Effect of spiral scanning laser power on arc thermal field in double pulsed CMT

To study the effect of spiral scanning laser power on the arc thermal field, droplet transfer, and porosity defects in aluminum alloy double pulsed CMT additive manufacturing, the comparative experiments with variable laser power were conducted. The infrared thermography, spectral measurement, and high-speed imaging technology were used to analyze the arc radial temperature variation near the molten pool surface, the plasma behavior of the intersection region, the droplet transition, and the porosity defects when the scanning laser was introduced. The results indicated that the arc radial temperature near the molten pool surface exhibited significant fluctuations and a steep temperature gradient with low arc stability in the double pulsed CMT. When the laser power was set to 600 ~ 1200 W, the arc radial temperature distribution became more uniform, and the temperature gradient significantly decreased, and the arc temperature was notably elevated (a maximum increase of 900 ℃) ,which promoted the ionization of Mg and Al atoms, resulting in more generation of Mg Ⅱ, Mg Ⅲ, Al Ⅱ, and Al Ⅲ ions, and improving the arc stability. At laser power of 600 W and 1200 W, the electron density increased by 6% and 17%, the electron temperature rase by 400 K and 800 K. The laser metal vapor effectively reduced the droplet transfer frequency, lessened the droplet impact on the molten pool and contributed to greater stability. The number of pores in the components decreased significantly, with their distribution became more dispersed; at a laser power of 1200 W, the porosity was almost eliminated.