Discharge state of laser induced and enhanced arc plasma

By using the high speed observation and spectral diagnosis, we compared and analyzed the welding penetration depth, plasma behavior, and plasma spectral feature of magnesium alloy during laser-arc hybrid welding, for understanding the characteristics of arc plasma in the welding process. Results show that there are three kinds of laser-arc combination styles, i.e. arc root separating from laser keyhole when laser beam does not pass through the arc plasma, arc root separating from laser keyhole when laser beam passes through the arc plasma, and the root of arc plasma right on the laser keyhole. When arc plasma roots the laser keyhole, it connects with the keyhole plasma, and a hybrid discharge happens. The keyhole part of the hybrid plasma possesses extreme electric conductivity as high as 1.2×104 S/m and approaches thermal equilibrium state, resulting in the fact that the laser induced and enhanced arc plasma has high electric current density (approximately 103 A/cm2) and energy utilization.