In situ Weak Magnetic-Assisted Thermal Stress Field Reduction Effect in Laser Welding
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IDUAL stress concentration of welds is one of the most serious origins of structural failures. Pre-heating and post-weld treatment have been used to reduce the residual stresses of weld structures.[1–3] However, most of these methods were limited by manufacturing conditions such as structure size, material properties, and production costs. For instance, in terms of post-weld treatments, annealing and mechanical impacting are considered the most effective methods in many industries, but their application is usually limited to large structures.[4,5] Recently, magnetic treatment after welding has been utilized as an effective method to reduce residual stress. For instance, the pulsed magnetic treatment has been found to relax the residual stresses. The mechanism of this relaxation is the even distribution of the dislocations
LVJIE LIANG, XINYU SHAO, and PING JIANG are with the State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology(HUST), Luoyu Rd, 1037 Wuhan, PR China. SHENGYONG PANG, CHUNMING WANG, and XIN CHEN are with the State Key Laboratory of Material Processing and Die & Mould Technology, Huazhong University of Science and Technology(HUST), Luoyu Rd, 1037 Wuhan, PR China. Contact e-mail: [email protected] Manuscript submitted February 08, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
caused by the magnetic field after the welding process. However, this method usually needs a strong-pulsed magnetic field and a complicated magnetic field generating device.[6–9] Here, we propose a new idea that the residual stress can be improved in situ by a simple weak permanent magnetic field during the laser welding process. We argue that this novel in situ effect is due to the influence of magneto-fluid dynamics on the liquid state weld pool in the welding process by a weak magnetic field. It is noted that controlling the weld pool via magnetic-fluid dynamics in laser welding was studied by Kern in 2000.[10] Recently, the enhancement of the quality of laser welds by magnetic fields has been studied, and the quality enhancement was mostly focused on the large penetration and inhibition of defects.[11–18] Numerical assessments have been carried out to investigate the mechanism of the influence of magnetic field in the laser welding process.[19–22] Researches about simulation and measurement have been carried out to study the residual stress in laser welding.[23–25] However, in these studies, the weak magnetic field was mainly used to mitigate the process defects, such as pores, undercuts, and spatters, during laser welding. No study, to our knowledge, has reported the in situ effect of magnetic field on the thermal stress field and residual stress in laser welding. In this paper, a new method to mitigate stress concentration is proposed, in which an axial (parallel to laser beam) external weak magnetic field is used
during the laser welding process of 304 stainless steel. The weak magnetic field is generated by a permanent magnet below the weld pool. Experiments are carried out t
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