轴肩形貌对搅拌摩擦焊缝金属塑性流动及组织性能的影响

发布时间：2018-05-02 17:04

本文选题：搅拌摩擦焊 + 轴肩形貌　；参考：《南昌航空大学》2015年硕士论文

【摘要】：本课题设计了内凹型、小通道凹型、大通道凹型、侧通道凹型和外凸型五种轴肩形貌的搅拌头,选用铝箔作标识材料,采用水平、纵向和横向镶嵌的方法将铝箔与2A12铝合金薄板进行搅拌摩擦焊的叠层试验,通过观察焊缝三维截面的标示材料形态,研究轴肩形貌对焊缝金属塑性流动的影响,总结其影响规律,建立不同轴肩形貌的搅拌头下获得的焊缝金属三维流动物理模型,并分析塑性流动对组织性能的影响,为控制搅拌摩擦焊缝成形提供实践依据。研究结果表明:轴肩下方金属受到的作用力发生变化,影响焊缝金属的塑性流动形态,进而改变焊缝横截面的形貌。增加轴肩锻压力可增大塑化金属层之间的摩擦力,有利于焊缝金属的塑性流动,减少了疏松缺陷,提高了焊缝的致密性。采用小通道凹槽轴肩的搅拌头焊接,可增大轴肩作用区内的塑化金属流动速度;同时增强了“抽吸-挤压”效应,单位时间内轴肩驱动至搅拌针作用区及焊缝下部的塑化金属量增多,焊核宽度增大。通道过大,轴肩包裹的高温塑化金属过多,金属粘性过低,不利于焊缝金属的迁移,出现疏松或孔洞缺陷。轴肩结构为侧通道凹槽,可增大焊缝金属水平运动的锻压力,向下迁移的金属流截面积增大,焊核尺寸随之增大。轴肩形貌为外凸时,有利于驱动塑化金属向搅拌针根部流动,与螺旋内凹结构共同作用,驱动塑化金属的迁移量最多,焊核宽度最大,洋葱环中心高度最低。采用侧通道凹槽轴肩搅拌头获得的接头平均抗拉强度最高,为278.95MPa(达母材的64.3%);外凸轴肩的接头抗拉强度最低,为196.04MPa。侧通道凹槽轴肩驱动塑化金属辐射状向下迁移,阻止了包铝层向上伸入;在外凸轴肩的驱动作用下,塑化金属向焊缝底部迁移时产生的挤压力最大,包铝层向上伸入高度最大,焊核边界的包铝层成为接头受拉伸载荷的起裂和扩展区。
[Abstract]:In this paper, five kinds of shaft-shoulder shafts with concave shape, small channel concave, big channel concave, side channel concave and convex shape are designed. Aluminum foil is used as the marking material. The longitudinal and transverse inlay method was applied to the friction stir welding of aluminum foil and 2A12 aluminum alloy sheet. By observing the shape of the marking material of the three-dimensional section of the weld, the influence of the shaft-shoulder morphology on the plastic flow of the weld metal was studied. The influence law is summarized, and the three-dimensional flow physical model of weld metal under different shaft-shoulder head is established, and the influence of plastic flow on microstructure and properties is analyzed, which provides the practical basis for controlling the formation of friction stir weld. The results show that the force acting on the metal under the shaft shoulder changes, which affects the plastic flow pattern of the weld metal and then changes the shape of the cross section of the weld. The friction between plasticized metal layers can be increased by increasing the pressure of shaft shoulder forging, which is beneficial to the plastic flow of the weld metal, reduces the loose defect and improves the density of the weld. The flow rate of plasticized metal in the action zone of the shaft shoulder can be increased by welding the stirring head of the shaft shoulder with a small channel groove, and the effect of "suction and extrusion" is also enhanced. In unit time, the amount of plasticized metal and the width of nugget are increased from the shaft-shoulder drive to the action zone of the stirring needle and the lower part of the weld. When the channel is too large, too many plasticized metals are wrapped in the shaft shoulder, and the metal viscosity is too low, which is not conducive to the transfer of weld metal, resulting in porosity or hole defects. The shaft-shoulder structure is a side channel groove, which can increase the forging pressure of the horizontal movement of the weld metal, increase the cross section area of the metal flowing down, and increase the size of the welding nugget. When the shape of the shaft shoulder is convex, it is advantageous to drive the plasticizing metal to the root of the agitated needle, and to act together with the spiral concave structure. The mobility of the propelling plasticized metal is the most, the width of the weld core is the largest, and the height of the center of the onion ring is the lowest. The average tensile strength of the joint with side channel groove shaft-shoulder mixing head is the highest, which is 278.95 MPA (64.3% of base metal), and the joint with convex shaft shoulder is the lowest (196.04 MPA). The lateral channel recessed shafts drive the plasticized metal radiate downward to prevent the aluminum cladding from extending upward, while the extruding force of plasticized metal moving to the bottom of the weld is the largest, and the aluminum clad layer reaches the maximum height when the external convex shafts are driven by the shafts. The clad aluminum layer at the nuke boundary becomes the crack initiation and extension zone of the joint under tensile load.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG453.9

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