Porosity in Aluminum Welds

Porosity constitutes the main defect in aluminium welds. It is generally assumed that the basic reason for its formation is the presence of hydrogen. Hydrogen can originate from a variety of sources. Major sources of hydrogen are surface contamination of both the parent and deposited metals in the form of hydroxides, hydrocarbons or oxides with adsorbed moisture. Another source of hydrogen can be impurity of the gas shield associated with either moisture or air sucked into the arc atmosphere if an incorrect welding procedure is adopted. It has been found that even 2 ppm of hydrogen in the molten metal, or 250 ppm of hydrogen in the gas shield can be sufficient to produce porosity in aluminium welds.