Seal

Flux for soldering aluminum

Once upon a time, I thought that aluminum soldering was done in factories and was not done at home. However, over time, this misconception has dissipated. This article is about how to solder aluminum at home and what to use to solder aluminum.

At school, the topic of aluminum was previously discussed in chemistry and physics lessons about its properties; it has excellent electrical conductivity and thermal conductivity, but is very difficult to solder. The difficulty of soldering it is due to the fact that an oxide film instantly forms on the cleaned surface, which is very resistant to various aggressive environments.

Once upon a time I came across such information that soldering is carried out with a solder consisting of tin and zinc or tin and bismuth. However, practice shows that it can be soldered quite normally with conventional POS 40 and POS 60 solders. It doesn’t matter what you solder with, the main thing is how.

The mechanical strength of such soldering is small, but what is mainly required is not the strength, but the electrical conductivity of the joint. I can’t say what else can be used to solder aluminum besides these solders; I haven’t tried it. You can also solder with lead, the main thing is that the soldering iron has enough power and heats it up to a sufficient temperature.

Soldering iron

As mentioned above, aluminum has increased thermal conductivity, which is why cooling radiators are made from it. Therefore, for soldering large elements, the power of the soldering iron should be high, 100 - 200 W. If, of course, these are two small wires, then perhaps 60 - 100 W will be enough power.

Fluxes

Nowadays there are no problems with the choice of means, but previously I had to use anything to tin aluminum - aspirin, technical petroleum jelly, grease. For soldering aluminum at home, I chose two good fluxes F-64 and FTBf - A, and FIM flux also has good results. This is perhaps the most important thing, the better the flux, the easier the soldering.

The main thing is not to run into a fake, but there is enough of that now, you buy this “Flux for soldering aluminum”, but it’s no good. By the way, regarding the question of what else can be used to tin aluminum, there is such a flux F-34, this can be said just by its composition that it is aspirin. Aluminum can also be tinned with soldering oil.

Tinning methods

With good flux, the process of tinning and soldering is not a problem. It’s another matter if you don’t have one at hand, here the process becomes more labor-intensive.

The most important thing in the tinning process is to prevent contact of the surface being cleaned with oxygen. Therefore, the surface to be cleaned is thickly lubricated or filled with flux, and if necessary, it can be heated a little. You can simply, if the product is small, for example wires, clean them directly in the solution, pouring it into something.

Regarding the method of soldering aluminum with a soldering iron with a rosin solution, I did something like this. I pre-cleaned the surface, lubricated it with a solution and sprinkled it with copper or iron filings. Then, pressing with the soldering iron tip (the harder the better) and stripping off the oxide, I tinned it with regular solder.

Sometimes, if it was necessary to solder two wires, aluminum for example and copper, I used this method. I twisted the two ends of the wire and welded them with a current discharge using a graphite core from a battery. For such “welding” I used a 6-12 volt transformer with a current of 3 amperes. We connect one end of the wire from the transformer to a twist, and screw the battery rod to the second (you can use a brush from the engine). When touched, an arc appears and the ends are soldered into a ball.

So soldering aluminum at home is quite possible and not such a difficult task. A little practice and that's it.

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 cited as an argument:

1. upon contact with air, a chemically resistant and refractory oxide film (AL 2 O 3) is formed on the surface of the aluminum part, resulting in an obstacle to the tinning process;
2. The soldering process is significantly complicated by the fact that aluminum melts at a temperature of 660°C (for alloys this ranges from 500 to 640°C). In addition, the metal loses 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.

Considering the above factors, it is truly impossible to solder aluminum using conventional means. The use of strong fluxes in combination with the use of special solders will help solve the problem. Let us consider these materials in detail.

Solder

Commonly used low-melting solder bases are tin (Sn), lead (Pb), cadmium (Cd), bismuth (Bi) and zinc (Zn). The problem is that aluminum is practically insoluble in these metals (with the exception of zinc), which makes the connection unreliable.

By using a flux with high activity and properly treating the joints, you can use tin-lead solder, but it is better to avoid such a solution. Moreover, a solder joint based on the Sn-Pb system has low corrosion resistance. Applying a paint coating to the soldering area allows you to get rid of this drawback.

For soldering aluminum parts, it is advisable 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 TsOP-40 (Sn - 60%, Zn - 40%).

Note that the higher the percentage of zinc in the solder, the stronger the connection 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, like the above-mentioned domestic solder 34A, 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 is necessary to take into account that not all of them can be active towards aluminum. We can recommend using products from a domestic manufacturer for such purposes - F-59A, F-61A, F-64, they consist of ammonium fluoroborates with the addition of triethanolamine. As a rule, the bottle is marked “for aluminum” or “for aluminum soldering.”

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

Surface preparation

Before you begin tinning, you must complete the following steps:

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

It should be taken into account that it will not be possible to completely remove the oxide film, since a new formation will immediately appear in the cleaned area. Therefore, stripping is carried out not with the goal of completely removing the film, but to reduce its thickness in order to simplify the task of the flux.

Heating the soldering area

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

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

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

• Do not overheat the base metal, as it may melt. Therefore, it is necessary to regularly monitor the temperature during the process. This can be done by touching the solder to the heated element. 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 promotes 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 soldering area is degreased and cleaned;
• the parts are fixed in the desired position;
• the connection area heats up;
• touch the solder rod (containing active flux) to the joint. If flux-free solder is used, then flux is applied to destroy the oxide film, after which a solid piece of solder is rubbed over the soldering area.

A brush with steel wire bristles is also used to break down the aluminum oxide film. This simple tool is used to rub molten solder over an aluminum surface.

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

What to do if you don’t have the necessary materials?

When it is not possible to prepare all the materials necessary for soldering, you can use an alternative method that uses tin or tin-lead solder. As for the flux, it is replaced by rosin. To prevent the formation of a new aluminum oxide film 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 its sting. You can increase the effectiveness of the process by adding metal filings to the rosin.

The process is carried out as follows:

• use a heated tinned soldering iron to melt the rosin at the soldering site;
• When the rosin completely covers the surface, they begin to rub it with a soldering iron tip. As a result, metal filings and stings 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 is destroyed, 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 questionable.

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

Industrial production of aluminum, by historical standards, began relatively recently. But during this time, this material has firmly entered our lives. Its main parameters - high electrical and thermal conductivity, low weight, resistance to corrosion - have led to the fact that this metal has become the main material used in the aviation and space industries. In addition, it is impossible to imagine the streets of our cities without aluminum; translucent structures (doors, windows, stained glass), advertising structures and much more are made from it.

When processing it, it is permissible to use almost all types of processing - turning, stamping, casting, welding and soldering. The latest methods are used to produce permanent connections from aluminum blanks.

General principles of soldering aluminum at home

Many people sincerely believe that soldering aluminum at home is a rather complicated process. But in fact, everything is not so bad. If you use the appropriate solders and fluxes, then there should not be any particular difficulties. If a home craftsman solders aluminum parts using materials intended for copper or steel, the result will most likely be negative.

Process Features

The difficulties of soldering aluminum are primarily due to the fact that there is an oxide film on its surface, which, unlike the base metal, has a higher melting point and is highly resistant to various chemicals. It is this film that creates serious obstacles when using traditional solders and fluxes, and for example, if you solder aluminum with tin, it is difficult to guarantee a high-quality result. To remove this film, either mechanical action or fluxes that contain strong chemicals are used.

The base metal itself, in this case aluminum, has a low melting point, about 660 °C. Such a difference between the melting temperature of the oxide film and the base metal also leads to complications in soldering.

This property of aluminum results in the heated aluminum becoming less durable. Thus, aluminum structures begin to lose stability already at a temperature of 250-300 °C. In addition, aluminum alloys may contain materials that begin to melt at temperatures of 500-650 °C.

A large number of solders include tin, cadmium and other components. Aluminum has difficulty coming into contact with these materials and this in turn leads to the fact that the seams produced using these solders are characterized by low reliability and strength. Meanwhile, zinc and aluminum have good solubility in each other. The use of zinc in solders makes it possible to impart high strength parameters to the seam.

Use of transformer oil

As noted above, the main obstacle when performing soldering is the presence of an oxide film. Before soldering aluminum it must be eliminated. To remove it, different methods are used, ranging from the use of an abrasive tool to special fluxes. In addition, there are “folk” methods. One of them is related to the use of transformer oil.

To remove the oxide film, the following composition is used: transformer oil is added to the abrasive powder. With constant stirring, the result should be a paste-like mass. It must be applied to a previously cleaned soldering area. After this, the soldering iron tip must be thoroughly tinned and the prepared areas must be rubbed until tin appears. After this, the soldering areas must be washed and work can continue.

What kind of solder is used for soldering aluminum?

Most solders contain substances that do not dissolve in aluminum. That is why, to create permanent connections of aluminum parts, so-called refractory solders are used, made on the basis of aluminum, cadmium, zinc and some other substances.

Low-melting solders are also used for soldering aluminum.

Their use allows you to perform work at low temperatures. This allows connections to be created without changing the properties of the aluminum. But it should immediately be noted that the use of such materials cannot ensure the proper degree of corrosion resistance and strength of the joint.

Optimal soldering results can be obtained by using a composition that contains aluminum, copper, and zinc. Work with such solders must be performed with a soldering iron, the tip of which is heated to 350 °C. When connecting parts, you need to use flux, which consists of a mixture of oleic acid and lithium iodide.

The composition for joining aluminum parts can be prepared at home, or you can simply purchase it in a store.

One of the commercially available solders for aluminum is HTS-2000. Soldering can be done with this solder without using flux. The great thing about this compound is that it can penetrate the oxide film and can create strong molecular bonds. The service life of connections made using this alloy is 10 years.

How to solder correctly using a torch

The need for soldering aluminum and its alloys may arise both in industrial and domestic conditions. This process can be used when performing repairs on parts, but sometimes you have to deal with more extensive work.

Processing aluminum is associated with a number of difficulties and therefore traditional soldering technology materials do not always guarantee the proper result.

One of the frequently used methods for obtaining permanent connections is directly related to the use of a gas burner.

Working with aluminum means that the oxide film that is on the surface of the part prevents the parts from joining.

Soldering with a torch is significantly different from working with a soldering iron and is rightfully considered more practical. While working with the burner, the master can adjust the temperature. And this provides additional opportunities for surface treatment of workpieces. In this case, the thickness of the material does not play a special role. Sometimes when working with a burner, fluxes and additional surface treatment agents are used.

Soldering aluminum with a gas torch in a home workshop allows you to preheat workpieces and consumables.

Undoubtedly, to obtain a high-quality connection, experience is required. The fact is that aluminum has a low melting point; therefore, consumables used in soldering have good fluidity. If the master makes a mistake, then there is a high probability that the solder will simply spread over the workpiece without ever getting into the seam.

What flux to use

Advantages

Soldering is one of the ways to obtain permanent metal joints. But unlike other methods, until recently it was characterized by low productivity and low strength at the junction. This and a number of other reasons led to the fact that it did not receive widespread industrial use.

With the development of technology, methods for connecting parts using an electron beam and ultrasonic waves have become available. The emergence of special solders and fluxes has significantly improved the quality of solder joints.

Modern soldering technologies make it possible to use finished products without further processing on mechanical equipment. Soldering has become one of the main technological processes in mechanical engineering, aviation and space industries and, of course, electronics.

Soldering has a number of undoubted advantages compared to welding. The process of joining parts in this way takes place with significantly less heat consumption. In other words, during this process there are no major changes in the structure of the metal. Its physical and chemical parameters remain virtually unchanged. After soldering, phenomena such as residual deformation may occur; its dimensions are incomparable with those that remain after, for example, welding in a cloud of shielding gases.

That is why the use of soldering guarantees more accurate compliance with the dimensions specified in the technical documentation for the product. Using this method allows you to join dissimilar metals. In addition, we can say that these processes can be automated quite easily.

Flaws

When talking about soldering aluminum parts, we must always remember that to work with it it is necessary to use special solders and fluxes that are able to meet the requirements for the quality of the resulting joints.

The slightest violation of technology or the use of unsuitable materials will lead to the fact that the resulting seam will not meet quality requirements.

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.

Return to contents

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 PIC solders. 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 clean the metal until it shines, using rosin crumbs or soldering acid, put a piece of tin in the 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.

In the production of household appliances, aluminum and its alloys: silumin, duralumin are used very widely. These materials are used to make both product bodies and wires for various devices.

What should you do if you need to solder an aluminum part or solder a fallen wire made of this lightweight material? Soldering metals in general, and aluminum in particular, is, as a rule, a non-trivial task that requires knowledge and experience. Both aluminum itself and its alloys have unpleasant properties. When exposed to atmospheric oxygen, parts made of this metal become coated with a strong oxide film, which makes soldering aluminum a difficult task. After all, the oxide prevents the reliable connection of the parts being soldered. In this material you can read about how to correctly solder aluminum at home using solders that contain lead: POS-50, POS-61 and POS-90.

First way. If you need to solder a pair of aluminum wires to each other, you should first tin them thoroughly. Rosin is applied to the ends of the soldered wires, medium-sized sandpaper is placed underneath, and the wire is pressed against this sandpaper with a hot soldering iron (which also needs to be tinned first). During the process, you need to constantly add rosin; under no circumstances should you remove the soldering iron from the metal. This operation is repeated many times until the wires are tinned properly. Then you can start soldering. If instead of rosin you use alkaline oil for cleaning weapons or mineral oil, which is used to lubricate sewing machines, then both preparation for the process and the soldering of aluminum itself will not cause difficulties. If, of course, you have at least a little experience in these matters.

Second way. It is good to solder aluminum sheets. Rosin, in which small metal filings are crushed, is applied to the seam, then you need to go over the seam several times with a tinned hot soldering iron, constantly adding solder. The point of this method is that the sawdust with sharp corners will begin to scratch and tear off the oxide film, and when it does not interfere, the tin from the solder connects well to the base, and soldering aluminum becomes an easy task.

The main thing is to remember the rule: the thicker the aluminum sheet, the more powerful the soldering iron should be. If you are faced with the task of soldering thin sheets, a 50 W soldering iron will do the job. In the case where the sheet thickness is a millimeter or a little more, you will need a 90 W soldering iron. And if you need to solder aluminum in sheets that consist of two-millimeter thick plates, then before soldering you will have to preheat the metal, then apply flux and then begin the soldering process. In the second method, as in the first, you can use mineral-based oil instead of flux.

Third option. Before proceeding directly to soldering, you should perform the “copper plating” procedure on the element that you took into work. A galvanizing installation is suitable for these purposes, but if it is not at hand, you can do without it. Start by applying concentrated copper sulfate to the sanded area. Then connect the negative terminal of the battery or accumulator to this part. Connect the positive contact to the copper wire, fixed to the fleecy part in such a way that it does not touch the surface of the aluminum due to the protruding bristles. After a certain time, a thin layer of copper will be deposited at the point of the part that you are about to solder. It must be washed with water, dried, and then tinned in the standard way (using a soldering iron).