激光辅助加热搅拌摩擦焊数值模拟与实验研究

发布时间：2018-11-02 09:05

【摘要】：搅拌摩擦焊技术以其焊后残余应力小、变形小和焊接接头强度高等优点被广泛应用于铝合金、镁合金和铜合金等材料的焊接。它已被成功应用于航空、航天、铁道车辆、造船和汽车等制造领域。但搅拌摩擦焊技术在高熔点材料上的应用仍然受限于搅拌头的寿命。在焊接过程中,搅拌针承受着巨大的剪切力和摩擦磨损。预热工件可以软化被焊材料,是提高搅拌头寿命的方法之一。本文进行了Q235钢激光辅助加热搅拌摩擦焊数值模拟与实验研究。首先,建立了包含激光与搅拌头双热源的激光辅助加热搅拌摩擦焊接热源模型。模型考虑了激光对工件材料的预热、轴肩与工件的摩擦产热及搅拌针与工件材料的剪切变形产热。复合焊接过程中,激光起到辅助加热的作用,因此选用高斯面热源模型。第二,在上述热源模型的基础上,建立了激光辅助加热搅拌摩擦焊接传热传质数学模型,利用计算流体动力学软件FLUENT对模型进行了数值模拟,获得了被焊工件的温度场与流场分布。分析了辅助加热搅拌摩擦焊过程中激光功率、搅拌头转速和焊接速度等工艺参数对温度场和流场的影响。对比分析了有无激光热源对焊接温度场和流场的影响。模拟分析可以获得试件内部的温度、应力、应变、速率、流动压力和剪切力等关键场力的分布。第三,依据模拟分析的结果,进行了Q235钢激光辅助加热搅拌摩擦焊焊接实验。采用钨钼合金搅拌头,在改制的搅拌摩擦焊机上进行焊接实验研究。研究了下压量、搅拌头转速和焊接速度对焊缝形貌的影响。通过金相观测,分析了焊接接头热影响区、热力影响区和焊核区的显微结构。通过显微硬度测定和拉伸实验,研究了焊接接头的力学性能。
[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.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG453.9

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