The Study Of Thermomechanical Function In Friction Stir Welding

Friction stir weiding (FSW) was a new solid-state joining-technology which had solved the problem of joining hard-to-weld (by conventional welding technology) metals such as aluminum alloys, copper and magnesium since it was invented. Its excellent welding properties has been widely studied by many domestic and foreign researchers. How to achieve an excellent quality of the joint in the process of FSW was the principle preoccupation of the study, and the study of the basic factors which influence the quality of the joint was the emphasis of the preoccupation. Many investigations have been carried out on the relationship between processing parameters and joint quality, and the corresponding relationship had been put forward in the published papers. In order to reveal the weld formation mechanisms further, how the processing parameters affect the joint quality through the interaction of the basic factors of heat and force on the flow pattern of the plastic material and the grain size of the joint was analyzed in this study based or. the results of the previous studies. Theoretical calculation and processing experiments were included in the study.Data required in the theoretical calculation was achieved through three experiments as following: (1) The output power of the electromotor drives the horizontal workbench of the friction stir welding machine used in experiment was detected in order to calculate the force between stir pin and welded material;(2) Friction coefficient between the tool material and the welded material under elevated temperature was detected, preparing for calculating the friction force between them;(3) Considered as standard of the flow of the plastic material, shear strength of the welded material under elevated temperature was detected.In the part of experiment, factors influence the width of the flow region of the plastic material and the degree of the influence were ascertained through comparing the micro-pattern of the joint to the result of the calculation. The influence of the heat and force on the flow of the plastic material was analyzed through observing the microstructure at varied locations of the weld line. Lamination was observed through the thickness of the joint dues to the different flow mechanism of the material underthe function of heat and force. Meanwhile, relationship between the grain size and the function of heat and force in the varied region of the joint was analyzed. It could be concluded: The grain size in the varied region of the joint was different because the function of the heat and force was different. Finally, factors induce the defects in the joint from the aspect of thermomechanical function was concluded through comparing and analyzing joints under different processing parameters.This study established foundation for further understanding of the welding mechanism of the friction stir welding and further analysis of the factors influence the formation of the weld. It was valuable for understanding the relationship between processing parameters and quality of the joint. It also had practical value to ascertain welding parameter, optimize processing technology and control the microstructure and quality of the joint.