Guide to Aluminum Brazing

June 6, 2021

Aluminum brazing has become prevalent in the manufacturing industry, repair shops, automotive industry, or even at the homes of our DIY guys and hobbyists. 

Most manufacturers and repair companies are using all-aluminum or mostly aluminum components for repair of holes, cracks, rivets, leaks, threads, broken ears. This is also to quickly cast aluminum or iron and fabricate aluminum easily, thus repairing the broken part and sometimes making it stronger than new.

Guide to Aluminum Brazing
aluminum soldered together

This is because aluminium brazing alloys carry an all-aluminum structure with good destruction resistance and great strength.

Aluminum brazing is very doable even for beginners. You don't have to be called a professional to braze aluminum professionally.

To do so, let's first take a good look at the brazing process itself and understand how it actually works.

Basics of Aluminium Brazing

What is aluminum brazing?

brazing aluminum

Aluminum brazing is a popular metal joining process in which the base metal is not melted, but joined through heating up aluminum brazing rods or fillers. 

Once it reaches the melting point, you can use it to either attach metal pieces together or fill in cracks, holes and gaps present in any given object.

After that, as the temperature of the molten aluminum falls, it starts to solidify and settle, thus completing the aluminum brazing process.

What are the methods of aluminum brazing?

  • Torch brazing is obtained by heating the parts to be brazed with an oxyfuel gas torch or propane torches. This uses a chemically aggressive combination of chlorides and fluorides called flux that melts at a temp just below the filler metal. Very thin or very fine structures can be really difficult to braze because of the inability to evenly heat the parts. Brazing filler metal may be pre-placed at the joint or fed from handheld filler metal. Cleaning and fluxing are sometimes needed.
  • Dip brazing aluminum is done in a large amount of molten salt bath containing the flux held in a ceramic pot at dip brazing temperature by direct resistance heating. The filler metal is poured around the braze joint, and the part is dipped into the bath. This method is often applied for projects that require multiple joints.
  • Fluxless vacuum brazing: this does not include the critical post braze cleaning phase that must support brazing when the flux is included. Aluminum brazing flux is corrosive and could cause breakage if it’s not thoroughly cleaned out. Flux removal is done by soaking and rinsing in water or by chemical cleaning.
  • Furnace brazing: this type of method is performed in gas, oil, or electrically heated furnaces. Temperature must be regulated within 5ºF (2.8ºC) and is vital to secure consistent results. Continuous circulation of the furnace atmosphere is desirable since it reduces brazing time and results in more equal heating. Products of combustion in the furnace can be damaging to brazing and satisfactory quality of brazed assemblies in the heat treatable alloys.

Pros

bike frame with brazed joints
  • Smooth good-looking joint: They produced a clean joint; the completed joint may require a little or no finishing at all. It is profitable in the long run because it does not require an additional secondary operation which may cost you much.
  • Better tolerance: Brazing does not melt the base metal, thus allowing a much stricter control of the metal's tolerance.
  • Works on a variety of alloys: Brazing is used to bond a variety of metals, making it a good choice for many different kinds of aluminum-based projects.
  • Cost-effective: This is sure to be cost wise because this does not require argon gas, wire spool, gloves and shield, or electricity.
  • Novice metalworking skill required: Not a professional? Not a problem at all! It is very simple that even beginners and first timers can do it.
  • Portable and convenient: One thing that welders love about aluminum brazing is it's easy to bring anywhere that the job is needed. Easily stored and packed. 
  • Quick Repair: Aluminum brazing is a much faster metal-fabrication technique than TIG welding and other forms of welding. Nonetheless, it has equivalent strength to these other metalworking skills. Thus, makes aluminum brazing a good alternative for metalworking jobs that must be performed quickly or as part of an assembly line.
  • Safety: No need to worry with electrical concerns. While aluminum brazing still involves high heat that can potentially burn, aluminum brazing with a propane torch is not required because you will not need high voltage electricity in this process. 

Cons

  • Not effective in higher temperature: brazing in produces joints that are not as well equipped for high-temperature applications as welds because of the low melting point of filler material.
  • Aesthetic disadvantage: The color of the joint is often not the same from that of the base metal, thus creating an aesthetic disadvantage.
  • Weak joint compared to welding: Producing lower strength joints compared to welding.
  • Metal must be very closed: this is to ensure holding action of molten filler metal.
  • Cleaning of the flux is required: not being able to clean the brazing assemblies and can cause corrosion. 
  • Limited job size: large plates of metal can't braze.

Equipments needed

equipment for aluminum brazing
  • Base metal pieces: this is basically the two pieces of metal that you will connect or the metal surfaces that needs to be repaired. 
  • Brazing metal rod: A brazing rod is a tool that is used to fabricate two pieces of metal together during the brazing process. This is basically the same thing as the traditional welding rod, but it is made specifically for brazing that's opposite to the alternative.
  • Propane torch: A propane torch is basically used for the application of flame or heat which uses propane, a hydrocarbon gas, for its fuel. 
  • Auto darkening welding helmet: A welding helmet, also known as “hood,” is one of the most necessary pieces of PPE that any welder must have. A good helmet protects the eyes and skin not only from severe sparks, but also from potentially vision-damaging ultraviolet and infrared rays emitted by the arc.
  • Welding gloves: Welding gloves are personal protective equipment (PPE) that protects your hands from the hazards of welding. These gloves allow digit articulation while protecting you from electrical shock, extreme heat, and ultraviolet and infrared radiation, and also provide abrasion resistance and enhanced grip.
  • Welding apron: Welding aprons cover the front of the worker's torso to the knee or lower to protect workers from burns and injuries caused by flying sparks and debris encountered while welding. This apron is worn over your work clothes and has adjustable neck and waist straps for a secure fit.

How to braze aluminum?

Follow these 4 easy steps and secure your way in brazing aluminum successfully.

Preparation

rods for brazing

Start by ensuring that you have a safe environment to braze aluminum. One of these is proper ventilation.

Remember that this method involves torches and heat. Being sure to braze in an area with proper ventilation can prevent these dangerous fumes from being inhaled.

For this task, you will also need the set of equipment needed that is stated above.

Another thing to secure is the thorough cleaning of your base metal. This is quite important to get tough and leak-proof joints made via brazing. When two metals are being fused together, it's always best that you first clean it off.

Cutting your pieces to length is also part of the preparation process. Aluminum is soft enough for cutting with standard woodworking saw blades or chop saws. 

Chamfering

Then, chamfer the edges to let a channel for a brazing material.

It is a must that the aluminum is clean before brazing. Vise up the tubing and start heating the aluminum using your propane torch.

Melting

melting aluminum

The melting point of aluminum is at 1,200 degrees F, but the brazing rod will melt at about 700 degrees F. The tubing will become hot enough for about 5 minutes. You’ll see that it’s warm enough when the rod begins to melt on contact. 

You can start heating up the side of the steel pipe that is most comfortable for you (e.g; right side for the right handed people). Using the torch, melt off a piece of the filler rod onto the end of the pipe. 

Take note that after placing a partial amount of melted filler on the end of the base metal, use the molten metal itself to melt more of the rod. Never use the torch flame.  In case you see white smoke rising from the molten metal, that would signify a poor and weak tolerance to breakage. 

Cleaning

cleaning after brazing

Always remember that aluminum brazing can provide really strong bonding but if it's not properly post-cleaned, it might not be as how you expect it to be.

Cleaning is the essential and the last step in the brazing process.

Brazing fluxes promote corrosion if not removed from the parts that's why it is very important to clean the braze assemblies.

Any acidic element will be removed by a thorough water rinse.

To do so, you can immerse the heated parts in boiling water as soon as the brazing alloy solidifies. This is one satisfactory way of cleaning out the major portion of the flux. To avoid distortion from quenching, the heated part must be cooled in air before immersing it in the boiling water.

Another effective cleaning method is to dip the parts in a 10 percent nitric plus 0.25 percent hydrofluoric acid solution at room temperature for 5 to 10 minutes followed by a hot water rinse.

Conclusion

If you’re new to the world of metals, learning how aluminum brazing will certainly be a great way to start off your knowledge into the world of metalworking.

If you’ve never considered aluminum brazing as a metalworking technique, it's time for you to think again!

Aluminum brazing won't surely fail you! 

It has many excellent characteristics and the best alternatives to welding that make it very useful to every welder. 

By reading and understanding all the necessary details given above, we are certain that you now know all the information regarding aluminum brazing.

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