How to arc weld aluminum


The main characteristics of aluminum which influence the welding process are hydrogen solubility, aluminum oxides, thermal conductivity, thermal expansion, and solidification shrinkage.  Weld porosity in aluminum is caused principally by bubbles of hydrogen that form in the solidifying weld pool. The hydrogen solubility of aluminum increases almost twenty times as the material makes the transition from solid to liquid state and continues to increase as the temperature increases.  Hydrogen absorbed during its molten state is forced out of solution as the aluminum cools and changes to its solid state. The hydrogen is trapped in bubbles and cannot effectively be removed from the weld. As the hydrogen comes out of solution, it can be a source of porosity or voids that can connect to form leak paths in a vacuum environment. The molten-solid hydrogen solubility ratio for aluminum is 36 times higher than for iron. This makes aluminum welds much more sensitive to this source of porosity than those of stainless steel. Hydrogen contamination usually comes from moisture or oil on the surface being welded. The parts to be welded must be cleaned very well in a detergent bath and dried before welding.


Aluminum requires very thorough preparation and starts by using a good chemical aluminum cleaner. Aluminum has an anodized surface and this must be wire brushed, sanded or ground off the surfaces to be welded, as well as anywhere the ground clamp is to be placed.


If joining thick metal pieces, they should first have their edges beveled with a metal grinder. The angle of the bevel should be approximately sixty degrees at the point of contact.

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