• Condensation on the plate— High humidity and change in temperature (crossing a dew point) can result in condensation on the plate surface. When welding in high humidity, it is relatively easy to acquire moisture from small fluctuations in temperature — Fig. 4. • Hydrated aluminum oxide— Aluminum has a protective oxide layer, and when the aluminum oxide is exposed to moisture, potential problems with porosity arise. The aluminum oxide layer is porous and can absorb moisture, grow in thickness, and become a major problem when attempting to produce welds that are required to be relatively porosity free. This problem can occur on both the base metal and filler metal. Other Contamination Considerations Shielding during Welding Exposure and contamination of the molten weld metal to the surrounding atmosphere during welding is one consideration 26 WELDING JOURNAL / APRIL 2015 Fig. 4 — At high humidity, small differences between the aluminum base metal or filler metal temperature and the air temperature can cause moisture condensation. For example, at a relative humidity of 90% (shown across the top of the table) and ambient air temperature of 70°F (shown down the left side of the table), the weld wire or aluminum plate need only be 3°F lower (67°F shown in the intersecting lighter box) in temperature than the ambient air before it will cross the dew point and produce moisture. when examining a porosity problem. This situation may occur because of inadequate gas shielding during welding. Following are some examples: • Welding in drafty conditions — Strong drafts due to open doors or fans directed at the area of welding can remove the shielding gas during the welding operation. • Excessive spatter buildup inside the gas nozzle when gas metal arc welding (GMAW) — This condition can restrict gas flow and reduce the efficiency of the shielding gas. • Incorrect standoff distance— Changes in the distance from the end of the nozzle to the surface of the For info, go to www.aws.org/adindex
Welding Journal | April 2015
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