Large amounts of welding fumes are produced in joining aluminium-magnesium alloys with DC pulsed MIG process. Welding fumes consist of magnesium oxide, aluminium oxide and pure aluminium. Magnesium element evaporates from both the surface and inside of droplets that are superheated. Evaporation inside of droplets produces magnesium bubbles, leading to violent explosions of droplets and emissions of magnesium vapour and liquid spatters. Part of magnesium vapour escaped from the shielded arc area is oxidised and then becomes super fine fume particulates that their shapes can not be recognized even with transmission electron microscope. Part of spatters ejected from the shielded arc area are partially or completely oxidised and then become fume particulates. In AC pulsed MIG welding the average heat content of droplets is low, and besides, the temperature distribution inside a droplet is deduced to be more uniform compared with that of DC pulsed MIG welding. In consequence, the evaporation of magnesium is restrained so that both frequency and violence of droplet explosions decrease clearly. AC pulsed MIG welding process can effectively control welding fumes at source in joining aluminium-magnesium alloys.
