4. Discussion
4.1. Arc stabilized mechanism
According to the reported theory in laser–arc hybrid welding
and the physical characterization of pure MIG welding of Mg alloy,
the arc stabilized mechanism in current study is described as the
following two factors.
First, the truth that laser keyhole or laser induced plasma plume
fixes the arc root during the hybrid welding to improve the igniting
ability of the arc. According to the principle of minimum voltage, the
arc prefers to pass through the channel with higher conductivity.
Because the laser keyhole consists of large amount of high temperature
electrons and metallic ions, its conductivity is far higher
than that of cold substrate. The arc is then easily fixed and led by
laser keyhole rather than wanders as it is usually in pure MIG welding.
In the study of laser–MIG hybrid welding carried out by Sugino
et al. (2004), an obvious electronic channel was observed between
the laser plasma and the arc column, as shown in Fig. 13, indicating
obvious leading effect of laser beam on arc root. Based on this
laser leading effect, the arc can burn continually or be ignited again
rapidly during the hybrid welding after extinguishing temporarily