Satisfactory butt, lap, and fillet welds can be made with an oxyfuel gas torch on sections of aluminum ranging up to 25 mm (1 in.) in thickness. The oxyfuel gas welding process would only be used where a source of electric power is not available for arc welding. Oxyhydrogen or oxyacetylene flames produce the heat necessary to offset the high thermal conductivity of the aluminum. Generally, the other oxygen-gas combinations do not provide sufficient heat for welding, but may be used for preheating, which is often needed when joining thick sections.

Overlap joints are not recommended for gas welding because there is danger of flux entrapment in the overlap. When possible, the joint should be designed as a butt weld. If an overlap joint is made, it should be completely welded around the edges to seal the overlapped area.

Preheating is essential in gas welding to allow proper fusion. Sections thicker than 6 mm (1/4 in.) should be preheated to 310 to 370°C (600 to 700°F). Preheating above 425°C (800°F) is not recommended because there is danger of melting some of the alloying constituents. Heat should be applied uniformly to both parts being joined. See OXYFUEL GAS WELDING.

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