【摘要】：ZL205A是強(qiáng)度高、綜合性能較好的鑄造鋁合金,同時(shí)還具有良好機(jī)械加工性能,是航空航天以及汽車工業(yè)領(lǐng)域的重要結(jié)構(gòu)材料。但是ZL205A合金鑄造性能較差,大型鑄件生產(chǎn)過(guò)程中易形成疏松、偏析等缺陷,疏松與偏析成為影響該合金大型鑄件性能的主要缺陷。開(kāi)發(fā)或者完善現(xiàn)有的鑄造工藝,避免疏松和偏析缺陷的發(fā)生,對(duì)ZL205A合金在大型鑄件上的應(yīng)用具有重要的意義。本文利用行波磁場(chǎng)在合金熔體中產(chǎn)生的特殊作用力,對(duì)合金溶質(zhì)分布以及凝固補(bǔ)縮產(chǎn)生作用,達(dá)到消除比重偏析、增加凝固補(bǔ)縮的目的。通過(guò)數(shù)值模擬,分析了勵(lì)磁電流強(qiáng)度、勵(lì)磁電流頻率等行波磁場(chǎng)控制參數(shù)和鑄件位置、鑄件壁厚等鑄件的結(jié)構(gòu)參數(shù)對(duì)鑄件內(nèi)各位置的電磁力和平均電磁力密度的影響規(guī)律。各位置處的電磁力及鑄件的平均電磁力密度與勵(lì)磁電流強(qiáng)度的平方呈線性關(guān)系,隨著勵(lì)磁電流強(qiáng)度的增加,各位置處的電磁力及鑄件的平均電磁力密度迅速增加。隨著勵(lì)磁電流頻率增加,各位置處的電磁力及鑄件的平均電磁力密度均存在極限值,其數(shù)值先增加后減小。隨著鑄件與行波磁場(chǎng)發(fā)生器相對(duì)距離和鑄件壁厚的增加,各位置處的電磁力及鑄件的平均電磁力密度均明顯地減小,分布趨向平緩。以衰減系數(shù)表示電磁力在合金熔體內(nèi)衰減速度,衰減系數(shù)越大,合金熔體內(nèi)感應(yīng)產(chǎn)生的電磁力衰減速度越快。建立了與衰減系數(shù)相關(guān)的電磁力空間分布函數(shù),并基于此函數(shù)建立了行波磁場(chǎng)對(duì)合金熔體壓力梯度和流場(chǎng)的影響模型。研究了平均電磁力密度、衰減系數(shù)表示的電磁力在不同壁厚鑄件的合金熔體流動(dòng)的速率分布以及臨界零速率位置的影響規(guī)律。隨著平均電磁力密度的增加,行波磁場(chǎng)引起的合金熔體的速率呈線性增加;隨著衰減系數(shù)的增加,合金熔體的形成環(huán)流的流動(dòng)速率先增加后減小,也就是流動(dòng)速率存在極值,隨著鑄件壁厚以及電磁力衰減系數(shù)的增加,臨界零速率位置逐漸向行波磁場(chǎng)發(fā)生器一側(cè)偏移。ZL205A合金是多組元多相合金,其凝固過(guò)程中出現(xiàn)的各相比重存在差異,很容易由于各相受力不均形成相的偏聚,甚至形成偏析缺陷。各相的電導(dǎo)率也存在較大差異,在電磁場(chǎng)作用下也會(huì)出現(xiàn)類似的現(xiàn)象。偏析現(xiàn)象主要表現(xiàn)為溶質(zhì)和相分布不均勻,本文先以ZL205A合金中的溶質(zhì)Cu為研究對(duì)象,通過(guò)實(shí)驗(yàn)研究發(fā)現(xiàn),行波磁場(chǎng)的勵(lì)磁電流強(qiáng)度的越大,成分分布的越均勻。進(jìn)一步對(duì)容易形成比重偏析的相進(jìn)行研究發(fā)現(xiàn),行波磁場(chǎng)的勵(lì)磁電流強(qiáng)度越大,相分布得越均勻,相應(yīng)形成的晶粒尺寸也比較均勻。通過(guò)分析發(fā)現(xiàn)這是由于行波磁場(chǎng)在合金熔體內(nèi)形成的電磁力誘發(fā)了合金熔體的流動(dòng),隨著熔體流動(dòng)速率的增加,相間粘滯力超過(guò)各相之間電磁力和比重的差異,使得ZL205A合金鑄件的凝固組織,隨著流動(dòng)速率的增加各相的分布也更加均勻。對(duì)不同壁厚鑄件在凝固過(guò)程中施加行波磁場(chǎng),研究了行波磁場(chǎng)對(duì)ZL205A合金鑄件密度、凝固組織、抗拉強(qiáng)度和延伸率以及斷口形貌等方面的影響規(guī)律。研究發(fā)現(xiàn),行波磁場(chǎng)可以明顯地促進(jìn)合金的凝固補(bǔ)縮過(guò)程;其補(bǔ)縮效果與鑄件壁厚、行波磁場(chǎng)方向有關(guān),合金熔體內(nèi)感應(yīng)產(chǎn)生的電磁力與合金熔體補(bǔ)縮方向相同時(shí)可以促進(jìn)補(bǔ)縮過(guò)程進(jìn)行;對(duì)于一定壁厚的鑄件,存在最佳的勵(lì)磁電流強(qiáng)度,超過(guò)這個(gè)強(qiáng)度后,行波磁場(chǎng)對(duì)凝固補(bǔ)縮的促進(jìn)作用逐漸減弱;當(dāng)鑄件壁厚增加,行波磁場(chǎng)作用下合金熔體內(nèi)更容易形成環(huán)形流動(dòng),這種流動(dòng)通過(guò)阻礙枝晶和晶粒搭接減小補(bǔ)縮阻力,但是隨著環(huán)流速率的增加,促進(jìn)了鑄件成分均勻化的過(guò)程中,使溫度分布均勻化,從而增加了糊狀區(qū)的厚度,增加了補(bǔ)縮阻力,因此行波磁場(chǎng)對(duì)ZL205A合金凝固補(bǔ)縮效果存在極值,即存在最佳作用效果。
[Abstract]:ZL205A is a kind of cast aluminum alloy with high strength and good comprehensive properties. It is also an important structural material in aerospace and automotive industries. However, the casting properties of ZL205A alloy are poor, and it is easy to form defects such as porosity and segregation during the production of large castings. Major defects in the properties of ZL205A castings. Developing or perfecting the existing casting technology to avoid porosity and segregation defects is of great significance to the application of ZL205A alloy in large castings. The effects of traveling wave magnetic field control parameters such as excitation current intensity, excitation current frequency, casting position and casting wall thickness on electromagnetic force and average electromagnetic force density in each position of the casting were analyzed by numerical simulation. The average electromagnetic force density is linear with the square of the excitation current intensity. With the increase of the excitation current intensity, the electromagnetic force at each position and the average electromagnetic force density of the casting increase rapidly. With the increase of the relative distance between the casting and the traveling wave magnetic field generator and the wall thickness of the casting, the electromagnetic force and the average electromagnetic force density of the casting at each position decrease obviously and the distribution tends to be gentle. The faster the velocity is, the spatial distribution function of electromagnetic force related to attenuation coefficient is established. Based on this function, the influence model of traveling wave magnetic field on pressure gradient and flow field of alloy melt is established. With the increase of the average electromagnetic force density, the velocity of alloy melt caused by traveling wave magnetic field increases linearly; with the increase of attenuation coefficient, the flow rate of alloy melt forming circulation first increases and then decreases, that is, the flow rate has an extreme value, with the increase of casting wall thickness and electromagnetic force attenuation coefficient. ZL205A alloy is a multi-component multi-phase alloy, and its specific gravity varies during solidification. It is easy to form phase segregation or even segregation defects due to uneven force on each phase. The conductivity of each phase is also quite different, and also under the action of electromagnetic field. Similar phenomena may occur. Segregation is mainly manifested by the inhomogeneous distribution of solutes and phases. In this paper, the solute Cu in ZL205A alloy is taken as the research object. It is found that the greater the excitation current intensity of traveling wave magnetic field, the more uniform the composition distribution. The larger the excitation current intensity, the more homogeneous the phase distribution and the corresponding grain size are. It is found that the electromagnetic force formed by traveling wave magnetic field in the alloy melt induces the flow of alloy melt. With the increase of melt flow rate, the phase viscosity force exceeds the difference of electromagnetic force and specific gravity between the phases. The effect of traveling wave magnetic field on density, solidification structure, tensile strength, elongation and fracture morphology of ZL205A alloy castings with different wall thickness was studied. Traveling wave magnetic field can obviously promote the solidification and feeding process of the alloy; its feeding effect is related to the thickness of the casting wall and the direction of traveling wave magnetic field; the electromagnetic force produced in the alloy melt can promote the feeding process when the feeding direction is the same as that of the alloy melt; for the casting with a certain wall thickness, there is an optimum excitation current intensity, which exceeds this one. The effect of traveling wave magnetic field on solidification and feeding is gradually weakened after strength, and the annular flow is easier to form in the melt of the alloy when the wall thickness of the casting increases. This flow reduces feeding resistance by hindering the overlap of dendrites and grains, but with the increase of circulating velocity, the homogenization of the casting composition is promoted and the temperature is increased. The uniform degree distribution increases the thickness of paste zone and the feeding resistance, so the traveling wave magnetic field has an extreme value on the solidification feeding effect of ZL205A alloy, that is, there is an optimum effect.
【學(xué)位授予單位】：哈爾濱工業(yè)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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