AZ61镁合金双轴肩搅拌摩擦焊工艺及机理研究

发布时间：2018-06-15 06:16

本文选题：双轴肩搅拌摩擦焊 + AZ61镁合金　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：双轴肩搅拌摩擦焊技术是在常规搅拌摩擦焊技术的基础上发展起而来,其在保留了固相连接技术优点的基础上,又简化了焊接工装、克服了焊缝根部未焊合缺陷等问题。本文针对5mm厚AZ61镁合金开展工艺与机理研究,设计了双轴肩搅拌头,实施了焊接工艺试验,得到了合适的焊接工艺参数区间,揭示了工艺参数与接头成形、焊接过程参数、接头微观组织及力学性能的联系,从而阐明接头形成机理,为工程应用奠定理论基础。焊接工艺试验结果表明AZ61镁合金双轴肩搅拌摩擦焊焊接工艺参数区间较窄,通过合理的焊具设计在一定工艺范围内能够获得成形良好、无缺陷的接头。为了建立过程参数与接头成形的对应关系,为工艺参数的优化提供指导,对焊接过程特征参数进行测量。发现随着搅拌头转速的提高,热输入量增大导致测温点监测到的峰值温度提高,主轴和X轴输出扭矩均有所下降;而随着焊接速度的提高,焊接线能量下降,材料软化程度不足,测温点峰值温度降低,主轴和X轴输出扭矩升高。当温度或扭矩过高或过低时,都无法形成连续的无缺陷焊缝。由于有两个轴肩的存在,AZ61镁合金双轴肩搅拌摩擦焊焊缝区域呈哑铃状,对接头进行微观组织分析可以发现接头可分为母材、热影响区、热机影响区和焊核区四个区域。焊核区内均为细小的等轴晶,且沿厚度方向晶粒尺寸没有明显变化;接头的热机影响区也主要由等轴晶组成;热影响区的组织较为粗大;焊核区、热机影响区和热影响区的平均晶粒尺寸和焊接工艺参数明显相关,均随着搅拌头转速的升高而增大,随着焊接速度的升高而减小。接头力学性能分析结果表明,AZ61镁合金双轴肩搅拌摩擦焊接头硬度整体接头硬度分布均匀,各区域硬度值均在52-65HRC之间波动。工艺参数对接头热影响区和热机影响区的显微硬度无明显影响。在热输入量较低的焊接工艺条件下,接头焊核区的显微硬度高于其他区域。拉伸试验表明有缺陷接头的拉伸性能很差,断口表面呈现韧脆混合型断裂,而无缺陷接头的拉伸性能良好,其最大抗拉强度可达213MPa,相当于母材的80%,呈韧性断裂。冲击试验结果表明,工艺参数对接头的冲击性能有明显影响,而焊核区的冲击吸收功始终高于热影响区和母材,热影响区冲击试样呈现韧脆混合型断裂而焊核区试样呈现韧性断裂。
[Abstract]:The technology of double shaft shoulder friction stir welding is developed on the basis of the conventional friction stir welding technology. On the basis of retaining the advantages of solid phase joining technology, it also simplifies the welding equipment and overcomes the problems such as the failure to weld at the root of the weld, and so on. In this paper, the technology and mechanism of 5mm thick AZ61 magnesium alloy are studied, the double shaft shoulder mixing head is designed, the welding process test is carried out, the appropriate welding process parameter interval is obtained, and the process parameters and joint forming and welding process parameters are revealed. The connection between the microstructure and mechanical properties of the joints can clarify the formation mechanism of the joints and lay a theoretical foundation for the engineering application. The results of welding test show that the range of welding parameters of AZ61 magnesium alloy with double shaft shoulder friction stir welding is narrow, and the joints with good shape and no defects can be obtained by reasonable design of welding tools. In order to establish the corresponding relationship between process parameters and joint forming and to provide guidance for optimization of process parameters, the characteristic parameters of welding process were measured. It is found that with the increase of the rotating speed of the mixing head, the increase of the heat input leads to the increase of the peak temperature detected at the temperature measuring point, and the decrease of the output torque of the spindle and the X axis, and the decrease of the welding line energy with the increase of the welding speed. The softening degree of the material is insufficient, the peak temperature of the temperature measuring point is decreased, and the output torque of the spindle and X axis is increased. When the temperature or torque is too high or too low, no continuous defect weld can be formed. Due to the existence of two shafts, the weld zone of friction stir welding of magnesium alloy AZ61 magnesium alloy with double shafts is dumbbell-like. By analyzing the microstructure of the joint, it can be found that the joint can be divided into four regions: base metal, heat affected zone, heat engine affected zone and nuke zone. The nugget zone is small equiaxed crystal, and the grain size does not change obviously along the thickness direction. The thermal machine-affected zone of the joint is also mainly composed of equiaxed crystal, the microstructure of the heat-affected zone is relatively large, the weld nugget zone, The average grain size of the heat affected zone and the heat affected zone are significantly correlated with the welding process parameters, both of which increase with the increase of the rotating speed of the stirring head and decrease with the increase of the welding speed. The mechanical properties of the joints show that the hardness distribution of the joint is uniform and the hardness values of the joints fluctuate between 52-65HRC. The process parameters have no obvious effect on the microhardness of the heat-affected zone and the heat-affected zone of the joint. Under the condition of low heat input, the microhardness of joint nugget zone is higher than that of other regions. The tensile tests show that the tensile properties of the defective joints are very poor, and the fracture surfaces exhibit ductile and brittle mixed fracture, while the non-defective joints have good tensile properties. The maximum tensile strength of the joints is up to 213MPa, which is equivalent to 80% of the base metal, showing ductile fracture. The impact test results show that the process parameters have a significant effect on the impact properties of the joints, and the impact absorption energy in the nugget zone is always higher than that in the heat-affected zone and the base metal. The impact specimens in the heat affected zone exhibit ductile and brittle mixed fracture, while the specimens in the nuke zone show ductile fracture.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.19

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