AA7108铝合金板搅拌摩擦焊接残余应力.doc

摘要搅拌摩擦焊接是一种革命性的连接过程,近年来在研究、开发和应用取得了巨大的增长。 为了更好地描述焊接,残余应力正在成为必要的评估,因为这些残余应力作为初始属性，也可以修改结构。我们将运用超声波法测量残余应力，这种方法的优势是无损、方便、便宜、快速。 本实验用于加入了搅拌摩擦焊(FSW)的AA7108-T79，实验结果显示小压缩残余应力在基材和高拉伸残余应力的热影响区内。 这种方法的优势是已经被证明过的并且结果是明朗的。关键词：搅拌摩擦焊；残余应力；超声波方法；AA7108-T791 介绍时效硬化铝合金如2 xxx,6 xxx和7 xxx系列难以用扩散焊的方法来焊接，为了解决这个问题，一种新的焊接技术由Wayne Thomas在1991年在焊接协会中提出，这种方法尤其对铝合金的焊接有着显著的优点。这种新的焊接方法被叫做搅拌摩擦焊（FSW）。1在搅拌摩擦焊中的焊接残余应力预期会比常规的方法低很多，因为搅拌摩擦焊的线能量跟其他熔焊相比低很多，然而由于这种方法需要刚性夹持，所以产生的残余应力也是相当大的。所以对于搅拌摩擦焊的焊接残余应力的研究也是相当有价值的。22 残余应力的测量2.1 检验标准测量是在两种不同的标准中进行，一个是母材，一个是热处理状态的材料。试样在其屈服极限值（400MPa）之下来进行试验。2.2表面残余应力测量在所测量的三个不同的位置，焊珠上的残余应力的比其他位置的大。一般来说，其残余应力可以达到屈服极限的一半，最大值出现在焊接热影响区附近。从所测的应力值来看，超声波测量的值与x射线测量的值相差无几。33 结论在实验室的实验条件下，用超声波测量AA 7108-T79铝合金搅拌摩擦焊残余应力是可行的。结果显示，在母材附近存在较小的压应力，而在焊接热影响区附近有较大的拉应力。这种方法已经被证明是无损、轻便和高效的，由于这些优点使超声波测量适用于实验室和生产线。4 致谢感谢科技论文写作老师这么长时间的教导和帮助，并且给了我们很多很好的建议，使我知道了论文的质量重于字数，越是好的论文其核心的内容就越是明确，希望以后我也可以写出好的论文。参考文献1 R.S. Mishra and Z.Y. Ma, Friction stir welding and processing, Mater. Sci. Eng. R 50 (2005),pp. 178.2 G. Buffa, J. Hua, R. Shivpuri, and L. Fratini, Design of friction stir welding tool using thecontinuum based FEM model, Mater. Sci. Eng. A 419 (2006), pp. 381388.3 M.Z.H. Khandkar, J.A. Khan, A.P. Reynolds, and M.A. Sutton, Predicting residual stresses infriction stir welded metals, J. Mater. Process. Technol. 174 (2006), pp. 195203.AbstractFriction stir welding is a revolutionary joining process which has seen remarkable growth in research, development and application in recent years. In order to better characteries the welding, it is becoming necessary to evaluate the residual stresses, because these can modify aswell the structure as the initial properties of material. In the current work, we will focus particularly in the method of measurements based on ultrasonic waves. This method has the advantage of being nondestructive, easy, inexpensive and fast to use in aitu. The experimental results obtained onAA7108-T79 aluminum alloy joined by friction stir welding (FSW), showed small compressive residual stresses in the base material and high tensile residual stresses in the heat affected zone. Advantages bound to this method were proved and results remain very promising.Keywords: friction stir welding; residual stresses; ultrasonic method; AA7108-T791 IntroductionAluminum alloy swith age hardening, such as 2XXX, 6XXXand 7XXXseries are difficult to weld by fusion welding methods. Consequently, as a solution for this concern, a new joining technique of welding was invented by Mr Wayne Thomas at The Welding Institute of UK in 1991, and has become one of the best techniques for joining metallic structures, in particular, Aluminum alloys This new process is called friction stir welding (FSW).The residual stresses are expected to be much lower in FSW, because of the low temperature level compared with the fusion welding techniques. However, the very rigid clamping arrangement used in FSW exerts a much higher restraint on the deformation of the welded plates than the more compliant clamps used for fixing the parts during conventional welding processes.2 Residual stress measurement 2.1Calibration testsThe measurements are carried out in two different zones: the parent metal and heat affected zone. The sample was tested under its yield stress (400 MPa). 2.2 Superficial residual stresses evaluationFor the three positions of y, the residual stresses are higher on the level of the weld bead. Generally, they reach nearly 50% of material yield strength (Figure 7). The maximum is reached in the vicinity of the heat affected zone.3 Conclusion The ultrasonic stress measurement method described in this paper enabled, in laboratory experimental conditions, the evaluation of residual stresses on AA 7108-T79 aluminum alloy sheets joined by FSW. A comparison was made with stress measurement obtained by X-ray diffraction. The results show a small compressive residual stresses in the parent metal and high tensile residual stresses in the heat affected zone. The potentialities of the proposed method were confirmed: the nondestructive character, the portability of material and its rapidity. All those advantageous allow its use in aitu and on production lines.4 AcknowledgmentThanks to science and technology thesis writing teachers teach and help for such a long time and gave us a lot of good advice，I know the quality of the paper focuses on words，The more good paper of its core content is the more clear, hope later I can also write good paper.References1 R.S. Mishra and Z.Y. Ma, Friction stir welding and processing, Mater. Sci. Eng. R 50 (2005),pp. 178.2 G. Buffa, J. Hua, R. Shivpuri, and L. Fratini, Design of friction stir welding tool using