Improvement of penetration ability of heat source for 316 stainless steel welds produced by alternating magnetic field assisted laser-MIG hybrid welding
Introduction
Recently, laser-arc hybrid welding technology combining both heat sources of laser and arc has attracted widespread attentions, due to its unique advantages, as stated by (Steen William, 1980). (Bagger and Olsen, 2005) also reported that compared to single laser welding or arc welding, laser-arc hybrid welding possessed better gap bridging, faster welding speed and higher penetration depth, benefiting from the strong laser-arc synergistic effects. However, (Dilthey and Wieschemann, 1999) pointed out that the coupling process of laser beam and arc was complicated when considering the interaction between heat sources and base material during laser-arc hybrid welding. Droplet transition, characteristics of arc plasma and laser-induced plasma, melt flowing and keyhole behaviors are included in laser-MIG hybrid welding process. Meanwhile, these characteristics have significant influences on quality of laser-MIG hybrid welded joint.
The weld depth, as a main characteristic of weld quality, has always been the focus of attention by relevant scholars. For laser-arc hybrid welding method, the weld depth was mainly determined by laser heat source, due to stronger penetration ability of laser energy. The relevant studies about the penetration ability of single laser welding method have been performed and the mechanism of laser-induced plasma plume on laser penetration ability has been clarified. (Chiang and Aibright, 1992) found that the heat transfer efficiencies in laser beam welding could be suppressed by lase-induced plasma plume during CO2 laser welding of mild steel. (Zuo et al., 1998) also pointed out that laser-induced plasma could shield incident laser beam and about 50 % incident laser energy would be absorbed when plasma shielding occurred during high power CO2 laser materials processing. (Kawahito et al., 2009) studied the attenuation effect of plasma plume on near-infrared laser beam and suggested that the attenuation of laser energy was about 3 %–13 % during laser welding by probe laser beam measurements, and similar results have also been found by (Shcheglov et al., 2011). Besides, (Gao et al., 2015) studied the characteristics of laser-induced plasma plume during fiber laser welding aluminum alloy and found that the laser beam energy was attenuated by plasma plume in laser beam path by absorption, refraction and scattering. The shielding effect was dominated by the inverse bremsstrahlung effect of plasma. Based on above studies, to decrease the shielding effect of plasma plume on laser energy and improve penetration depth, various methods including side-assisted gas and application of vacuum or subatmospheric pressure were employed in laser welding process, as discussed by (Katayama et al., 2011) and (Luo et al., 2015). However, these methods were not suitable for laser-arc hybrid welding to reduce the negative effect of laser-induced plasma plume, due to the existence of arc plasma. In addition, (Üstündağ et al., 2021) has proposed that the keyhole stability was also an important factor influencing the penetration ability of laser beam because part of laser energy was lost for maintaining the stability of keyhole. Compared to single laser welding, the melt flow was more complicated and the keyhole was more fluctuant during laser-MIG hybrid welding, due to the impact of the force by droplet transfer. With the expectation for expanding application of laser-MIG hybrid welding, it was necessary to seek an auxiliary method to improve penetration depth of laser-MIG hybrid welding under the premise of ensuring quality of welded joint.
In the past decades, magnetic field assisted welding technology has been employed in traditional arc welding or laser welding. The significant importance of the magnetic field on arc behaviors, droplet transition, laser-induced plasma and melt flow has been studied. (Wang et al., 2017) suggested the external magnetic field could control the shape and movement of arc plasma by adjusting direction and parameters of magnetic field. (Bachmann et al., 2016) employed a steady magnetic field in laser welding process and found that the Hartmann effect produced by external magnetic field could affect the flow dynamics of melt in the molten pool. As (Tse et al., 1999) reported, the laser-induced plasma could be controlled by external magnetic field, leading to 7 % increase of the penetration depth during CO2 laser welding. (Li et al., 2018) claimed that the stabilization of keyhole could be improved by external magnetic field during laser full penetration welding. Moreover, (Üstündağ et al., 2021) studied the effect of an oscillating magnetic field on the keyhole stability and found that a direct influence of external magnetic forces on the flows in the keyhole surrounding was beneficial for keyhole stabilization. The aforementioned studies confirmed that the application of the external magnetic field had a significant influence on arc welding and laser welding process. However, the researches about effect of external magnetic field on penetration ability of laser-MIG hybrid welding were not carried out. The complicated interaction mechanism between magnetic field and characteristics of laser-MIG hybrid welding process should also be clarified.
Therefore, in this study, in order to explore the effect of external magnetic field on penetration ability of hybrid heat sources during laser-MIG hybrid welding, laser-MIG hybrid welding at various alternating magnetic flux density was performed. The characteristics of hybrid plasmas including arc plasma and laser-induced plasma under different magnetic flux density were monitored and the droplet transition and the dynamic behavior of the keyholes were observed through a “sandwich” test method. Moreover, the penetration mechanism of hybrid heat source to welded plate under alternating magnetic field was detailly studied.
Section snippets
Materials and welding setup
In this study, the 316 stainless steel plates with the dimension of 150 mm × 100 mm × 6 mm and the ER316 L filler wire with diameter of 1.2 mm were employed as welding materials. The chemical compositions of 316 stainless steel and ER316 L filler metal were listed in Table 1. Before welding, the 316 stainless steel plates were cleaned by alcohol to remove away the grease. The pure argon was employed as shielding gas to protect the molten pool.
A fiber laser system (IPG YLS-6000) coupled with an
Appearance and cross-sectional morphology
The laser-MIG hybrid welding tests under each magnetic flux density were performed at least three times to ensure the reliability of the experimental results. The typical appearance and cross-sectional morphology of 316 stainless steel laser-MIG hybrid welded joints under different magnetic flux density were shown in Fig. 3. In addition, the average values of weld cross-sectional features including weld depth, weld width and depth to width obtained under different magnetic flux density from
Conclusions
The following conclusions were obtained from the above results and discussion about change of penetration depth of 316 stainless steel laser-MIG hybrid welded joint under different magnetic flux density.
- (1)
Obvious differences on weld depth was observed in the laser-MIG hybrid welded joint under different magnetic flux density. The weld depth (3.14 ± 0.08 mm) and depth to width (0.503 ± 0.008) under LMFD with 20 m T was smaller than that (4.08 ± 0.06 mm and 0.709 ± 0.005) without an external
Author statement
Fuyun Liu: Data curation, Writing - original draft. Bingxiao Xu: Investigation. Kuijing Song: Methodology, Writing - review & editing. Caiwang Tan: Conceptualization, Methodology, Writing - review & editing. Hongyun Zhao: Supervision. Guodong Wang: Validation. Bo Chen: Writing - review & editing. Xiaoguo Song: Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The research was supported by National Natural Science Foundation of China (Grant No. 52074097) & (Grant No. 51875129).
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