"A literature review was conducted to determine the factors affecting porosity in welds deposited by GTAW and GMAW. Hydrogen is the dominant cause of porosity in aluminum alloy welds. The sources of hydrogen most commonly encountered in commercial welding practice are hydrocarbons (grease@ oils@ etc.) and moisture contaminants on surfaces of the filler metal and plate. These contaminants are immediately converted to atomic hydrogen by the arc and are subsequently transferred into the molten weld pool in accordance with Sievert's Law. Although both primary porosity (forming from the liquid) and secondary porosity (precipitating from the solid) may occur in welds@ only the more voluminous primary porosity is extensively covered in this review. Aluminum alloys are far more susceptible to porosity formation than all other structural metals because merely trace levels of hydrogen usually exceed the threshold concentration needed to nucleate bubbles in the molten weld pool. Alloying elements@ such as Cu@ Mg@ and Si@ significantly alter this threshold concentration. The size@ shape@ distribution and amount of hydrogen pores generated in the weld are dependent upon the solidification mode@ cooling rate@ degree of convective fluid flow@ welding parameters@ bead shape@ shielding gas mixture and external pressure. ""Getters"" such as cobalt and freon are effective in reducing porosity."
BULLETIN 290-1983 history
1983BULLETIN 290-1983 FACTORS AFFECTING POROSITY IN ALUMINUM WELDS – A REVIEW