Cold soldering aluminum. How to solder aluminum with soft solder. Soldering with rosin

There is a widespread belief that it is impossible to solder or tin aluminum (as well as alloys based on it) without special equipment for this.

Two factors are given as an argument:

upon contact with air, a chemically resistant and refractory oxide film (AL 2 O 3) is formed on the surface of the aluminum part, as a result of which an obstacle is created for the tinning process;
the soldering process is significantly complicated by the fact that aluminum melts at a temperature of 660°C (for alloys, this range is from 500 to 640°C). In addition, the metal loses its strength when, during the heating process, its temperature rises to 300 ° C (for alloys up to 250 ° C), which can cause a violation of the stability of aluminum structures.

Given the above factors, it is really impossible to solder aluminum with conventional means. The use of strong fluxes, combined with the use of special solders, will help to solve the problem. Let's consider these materials in detail.

Solder

Commonly used solder bases are tin (Sn), lead (Pb), cadmium (Cd), bismuth (Bi), and zinc (Zn). The problem is that aluminum practically does not dissolve in these metals (with the exception of zinc), which makes the connection unreliable.

By using a highly active flux and properly treating the joints, it is possible to use tin-lead solder, but it is better to refuse such a decision. Moreover, the solder joint based on the Sn-Pb system has low corrosion resistance. Applying a paint and varnish coating to the place of soldering allows you to get rid of this drawback.

For soldering aluminum parts, it is desirable to use solder based on silicon, copper, aluminum, silver or zinc. For example 34A, which consists of aluminum (66%), copper (28%) and silicon (6%), or the more common DSP-40 (Sn - 60%, Zn - 40%).

Note that the greater the percentage of zinc in the composition of the solder, the stronger the connection will be and the higher its resistance to corrosion.

High-temperature solder is considered to be solder consisting of metals such as copper, silicon and aluminum. For example, as the domestic solder 34A mentioned above, or its foreign analogue "Aluminium-13", which contains 87% aluminum and 13% silicon, which allows soldering at temperatures from 590 to 600 ° C.

Flux

When choosing a flux, it must be taken into account that not all of them can be active towards aluminum. We can recommend using for such purposes the products of a domestic manufacturer - F-59A, F-61A, F-64, they consist of ammonium fluoroborates with the addition of triethanolamine. As a rule, there is a mark on the vial - “for aluminum” or “for soldering aluminum”.

For high-temperature soldering, you should purchase flux, manufactured under the brand name 34A. It consists of potassium chloride (50%), lithium chloride (32%), sodium fluoride (10%) and zinc chloride (8%). Such a composition is most optimal if high-temperature soldering is performed.

Surface preparation

Before you start tinning, you must perform the following steps:

degrease the surface with acetone, gasoline or any other solvent;
remove the oxide film from the place where the soldering will be performed. For cleaning, sandpaper, an abrasive wheel or a brush with steel wire bristles are used. Alternatively, etching can be used, but this procedure is not so common due to its specificity.

It should be borne in mind that it will not be possible to completely remove the oxide film, since a new formation instantly appears in the cleaned place. Therefore, stripping is carried out not to completely remove the film, but to reduce its thickness in order to simplify the task of the flux.

Solder point heating

For soldering small parts, you can use a soldering iron with a power of at least 100W. Massive objects will require a more powerful heating tool.

The best option for heating is to use a gas burner or a blowtorch.

When using the burner as a heating tool, the following nuances should be taken into account:

do not overheat the base metal, as it may melt. Therefore, the temperature must be regularly monitored during the process. This can be done by touching the heated element with solder. Melting the solder will let you know that the required temperature has been reached;
oxygen should not be used to enrich the gas mixture, since it contributes to the strong oxidation of the metal surface.

Soldering instructions

The process of soldering aluminum parts does not have its own distinctive features, it is carried out in the same way as with steel or copper.

The algorithm of actions is as follows:

the place of soldering is degreased and cleaned;
parts are fixed in the desired position;
the junction heats up;
touch the solder rod (containing active flux) to the joint. If a flux-free solder is used, then a flux is applied to destroy the oxide film, after which a hard piece of solder is rubbed at the place of soldering.

A steel wire bristle brush is also used to break down the aluminum oxide film. With this simple tool, molten solder is rubbed onto an aluminum surface.

Soldering aluminum - complete video instruction
https://www.youtube.com/watch?v=ESFInizLE9U

What to do if the necessary materials are not available?

When it is not possible to prepare all the materials needed for soldering, an alternative method can be used, which uses tin or tin-lead solder. As for the flux, it is replaced by rosin. In order not to form a new film of aluminum oxide in place of the old one, stripping is carried out under a layer of molten rosin.

The soldering iron, in addition to its direct purpose, will be used as a tool that destroys the oxide film. To do this, a special scraper is put on his sting. You can increase the effectiveness of the process by adding metal filings to the rosin.

The process is as follows:

with a heated tin-plated soldering iron, rosin is melted at the place of soldering;
when the rosin completely covers the surface, they begin to rub it with a soldering iron tip. As a result, metal filings and a sting destroy the aluminum oxide film. Since the layer of molten rosin does not allow air to penetrate to the aluminum surface, an oxide film does not form on it. As the film breaks down, tinning of the part will occur;
when the tinning process is completed, the parts are joined and heated until the melting temperature of the solder is reached.

It must be warned that the process of soldering aluminum without special materials is a rather troublesome process with no guarantee of successful completion. Therefore, it is better not to waste your time and energy on such work, especially since the quality and reliability of such a connection will be doubtful.

It is much easier to buy active flux and high-temperature solder, with which soldering aluminum even at home will not cause difficulties.

Usually aluminum soldering is carried out within the framework of industrial workshops. At home, this procedure is quite problematic to carry out, because after stripping, an oxide film appears on the metal surface almost immediately, which complicates the process. However, do not be upset, after all, there are several ways to solder aluminum with your own hands, when the oxide film that covers the part is destroyed immediately at the time of soldering.

Characteristics of aluminum as a metal

Aluminum is characterized by high rates of electrical and thermal conductivity, corrosion and frost resistance, as well as ductility. The melting point of this metal is about 660 degrees Celsius.

Depending on the level of purification, primary aluminum can be of high or technical purity. Technical aluminum is obtained by electrolysis of cryolite-alumina melts. Another type of aluminum, high purity, is formed after additional purification of technical aluminum. The main difference between highly purified and technical aluminum is related to the difference in the corrosion resistance of the metal to certain media. Naturally, the higher the degree of purification of aluminum, the more expensive aluminum.

An important property of aluminum is its high electrical conductivity; it is inferior in this indicator only to silver, gold and copper. The combination of high electrical conductivity and low density makes aluminum a serious competitor to copper in the field of cable and wire production. Long-term annealing of aluminum at 350 degrees improves the conductivity of the metal, and hardening worsens it. The electrical conductivity of aluminum reaches 60-65% of the conductivity of copper and increases with a decrease in the content of impurities.

In terms of thermal conductivity, aluminum is second only to copper and silver, exceeding the thermal conductivity of mild steel by three times, which can be found in the video on aluminum soldering. The reflectivity of a metal depends on its purity. The reflectivity for foil with 99.5% aluminum is 84%.

Aluminum itself is a reactive metal. However, in air, the metal is covered with a thin film of aluminum oxide - about a micron. Possessing chemical inertness and high strength, it protects the material from oxidation and determines the high level of its anti-corrosion properties in many environments. The oxide film in high-purity aluminum is continuous and non-porous, and has strong adhesion to the metal itself.

Therefore, high purity aluminum is very resistant to inorganic acids, alkalis, sea water and air. The adhesion of aluminum to the oxide film at the location of impurities deteriorates markedly, and these places are vulnerable to corrosion. For example, in relation to non-concentrated hydrochloric acid, the resistance of technical and refined aluminum differs by 10 times.

Application of aluminum and alloys

Aluminum is widely used as a structural material due to its main advantages - lightness, malleability of stamping, corrosion resistance, high thermal conductivity, non-toxicity of its compounds. In particular, these characteristics have made aluminum popular in the manufacture of aluminum foil, cookware and packaging in the food industry.

But metal, due to its low strength, is used exclusively for unloaded structural elements in cases where electrical or thermal conductivity, ductility and corrosion resistance are brought to the fore. Such a disadvantage as low strength is compensated by alloying aluminum with a small amount of magnesium and copper. The alloy is called duralumin.

The electrical conductivity of aluminum can be compared with copper, but aluminum is cheaper. Therefore, this material is widely used in electrical engineering for the production of wires, their shielding, and in the manufacture of conductors in chips in microelectronics. The introduction of aluminum alloys in construction reduces metal consumption, increases the reliability and durability of structures when used in extreme conditions.

At the present stage of evolution of aviation, aluminum alloys are the main structural materials. The latest invention is aluminum foam, which is also called "metal foam", it is predicted a great future. However, aluminum as an electrical material has one unpleasant property - the difficulty of soldering aluminum due to a strong oxide film.

Features of aluminum soldering

The problems that relate to soldering aluminum can be explained by the fact that the surface of this material is covered with a thin, very strong and elastic oxide film. From everyday acquaintance with objects made of aluminum or its alloy, many people have the misconception that, like noble metals, aluminum is not prone to oxidation in the atmosphere. The oxide film, like most other oxides, is inert and poorly wetted by molten metal, so this film must first be removed during soldering.

Removing the oxide film

The oxide cannot be removed by mechanical methods, because when the aluminum surface comes into contact with water or air, it is again instantly covered with an oxide film. Fluxes, as a rule, do not dissolve the oxide. That is why the soldering of aluminum and products made from it is considered a rather difficult task, and the technology for soldering aluminum differs in many respects from the technology for soldering other metals.

For mechanical cleaning of the surface from oxide, it is recommended to clean the metal under the oil film, however, in this case, the oil must be completely dehydrated, for which it is recommended to warm it up for some time at a temperature of about 150-200 degrees. It is best to use mineral oils or vacuum VM-4, VM-1.

A method is also proposed for cleaning the surface using coarse iron filings, which are rubbed over the metal surface under a layer of rosin or oil with a soldering iron tip along with solder. In this case, the sawdust acts as an abrasive, while the tinning process takes place. A more reliable soldering of aluminum can be obtained by tinning the metal over a copper sublayer, which is electrolytically deposited on the surface of the material.

For the same purpose, you can use a zinc sublayer, which is applied in the same way as in the aluminum chromium plating recipe. The oxide film is more reliably removed using special active fluxes. It is good to combine the procedure of mechanical surface treatment with the use of active fluxes.

Soldering with rosin

To solder two aluminum wires, they must first be tinned. To do this, cover the end of the wire with rosin, place it on a sandpaper that has a medium grain, and press it with a hot tinned soldering iron to the sandpaper. Also for soldering, you can use a solution of rosin known to us in diethyl ether. At the same time, the soldering iron is not taken away from the wire and rosin is added to the tinned end.

The wire is tinned perfectly, but all manipulations must be repeated several times. After that, soldering aluminum at home goes on as usual. You can also get a good result if you take instead of rosin mineral oil for a sewing machine and precision mechanisms or alkaline oil, which is intended for cleaning after firing a weapon.

Solder aluminum with a well-heated soldering iron. To connect thin aluminum, it is necessary that the soldering iron has a power of 50 W, for metal with a thickness of about 1 millimeter or more, a power of about 90 W is desirable. When soldering a material that has a thickness of more than 2 millimeters, the place to be soldered must first be heated with a soldering iron.

Electrochemical technique

The second way to solder aluminum is that before direct soldering, the surface (plate or wire) must first be copper-plated using the simplest plating installation. However, you can do it easier. Clean the soldering area with sandpaper and gently apply a couple of drops of saturated copper sulphate to it.

Next, connect the negative pole of the current source (rectifier, battery, flashlight battery) to the aluminum part, and connect a piece of copper wire without insulation 1-1.2 mm thick, which is located in a special device, to the positive pole.

The copper wire must be in the bristles of the toothbrush in such a way that it does not touch the surface during the friction of the bristles - the procedure for coppering the part. After a certain time, a layer of red copper will be deposited on the surface of the aluminum part as a result of electrolysis, which is tinned after washing and drying in the traditional way using a soldering iron.

Alternatively, you can use hydrochloric battery acid instead of a vitriol solution when soldering aluminum with your own hands: you need to drop a little substance into the place of soldering and then drive along the contact pad with a copper drive. Copper precipitation will occur faster than in the first option, but the acid must be handled with care.

So that the acid does not corrode the extra area, it should be filled with paraffin or sealed with adhesive tape, exposing the desired area. The place of soldering must be washed thoroughly with water. Thus, it is possible to carry out reliable soldering of aluminum and copper, while the pads will have a neat shape.

Soldering aluminum with solders

When soldering aluminum with solder, the main task lies in the initial coating of the metal surface with a layer of solder and soldering parts that are tinned with solder. Tinned aluminum parts can be soldered not only to each other, but also to parts made of other alloys and metals.

You can braze aluminum with zinc, tin or cadmium-based low-melting solders and aluminum-based refractory solders. Low-melting solders are considered convenient because they allow the process of soldering aluminum with tin at low temperatures (150-400 degrees) and thereby avoid a significant change in the original properties of aluminum.

Aluminum compounds that are brazed with low-melting solders, especially cadmium and tin alloys, form an unstable pair from a corrosive position and are poorly resistant to corrosion damage. The most reliable are more refractory aluminum-based solders that contain copper, zinc and silicon.

The simplest of them is aluminum-silicon alloy (11.7%). An even more reliable result is given by a low-melting aluminum alloy with 28% Cu and 6% Si. Soldering is done with an ordinary soldering iron, its tip is heated to a temperature of 350 degrees Celsius, using a flux, which is a mixture of lithium iodide and oleic acid.

Soldering of aluminum alloys

Using 34A solder and 34A flux, you can solder not only aluminum itself, but also certain aluminum alloys. Soldering is easiest for AMts and Avial alloys, more difficult for duralumin, B95, AK4 and cast alloys that have a lower melting point. It is possible to solder alloy B95 and duralumin with 34A solder only in the manufacture of small products and with great care to avoid overburning or the formation of metal melt during the soldering process.

Due to the high heating during soldering, the B95 alloy and duralumin pass into the annealed state, while losses of at least 30% of the strength of the material in the soldering area are observed, and its strength in the event of material burnout drops by more than half.

When heating, it is also necessary to take into account the risk of metal warping, so we will not recommend soldering loaded and large-sized parts made of B95 alloy and duralumin with a torch. It is also safer and more expedient to solder small duralumin products in an oven than with a torch, where you can adjust the soldering temperature more precisely and thereby avoid warping and overburning of parts.

To remove persistent Al2O3 oxide, it is customary to use especially active fluxes. Fluxes based on aluminum, which are known under the indices NITI-18 and 34A, have received the widest application in aluminum soldering. When using flux 34A, it is worth remembering that it is capable of causing severe metal corrosion, so flux residues after soldering must be removed.

For this purpose, a soldered product must be subjected to special processing:

Rinse with brushes in hot water (temperature 70-80 degrees) for 15-20 minutes;
Rinse in cold running water for another 20-30 minutes;
Treat in a solution of chromic anhydride;
Rinse in cold water;
Dry at a temperature of about 80-120 degrees Celsius for 20 minutes - half an hour.

Thus, in order to solder this metal, you need to stock up on special equipment for soldering aluminum and choose one of the soldering methods: soldering with mechanical destruction of the oxide or with chemical destruction of the film.

Soldering aluminum at home can be considered a difficult task. But with the right approach and compliance with the appropriate technology, it is quite possible to perform it even for an inexperienced master.

Problems often arise when using the wrong flux, for example when brazing steel or copper. It is very important to use a special agent for soldering aluminum, as well as a suitable solder. In the case of their use, soldering aluminum will not cause any particular difficulties.

Features of aluminum soldering

Soldering aluminum at home can be accompanied by some difficulties that are associated with the special characteristics of this metal. In particular, with the fact that the surface of aluminum parts is covered with an oxide film. It interferes with the process of making connections due to the high melting point, which exceeds the properties of pure aluminum. Also, the oxide film is resistant to aggressive environments and active chemicals. Because of this, the film prevents the connection of aluminum parts and solder.

To avoid such difficulties, it is worth cleaning the surface of the products from the film, which can be done using abrasive materials or the use of flux. The flux consists of potent substances that can destroy the oxide.

The melting point of aluminum, unlike oxide, is much lower, about 660 degrees, which often causes complications. When overheated, aluminum can significantly lose strength, deform, or become completely unusable.

Solders containing such components should be avoided. They do not bond well with aluminum, which causes a poor-quality connection.

Zinc interacts best with aluminum, which has a good solubility property.

Soldering methods at home

There are several soldering methods, the most popular being soldering and aluminum brazing with a gas torch. There are three ways to solder parts:

Rosin soldering is used to connect small aluminum parts, wires and cables. To do this, clean the work area and cover with rosin. Then press with a heated soldering iron several times. For these purposes, you need to use a rosin solution in diethyl ether.

Soldering is performed without leaving the work area, followed by the addition of rosin. It is recommended to use a 50W soldering iron. If the thickness of the parts and wire exceeds 1 mm, the power should be increased to 100 W, and it is better to warm up thicker objects in advance.

This method is most widely used in electrical work and soldering automotive parts. Parts must be tinned before work is done. This allows you to connect parts with other alloys and metals. In this case, aluminum is soldered with tin or solder containing zinc and cadmium. This allows you to make connections at a temperature of 400 degrees, which does not affect the physical properties of aluminum.

Solder is essential when using almost all soldering methods, whether using a soldering iron or a torch.
The electrochemical method involves the creation of a galvanic coating, which is performed using a special installation or manually. To do this, apply a solution of copper sulfate to the cleaned surface. After this procedure, the parts are affected by a negative electric pole.

Materials and tools

To perform aluminum brazing, you should have a variety of materials and tools, which include heating tools, solders and fluxes.

Most often, an electric soldering iron is used as a heating tool. It can be considered a versatile tool that is easy to use at home. But it can only be used to repair small items, usually small-diameter tubes, wires and cables, and small electrical appliances. It can be used at home in a ventilated area, as it does not require special conditions and a lot of space.

Large items should be soldered using a gas torch powered by argon, propane or butane. At home, you can also use a blowtorch.
When using burners, it is necessary to strictly control the supply of the flame, which must be characterized by maintaining the balance of gas and oxygen. When working, the flame should be bright blue. Any color changes may indicate an excess of oxygen.
Solders for aluminum brazing
Soldering aluminum with solder is a very difficult task. Therefore, the choice of solder is important for creating a quality seam and a strong connection. When using a conventional soldering iron, you need to select solder from a metal that has a low melting point. The most common alloys are:
zinc-tin;
bismuth-tin;
copper-tin.

These types are very often called amateur radio. They have a low melting point, which is very important for keeping aluminum in its original state without changing the structure and physical properties. The cost of such solders is low, so their purchase becomes affordable for home craftsmen.
But their use has a number of disadvantages and a limited scope. So, the connection of objects with the help of such solder does not differ in high strength and reliability. Therefore, they are used almost exclusively in the repair of electrical equipment, including the connection of wires and cables.
When repairing large-sized aluminum objects with the help of such solders, the connection will quickly lose strength and collapse. In such cases, it is better to use refractory solder, which includes zinc and tin.
But to create strong joints, refractory solders containing aluminum, copper and silicon should be used. Due to the presence of aluminum in the composition, the solder dissolves well in the structure of the repaired item.

It is impossible to use such solder when working with a soldering iron, since their melting point is about 600 degrees. Therefore, to work with them, you need to have a gas burner.
It should be noted that when soldering with a gas burner, the metal of the workpiece does not melt, only the solder will melt.
When brazing aluminum, you need to use special fluxes, since not every flux is active with respect to aluminum. Substances based on ammonium fluoroborator and triethanolamine are considered to be the most suitable. Most special fluxes are marked with a special marking that indicates their use in aluminum brazing.
If it is necessary to work at high temperatures, attention should be paid to mixtures containing potassium chloride, which is half; potassium chloride; sodium fluorite and zinc chloride. This composition allows you to create the most optimal conditions for high-temperature work.
Step-by-step instruction
Soldering technology depends on the way the work is done. But the preparatory stage is almost identical in all cases. You should start work with the following operations:
degreasing the workpiece surface with a solvent, for example, gasoline or acetone;
cleaning of the oxide film, which can be done with a wire brush, sandpaper or other abrasive material.

Then you should warm up the place of soldering work. Depending on the size of the item, you can do this with a soldering iron or a torch. In this case, several recommendations should be observed:
It is not recommended to overheat the surface - this can lead to melting of aluminum. Heating control can be carried out using solder, if it starts to melt when touching the workpiece, this means that the heating temperature is optimal and subsequent heating should be stopped.
There is no need to use additional oxygen saturation, which can lead to a chemical reaction with aluminum and the creation of an oxide film.

Soldering work should be carried out depending on the type of heating object. When using a gas burner, apply solder with flux to the work surface and then heat it up.
It is very important to completely melt the solder, but not overheat the workpiece. With a soldering iron, this is easier to do, but it is difficult to perform a large amount of work in this case.

By controlling the solder movement speed and the exposure temperature, it is possible to create a seam with the desired thickness and structure. To improve the quality of work, preliminary tinning of the processing site and treatment with an anti-corrosion agent are recommended.

Soldering copper, brass and steel wires and parts is not difficult for craftsmen, but if you have to deal with aluminum surfaces, then the solder does not even stick to the product, and soldering turns into torment. The difficulties are caused by the fact that a thin but very strong film of Al2O3 oxide is formed on the surface of this metal. You can remove this film mechanically - for example, clean the product with a needle file, but upon contact with air or water, the metal will immediately be covered with a film again.

Despite the difficulties encountered, it is possible to solder aluminum products. There are several ways to solder aluminum.

Soldering aluminum alloys

Excellent results can be obtained using the following alloys:

two parts zinc and eight parts tin
one part copper and 99 parts tin
one part bismuth and 30 parts tin

Before soldering, both the alloy and the part itself must be well heated. It should also be remembered that soldering acid must be used with this method of soldering.

Soldering aluminum with special fluxes

Standard fluxes do not dissolve the oxide film on the surface of aluminum, so special active fluxes must be used.

Flux for aluminum soldering is used to work with tin-lead solders at an operating temperature of 250-360 degrees. Such a flux, both during soldering and tinning, removes the oxide film well, cleans the metal surface and, as a result, the solder spreads better over the surface. All this leads to the creation of a more dense and durable connection of the alloyed parts. Excess of this flux is easily removed with solvents, alcohol or special liquids.

Other ways to solder aluminum

There are non-standard ways to solve this problem, for example:

The place of soldering on the aluminum product is carefully cleaned and a couple of drops of concentrated copper sulphate are applied. A small piece of copper wire is stripped, folded into a circle with a diameter equal to the place of soldering, and the free end of the wire is connected to the “plus” of the 4.5 volt battery output. A piece of wire with a rolled circle is dipped into a small amount of blue vitriol. The minus of the battery must be connected to the part, on which a certain layer of copper will settle after a while. After drying, the necessary parts or wires can be welded to this place in the usual way.
In this case, an abrasive powder is used, mixed with a small amount of transformer oil to form a liquid paste. This paste is applied to cleaned products for soldering. Next, the soldering iron is well served and rubbed these places until a layer of tin is released on the surface. Then the parts are washed and then soldered in the usual way.
This method requires a transformer. Its minus is connected to the product, and a large copper wire, consisting of smaller cores, is connected to the plus. If this wire is connected for a short time to the place to be soldered, then copper and aluminum will be micro-soldered, which will later allow the wires to be soldered in the usual way. Soldering acid can be used to simplify the process.

Soldering aluminum utensils (without soldering iron)

Aluminum utensils are in some demand among housewives, but sometimes they break down, and in order not to buy a new one (which costs a lot), you can repair such products by soldering without a soldering iron. The following method is suitable for sealing small holes (up to 7 mm in diameter).

It is necessary to clean the place of soldering to a metallic sheen with sandpaper or a file. If the dishes are enameled, then around the hole to be sealed, the enamel must be removed within a radius of 5 millimeters. To do this, the enamel is beaten off with light taps of the hammer from the dishes. Then be sure to clean the metal.
The place of soldering is lubricated with soldering acid or covered with crushed rosin. From the inside, a piece of tin is superimposed on the hole, and then the container is heated over the fire of a kitchen stove. If the dishes are enameled, then it is better to heat them over an alcohol lamp - this gives more point heating, and therefore the rest of the enamel will not crack from high temperature.
When heated, the tin melts and tightly closes the hole in the dish. In this case, the help of a soldering iron is not needed.

Aluminum is highly durable and a good conductor of heat and electricity. It has a low specific gravity, is convenient for processing, and is environmentally friendly. However, all these positive qualities create almost insurmountable obstacles in solving the problem of how to solder aluminum at home with a soldering iron. This cannot be done using traditional methods, so you have to use special welding methods and optimally selected materials.

Technical difficulties in soldering aluminum products and parts

Soldering aluminum structures and other elements is always quite difficult, especially if it is done at home by novice craftsmen who have not fully studied the process. Basically, such soldering is carried out by industrial methods on special equipment. However, it is quite possible to create the most suitable conditions for welding parts made of aluminum.

To achieve this goal, it is necessary to solve several technical problems:

The biggest problem with soldering is oxidation in the form of a film that appears on the surface as a result of the contact of aluminum and air. Even if the metal is prepared, plaque forms on it almost immediately after that. Such a film coating interferes with the joining process and adds many problems during the tinning and soldering process. In this situation, the usual types are completely unsuitable, since they do not guarantee a quality connection. The film is removed either physically and mechanically or with the help of strong chemicals.
The high temperatures at which aluminum begins to melt should also be taken into account. It reaches a maximum of 600 0 C. There is a temperature difference between the soldered metal and its film, causing difficulties in the soldering process.
Due to the temperature regime, aluminum in the process of heating begins to noticeably lose its strength. This moment comes already when the material being welded is heated to 250-300 degrees. Some aluminum alloys contain components whose melting point is different from that of the base metal.
Weak interaction of aluminum with traditional types of solders, consisting mainly of tin, cadmium and other elements. This leads to insufficient strength characteristics and reliability of the created seams. The problem of how to solder is solved by means of special solders containing zinc, which, in turn, is in excellent contact with aluminum and penetrates into it. Cohesion occurs, reaching the molecular level, providing the necessary strength of the connection.

Preparation for soldering aluminum parts

Great importance is attached to the preparation of aluminum for the upcoming soldering.

To do this, there are several ways to ensure the reliability of the connection:

The connection area is preliminarily degreased and treated with rosin. After the substance is applied to the surface, an emery cloth is also laid here. Next, you need to turn on a powerful soldering iron and firmly press the sandpaper to the surface with it.
After that, the surface is rubbed and polished, and the junction itself is simultaneously subjected to tinning. An aluminum part is installed on the prepared surface, which can be soldered in the usual way. If necessary, rosin can be replaced with oil used in sewing machines.
In the second variant, metal shavings are added to the rosin, after which the resulting mixture is applied to the surface of the place of the future connection. The soldering iron tip must be well heated and tinned, and then rubbed with it over the entire working surface of the parts to be soldered until the chips melt. At the same time, solder is added here. In this case, the oxide is removed mechanically, and the solder immediately gets to the surface and protects it from the reappearance of the oxide film.
The third way is to pre-clean the surface. For this purpose, copper is used, through which the oxide film is removed. This method is one of the most difficult, since copper plating of the surface must be carried out in a special bath.

Selection of solder and flux for aluminum

Solders based on tin and lead can be used for welding aluminum wires, elements and parts, provided they are thoroughly cleaned. Such soldering should be carried out using special flux solutions consisting of highly active substances. However, such compounds have insufficient strength due to the weak interaction of aluminum products with tin and lead, and the tendency to form corrosion. Therefore, special compositions are used in the form of an anti-corrosion coating of surfaces made of this metal.

These compositions include solders containing copper, zinc, aluminum and silicon. They are produced both in our country and abroad. Among domestic brands, TsOP-40 is most widely used, the content of which is 40% zinc and 60% tin, as well as compound 34A with aluminum (66%), copper (28%) and silicon (6%). The zinc content affects not only the strength of aluminum contacts, but also their resistance to corrosion.

Of all known solders, the minimum temperature at which they begin to melt is tin-lead-based compositions. The highest melting point belongs to compounds with an aluminum-silicon structure, as well as with aluminum, copper and silicon. Similar types of solders in the first case melt when the temperature reaches 590-600 degrees, and in the second - at 530-550 degrees. They are selected for each specific case when parts with large dimensions, good heat dissipation or refractory aluminum joints are connected.

Technological processes are inextricably linked with special types of fluxes used for better interaction of all welding components.

The selection of the most suitable material is considered a rather difficult undertaking. This is especially important when tin-lead solder is used in the workflow. The structure of such fluxes includes elements that form its increased activity when interacting with aluminum. Among them, triethanolamine, ammonium fluoroborate, zinc fluoroborate and other similar components can be noted.

One of the most popular Russian-made fluxing agents is F64, which is highly active. The quality of this connection allows you to solder aluminum metal parts without removing the refractory oxide coating located on the surface.

Soldering aluminum components

The procedure and technical process for welding aluminum is exactly the same as for other types of non-ferrous metals.

Among home craftsmen, the following two options are most often used:

High temperature soldering used for welding large size elements. This category includes aluminum structures with thick walls and increased weight, for which a temperature of 550-650 0 C is required for heating.
Soldering at low temperatures of 250-300 0 С, which is quite enough for mounting wires of electronic equipment and welding small items used in everyday life. In the same mode, aluminum wires are connected to any electrical network.

High temperature connections are made using special heating elements. One of them is a burner that requires gas in the form of propane or butane to operate. If such a burner is not available, home craftsmen use various types of blowtorches. Welding at high temperature requires constant monitoring of the degree of heating of the surfaces of the parts to be joined. To do this, one of the refractory solders is taken in a small amount, and after it begins to melt, we can talk about reaching the desired temperature. In this case, the heating of the part stops, otherwise it will simply melt and collapse.

Soldering at low temperature is carried out with a 100-200 W electric soldering iron. The power of the soldering iron depends on the size of the components to be connected: the larger the part, the more efficient the soldering iron will be required in order to heat it up. The conductors are easily connected with a 50W soldering iron.

Regardless of the temperature regime, the connections are made in the same way, and all actions are performed in the following order:

The place of the future connection of parts or cables is processed mechanically. To do this, any cleaning agents are used that weaken the oxidative coating, providing a more complete interaction with the flux substance.
The junction must be degreased with acetone, gasoline, alcohol and other organic solvents.
Before soldering aluminum with a soldering iron or a torch at home, the parts are firmly fixed in the most convenient position.
The flux is applied to the prepared plane. If the substance is applied in liquid form, then it is applied with a brush.
The connection point is heated using an electric soldering iron of sufficient power or a gas burner. Next, molten solder is applied here and distributed in an even layer.
Metal surfaces are connected and fixed in position.
After the solder has cooled and the parts have set, the joint is washed with running water. Flux residues are washed out and do not cause further corrosion.