Aluminum is a really difficult material to weld without the proper tools. You need to get a specific solder or brazing alloy for aluminum or designed to combine it with other different metals. Once you have procured the material online or from a well-stocked hardware store, the greatest difficulty is in working quickly enough to weld the aluminum immediately after the oxide layer has been removed from the surface.
Steps
Part 1 of 2: Getting Started
Step 1. Try to identify the alloy if possible
Aluminum can be welded even if it is not the simplest material to work with. Many objects are built with aluminum alloys: most of them can be welded following the same procedures, although some are more problematic and require specific tools. Aluminum alloy is identified with a letter or number, so check for specific instructions or requirements. Unfortunately, aluminum alloy objects without labels or distinctive signs are not easy to catalog, and professional identification guides are only useful if welding aluminum is your job. The only solution is to try welding, hoping to be lucky.
If you want to combine aluminum with another material, usually the characteristics of aluminum are the limiting factor, so the precise identification of the alloy is not essential. Remember that some combinations, such as steel and aluminum, are very difficult to make and require special welding methods instead of a bonding material
Step 2. Choose a low temperature bonding material
Aluminum has a relatively low melting point (660 ° C) which, combined with the high thermal conductivity, makes it practically impossible to weld with generic bonding materials. You must use a filler material with a low melting temperature and you will need to order it on the internet. Usually a combination of aluminum, silicone and / or zinc is used, but always read the label to be sure it is the right product for the type of work you want to carry out (for example aluminum-aluminum or copper-aluminum welding).
- Technically, bonding materials that melt at temperatures above 450 ° C join the materials by brazing and not by welding. Brazing creates a stronger bond, but soldering is preferred when joining electrical circuits and other delicate materials.
- As far as possible, avoid all filler materials that contain lead.
Step 3. Choose a flux
It is imperative that it is specific for aluminum or for the type of combination you want to weld (much more than the binder material). The best choice is to buy it along with the filler material, as they will have to cooperate to produce a good weld. The flux operating temperature must be very close to the melting point of the soldering material; buy one for brazing if you have chosen a solder that melts above 450 ° C.
Some brazing fluxes are not suitable for welding thin aluminum foil or wire. If so, look for the ones with the words "dip brazing"
Step 4. Choose a heat source
You can use a welding machine to join aluminum wires, but other types of jobs require a propane torch. Usually the torches are used at low temperatures whose flame reaches 315-425 ° C.
If the torch is not suitable for the environment in which you will be working, get a 150 watt welding machine
Step 5. Purchase optional materials
You will need a clamp if you are joining more than one piece of metal together rather than making repairs to an object. A pickling solution to remove post weld oxides is also highly recommended. Some resin-based fluxes must be cleaned with acetone.
Step 6. Organize a safe workplace
Protect yourself from toxic fumes by wearing a respirator and working in a well-ventilated area. A protective mask or goggles are also highly recommended; wear clothes made of natural fibers and don't forget a pair of thick leather gloves. Keep a fire extinguisher handy and work only on fireproof surfaces.
Part 2 of 2: Welding the Aluminum
Step 1. Treat each piece with the filler material, if you need to perform complicated welds (optional)
Joints that are very large or have poorly weldable materials (such as aluminum and steel) should be pre-tinned by applying a thin layer of solder material on each end. Follow the instructions listed here for each piece you wish to weld and then repeat the procedure with the two elements joined together.
Ignore this step if you are using the filler material to repair a hole or crack on a single object
Step 2. Clean the aluminum with a stainless steel brush
Thanks to contact with air, an oxide layer rapidly develops on the surface of aluminum objects, which prevents welding. Scrub the material with a wire brush, but read the instructions below first. Be ready to clean, apply the flux and the filler material in a quick sequence to prevent oxidation from re-forming.
Old aluminum with a thick layer of oxidation or with other residues must be sanded, sanded or cleaned with isopropyl alcohol and acetone
Step 3. Join the base of the two metal pieces with a clamp
If you need to combine two materials (and not adjust an object) you must join them respecting the orientation and position necessary for your project. A small gap should remain between them which will be filled with the filler material; make sure it is no greater than 1 mm (or even less).
- If the two surfaces do not fit together, you will need to sand and sand them.
- Since, during these phases, the aluminum could oxidize again, you should fasten the two pieces loosely, clean them in this position and then close the clamp.
Step 4. Apply flux
Immediately after cleaning the metal, apply the flux to the area to be welded. For this operation, use a small metal tool or a welding bar: by doing this you avoid the formation of oxide and drag the filler material along the entire length of the joint.
- If you're soldering wires, dip them in liquid flux.
- If you purchased powdered flux, read the instructions on the package to mix it.
Step 5. Heat the metal
Use the torch or soldering iron to heat the metal near the joining area starting at the bottom of the piece. A direct flame on the area to be soldered risks overheating both the solder and the flux. If you are using a torch, keep the tip about 10-15cm from the metal. Move the heat source constantly in small circular motions to heat the area evenly.
- If you are using a soldering iron, it may take up to 10 minutes for it to reach operating temperature.
- If the flux turns black, wait for the area to cool, clean it, and start over.
Step 6. Apply the filler material
Most fluxes will boil and turn light brown when the right temperature is reached. At this point, drag the bar or wire of bonding material along the joint while continuing to indirectly heat the area on the opposite side of the metal or on a nearby surface. The filler material must be dragged along the crack with a slow and constant movement to create a uniform joint. Creating a strong and beautiful weld takes a lot of practice, especially if it's a job you've never done before.
If the welding material does not bond to aluminum, the oxidation layer may have reformed, in which case you must clean the area again and weld immediately. The cause could also lie in an unsuitable filler material, or the aluminum alloy you are treating is particularly difficult to weld
Step 7. Remove the excess flux and oxide
If you have used a water-based flux, you can remove the residues with water once the metal has cooled. If you have used a resin-based product, you must clean with acetone. When all the flux has been removed, you can dip the piece in the pickling mixture to remove any oxidation that has been created with the heat.
Advice
- Aluminum is an excellent conductor of heat. This makes it difficult to heat an area to be welded while the whole piece is still hot. If you cannot melt the material to be welded, place the piece of aluminum on a wire mesh backing or on top of another heat sink with a smaller surface. Alternatively, use a warmer flashlight.
- Sometimes it is necessary to heat the tip of the bar with a flame to help the filler material melt more easily on the area to be welded. Be careful, because if the bar overheats the solder will not hold.
