温度场对5A06铝合金FSW焊缝成形与接头组织的影响

发布时间：2018-05-21 03:43

本文选题：5A06铝合金 + 搅拌摩擦焊　；参考：《太原科技大学》2017年硕士论文

【摘要】：搅拌摩擦焊技术是新型固相连接方法,可以有效解决传统熔化焊接方法中易出现的热裂纹、接头热影响区软化及焊接变形等问题,为铝合金等低熔点金属的焊接提供了新方法。搅拌摩擦焊接过程复杂,而焊接温度场能够直观地反映接头温度分布情况,通过温度场的模拟研究可以进一步了解其焊接机制,对焊接参数的优化及避免缺陷形成具有重要指导意义。本文首先建立了5A06铝合金搅拌摩擦焊接过程的热输入模型,采用ANSYS有限元分析软件对不同工艺参数下的焊接温度场进行数值模拟,研究搅拌摩擦焊接过程温度场分布规律以及搅拌头转速和焊接速度对温度场的影响;通过对比模拟与试验方法所测热循环结果,验证模型准确性;使用超景深显微镜观察焊缝表面成形、内部缺陷及焊核区微观组织;利用显微硬度计测试接头横截面硬度。得到如下结论:温度场模拟结果显示焊缝中心温度低于轴肩边缘,轴肩外侧峰值温度随距焊缝中心距离增大而降低,焊缝两侧温度场对称分布。搅拌头转速影响峰值温度,而焊接速度影响峰值温度停留时间,转速增大,峰值温度升高,焊速增大,峰值温度停留时间减少。试验与模拟结果对比表明本文采用的热量自适应热源模型能够准确模拟焊接过程温度场分布规律。对于12 mm厚铝合金,最佳焊接参数为ω=220 r/min,v=8 cm/min,此时焊缝峰值温度达到377°C,材料软化程度及流动性较好,可以得到无缺陷、成形良好的焊缝。5A06铝合金接头显微硬度与晶粒大小有关,焊核区组织发生动态再结晶,转变为均匀细小等轴晶,该区域硬度值与母材相比提高了约15%,达到84 HV。在接头横截面硬度呈“n”型分布,而焊缝厚度方向上晶粒尺寸与硬度无明显变化。搅拌头转速提高,焊核区晶粒长大,显微硬度有降低趋势;焊接速度对晶粒尺寸及显微硬度影响较小。
[Abstract]:Friction stir welding (FSW) is a new solid-phase bonding method, which can effectively solve the problems such as hot crack, heat affected zone softening and welding deformation, which can be used to weld low melting point metals such as aluminum alloy. The process of friction stir welding is complex, and the welding temperature field can directly reflect the temperature distribution of the joint. Through the simulation of the temperature field, the welding mechanism can be further understood. It is of great significance to optimize the welding parameters and avoid the formation of defects. In this paper, the heat input model of 5A06 aluminum alloy friction stir welding process is established, and the numerical simulation of welding temperature field under different process parameters is carried out by using ANSYS finite element analysis software. The distribution of temperature field in friction stir welding process and the effect of rotating speed and welding speed of stir head on temperature field were studied, and the accuracy of the model was verified by comparing the results of heat cycle measured by simulation and test methods. The weld surface forming, internal defects and microstructure of the nuke zone were observed by using the hyperfield depth microscope, and the cross section hardness of the joint was measured by microhardness meter. The results show that the center temperature of the weld is lower than the edge of the shaft shoulder and the peak temperature of the outside side of the shaft shoulder decreases with the increase of the distance from the center of the weld and the temperature field on both sides of the weld is symmetrically distributed. The rotating speed of the mixing head affects the peak temperature, while the welding speed affects the residence time of the peak temperature, the rotational speed increases, the peak temperature increases, the welding speed increases, and the peak temperature residence time decreases. The comparison of experimental and simulation results shows that the heat adaptive heat source model can accurately simulate the distribution of temperature field in welding process. For 12mm thick aluminum alloy, the optimum welding parameter is 蠅 220rmin / min / 8 cm / min, and the peak weld temperature reaches 377 掳C, the softening degree and fluidity of the material are good, and there is no defect. The microhardness of the well-formed weld. 5A06 aluminum alloy joint is related to the grain size. Dynamic recrystallization takes place in the microstructure of the nugget zone, which is transformed into uniform fine equiaxed crystal. Compared with the base metal, the hardness of the region is increased by about 15%, reaching 84 HV. The hardness of the cross section of the joint is "n" distributed, but the grain size and hardness have no obvious change in the direction of weld thickness. With the increase of the rotating speed of the mixing head, the grain size in the nugget region grows and the microhardness decreases, and the effect of welding speed on the grain size and microhardness is small.
【学位授予单位】：太原科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

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