Aluminum and its alloys are often used to create various technical and technological structures. Pure aluminum is not used as widely as its alloys, due to its low strength properties and high ductility. It should be noted that before welding aluminum, it is necessary to take into account the peculiarities of the welding process, due to the physical and chemical properties of this metal.
The scheme of technology of spot welding of aluminum.
The main problem with the connection of aluminum is the continuous formation on the surface of the welded metal oxide film Al2O3, which is refractory and interferes with fusion. In addition, aluminum oxides have a rather high melting point (+ 2050 ° C) compared with the same indicator for the metal itself (+ 658 ° C), which makes its own adjustments to the process. Aluminum has a high thermal conductivity, which entails the use of special techniques and methods.
Types of aluminum welding
The melting point of aluminum.
You can weld aluminum using the following types of welding:
- electric arc (automatic, manual);
- argon arc (automatic, semi-automatic and manual);
Let us consider the most common and effective method of aluminum welding - using a manual electrode by argon-arc welding on direct current with reverse polarity.Back to table of contents
Argon arc welding
Scheme of argon arc welding of aluminum.
The advantages of this type are the lack of use of auxiliary materials (electrode coatings, fluxes). The process is carried out manually, semi-automatic and automatic methods.
It should be noted that any welding work should be carried out only on serviceable equipment, in a well-ventilated room or indoors with a supply and exhaust ventilation and the use of personal protective equipment (shield, leather gloves, overalls, safety shoes).Back to table of contents
Materials and tools for manual argon arc welding
Safety during welding.
For this type of aluminum compound, a tungsten electrode with direct current and reverse polarity will require:
- solvent (acetone, gasoline);
- metal brush;
- etching solution;
- nitric acid (solution);
- metal preparation bath;
- non-consumable tungsten electrodes;
- welding machine or welding machine for argon arc welding with a specific type of torch, tungsten electrodes, dried argon (purity 99.8%), welding holders, filler wire of the required diameter;
- corrosion-resistant steel (copper) lining;
- personal protective equipment (shield, leather gloves, rubber gloves), overalls, safety shoes.
Metal preparation before welding
Scheme of a semiautomatic device for aluminum welding.
Before cooking aluminum with any kind, aluminum parts are subjected to preliminary preparation, which consists in degreasing the surface of the material and dissolving the oxide film.
Metal degreasing is carried out by treating its surface with solvents (acetone, gasoline, etc.). After that, clean the oxides mechanically with a brush or by etching using chemical solutions (sodium hydroxide - 45-55 g, sodium fluoride - 10-50 g, water - 1 l). Then the aluminum is washed with pure water for 0.5-1 minutes, then the metal surface is neutralized with nitric acid (solution of 25-30% for 1-2 minutes), then the metal is washed in running water, then in hot water, then the metal is dried until completely dry.
Such preparation is carried out not earlier than 2-4 hours before welding. In the same way should be processed wire for additives in the case of its application.Back to table of contents
Aluminum Compound Technology
The main characteristics of coated electrodes for aluminum welding.
Aluminum sheets with a thickness of less than 5 mm are boiled without separating the edges. With aluminum thickness up to 20-25 mm, work can be carried out without preheating the material. If the parts have a thickness of more than 20 mm, then the material should be preheated to 300-400 ° C.
Argon arc welding can be performed on alternating or direct current (reverse polarity). When working on alternating current, oscillators-stabilizers of the welding arc are used. Non-consumable electrode welding is performed on direct current with reverse polarity and on alternating current, with or without an additive material. In the role of the filler wire use wire brand AK domestic production according to GOST 7878-75 or foreign analogues. When welding T-shaped, angular or butt joints, the use of filler material is mandatory. In the case of work on flanging and butt with a small thickness of aluminum additives are not used. The parameters (diameter D) wire additive for manual work is selected based on the thickness of aluminum (S):
- S up to 2 mm, D additives up to 1-1,5;
- S = 2-5 mm, D additives = 1.5-3;
- S over 5 mm, D additives = 3-4.
In argon-arc welding, tungsten electrodes are used with a thickness of 0.8-8.0 mm and lanthanized tungsten of domestic or foreign production. Their diameter is chosen according to the type of current and the values of its force (I). So, at a constant current with reverse polarity:
- D electrode = 1 mm, I to 10 A;
- D electrode = 2 mm, I = 10-30 A;
- D electrode = 3 mm, I = 20-40 A;
- D electrode = 4 mm, I = 40-80 A;
- D electrode = 5 mm, I = 60-100 A;
- D electrode = 6 mm, I = 80-130 A.
The process of manual argon arc welding of aluminum elements and structures consists of several stages.
Perform this kind of work on a lining of stainless steel or copper sheets. The choice of mode (current I, argon flow rate Q) of argon arc welding with tungsten electrodes depends on the cross section of the parts to be welded (S), the presence of additives or flanging and has the following parameters:
- end-to-end with additive, S = 1.0 mm, I = 65-85 A, Q = 4-5 l / min;
- end-to-end with an additive, S = 1.2, I = 70-90 A, Q = 5-6 l / min;
- end-to-end with additive, S = 1.5, I = 80-100 A, Q = 7-8 l / min;
- end-to-end with an additive, S = 2.0, I = 90-110 A, Q = 7-8 l / min;
- end-to-end with additive, S = 3.0, I = 100-120 A, Q = 8-9 l / min;
- without butt-add, S = 0.8 mm, I = 45-55 A, Q = 4-5 l / min;
- without butt-additive, S = 1.0, I = 50-65 A, Q = 4-5 l / min;
- without butt-additive, S = 1.2, I = 60-70 A, Q = 5-6 l / min;
- without butt orifice, S = 1.5, I = 70-90 A, Q = 7-8 l / min;
- without butt-additive, S = 2.0, I = 90-110 A, Q = 7-8 l / min;
- without butt-additive, S = 3.0, I = 100-120 A, Q = 8-9 l / min;
- flare, S = 0.8 mm, I = 40-45 A, Q = 4-5 l / min;
- flare, S = 1.0, I = 45-55 A, Q = 4-5 l / min;
- flanging, S = 1.2, I = 55-70 A, Q = 5-6 l / min;
- flanging, S = 1.5, I = 70-85 A, Q = 7-8 l / min.
For manual argon arc welding with non-consumable electrode, special domestic units such as UDAR, UDG or their foreign analogues are used.
The process of argon-arc connection of parts manually begins with the excitation (ignition) of the arc. Before this, turn on the supply of argon and set the appropriate amperage according to the selected mode. The arc is ignited in the following ways: by striking the electrode on the surface of aluminum and by touching the perpendicular electrode at the point of origin. If there is a break in the arc, then the next ignition is made in front of the crater on the welded aluminum, and then returned to the already deposited material in order to bring pollution from the crater to the surface. Further, the work is carried out in the desired direction. It should be noted that when carrying out manual argon-arc welding, it is not necessary to perform oscillatory movements with a torch, since possible violation of the protection of the welding zone. The angle between the plane of the product and the axis of the burner should be from 75 to 80 °. And the angle between the product and the filler wire when it is used - 15-20 °. The burner should be moved after the filler bar.
The location of the seam in space determines the location of the electrode. Move the electrode "away from you" or "towards yourself." According to the trajectory of its movement receive medium or narrow seams. The type of movement of the electrode determines the heating or not heating of the metal edges.
The type of movement of the electrode and the filler rod when it is used is chosen based on the requirements for the seam and according to the reference data.
The seams are made medium (from 350 to 1000 mm), long (over 1000 mm) and short (from 250 to 300 mm). Long seams are boiled in parts of 250-300 mm. Depending on the thickness of the parts, the seams can be single-layer (single-pass) and multi-layer (multi-pass). Single ply seams are economical and fast in execution, but the suture metal has insufficient ductility. In the case of a multilayer weld, the welded metal has good mechanical properties. When carrying out multilayer work for aluminum with a thickness of more than 20-25 mm, the first main layer should be qualitatively performed, which determines the strength properties of the entire weld.
After the seams are completed, the supply of argon is turned off and the seams are subjected to additional processing - the slag residues are removed from the seam surface, since slag tends to corrode metal. Slag removal is carried out by washing the seam in hot water.
It should be noted that it is possible to cook aluminum with an electrode not only with manual argon arc welding, but also with manual arc welding, as well as automatic arc welding. However, these types of welding parts made of aluminum are not widely used due to the use of fluxes, as well as due to a number of features of the electrodes used and the poor quality of the seams. With automatic argon-arc and semi-automatic argon-arc welding, high quality of welds is preserved without the need to use flux. The most inefficient type of aluminum compound is gas welding using gas torches and fluxes.