Welding of metals has long been used around the world. If welding of steel structures does not cause problems, then the possibility of welding aluminum is doubtful for many. However, many doubts will disappear if you decide how to boil aluminum with argon.
TIG apparatus for argon arc welding.
Aluminum is indeed a specific material and causes some additional requirements. Numerous aluminum alloys, which are widely used both in production and in everyday life, further complicate the picture. Despite some difficulties, the problem of how to boil aluminum with argon is quite easy to solve, even in domestic conditions.
The process of argon arc welding.
One of the main problems when welding aluminum is its rapid oxidation in air. A very refractory aluminum oxide appears on the surface of aluminum (it melts at a temperature above 2000 ° C) and forms a dense film. Before or during work, this film must be removed.
Exposure to high temperatures significantly reduces the mechanical strength of aluminum, which can lead to the destruction of the material in areas adjacent to the weld. In addition, aluminum has a high fluidity of the melt, which complicates its retention in the weld zone. The color of aluminum does not change during heating, which does not allow precise control of the zone and the degree of heating.
Aluminum has an increased linear expansion coefficient with a low modulus of elasticity, which explains its desire for deformation. To eliminate the risk of deformations in the welding zone, it is necessary to carry out, for example, preheating.
The increased thermal conductivity of aluminum requires a higher amount of heat to weld it; therefore, the energy consumption and power of the current source increase. For aluminum, and especially for its alloys with magnesium, hydrogen porosity appears in the weld. During welding, there is a high risk of hot cracking of the weld material caused by stresses during its crystallization.Back to table of contents
Argon welding principle
Schematic diagram of argon arc welding.
A sufficiently effective way to cook aluminum is welding with an electric arc, melting the metal in an inert environment. The inertness of the environment in the welding zone is ensured by the supply of high purity argon. The use of a mixture of argon and helium is allowed. Such an environment allows to protect the material being welded from oxidation at elevated temperatures during welding due to the fact that argon practically does not enter into chemical bonds with other materials itself and at the same time displaces the air from the welding zone.
Electric arc welding in argon is carried out using a special tool - a torch. The burner contains a channel through which argon is supplied to the work area. An electrode is installed inside the burner. The top of the burner and the electrode are cooled with liquid. Melting and non-melting electrodes can be used as electrodes. To provide the weld metal with metal, an filler rod or wire is used, the material of which, when melted during heating, fills the volume of the weld. The bar is fed to the welding zone outside the torch.
Welding of metal is performed using an electric arc, which is ignited between the metal surface and the electrode. For ignition and maintenance of the arc, a welding current of direct or alternating voltage is applied to the electrode.Back to table of contents
Scheme of argon welding with tungsten electrode.
The specificity of aluminum welding is the requirement for thorough surface preparation before starting work. The main task of preparation is to destroy the oxide film, and this is carried out in several stages. First of all, the surface is cleaned from dust and dirt, and the edges of the joined blanks are cleaned and slightly rounded at the top with a file.
In the next step, the surface is treated with a solvent. For aluminum and its alloys, use organic solvents or an alkaline solution of the following composition: 50 g of sodium phosphate, 50 g of soda, 30 g of liquid silicate glass per liter of water. It is advisable to heat the solution before processing.
After cleaning with a solvent, the aluminum is machined with a metal brush. Such a brush can be made of wire with a diameter of 0.1-0.2 mm. All surface treatment of the material should be completed no later than 3 hours before the start of work, in order to avoid the appearance of a new film.Back to table of contents
The use of non-consumable electrodes
Scheme of argon welding of aluminum.
Aluminum can be welded using an electrode that does not melt in the weld zone. Such an electrode only ensures the formation of an electric arc between it and the surface of the workpiece. The metal to fill the weld is formed by melting the filler wire.
Most often, tungsten electrodes are used as non-consumable during welding electrodes. The diameter of such electrodes is 2-6 mm. Aluminum billets with a thickness of up to 12 mm are cooked with tungsten electrodes.
Aluminum welding using tungsten electrodes is carried out, usually, on standard welding installations of the UDG type, which ensure the supply of alternating current with the necessary force. The unit is capable of supplying argon at a rate of up to 15 l / min. The magnitude of the alternating voltage in the welding circuit when using argon is maintained at 15-20 V.
Table selection wire for aluminum welding.
As a filler material is used aluminum wire based on pure aluminum type AO or HELL. When working with aluminum alloys, a wire or rod is used with a composition similar to or similar to the composition of the alloy. So, for aluminum-magnesium alloys, an additive is used from the same alloy with magnesium content slightly (up to 1.5%) exceeding its content in the alloy itself.
The mode of aluminum welding with tungsten electrodes depends on the diameter of the electrode and the thickness of aluminum. We can recommend some specific process parameters. So, for welding sheets up to 2 mm thick, an electrode with a diameter of 2 mm should be used for filler wire up to 2 mm in diameter, and set the strength of the welding current to 50-70 A. For a billet 4-6 mm thick and an electrode with a diameter of 3 mm, the diameter of the additive is up 3 mm, current - 100-130 A, and with an electrode with a diameter of 4 mm, the current increases to 160-180 A. Welding of aluminum with a thickness of 10 mm with a 5 mm electrode requires setting the strength of the welding current to 220-300 A.
The scheme of gas welding aluminum.
Aluminum is welded using non-consumable electrodes in one or several passes, depending on the thickness of the blanks. If the thickness of aluminum is up to 3 mm, the welding process can be performed in a single pass (provided that a ceramic lining under the weld is used to hold the melt). Welding aluminum with a thickness of up to 6 mm will require two passes. Welding with a thickness of more than 6 mm necessitates the creation of bevels on the edges of the welded workpieces and four welding passes.
The ignition of the arc in argon (especially when using tungsten electrodes) by touching the metal surface with an electrode is not used. The most effective method is the use of an oscillator that supplies high-frequency high-voltage pulses to the electrode. These pulses ionize the arc zone and ensure its ignition when welding current is applied without touching the metal surface with an electrode. In the absence of an oscillator, the arc can be ignited only by increasing the welding current with a minimum arc gap.Back to table of contents
DC: the use of melting electrodes
Table welding modes aluminum.
Aluminum welding with direct current in argon is possible with the use of melting electrodes. Such electrodes under the action of an electric arc melt and fill the space between the welded parts. The use of additives in this case is not necessary.
When creating a DC arc, welding inverters are used, for example, vd-200 type. The main advantage of welding with direct current is the stability of the arc and the possibility of smooth adjustment of the welding current. The arc is ignited and maintained by a constant current of reverse polarity. This polarity ensures the destruction of the oxide film on the surface of aluminum, which also applies to the advantage of the method.
Recently, coated ozana-1 electrodes for technical aluminum and ozan-2 electrodes for some aluminum alloys have been widely used as melting electrodes.
The method of argon welding using a melting electrode.
These electrodes form the composition of the weld, close to the material itself. The consumption of electrodes like "ozan" on average is 2-2.2 kg per kilogram of weld metal. Of the other consumable electrodes, OK96.10 electrodes with a coating of alkaline salts for technical aluminum, as well as OK96.20 electrodes for alloys, incl. aluminum-magnesium alloys.
Melting electrodes for aluminum have a high hygroscopicity, so before use they require drying at a temperature of up to 150 ° C for at least half an hour. Moreover, their use after drying should be no more than a day.
The mode depends on the diameter of the electrodes and the thickness of the metal. When welding aluminum with a thickness of up to 10 mm, the following recommendations should be followed: when the electrode diameter is 3 mm, the DC force is set within 60-90 A, with a diameter of 4 mm - 90-125 A, and with a diameter of 5 mm - 120-150 A. When welding displacement of the electrode in the transverse direction should be made minimal.
To form a high-quality metal structure in the welding zone, the edges and adjacent areas of aluminum parts must be preheated, for example, using a gas torch.
The heating temperature is selected taking into account the grade of material and thickness. On average, heating up to 400 degrees is required. After the end of the welding process, it is necessary to ensure slow cooling of the weld.Back to table of contents
The quality of the weld is improved during the additional processing of the edges of the joined blanks. When welding aluminum with a thickness of less than 5 mm, edge processing is usually not carried out. In the case of welding of aluminum with a thickness of 5-10 mm, it is recommended to grind off the upper edge of the edge, forming a V-shaped weld. When working with metal with a thickness of more than 10 mm, X-shaped edge processing is often used, i.e. chamfer removed and the top and bottom. In addition, the weld is formed on both sides of the workpiece.
Aluminum welding is recommended only butt. Such types of compounds, such as overlapping or T-shaped, create the danger of slag accumulation in the gaps, which will cause increased corrosion of adjacent metal areas.
After the formation of the weld must be carefully cleaned of slag. Even a small residue leads to chemical interactions that destroy the metal. Slag is removed by hot water washing and mechanical cleaning with a metal brush.
During the work it is necessary to control the incoming argon. Stop flow is not valid.Back to table of contents
When welding aluminum you need the following tool:
- torch gas or blowtorch;
- emery circle;
- metal brush;
Electric arc welding in argon has shown its effectiveness in welding aluminum and its alloys. It is quite possible to boil aluminum in this way in the domestic conditions with the availability of equipment and certain skills.