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Aluminum and its alloys are only slightly inferior in strength to steel, but they are very easy to process, have a decent appearance and have excellent qualities such as thermal and electrical conductivity. However, along with these properties there is the difficulty of soldering them. The question of how to solder aluminum is asked not only by novice amateurs, but also by those who do not have difficulty soldering copper, brass and steel.
Soldering aluminum is a complex process, so you need to know all its technology.
Working with aluminum is not easy because of its ability to instantly oxidize in air, as a result of which the surface is covered with a thin film of Al2O3 oxide, which has increased resistance to aggressive environments. Therefore, special mercury fluxes or replacement tips for soldering irons are used, or, depending on the soldering method, the oxide is removed in various ways.
Before soldering aluminum, they resort to mechanical removal of the film, cleaning the work area with a file, but contact of aluminum with water or air leads to the original state - the appearance of the same film.
For soldering aluminum, you can use a special flux.
Experts advise cleaning the soldering area with a brick or sand, without removing the dust, but applying molten rosin directly to it, then rubbing it with a soldering iron, pressing firmly with the tip. This will help break down the thin film that formed before applying the rosin.
Also, the stripped aluminum is filled with rosin and sprinkled with filings from an iron nail obtained during the filing process. Next, you need to tin the surface with a soldering iron, carefully rubbing it with the tip. Iron chips will destroy the film, while rosin will prevent the formation of a new film.
Chemical stripping methods
It is important not to allow the aluminum being stripped to come into contact with air; for this purpose, the soldering area is filled with flux or rosin, while heating it. Often small elements, such as wires, are dropped directly into rosin or flux poured into a container.
In addition to the mechanical method of removing oxide, there are several so-called chemical methods.
Cleaning aluminum before soldering can be done using copper sulfate.
Cleaning with copper sulfate. The point where solder needs to be made is cleaned with a file and moistened with two or three drops of copper sulfate solution. The aluminum base is connected to the negative pole of the battery or accumulator; a small piece of copper wire, stripped and connected to the positive pole, is lowered into the solution without touching the base. After turning on the 4.5 volt battery, a copper coating forms on the aluminum after a short period of time. The desired part is then soldered to the dried copper.
Use of abrasive powder. A liquid paste is prepared by mixing powder and transformer oil, which is applied to the cleaned surface and then rubbed in with a soldering iron until a layer of tin appears.
Another method is transformer. The product is connected to its negative side, a copper wire containing several cores is connected to its positive side. After closing the circuit, microwelding of aluminum and copper will occur. To speed up the process, soldering acid is used.
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Application of fluxes and solders
For soldering large parts, such as cooling radiators, soldering irons with high power (100-200 W) are used; soldering irons with a power of 60-100 W can handle small elements quite successfully. Of course, the solder area is not particularly strong, but this is not required.
At home, fluxes F-64, FTBf-A, and FIM are suitable for soldering aluminum. Of course, you can use aspirin, technical petroleum jelly, grease, solder fat, and stearin as a flux.
Using special active fluxes makes soldering easier; they cope well with the oxide film, provided that the heating temperature is 250-360°C.
The solder is distributed over the entire joint surface, resulting in a strong connection between the parts. Flux must be removed using solvents, alcohol or a special liquid. The convenience of using such fluxes is that they are also used for soldering nickel, copper and steel.
As a rule, alloys of 2 parts zinc and 8 parts tin, or 1 part copper and 99 parts tin, or 1 part bismuth and 30 parts tin are used for soldering aluminum. Conventional solders PIC. 40 and POS. 60 also copes with the task.
Small holes (no more than 7 mm in diameter) in aluminum cookware can be soldered without a soldering iron. The existing enamel around the hole should be beaten 5 mm by lightly tapping with a hammer. Now you need to use a file or sandpaper to polish the metal until it shines, using rosin crumbs or soldering acid, put a piece of tin in a pan on the hole and heat it over an alcohol lamp, which provides spot heating without destroying the remaining enamel. The metal, melting, will completely close the hole.
So, if you have the desire, you can solder aluminum at home.
Today, not only wires are made from aluminum, but also various elements that ensure reliable operation of electrical installations and other equipment. Various methods are used to solder this material.
Melting with tin is the most effective, since it is freely available and the connection is high-quality and durable. This procedure is carried out using fluxes and is possible not only in production, but also at home. If other filler materials are used, the aluminum will melt.
Advantages of soldering
Among the advantages of this type are the following:
- low cost;
- tin is suitable for soldering parts of various thicknesses;
- the material quickly melts under the influence of temperature, covering the working surface to the slightest crack. When hardened, it forms a high-quality connection;
- melting does not take much time, since the melting point is low;
- Tin is freely available and can easily be purchased.
Negative qualities
In addition to the advantages of this method, there are also disadvantages:
- the finished connection may collapse under the influence of lower temperatures;
- the connection is not adapted to high mechanical loads;
- at home it is not always possible to achieve the desired result.
Features of tin soldering
The only problem is the appearance of an oxide film at the joint. To get rid of it, solvents, metal brushes, etc. are used. Also, much attention should be paid to the soldering temperature. High temperatures will destroy the source material, and low temperatures will not be able to provide a reliable and high-quality connection. For large metal thicknesses, the process is carried out in several layers.
Soldering methods
Many experts recommend using a gas burner. It is attached to the cylinder using hoses. Gas flow can be regulated by a valve. It enters the nozzle and is ignited, forming a stable flame, the temperature of which is regulated by changing the pressure.
Gasoline torches are also used, but gasoline vapors are not capable of producing a high temperature for soldering. Therefore, this method is used for joining thin metal parts.
Soldering with a soldering iron occurs using additional materials, for example. The equipment is connected to electricity and its end is heated to the melting point of tin and rosin.
Necessary equipment
In addition to tin, you should have the following tools:
- solvent;
- metal brush;
- soldering iron or torch;
- cutting tool.
- Flux.
Selection of solder and tools
Soldering of aluminum can be done using various methods, which depend on the composition of the solder. It should contain small amounts of lead, as well as zinc, which serves to lower the melting point. The soldering tool is selected depending on the personal preferences of the master and the thickness of the part. For example, for thin products it is better to use a torch.
Additional Information! The melting point of the solder should be as low as possible so that the finished connection does not collapse in cold weather.
Step-by-step instruction
First of all, prepare the surface by cleaning it from rust and other debris using a wire brush. Next, the surface must be degreased, which a solvent will help to do.
If oil deposits are not removed, the quality of the connection decreases. It will also help get rid of the oxide film, which is not destroyed by high temperatures. If work is carried out with wires, then they need to be tinned so that the procedure goes faster and they do not collapse.
Before joining metal products with large thickness, their edges are sharpened. After the preparatory stage, we move on to soldering. It happens in the following sequence:
- the soldering iron or burner is turned on and the required mode is selected;
- the soldering area is treated with flux;
- direct soldering is carried out by melting tin over an aluminum product;
- After soldering, the part is left to cool for a while, and then the quality of the connection is checked.
Note! When soldering metal of large thickness, you should not fuse the seam in one place, but apply tin in layers.
There are 6 modes, each of which has special parameters. They depend on the brand of the source material. Knowing this indicator, the percentage of tin, lead and other metals, as well as the melting point, are determined.
Safety regulations
During work, pay attention to the switched on tools (soldering iron or torch). When working with gas, it is necessary to check the integrity of the hose and the condition of the cylinder.
Important! Some types of fluxes evaporate harmful substances when heated, so the work area should be well ventilated.
You can solder aluminum. Although wires made of this metal can be easier to connect in other ways: through screw terminal blocks, by welding. Often in junction boxes the aluminum wires were simply twisted tightly. This method was used when apartments usually did not have particularly high energy consumption.
But now, with the saturation of the market with powerful and varied household appliances, it is necessary to bring the entire household power supply network to a quality that would be oriented towards serious energy consumption, approaching industrial consumption. And in this case, it is better to solder aluminum at home than to twist it.
Properties of aluminum as a metal and conductor
Aluminum stands in the periodic table immediately behind sodium and magnesium - active metals, even flammable in air. Therefore, it is a light and very active metal. Its thermal and electrical conductivity is lower than that of copper. But since aluminum is lighter than copper, products made from it, where precisely these properties are important, with the same mass turn out to be geometrically large in size. And due to convection, heat removal from aluminum parts can be greater than from copper parts.
Aluminum's activity works against soldering, a standard electrical and mechanical joining operation for many metals. Because the activity is such that it immediately oxidizes in air. And it is covered with an impenetrable film of corundum - Al 2 O 3. Other aluminum compounds are also very strong, which makes the extraction of this most common metal in the earth’s crust energy-intensive: to produce 1 ton of aluminum you need to spend 17 megawatts/hours of electricity.
Only in our country this did not turn out to be an obstacle to large volumes of production and widespread use of this metal.
In addition to aluminum itself, alloys based on it are used - duralumin and silumin.
If pure aluminum is used mainly for electrical engineering, then various products are made from alloys: from silumin - cast things (meat grinders, dishes), thrust structures, from duralumin - frames, body parts, mounting profiles.
The alloys seem to work against the eternal enemy of aluminum solders - the oxide film - and they must be soldered well. However, the soldering of duralumin and silumin itself violates the valuable properties of these alloys at the joints, which makes the soldering fragile and quickly destroyed.
Therefore, aluminum needs to be soldered as such, and products made from its alloys can be tried to be soldered, but only where special requirements for the mechanical strength of the things being soldered are not expected.
Work order
The usual soldering steps and tools apply when soldering aluminum. It’s just that aluminum is such that it is stricter when it comes to the choice of components.
Soldering aluminum at home requires:
- A powerful soldering iron (60–100 W or more) is sufficient. This is due to the heat capacity and thermal conductivity of aluminum. This metal removes heat very strongly from the soldering area.
- The use of additional materials and tools for processing the metal surface: emery, needle file; copper sulfate for tinning; iron or copper thin filings.
- The use of special fluxes that envelop the surface of the metal, preventing immediate oxidation by atmospheric oxygen or dissolving the oxide in acid.
- The use of other substances that create a film on the surface (solid oil, machine oil, solder fat, technical petroleum jelly, aspirin, stearin).
- Solder based on tin and zinc (8:2); tin with copper (99:1); tin with bismuth; POS 40; POS 60; solder for soldering aluminum.
- Mandatory pre-tinning of the metal surface.
- Thorough subsequent rinsing of the soldering areas in warm water to remove residual acid and flux.
A great variety of fluxes for soldering aluminum are sold - liquid, paste, pencil, gel: F-34a, F-59A, FTBf-A, F61A, F-63, FTKA, F-64 and others.
The surfaces to be soldered must be cleaned, treated with a file or sandpaper. After this, heat and apply an even layer of flux.
Tinning the metal surface
It is necessary, in a hot state under a layer of flux, to damage the Al 2 O 3 layer, which, after mechanical stripping, has managed to form on the aluminum, and at the same time apply a layer of solder. Such damaging elements may be abrasive particles, or thin iron or copper filings, or crystals of copper sulfate added to the flux. They should, without waiting for the flux to dry or burn out, apply a layer of solder with a soldering iron and rub it into the surface with a tip. When carrying out work in a house or apartment, it is necessary to remember that the components of fluxes are caustic and toxic; when heated with a soldering iron, they boil and smoke. It is necessary to work in a ventilated area.
Soldering
Soldering copper and aluminum is no more difficult than soldering aluminum to copper. Both surfaces must be tinned; copper undergoes this without much resistance, you just need to clean it and rosin it before tinning. Copper and aluminum make excellent alloys, as well as soldering aluminum with tin; this does not present any other difficulties other than overcoming the oxide film.
The pre-tinned wires are twisted and soldered so that the solder seals the gaps between the wires.
Extended objects, such as pipes or tubes, tin flasks, are soldered to aluminum in exactly the same way. If a small part is soldered onto a wide surface with high heat dissipation (for example, a flask), then the soldered area can be additionally heated on a gas stove or burner.
It is possible to solder small holes according to the following rule: clean the surface, tin, cool a little, put a covering piece of tin or solder on the hole, carefully use a soldering iron or a jet of flame from a burner to achieve soldering of this place.
Final processing
So, when the answers to the questions “how to solder?”, “what to solder with?”, “what to solder?” left behind, the work is done, then before admiring the welded brainchild, you need to do the final finishing touches. At the same time, clean the soldered area from any irregularities, carefully solder off excess drops of solder, and after cooling, lightly check the soldering for strength. After soldering aluminum using materials containing chemical reagents, it is necessary to thoroughly rinse with water, wipe with a cloth lightly soaked in soda solution, and dry.
The difficulty of soldering aluminum not only at home, but also in industrial production conditions is primarily due to the special properties of this metal, which makes it fundamentally different from other types of non-ferrous metals actively used both in industry and in everyday life.
The metal aluminum has a whole set of paradoxical properties, that is, properties that are mutually exclusive, but nevertheless easily coexist in one metal.
On the one hand, it is a very fusible metal; the melting point of pure aluminum is 660 degrees. It is a chemically very active metal. Aluminum is capable of instantly entering into chemical reactions with almost all active substances. It is a very soft and not very durable metal.
On the other hand, the extremely high chemical activity of aluminum leads to the fact that it instantly enters into a chemical reaction with oxygen contained in the surrounding air, forming a film of aluminum oxide on its surface: Al2O3. Aluminum oxide has a second name - corundum. This is a very durable, completely chemically inert substance. Melting point: 2400 degrees. Used in industry as a fire-resistant material.
Thus, we can say that in everyday life, despite objects made of aluminum surrounding us on all sides, we do not know its true nature, since real aluminum is always hidden from us under the impenetrable curtain of its oxide. It is aluminum oxide that determines such properties of this metal as its extremely high resistance to inorganic acids and alkalis, resistance to corrosion in sea water and atmospheric air, high reflectivity and high environmental friendliness.
And this same aluminum oxide turns conventional soldering into a rather complex technological process, requiring the use of special fluxes, special solders and some specific methods for its successful implementation.
The essence of the soldering process of any metal, including aluminum, is the introduction of a special binding substance in a molten state into the space between the parts being soldered. This substance is called solder. When solidified, it reliably connects to two metal surfaces and forms a single connection.
Soldering difficulties
Therefore, the main difficulty lies in the problem of removing the practically irremovable oxide film from the metal surface.
The second difficulty is in the low melting point of aluminum. The fact is that the most durable connection is obtained by using so-called refractory solders. The melting point of which is 550−650 degrees. Considering the fact that aluminum melts at a temperature of 660 degrees, when soldering small aluminum products it is extremely difficult not to destroy the aluminum structure itself by melting it along with the solder.
Removing oxide film
The problem of removing surface films are solved in two fundamentally different ways:
- By using special active fluxes with preliminary mechanical cleaning of the metal surface.
- Using the process of electrolysis.
Active fluxes
If you really want to, you can make soldering flux with your own hands, in your kitchen or workshop. But for this it is necessary to deal with very dangerous chemically active substances such as acids or alkalis. In addition, in specialized stores there is a huge selection of different brands of fluxes, both ordinary and highly specialized, and their prices are low. Therefore, we will leave the production of acid for soldering with our own hands to special soldering fans, and we ourselves will try to understand the assortment that the industry offers us.
- F-34A. Special flux. Melts at a temperature of 420−620 degrees. Used with refractory solders. Composition: Potassium chloride 50% Lithium chloride 32% Sodium fluoride 10% Zinc chloride 8%
- F-61A. Flux for aluminum. Melting occurs at a temperature of 150−320 degrees. Used with conventional tin-lead solders. Composition: Zinc fluoroborate 10% Ammonium fluoroborate 8% Triethanolamine 82%
- F-64. Highly active flux for aluminum alloys. Melts at a temperature of 180−350 degrees. Ingredients: surfactants.
- NITI-18 (F-380). Special flux for aluminum alloys. Soldering temperature 390−620 degrees.
- A-214. Universal no-clean flux of medium activity.
Before applying flux, the metal surface must first be cleaned of contaminants and degreased. This is done using gasoline or acetone. After this, mechanical processing is carried out using various abrasive devices: emery cloth, metal brush, grinding wheels and other similar devices. The purpose of these actions- weaken the oxide film, because it is basically impossible to remove it, since a new one is instantly formed instead of the old one. But the new film is much thinner and weaker than the old one, so this technique makes it easier for the flux to penetrate the surface oxide barrier.
Electrochemical method (electrolysis process)
The essence of this method is that the surface of aluminum, along with its invincible oxide, is simply replaced by a copper surface. And soldering copper is much easier, faster and more reliable. This is done using a simple galvanic installation..
Soldering alloys
Conventional solders used for soldering non-ferrous metals contain tin and lead as the main components, as well as cadmium, bismuth and zinc as additional components. For aluminum, such a composition is extremely undesirable, due to the fact that it practically does not dissolve in these metals (with the exception of zinc), so work with solder of such a composition will be extremely weak and unreliable. In addition, all lead-tin based solders have very low corrosion resistance. Therefore, soldering aluminum with tin is undesirable.
Special solders are used for aluminum, which include aluminum itself, as well as silicon, copper, silver and zinc.
The more in solder for aluminum contains zinc, the more it is highly durable and corrosion resistant. The content of copper, silicon and aluminum increases the melting point of the solder, making it refractory. Which solder to choose depends on the tasks facing the parts being soldered.
As a rule, refractory solders have a melting point comparable to the melting point of aluminum itself, so they are used mainly for soldering large, massive aluminum parts. In this case, it is possible to ensure good heat removal due to the large mass of soldered surfaces and thereby prevent the destruction of the structure as a result of its melting along with the solder.
Brass solder is not used for aluminum.
The technology of the aluminum soldering process is no different from soldering any other metal and consists of a number of sequential actions:
Warming up the surfaces to be soldered
For soldering small aluminum parts For example, for wires, as a rule, an electric soldering iron with a power of 50 to 100 W is used, depending on the cross-section of the wire. For more massive parts, for example, pots, car radiators, it is advisable to use more powerful heat sources. As a rule, this is a blowtorch or gas torch. When soldering aluminum with a gas torch and heating the surfaces to be soldered, you must adhere to the following rules:
Using rosin
To solder and solder small cross-section aluminum wires, you can successfully use lead-tin solders using rosin as a flux. In this case, abrasive treatment of the wire surface is carried out under a layer of molten rosin, and a hot soldering iron tip is used as an abrasive tool, as well as a small amount of metal filings.
It should be noted that this method is only suitable for small-sized thin-walled parts or for wires of small cross-section. In all other cases, it is necessary to use special aluminum fluxes and refractory solders intended for soldering aluminum.
Disadvantages of soldering aluminum
You must always remember that soldering is not welding. It does not affect the internal structure of the metal in any way, and therefore the soldering site is always several orders of magnitude weaker in strength characteristics than the metal being soldered itself. The soldering area must not be subjected to high mechanical and temperature loads. Otherwise, the soldered parts will collapse very quickly. The only option when soldering is more appropriate than welding is soldering aluminum wires in electrical appliances or soldering a leaky car radiator when it is not possible to replace it with a new one.
It is advisable to exclude from home practice soldering and tinning of leaky aluminum pots, mugs and other pans. Aluminum solders and fluxes contain highly toxic substances. In this case, thoroughly washing the soldering area in running water will look like playing Russian roulette.
Despite the fact that in modern construction, during electrical work, aluminum cables are increasingly being replaced by copper cables, aluminum remains an indispensable material in the manufacture of large-section wires and cables.
The reasons for this lie on the surface - the electrical resistivity of aluminum is approximately one and a half times greater than that of copper, and the volumetric weight is three times less.
With a large conductor cross-section, when weight is more important than strength, the choice in favor of aluminum is obvious. The cross-sectional area of an aluminum conductor will be one and a half times greater than that of a copper conductor, and at the same time, aluminum will still be two times lighter than copper. Soldering, among other methods, is used to connect wires.
The problem with using aluminum conductors is their rapid oxidation. The oxide film significantly impedes the passage of electric current during connections. To do this, twisted aluminum wires are soldered.
You can solder aluminum wires in a junction box using a soldering iron or a gas torch. It is more difficult to use a soldering iron due to the inability to accurately heat to the required temperature. And for aluminum, overheating is just as unacceptable as underheating.
Metal has high thermal conductivity, and the insulation over a large area from the soldering point can simply melt.
It is easier to regulate the heating temperature with a gas burner, but it takes a long time to prepare the surface. However, it is the torch that will need to be used if it is necessary to solder any massive parts to each other. In any case, when soldering aluminum wires, they need to be prepared.
Preliminary processing
The difficulty with soldering is that aluminum itself is a very low-melting material (660 ℃) and if heated carelessly it can melt.
Another factor that makes soldering aluminum wires difficult is rapid oxidation in air.
The oxide film on the surface of the material reliably protects aluminum from the effects of all kinds of external factors, but it also prevents the adhesion of solder to the material and must be removed.
It is almost impossible to mechanically remove the oxide film under normal conditions. The material is instantly oxidized and covered with a new film. You can mechanically remove the oxide film under the oil layer.
But before this, the oil must be heated to 200 ℃ in order to remove any active oxygen that may be present there. This method is very inconvenient at home and labor-intensive.
Therefore, the ends of aluminum conductors must be tinned before soldering. Using rosin or most other fluxes will not work due to the high chemical resistance of the oxide film. It does not dissolve even with organic acids.
To tin the wires, you must use both a special flux and a mechanical method.
Of course, this must be done before the wires are twisted, otherwise it will not be possible to mechanically clean the entire surface of the wire. Only the tinned ends can be twisted together and soldered.
Working with a soldering iron
In order to solder aluminum with a soldering iron, there are several methods, the essence of which is to clean immediately under the flux layer in direct contact with the molten solder.
The first method is that aluminum conductors, before soldering, are cleaned with a hot tinned soldering iron using a mixture of rosin and steel filings.
Sawdust has an abrasive effect, rosin removes all impurities and immediately the cleaned areas are covered with solder, which should be on the soldering iron tip.
The second method involves stripping the aluminum wire on medium-grit sandpaper directly under the influence of a hot soldering iron with solder and flux.
Gas burner
Processing with a gas burner is carried out when the parts are in the position relative to each other in which they will be used. The processing smoothly transitions into the soldering process itself.
This happens as follows:
- the burner heats the surfaces of aluminum parts;
- upon reaching the temperature at which the metal is reduced from the oxide, the film is mechanically peeled off;
- under the influence of a flame, the parts are coated with flux, and solder is introduced into the soldering area.
If the parts are thick, then their edges must be cut at an angle of 45°. Typically, heating occurs to the melting point of tin, when the solder spreads and fills the twist groove.
Differences in technology when using flux
Thanks to the achievements of modern science and technology, compositions have been obtained that actively dissolve the oxide film and protect the material from further oxidation.
Examples of such drugs are formulations labeled F-59A and F-61A. The letter A means that these compounds are intended for soldering aluminum.
When using these fluxes, soldering aluminum wires is greatly facilitated. It is enough to simply treat the finished twist with flux, without even heating it, and then, after heating it with a soldering iron or torch, apply solder.
It will spread over the entire surface of the wires and adhere well, providing a strong and electrically conductive solder joint.
Features of soldering stranded wires
Stranded wires must be soldered only using a special flux, since their mechanical processing is almost impossible. Soldering technology differs in that each wire must first be well treated with flux.
To do this, the bundle will have to be untwisted and fluffed. After processing, each thin wire conductor is covered with solder and the bundle is twisted. After this, twist the two ends and solder it.
Can it be connected to copper?
Situations often arise when it is necessary to connect an aluminum wire to a copper wire. This is perhaps the only case where soldering cannot be used.
It's all about the aluminum itself. It cannot be soldered to other metals at all due to its physical and chemical properties. When connecting directly to copper, galvanic corrosion will occur between the two active metals and will quickly destroy the connection.
And if they are soldered using solder that is neutral to both materials, then the different coefficients of thermal expansion of the metals will quickly destroy the soldered contact. After all, when current passes through a conductor, it will certainly heat up, and after switching off, it will cool down.
Safety precautions
When soldering aluminum wires, it comes down to observing general precautions when working with electric heating devices, with open flames and with aggressive liquids, such as fluxes.
It is unacceptable to use faulty soldering irons with damaged insulation and with more power than necessary.
Do not use burners near flammable objects. When working indoors, forced ventilation must be properly organized.
Difficulties in soldering aluminum wires
The main difficulty when soldering aluminum wires, as indicated above, is the presence of an oxide film on the surface of the metal. Fighting it greatly slows down the soldering process.
And if you consider that aluminum wires are now used mainly for laying external power wiring, it becomes obvious that a regular soldering iron and sandpaper will not be enough in this case. Welding is increasingly being used to connect such wires.
