Abstract
To reveal the enhancing energy coupling effect of plasma, a comparison of the welding mode transformation process during 1-µm and 10-µm laser welding of aluminum alloys is carried out through experimental observation and theoretical analysis. The heat conduction welding stage hardly exists in 10-µm laser welding and obviously exists in 1-µm laser welding. Alloy composition and surface roughness of the welded plate hardly influence the deep penetration welding threshold (DPWT) of the 10-µm laser, whereas they have a significant impact on that of the 1-µm laser. In addition, 1-µm laser welding and 10-µm laser welding have similar DPWTs. These phenomena are attributed to the formation of plasma near the workpiece surface during 10-µm laser welding owing to metal vapor breakdown by 10-µm laser irradiation. The plasma remarkably enhances the energy coupling between the 10-µm laser and workpiece by thermal conduction, and the DPWT of the 10-µm laser is thus reduced to approximately equal to that of the 1-µm laser.
Highlights
Laser welding has been considered as one of the most prospective welding technologies in the 21st century due to its overwhelming advantages such as inherent flexibility, weld beads with a high depth-to-width ratio, low heat input, and high welding efficiency.1–4 According to the laser wavelength, lasers can be divided into 1-μm and 10-μm lasers in the field of laser welding
The following conclusions can be drawn: (1) In 1-μm laser welding, the range of the P/d value is relatively large in the heat-conduction mode, and alloy composition and surface roughness have an apparent effect on the deep penetration welding threshold (DPWT)
(2) The melting threshold is quite close to the DPWT, and alloy composition and surface roughness of the welded plate hardly influence the DPWT during 10-μm laser welding
Summary
Laser welding has been considered as one of the most prospective welding technologies in the 21st century due to its overwhelming advantages such as inherent flexibility, weld beads with a high depth-to-width ratio, low heat input, and high welding efficiency. According to the laser wavelength, lasers can be divided into 1-μm and 10-μm lasers in the field of laser welding. Laser welding has been considered as one of the most prospective welding technologies in the 21st century due to its overwhelming advantages such as inherent flexibility, weld beads with a high depth-to-width ratio, low heat input, and high welding efficiency.. A lot of research studies suggest that many welding defects existing in 1-μm laser (i.e., fiber laser, Nd:YAG laser, or disk laser) welding, such as plenty of spatters, poor weld surface formation, and penetration fluctuations, are significantly different from those in 10-μm laser welding (i.e., CO2 laser). 1-μm laser cutting or welding of thick plates is inferior to that with a 10-μm laser. Study of the differences between 1-μm and 10-μm laser welding is expected to further optimize 1-μm and 10-μm laser welding technology.
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