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Study on Structure and Properties of Electric Current Supported Laser Welding for Aluminum Alloy

Author: GuoXinJian
Tutor: ChenYanBin
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: laser welding electric current microstructure tensile strength aluminum alloy
CLC: TG456.7
Type: Master's thesis
Year: 2011
Downloads: 138
Quote: 0
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Abstract


Aluminum has high reflectivity to laer and it is prone to pores, cracks and other defects during laser welding. Electric and magnetic field supported laser welding has shown to stabilize the welding process and improve the welding quality. However, previous researches were focused on experimental testing and process optimization, study on microstructure and properties was little. In this paper, study on microstructure and properties of electric field supported laser welding will be carried out.The base material is 2219 T6 aluminum alloy plates, and two wheels which are all on the top of the plates are used to introduce current to the workpiece. Size,frequency and duty cycle of the current are changed and good weld joints are obtained. In this study, the main work is focused on the fracture behavior and microstructure of the weld joint.The results of hardness test show that electric current supported laser welding can slightly increase the hardness of weld zone. The results of tensile test show that it can improve the mechanical properties of joints significantly, too. In this paper, weld fracture morphology and the second phase particles are also be analyzed by SEM and EDS. Fracture mechanisms of the weld jonts are investigated with in-situ tensile experiment, so that the effect of the second phase particles in the fracture process can be studied. On the other hand, electric current supported laser welding can reduce the strain hardening index of the weld joint, and change the fracture mode. The pore features are researched and the influence of pores on the fractrue mode is analyzed, and it also show that electric current supported laser welding can significantly reduce pores of weld joints.In order to explain the reason of the enhancement of the electric current supported laser welding joints, the influence of current size, frequency ande duty cycle on the macrostructure and microstructure of the joints by using of OM; and the results show that the electric current supported laser welding can refine the weld structure significantly. The shape and distribution of eutectic phase is observed by SEM, and the Cu content of the center of dendrite is measured by EDS; and the results show that the electric current supported laser welding can change the shape of the eutectic phase and increase the solute content. And the reason of weld structure and solute content which why changed are also be studied.Using physical simulation experiment, the existence of the magnetic stirring effec is proved; the effect of heat input and dendritic broken are also be studied. The kind of the phase in the weld is confirmed using XRD. The crystal lattice parameters under different process are be analyzed, and it shows that the electric current supported laser welding can increase the lattice distortion. The grain degrees of orientation under different parameters are analyzed too, and it shows that the current can make the grain orientation disorder.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding process > Special welding > Laser welding
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