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Study on Pulsed Laser Welding of Aluminium Alloys

Author: LinBingHua
Tutor: NiuRuiFeng
School: Xi'an University of Technology
Course: Materials Science and Engineering
Keywords: Pulsed laser welding Aluminium alloys Weld shaping Evaporation loss of Mg Numerical simulation
CLC: TG456.7
Type: Master's thesis
Year: 2009
Downloads: 80
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Abstract


Due to low density, high specific strength and excellent corrosion resistance, aluminium alloys are widely used as structural materials in automobile industry and aerospace industry. Welding defects such as gashole, crack and hot deformation are apt to be produced in the welds by traditional welding methods. As the laser welding has some characteristics such as energy concentration, small welding heat-input, narrow HAZ, and small deformation, it becomes one of the most promising welding methods for aluminum alloys.With reference to Nd:YAG pulse laser characteristics,orthogonal experiment was used to determine the best combination of welding parameters including welding current, pulse duration, welding speed and defocusing distance for 5A05 aluminium alloy plate with a thickness of 1mm. Based on the combination,the influence of individual welding parameter on surface morphology of the welds was investigated. The distribution of Mg element and the effect of these four parameters on evaporation loss of Mg element were analyzed, and the hardness of the welded joint was tested as well.The experimental results indicate that with the increase of welding current and pulse duration,penetration depth increases,while weld width increases and then decreases. Penetration depth decreases with increasing welding speed, but weld width increases and then decreases.The shaping of the welded joint becomes much better when the defocusing diatance is in the range of 8-10mm.In addition, the welding speed has a significant effect on the scale surface morphology of the welded joint.In order to achieve a better welded joint, welding current and speed should be matched each other. Mg loss rate decreases with the increase of welding current and pulse duration. While it increases with the increase of welding speed and defocusing distance. The welding hardness is higher close to the HAZ area along weld width direction, and the hardness decreases and then increases in weld depth direction.Pulse heat source model was established in this investigation.The temperature field and residual stress field were simulated with ANSYS software during the welding process. The residual stress of butt joint was determind by XRD. The simulation results of weld cross-section shape and residual stress are in good agreement with the experimental results.The simulation results also show that isotherms of the temperature field are almost circular shape with no-tail phenomenon. With the movement of laser heat source, the pool’s highest temperature in the middle of workpiece is lower than that of both ends. Temperature with time-dependent appeares to wavilness and has a significant hot sedimentation effect. The investigation has a certain theoretical significance and application values for the study of the mechanism of pulsed laser welding.

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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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