(shù)對背寬比的影響次序?yàn)?焊接速度離焦量激光功率,實(shí)現(xiàn)焊縫最優(yōu)背寬比數(shù)據(jù)下的激光工藝參數(shù)為功率1400W,掃描速度800mm/min,離焦量為1mm;激光工藝參數(shù)對焊縫的堆高的影響次序?yàn)?焊接速度激光功率離焦量,實(shí)現(xiàn)焊縫最小堆高數(shù)據(jù)下的激光工藝參數(shù)為功率1400W,掃描速度900mm/min,離焦量為0;激光工藝參數(shù)對焊縫的變形角的影響次序?yàn)?激光功率離焦量焊接速度,實(shí)現(xiàn)焊縫最小變形數(shù)據(jù)下的激光工藝參數(shù)為功率1400W,掃描速度1000mm/min,離焦量為-1mm。(4)鈦合金薄板背反射激光焊接接頭組織和性能特性研究。以本文實(shí)驗(yàn)條件下優(yōu)化工藝參數(shù)所獲得的鈦合金薄板背反射激光焊接接頭為研究對象,較為系統(tǒng)地研究了焊接接頭的橫切面宏觀形貌、焊縫區(qū)和熱影響區(qū)的微觀組織、硬度沿焊縫橫切面的分布情況和拉伸強(qiáng)度及其斷口形貌,并與相同激光工藝參數(shù)下常規(guī)激光焊接同種鈦合金薄板試樣進(jìn)行對比。研究表明:相對于常規(guī)激光焊接,采用背反射激光焊接鈦合金薄板所獲得的焊縫呈現(xiàn)較為標(biāo)準(zhǔn)的“X形”,且正背面焊縫均較為平整;而且,背反射激光焊接焊縫中心區(qū)域晶粒略大,熱影響區(qū)中的過熱區(qū)和部分相變區(qū)要小,而正火區(qū)則要大。兩種焊接方式測得硬度分布均呈現(xiàn)出相似分布規(guī)律,但背反射焊縫區(qū)硬度低于常規(guī)激光焊,而其他區(qū)域則略高于常規(guī)激光焊,母材基本保持一致;兩種焊接方法下拉伸試件斷裂位置均處于近焊縫基體處,斷口均呈現(xiàn)出典型的韌窩特征即均屬于塑性斷裂。
[Abstract]:In view of the existing problems existing in the research on the back reflection laser welding of titanium alloy sheet, this paper takes the 1.5mm thick TC4 titanium alloy sheet as the subject and focuses on the theme of "the numerical analysis and characteristics of the low threshold back reflection laser welding of the titanium alloy sheet", and carries out the relevant theory and application basic research. The study of numerical simulation and analysis of field and stress field illustrates the change and distribution of the temperature field and stress field in the process of back reflection laser welding, and then lays a theoretical foundation for revealing the mechanism of back reflection laser welding forming. Meanwhile, the research on the forming process characteristics and the characteristics of the microstructure and properties through the laser welding of the back reflection laser welding of the titanium alloy sheet is verified. This new method of high efficiency and low threshold laser welding is suitable for thicker thin plates with a thickness of about 1 times larger than the existing research, which provides a technical support and application basis for further expansion of its application. The research work and the main achievements are as follows. (1) the numerical simulation and analysis of the temperature field of the laser welding process of the back reflection of the titanium alloy sheet. Based on the experimental verification of the "double heat source" temperature field model of the 0.8mm thick titanium alloy sheet back reflection laser welding process, the power and the power of the 1400W are set by setting the thickness of the 1.5mm. A new temperature field model is established by the scanning speed of 50mm/min. The temperature field of the back reflection laser welding process of 1.5mm thick titanium alloy sheet is simulated and analyzed. The study shows that the model can well simulate the distribution of temperature field in the process of back reflection laser welding, and the front and back of the thin plate are formed in a very short time. The stable temperature field similar to "teardrop", the front isotherm of the heat source is dense, the temperature gradient is large, the back end isotherm is relatively sparse and the temperature gradient is relatively small. The melting pool gradually transition from V shape to X shape temperature field time history, which describes the back auxiliary field formed in the back reflection laser welding process to the back of the workpiece two. The physical process of secondary heating; at the same time, with the increase of power or the decrease of scanning speed, the melting width and depth of molten pool gradually increase, the temperature gradient is proportional to the power, and the velocity is inversely proportional to the velocity. (2) the numerical simulation and analysis of the stress field in the process of laser welding of the back reflection of titanium alloy sheet. Based on the temperature field, the indirect coupling method is adopted. The stress field of the back reflection laser welding of titanium alloy sheet is simulated and analyzed. It is shown that the thermal stress increases with the time of welding in the process of back reflection laser welding of titanium alloy sheet, and the stress value of the titanium alloy sheet is most distributed at both ends and shows the comparison during the process of cooling. There are obvious boundary effects. At the same time, the residual stress on the upper surface of the transverse section of the weld is larger than the lower surface and the residual stress distribution is wider in the conventional laser welding, that is, the non reflective plate, and the residual stress curve of the upper and lower surfaces is higher and the residual stress distribution on the upper and lower surfaces is also basic. In addition, under different lines of energy, the longitudinal residual stress of the titanium alloy sheet with back reflection laser welding is very small, and the sensitivity of the energy of this surface to its welding residual stress is low. (3) study on the process characteristics of laser welding forming of the back reflection of the titanium alloy sheet. The three indexes of the back width ratio, the heap height and the deformation angle of the joint weld seam are used. The effect of laser technological parameters on the formability of low threshold laser welded joint with back reflection and its regularities were investigated. The results showed that under the experimental conditions, both the front and the back of the welding showed bright blue or golden yellow, the welding macroscopic morphology was better, the weld appearance had a typical X shaped weld; laser engineering was a laser worker. The influence sequence of the parameters on the back width ratio is: the laser power of the welding speed defocusing quantity, the laser process parameters under the optimal back width ratio of the weld are 1400W, the scanning speed is 800mm/min and the defocus amount is 1mm; the order of the influence of the laser process parameters to the heap height of the weld is the laser power defocuse of the welding speed, and the minimum heap height of the weld is realized. The laser process parameters of the data are 1400W, the scanning speed is 900mm/min and the defocus is 0. The order of the influence of the laser process parameters to the weld deformation angle is the laser power defocusing speed, the laser process parameters under the minimum deformation data of the weld are 1400W, the scanning speed is 1000mm/min, the defocus volume is -1mm. (4) titanium alloy thin. Study on the microstructure and properties of laser welded joint of plate back reflection. The laser welded joint of titanium alloy sheet, obtained by optimizing the technological parameters under the experimental conditions, was studied. The macroscopic morphology of the transverse section of the welded joint, the microstructure of the weld zone and the thermal shadow zone, and the hardness along the transverse section of the weld seam were systematically studied. The distribution and tensile strength and its fracture morphology are compared with the conventional laser welding of the same titanium alloy sheet under the same laser process parameters. The results show that compared with the conventional laser welding, the welding seam obtained by the back reflection laser welding of the titanium alloy sheet presents a more standard "X shape", and the weld on the front and back is more than that of the normal laser welding. In addition, the grain in the center area of the back reflection laser welding seam is slightly larger, the superheated area and the partial phase transition zone in the heat affected zone are small and the normalizing area is larger. The hardness distribution of the two welding methods shows a similar distribution law, but the hardness of the back reflection weld zone is lower than the conventional laser welding, while the other regions are slightly higher than the conventional laser welding. The parent material is basically the same. The fracture positions of the tensile specimens under the two welding methods are in the near weld base, and the fracture surfaces are typical of the dimples, that is, the plastic fracture.
【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG456.7

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