【摘要】：攪拌摩擦焊技術(shù)以其焊后殘余應(yīng)力小、變形小和焊接接頭強(qiáng)度高等優(yōu)點(diǎn)被廣泛應(yīng)用于鋁合金、鎂合金和銅合金等材料的焊接。它已被成功應(yīng)用于航空、航天、鐵道車輛、造船和汽車等制造領(lǐng)域。但攪拌摩擦焊技術(shù)在高熔點(diǎn)材料上的應(yīng)用仍然受限于攪拌頭的壽命。在焊接過程中,攪拌針承受著巨大的剪切力和摩擦磨損。預(yù)熱工件可以軟化被焊材料,是提高攪拌頭壽命的方法之一。本文進(jìn)行了Q235鋼激光輔助加熱攪拌摩擦焊數(shù)值模擬與實(shí)驗研究。首先,建立了包含激光與攪拌頭雙熱源的激光輔助加熱攪拌摩擦焊接熱源模型。模型考慮了激光對工件材料的預(yù)熱、軸肩與工件的摩擦產(chǎn)熱及攪拌針與工件材料的剪切變形產(chǎn)熱。復(fù)合焊接過程中,激光起到輔助加熱的作用,因此選用高斯面熱源模型。第二,在上述熱源模型的基礎(chǔ)上,建立了激光輔助加熱攪拌摩擦焊接傳熱傳質(zhì)數(shù)學(xué)模型,利用計算流體動力學(xué)軟件FLUENT對模型進(jìn)行了數(shù)值模擬,獲得了被焊工件的溫度場與流場分布。分析了輔助加熱攪拌摩擦焊過程中激光功率、攪拌頭轉(zhuǎn)速和焊接速度等工藝參數(shù)對溫度場和流場的影響。對比分析了有無激光熱源對焊接溫度場和流場的影響。模擬分析可以獲得試件內(nèi)部的溫度、應(yīng)力、應(yīng)變、速率、流動壓力和剪切力等關(guān)鍵場力的分布。第三,依據(jù)模擬分析的結(jié)果,進(jìn)行了Q235鋼激光輔助加熱攪拌摩擦焊焊接實(shí)驗。采用鎢鉬合金攪拌頭,在改制的攪拌摩擦焊機(jī)上進(jìn)行焊接實(shí)驗研究。研究了下壓量、攪拌頭轉(zhuǎn)速和焊接速度對焊縫形貌的影響。通過金相觀測,分析了焊接接頭熱影響區(qū)、熱力影響區(qū)和焊核區(qū)的顯微結(jié)構(gòu)。通過顯微硬度測定和拉伸實(shí)驗,研究了焊接接頭的力學(xué)性能。
[Abstract]:Friction stir welding (FSW) technology is widely used in welding of aluminum alloy magnesium alloy and copper alloy due to its advantages such as low residual stress small deformation and high strength of welded joint. It has been successfully used in aviation, aerospace, railway vehicles, shipbuilding and automotive manufacturing. However, the application of friction stir welding in high melting point materials is still limited by the life of stir head. In the welding process, the stirring needle is subjected to great shear force and friction and wear. Preheating workpiece can soften the welded material, which is one of the ways to increase the life of agitator. Numerical simulation and experimental study on laser assisted heating friction stir welding of Q235 steel have been carried out in this paper. Firstly, a heat source model of laser assisted heating friction stir welding (FSW) with laser and stir head is established. The model takes into account the preheating of the workpiece material by laser, the friction heat generation between the shaft shoulder and the workpiece, and the heat generation from the shear deformation between the stirring needle and the workpiece material. In the process of composite welding, laser plays the role of auxiliary heating, so Gao Si surface heat source model is chosen. Secondly, based on the above heat source model, the mathematical model of heat and mass transfer in laser assisted heating friction stir welding is established, and the numerical simulation of the model is carried out by using the computational fluid dynamics software FLUENT. The temperature field and flow field distribution of the welded workpiece are obtained. The effects of laser power, rotating speed of stir head and welding speed on the temperature field and flow field in the process of auxiliary heating friction stir welding are analyzed. The effect of laser heat source on welding temperature field and flow field is compared and analyzed. The distribution of critical field forces, such as temperature, stress, strain, rate, flow pressure and shear force, can be obtained by simulation analysis. Thirdly, based on the results of simulation analysis, the welding experiments of Q235 steel with laser assisted heating friction stir welding are carried out. The welding experiments were carried out on the modified friction stir welding machine with tungsten-molybdenum alloy stir head. The effects of pressure, stirring speed and welding speed on weld morphology were studied. The microstructure of heat affected zone, thermal affected zone and nuke zone of welded joint were analyzed by metallographic observation. The mechanical properties of welded joints were studied by microhardness measurement and tensile test.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG453.9

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