APRIL 2015 / WELDING JOURNAL 25 Hydrocarbons Hydrocarbons are a source of hydrogen and can sometimes be present on the surface of the base metal or on the filler metal. Following are some examples: • Contamination of plate surfaces — A thorough cleaning of plate surfaces that have hydrocarbons on them, such as lubricants, grease, oil, or paint, is necessary to remove hydrocarbon contamination prior to welding. • Exhaust contaminants on the plate surface from compressed air tools used for weld preparation— Make sure these tools do not transfer exhaust contaminants, oil, or moisture onto the plate surface. • The quality and cleanliness of the aluminum welding wire — This wire must be clean and free of any residual oil used during the wire manufacturing process. If the quality of the welding wire is inferior, it may be virtually impossible to produce acceptable porosity levels. • Antispatter compounds — This type of material, applied to the welding nozzle or plate surface, is not usually recommended for aluminum welding when low levels of porosity are desired. Moisture Through a number of sources, hydrogen containing moisture (H2O) can also be a source of contamination to the welding area. Following are some examples: • Water leaks — This can occur within the welding equipment if using a water-cooled welding system. • Inadequately pure shielding gas — Shielding gas should meet the minimum purity requirements specified by the appropriate welding code or standard. Additionally, contamination of shielding gas may also occur from imperfections within the gas delivery line, such as leaking pipes or hoses. Fig. 3 — The cause of porosity in aluminum welds is hydrogen, which as shown in this chart has a high solubility in molten aluminum but very low solubility in its solid state. For this reason, the potential for excessive amounts of porosity during arc welding of aluminum is considerably high. Fig. 2 — A macroetch examination of a fillet weld showing large, irregularshaped porosity. For info, go to www.aws.org/adindex
Welding Journal | April 2015
To see the actual publication please follow the link above