9413 Other Fusion Welding Processes

Fusion welding is any welding method that is performed by melting of the base metal or base and filler metal. It includes the arc welding processes mentioned above, and several others discussed below as they apply to aluminum.

Oxyfuel gas welding (OFW), or oxygas welding, was used to weld aluminum prior to development of gas-shielded arc welding. The fuel gas, which provides the heat to achieve coalescence, can be acetylene or hydrogen, but hydrogen gives better results for aluminum. The flux can be mixed and applied to the work prior to welding, or flux-coated rods used for shielded metal arc welding can be used to remove the oxide. Oxyfuel gas welding is usually confined to sheet metal of the lxxx and 3xxx alloys. Preheating is needed for parts over ^ in. (5 mm) thick. Problems include large heat-affected zones, distortion, flux residue removal labor and corrosion, and the high degree of skill required. The only advantage is the low cost of equipment; so oxyfuel gas welding of aluminum is generally limited to less developed countries where labor is inexpensive and capital is lacking.

Electrogas welding (EGW) is a variation on automatic MIG welding for single pass, vertical square butt joints such as in ship hulls and storage vessels. It has not been widely applied for aluminum because the sliding shoes needed to contain the weld pool at the root and face of the joint have tended to fuse to the molten aluminum and tear the weld bead.

Electroslag welding uses electric current through a flux without a shielding gas; the flux removes the oxide and provides the welding heat. This method has only been experimentally applied to aluminum for vertical welds in plate.

Electron beam welding (EBW) uses the heat from a narrow beam of highvelocity electrons to fuse plate. The result is a very narrow heat-affected zone and suitability for welding closely fitted, thick parts [even 6 in. (150 mm) thick] in one pass. A vacuum is needed or the electron beam is diffused; also, workers must be protected from X-rays resulting from the electrons colliding with the work. Thus electron beam welding must be done in a vacuum chamber or with a sliding seal vacuum and a lead-lined enclosure.

Laser beam welding (LBW) is an automatic welding process that uses a light beam for heat; for aluminum, a shielding gas is used also. Equipment is costly.

Thermit welding uses an exothermic chemical reaction to heat the metal and provide the filler; the process is contained in a graphite mold. Its application to aluminum is for splicing high-voltage aluminum conductors. These conductors must be kept dry because the copper and tin used in the filler have poor corrosion resistance when exposed to moisture.

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