Aluminum
Aluminum is a light, silver-colored metal with approximately one-third the density of steel or brass. It is a good conductor of electricity. Compared to other metals in steels, aluminum has a higher resistance to corrosion, protecting the oxide provided by the thin but tenacious film that forms on its surface.
Aluminum is also a good conductor of heat, more ductile and no magnetic metal with the melting point of 659°C in the pure form. The melting point of Aluminum alloys varies between about 520°C to 650°C.
Aluminum forms high strength alloys in conjunction with other metals such as Cu, Cr, Ni, Fe, Zn, Mn, Si, and Mg, because it is not particularly strong in its pure form.
The Aluminum and its alloys can be: Cast iron, Forged, Welded, Extruded, Rolled, etc.
In heavy-duty such as: dragline booms, traveling cranes, hoists, conveyor supports, bridges, etc.
In the process industry, Aluminum and its alloys are used as handle organic chemicals, petrochemicals and drugs. Tanks, drums, pipes, heat exchangers, gratings, smokestacks, drilling towers, precipitators, centrifuges, valves, fittings, etc.
This film has moisture that can react during fusion welding with the liquid metal in the molten weld pool, forming another oxide and liquefying hydrogen that can cause perforation.
the problem can also occur during welding. To avoid this problem the following measures can be taken:-
Gas welding and Brazing
In the gas welding and brazing process, the oxide film can be removed using a suitable welding flux. Metallic arc weldings
It can be removed by using an electrode with a suitable coating in metallic arc weldings.
Aluminum forms high strength alloys in conjunction with other metals such as Cu, Cr, Ni, Fe, Zn, Mn, Si, and Mg, because it is not particularly strong in its pure form.
The Aluminum and its alloys can be: Cast iron, Forged, Welded, Extruded, Rolled, etc.
Application of Aluminum and its alloys
The intense demand for aluminum and its alloys is very high today, mainly due to its attractive physical, mechanical and chemical properties. Aluminum and its alloys are often used in many ways such as:Transportation and Architectural field
Structural frameworks, Engine parts, Trim and decorative features, hardware, doors, window frames, tanks, furnishings, and fittings. Overhead conductors and heat exchanger parts,Food preparation equipment
Refrigeration, storage containers, bakery equipment, shipping containers, Mangles, waffle molds, Roofing, coping sills railings, fasteners, lighting fixtures, solar shading, grills, gratings, and Cryogenic applications, etc.In heavy-duty such as: dragline booms, traveling cranes, hoists, conveyor supports, bridges, etc.
In the process industry, Aluminum and its alloys are used as handle organic chemicals, petrochemicals and drugs. Tanks, drums, pipes, heat exchangers, gratings, smokestacks, drilling towers, precipitators, centrifuges, valves, fittings, etc.
Welding of Aluminium And its alloys
Compared to other metals, aluminum, and alloys have certain welding characteristics, which require some special attention during welding.Oxide film or Moisture
The important consideration is the effect of a thin film of oxide that always exists on the surface of the aluminum.This film has moisture that can react during fusion welding with the liquid metal in the molten weld pool, forming another oxide and liquefying hydrogen that can cause perforation.
Removing of Oxide film
The oxide film on the base metal surface is chemically or mechanically removed by brush or scrubbing prior to the welding operation.the problem can also occur during welding. To avoid this problem the following measures can be taken:-
Gas welding and Brazing
In the gas welding and brazing process, the oxide film can be removed using a suitable welding flux. Metallic arc weldings
It can be removed by using an electrode with a suitable coating in metallic arc weldings.
GMAW welding process
In the GMAW welding process, the oxide layer is removed by the arc cleaning action when the aluminum base metal forms the negative pole.
In AC tig welding, the cleaning of oxide is carried out in the positive half cycle and in the negative half, the electrode gets cooled down while the base metal gets heated up aiding adequate fusion in the joint interface.
GTAW Welding:-
GTAW welding is the most commonly used welding process today. With this process, a thin section of aluminum can be welded very well without adding any filler metal.
Tig welding resembles gas welding because both employ a heat source independent of the filler (metal)electrode. In the Gas welding process, Flux is used whereas shielding gas is used in the tig welding process.
Joint preparation
By the tig welding process,
there is a range from 1 to 10 mm for manual welding and 0.25 mm to 25 mm for automatic welding.
Shielding Gas
Usually, Argon gas is used for GTAW Welding process aluminum welding, because, in DCRP, it establishes an arc more easily and provides better arc control, but sometime Helium is used for the thicker section of aluminum when DCSP is used.A Mixture of Helium and Argon is used with DCSP to providing the deep, narrow penetration essential for the best properties and a minimum heat-affected zone.
Electrodes
Unalloyed tungsten and tungsten-zirconium electrodes are preferred for Ac welding. zirconiated electrodes are likely to be contaminated by aluminum and have a slightly higher current rating. The pure tungsten is minimized inclusions in the weld bead and current unbalance. When welding with AC the tip of the electrode should be hemispherical.
For DC welding of Aluminum, Thoriated tungsten is used, the tip of the tungsten should be ground to a blunt conical point, having an included angle between 60 to 120 degrees to attain maximum penetration.
In the GMAW welding process, the oxide layer is removed by the arc cleaning action when the aluminum base metal forms the negative pole.
Gas Tungsten Arc Welding
If DCRP is used in the Gas Tungsten arc welding process, the tungsten electrode will be overheated and the base metal may not melt adequately. Therefore AC is preferred for tig welding.In AC tig welding, the cleaning of oxide is carried out in the positive half cycle and in the negative half, the electrode gets cooled down while the base metal gets heated up aiding adequate fusion in the joint interface.
Welding Processes Used in Aluminium and its Alloys
The methods employed for welding aluminum and its alloy components can be discussed under the following heads:GTAW Welding:-
GTAW welding is the most commonly used welding process today. With this process, a thin section of aluminum can be welded very well without adding any filler metal.
Tig welding resembles gas welding because both employ a heat source independent of the filler (metal)electrode. In the Gas welding process, Flux is used whereas shielding gas is used in the tig welding process.
Joint preparation
By the tig welding process,
there is a range from 1 to 10 mm for manual welding and 0.25 mm to 25 mm for automatic welding.Shielding Gas
Usually, Argon gas is used for GTAW Welding process aluminum welding, because, in DCRP, it establishes an arc more easily and provides better arc control, but sometime Helium is used for the thicker section of aluminum when DCSP is used.A Mixture of Helium and Argon is used with DCSP to providing the deep, narrow penetration essential for the best properties and a minimum heat-affected zone.
Electrodes
Unalloyed tungsten and tungsten-zirconium electrodes are preferred for Ac welding. zirconiated electrodes are likely to be contaminated by aluminum and have a slightly higher current rating. The pure tungsten is minimized inclusions in the weld bead and current unbalance. When welding with AC the tip of the electrode should be hemispherical.
For DC welding of Aluminum, Thoriated tungsten is used, the tip of the tungsten should be ground to a blunt conical point, having an included angle between 60 to 120 degrees to attain maximum penetration.
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