Study On Pulsed MIG Welding And Low-power YAG Laser+Pulsed MIG Arc Hybrid Welding Technology

In the present paper, direct current pulsed metal inert-gas (DC-PMIG) welding is carried out on AZ31B magnesium alloy plates to obtain high-quality welding joints with different thickness using 1.6mm diameter of filler wire. The microstructures and mechanical properties of the joints were investigated by optical microscopy, scanning electron microscope, universal tensile testing machine and micro hardness tester after welding. The mechanism of metal transfer and the behavior of welding spatter were researched through high speed camera system, and the parameter ranges of stable welding process were found out. Stability control of welding process can be realized by using low-power YAG laser+pulsed MIG arc hybrid welding technology in which laser changes the mode and frequency of metal transfer. The main results are as follows:1. The metal transfer form of magnesium alloy using DC-PMIG welding is realized in mode of globular transfer, projected transfer and spray transfer. Spatters with their large sizes are produced in globular transfer form, and stable welding process with few spatters can be obtained in mode of projected transfer and spray transfer when Q is 242-271 J/cm, d is 1.6-0.9mm and N is 30-69Hz. Typical forms of welding spatter appear as globular repelled transfer and explosive transfer, and the phenomenon of the spatters above is closely related to the strained condition and transient state of droplets.2. Welding joints with continuous appearance, few spatters and scarcely any of welding defects can be obtained by optimizing parameters using DC-PMIG welding. Moreover, projected transfer form is adopted forâ… shape butt welding of 3mm thickness plates, and spray transfer form is adopted forâ…¤shape butt welding of 8mm thickness plates. The grain size of fusion zone is obviously smaller than that of heat affected zone and base metal, and the microstructures of fusion zone are uniform. The highest ultimate tensile strength of weld bead is 94.6% of that of base metal, the highest elongation of weld bead is 63.7% of that of base metal and the highest area reduction of weld bead is 1.7 times of that of base metal.3. Laser changes the mode and frequency of metal transfer by increasing the plasma fluid force which is the main force to promote metal transfer as a result of reducing the area of arc effective section. Compared to pulsed MIG welding, the metal transfer frequency of low-power YAG laser+pulsed MIG arc hybrid welding of magnesium alloy increases 43% and the spatter loss coefficient decreases 11%. The technology of low-power YAG laser+ pulsed MIG arc hybrid welding of magnesium alloy greatly enhances welding stability, improves appearance of weld and reduces welding spatter. The experiments prove the feasibility of this technology.