本文選題：擠壓壓力　切入點(diǎn)：超聲振動(dòng)　出處：《華南理工大學(xué)》2016年博士論文

【摘要】：隨著我國(guó)航空、航天、交通運(yùn)輸以及國(guó)防工業(yè)的發(fā)展,對(duì)高性能鋁合金產(chǎn)品的需求越來越大,而采用先進(jìn)的成形工藝是制備高性能鋁合金的關(guān)鍵。目前,在鋁合金鑄造過程中常采用施加物理外場(chǎng)的方法來改善其凝固組織,即通過物理外場(chǎng)所產(chǎn)生的一系列機(jī)械、物理、化學(xué)效應(yīng)來影響合金的形核和生長(zhǎng),達(dá)到破碎枝晶、細(xì)化晶粒等目的,最終有助于提升鑄錠的性能和質(zhì)量。目前在凝固過程中施加壓力或者超聲振動(dòng)已在金屬材料加工領(lǐng)域得到廣泛的應(yīng)用。為了克服單一物理外場(chǎng)的工藝缺陷以及進(jìn)一步提升鋁合金的性能,本論文提出一種在擠壓鑄造鋁合金過程中同時(shí)耦合高能超聲的新技術(shù),設(shè)計(jì)并制造了一個(gè)獨(dú)特的試驗(yàn)平臺(tái),能夠?qū)崿F(xiàn)超聲振動(dòng)與擠壓壓力的耦合,在此基礎(chǔ)上對(duì)超聲振動(dòng)系統(tǒng)各組元以及擠壓模具的關(guān)鍵參數(shù)進(jìn)行設(shè)計(jì)和優(yōu)化。隨后以Al-5.0Cu合金為研究對(duì)象,對(duì)超聲-壓力耦合作用下的凝固組織進(jìn)行數(shù)值模擬,并結(jié)合不同參數(shù)下的實(shí)驗(yàn)結(jié)果深入研究了耦合作用對(duì)合金凝固過程和微觀組織、力學(xué)性能的影響規(guī)律,最后對(duì)超聲-壓力耦合場(chǎng)的作用機(jī)制進(jìn)行探討。論文得到的主要結(jié)論如下:(1)研制了一套超聲-壓力耦合鑄造試驗(yàn)裝置�？紤]到超聲-壓力耦合鑄造中超聲振動(dòng)系統(tǒng)所受溫度、壓力載荷不斷變化,首先對(duì)超聲波換能器、發(fā)生器分別進(jìn)行阻抗匹配設(shè)計(jì)與諧振匹配設(shè)計(jì),保證了換能器的工作效率和發(fā)生器的能量傳輸效率;然后基于理論尺寸設(shè)計(jì)的基礎(chǔ)上,分別進(jìn)行了普通條件和高溫、高壓下的不同形狀(階梯形、圓錐形以及指數(shù)形)變幅桿的模態(tài)分析和諧響應(yīng)分析,發(fā)現(xiàn)階梯形和指數(shù)形變幅桿具有較大的振幅放大比,但階梯形變幅桿的尺寸突變會(huì)造成應(yīng)力集中以及能量傳輸?shù)膿p耗;為了得到更大的輸出端諧振振幅,設(shè)計(jì)了一套具有不同過渡形狀的多級(jí)復(fù)雜變幅桿,并進(jìn)行了不同工況下的模態(tài)和諧響應(yīng)分析,發(fā)現(xiàn)高溫、高壓下指數(shù)形過渡型變幅桿的振幅放大比最大,為144,同時(shí)高溫、高壓下的諧振頻率為19.943 kHz,與理想諧振頻率20 kHz最接近,最終選用指數(shù)形過渡段的復(fù)雜變幅桿為本文中的超聲振動(dòng)系統(tǒng)所用;為避免超聲能量的損耗以及保證楔形密封效果,對(duì)擠壓模具進(jìn)行了關(guān)鍵參數(shù)的正交優(yōu)化設(shè)計(jì),當(dāng)模具壁厚為25 mm,錐孔斜度為30°,孔內(nèi)直線段長(zhǎng)度為8 mm時(shí),側(cè)孔周圍的平均變形量最小,可以充分避免變幅桿的振動(dòng)能量的損失和楔形密封的失效。(2)對(duì)超聲-壓力耦合作用下Al-5.0Cu合金的凝固組織進(jìn)行了數(shù)值模擬。首先基于ProCAST反計(jì)算模塊建立了鑄件-模具界面換熱系數(shù)的反分析求解模型,對(duì)大量數(shù)據(jù)擬合得到不同工藝下的鑄件-模具界面換熱系數(shù)曲線;在此基礎(chǔ)上,在CAFE宏-微觀耦合計(jì)算模型中同時(shí)定義擠壓力和超聲聲強(qiáng),采用反分析法求解出的界面換熱系數(shù)曲線對(duì)Al-5.0Cu合金凝固組織的進(jìn)行模擬預(yù)測(cè),通過定量分析柱狀晶和等軸晶的比例、平均晶粒尺寸等結(jié)果,發(fā)現(xiàn)反分析界面換熱系數(shù)曲線下模擬出的微觀組織與實(shí)驗(yàn)結(jié)果的吻合度高于采用恒定界面換熱系數(shù)下的模擬結(jié)果。本文繼續(xù)通過數(shù)值模擬和實(shí)驗(yàn)結(jié)果對(duì)比的方法,優(yōu)化了計(jì)算模型各參數(shù)的取值范圍,最后通過對(duì)比不同超聲-壓力耦合參數(shù)下凝固組織的模擬結(jié)果和實(shí)驗(yàn)結(jié)果,進(jìn)一步說明了耦合作用可顯著降低平均晶粒尺寸,改善柱狀晶的比例。(3)分別研究了擠壓壓力、超聲振動(dòng)以及超聲-壓力耦合工藝對(duì)Al-5.0Cu合金凝固過程和微觀組織的影響規(guī)律。結(jié)果表明:擠壓壓力為75 MPa時(shí)熔體內(nèi)部的冷卻速度最大,擠壓力基本消除了孔洞等鑄造缺陷,同時(shí)還可以減小二次枝晶間距,但通過擠壓鑄造很難得到理想的細(xì)小均勻等軸晶組織;功率為1 kW的超聲振動(dòng)可以在變幅桿端面附近區(qū)域內(nèi)形成一定程度上得到細(xì)化的微觀組織,但隨著超聲能量的衰減,微觀組織細(xì)化程度不均勻,遠(yuǎn)離變幅桿端面的試樣微觀組織細(xì)化程度較弱;超聲-壓力耦合作用(75MPa+1 kW)可以進(jìn)一步減小晶粒尺寸,增加等軸晶組織的比例,并且各取樣位置的細(xì)化程度較均勻,耦合作用還可以改善θ相形貌,并提高ɑ(Al)基體中的Cu元素含量,起到固溶強(qiáng)化的作用。(4)分析了超聲-壓力耦合場(chǎng)在Al-Cu合金凝固過程的作用機(jī)制。首先分別分析了單一擠壓鑄造工藝和超聲振動(dòng)工藝對(duì)Al-Cu合金凝固過程的影響。接下來基于空化模型,通過開發(fā)二次子程序UDF以及添加源項(xiàng)的方式分別在空化模型中導(dǎo)入擠壓力和超聲聲流,分別模擬得到了單一超聲和超聲-壓力耦合作用下Al-5.0Cu合金熔體內(nèi)部的空化氣泡體積分?jǐn)?shù)、空化區(qū)域大小和強(qiáng)度以及熔體內(nèi)部壓力、流體速度等,發(fā)現(xiàn)耦合場(chǎng)會(huì)使得空化效應(yīng)的強(qiáng)度和區(qū)域增大,還可以改變?nèi)垠w內(nèi)部壓力分布和壓力梯度差,從而導(dǎo)致熔體內(nèi)部形成更強(qiáng)烈的對(duì)流,即超聲-壓力的耦合作用可以增強(qiáng)熔體內(nèi)部的空化效應(yīng)和聲流效應(yīng),這會(huì)導(dǎo)致熔體內(nèi)部出現(xiàn)更大過冷度,降低形核功,增加相變驅(qū)動(dòng)力,促進(jìn)更多的晶核產(chǎn)生和晶核游離,最終形成細(xì)小均勻的凝固組織。最后通過對(duì)不同工藝下的熔體內(nèi)部溫度分布以及宏、微觀組織的定量分析驗(yàn)證了數(shù)值模擬的預(yù)測(cè)。
[Abstract]:With China's aviation, aerospace, transportation and development of the defense industry, the demand for high performance Aluminum Alloy products and the forming of advanced technology is the key to the preparation of high performance Aluminum Alloy. At present, in the Aluminum Alloy casting method applied physics field is often used to improve the solidification structure. A series of mechanical field generated by physical, physical and chemical effects to influence the nucleation and growth of alloy, crushing the dendrite, grain refinement to eventually help to improve the performance and quality of ingot in solidification process. The pressure or ultrasonic vibration has been widely used in metal materials in order to process processing field. To overcome the defect of single physical field and further enhance the performance Aluminum Alloy, this paper proposes a Aluminum Alloy in squeeze casting process and new technology of high intensity ultrasonic coupling, The design and manufacture of a unique experiment platform, can realize the coupling of ultrasonic vibration and extrusion pressure, based on the key parameters of the ultrasonic vibration system components and extrusion die design and optimization. Then using Al-5.0Cu alloy as the research object, numerical simulation on solidification structure of ultrasonic coupling under pressure and combined with the different parameters of the experimental results of in-depth study of the coupling effect on solidification process and microstructure, influence of mechanical properties, discussed the mechanism of ultrasonic pressure at the coupling field. The main conclusions are as follows: (1) developed a set of ultrasonic pressure coupling casting experimental device is considered. The ultrasonic vibration system of ultrasonic pressure coupling in the casting temperature, pressure load changing, the ultrasonic transducer, the generator impedance matching design and resonance The matching design, to ensure the efficiency of energy transfer efficiency of the transducer and generator; and then the size of foundation design based on the theory, are common and high temperature conditions, different shapes under high pressure (stepped, and conical horn shape index) modal analysis and harmonic response analysis, it is found that the amplitude stepped and deformation index horn with large magnification ratio, but the mutation of steppedultrasonichorn size will cause stress concentration and energy transmission loss; in order to get the output resonant larger amplitude, designed a set of different transition shape of multi-stage complex horn, and the modal and harmonic response analysis under different conditions, the discovery of high amplitude, high pressure index shape transition horn amplification ratio is 144, while the maximum temperature, the resonant frequency under high pressure is 19.943 kHz, the most close to the ideal resonant frequency of 20 kHz, the most The final selection of complex exponential transition horn is used for ultrasonic vibration system in this paper; in order to avoid the loss of ultrasonic energy and ensure the wedge-shaped sealing effect, optimum design of extrusion die for the key parameters, when the mold wall thickness is 25 mm, cone angle for 30 degrees, straight line length in the hole 8 mm, the average amount of deformation around the side hole of the minimum, can fully avoid the loss of failure and wedge vibration energy of the horn seal. (2) on the solidification structure of Al-5.0Cu alloy under the coupling effect of ultrasonic pressure are simulated. Based on the analysis model of anti ProCAST anti - mold casting calculation module is established the interfacial heat transfer coefficient, the large amount of data obtained under different technological conditions of the casting mold interfacial heat transfer coefficient curve; on this basis, the CAFE macro microcosmic coupling calculation and extrusion pressure and ultra sound definition model Strong, is solved by the inverse analysis method of interfacial heat transfer coefficient curves were simulated on solidification of Al-5.0Cu alloy, through quantitative analysis of columnar and equiaxed ratio, average grain size results agree with the experimental results found that the microstructure analysis of interfacial heat transfer coefficient curve under the simulation of the degree is higher than that of the constant interface for simulation results under thermal coefficient. In this paper, through the method of comparison to numerical simulation and experimental results, the optimal range of calculation of the parameters in the model, the simulation results and experimental results by comparing the different ultrasonic pressure coupling parameters of coagulation of tissue, further explains that the coupling effect can significantly reduce the average grain size and improve the columnar crystal ratio. (3) the extrusion pressure of ultrasonic vibration and ultrasonic pressure coupling process on Al-5.0Cu alloy solidification process and microstructure. Sound rules. The results show that the cooling rate of the melt extrusion maximum internal pressure is 75 MPa, pressure casting defects such as voids basically eliminated, but also can reduce the two primary dendrite spacing, but by squeeze casting is difficult to get the desired uniform fine equiaxed grains; the power ultrasonic vibration of 1 kW can be formed the microstructure of a certain extent can be refined in the area near the horn tip, but with the attenuation of ultrasonic energy, microstructure inhomogeneity, away from the horn end of the sample microstructure is weaker; ultrasonic pressure coupling (75MPa+1 kW) can further reduce the increase of grain size, and equiaxed grains. The proportion and degree of refinement of each sampling location is uniform, the coupling effect can also improve the morphology and improve the theta, alpha (Al) Cu content in the matrix, the solid solution strengthening function (4) is analyzed. Ultrasonic pressure coupling field in the mechanism of the solidification of the Al-Cu alloy. Firstly analyses the single effect of extrusion casting technology and technology of ultrasonic vibration on the solidification of the Al-Cu alloy. Then based on cavitation model, through the development of two UDF and add subroutine source terms into the pressure and the flow in the ultrasonic cavitation model respectively. Simulated single ultrasound and ultrasound - pressure coupling internal Al-5.0Cu alloy melt cavitation bubble volume fraction, cavitation region size and strength and melt the internal pressure, fluid velocity, it is found that the coupling field makes the cavitation intensity and the area increases, but also can change the internal melt pressure distribution and pressure gradient, resulting in inside the melt convection formed more strongly, the coupling effect of ultrasonic cavitation effect and acoustic pressure can enhance the melt flow inside this effect. Will lead to more internal melt undercooling, reduce nucleation work, increase the transformation driving force, promote the nucleation and crystal nucleus generated more free, and ultimately the formation of fine and uniform structure. By the end of the different process of internal temperature distribution of melt and macro, quantitative analysis of the microstructure of the verified numerical simulation forecast.

【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG146.21

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