If you’re looking to bond or repair metals it’s good to know that you don’t need to be a professional boiler maker to get the job done.
With some insightful instructions online and the right equipment you’re able to easily move forward with the bonding or repairing of aluminium and cast aluminium and even cast iron quite quickly.
Whether you’re looking to repair a leak, broken ears, cracks or holes in any of the materials above, we’re happy to mention that you’re able to do this with ease and generally find a result that is even stronger than before.
It’s quite simple.
As you might already know, most aluminium based alloys can be effortlessly brazed, which is down to the fact that aluminium has an optimal melting point and also comes with fantastic corrosion resistance. On top of this, the strength and clean appearance of aluminium makes it a winner for repairs too.
For some quick insights, when it comes to brazing, there is some information on melting points you may need to know. To start, the melting point of the filler or the brazing filler metal that you’ll be using is essentially the same (or very close to) the material that you’re joining it to.
Though — you shouldn’t be able to melt the material you’re using as a base.
That said, you’ll need to be mindful of the temperature you’re using to ensure that there’s no chance of both materials melting and bonding together in an improper way.
The Basics of Braze Aluminium Welding
Before we dive into how to work with braze aluminium, there are a few things we need to go over to make sure you have everything you need to get the job done, and understand some key temperature metrics.
Off the top, braze or brazing is essentially the use of a gas-generated heat and the melting of a filler that contains no iron — aluminium for example — to glue or join two different metals together.
This means that you can also use this aluminium material to replace or add to a metal which may have been damaged or simply broken off. That said, this is a rather cheap and effective way to repair cracks and damage in metal.
Here’s some important things to note and a few materials you’ll need:
Equipment — a wire spool, some gloves, electricity, no argon gas and a shield.
Your Skills — to follow some basic instructions. Be sure not to use chemicals or special cleaners.
Danger and Safety —the use of electricity, though non-high voltage required.
Cleaning — you’ll need to ensure that impurities beneath the area you’re looking to adhere the aluminium too is kept clean. You may need to also strip the boiled aluminium of any impurities.
Aluminium — will need to be brought to 500 degrees F or 260 degrees C to melt.
Alloy Adherence — you will have to ensure you’re working with an aluminium alloy or a cast aluminium.
Time Spent — depending on your dexterity, however a lot quicker than typical welding.
Repair Ability — the brazing will work to fill just about all size holes, cracks and split metals with ease and the result will be far stronger than the original material.
Versatility of Aluminium — the single use of aluminium will be able to seal, rebuild, fill and bond metals without issue.
Why Choose Brazing Above Welding
For our readers concerned or not too sure about whether to go with brazing above welding, we have a few insights and tips for you below.
Aside from being a much smoother and quicker experience, you’ll be able to find that braze aluminium can essentially improve the strength of the original metal and also provide an outcome that exceeds the previous.
You’ll be less likely to be stuck dealing with similar issues such as cracking and metal tearing or breaking off when you’ve successfully completed and aluminium braze, and that said, we’re sure you’ll find the experience a whole lot better.
A few examples of the things you’ll be able to repair, restore and strengthen with brazing include:
- Fuel Tanks
- Vehicle Wheels or Rims
- Boats and Other Vessels
- A/C Lines
- Both Cast Iron and Aluminium Heads
Those examples out of the way, it’s quite simple to see that by following brazing above the traditional welding process, you’re getting a great result without as much complexity and cost.
To add, the brazing activity is essentially part of the welding process whereby you’re able to join metals together after you’ve heated a material to a suitable temperature. Typically, this temperature is around 840°F (449°C) and you’ll be able to then fill, repair or replace a broken or missing material without issue.
You’ll be able to easily distribute your filler material to the area needed and through capillary action, or a capillary bonding process, find that you’ve repaired and strengthened your existing material beyond its original strength level — ideal for repairs in machinery and vehicles such as boats where a tougher strength is typically required to reduce the risk of the damage reoccurring.
The Brazing Processes
To go further into detail about brazing, we’ll take a look below at a few of the more common brazing processes and some that you may be able to undertake at your worksite or in your hobby shop.
Keep in mind that each workflow and process will depend on what your predicted or required outcome is expected to be.
Some brazing processes work better than others at specific workflows and you should always make certain that you’re undertaking the one that’s best for your product, material or the repair you’re looking to fulfil.
Traditional Torch Brazing or TB
One of the more common brazing processes is the traditional torch brazing process or TB for short. This is where you’ll be working to heat the parts of a material that you want to be brazed with an oxyfuel torch or gas torch.
In some cases, you’ll need to use more than one torch, and may even require the assistance of an offsider — sometimes with larger materials or vehicles, for example, you’ll need to work on brazing a large area at the same time to ensure bonding works correctly and the material you’re adhering doesn’t move or join incorrectly.
One thing to keep in mind is that if you’re needing to get the highest temperature possible out of your torch, or the alloy you’re using has a very high temperature requirement, you will need to draw upon different lighter or torch fuels.
In some cases, this will require the use of compressed air or oxygen to better produce heat in a small space.
The brazing filler material that you’re using will either need to be pre-placed in the joint or the area you’re looking to fill or repair — or it can be hand-filled as you’re working. Either of these are typical and may require some assistance or a few practice runs depending on how confident you are at the process.
To end, you may also be required to clean and flux depending on the outcome and the requirement.
The Different Aluminium Brazing Filler Metals
As we outlined above, when it comes to brazing you’re going to need to ensure that your filler metals are based on an aluminium alloy. That said, if you’re working on an aluminium metal and an aluminium alloy, the only metal that is going to adhere and capillary bond with these metals is another aluminium alloy.
You can often find these alloys and filler metals in either a wire form or as a shim stock, and so you’ll have to work to determine which option is the best for you and your project.
When it comes to placing or pre-placing the material as we mentioned above, the most effective and simplest way to do this is through utilising a brazing sheet. This sheet is going to be an aluminium alloy base, which is essentially aluminium alloy on both sides, or just one of the sides depending on what your requirements are.
In some cases, you can also make use of manganese or magnesium alloys too, though these will be heat treatable and core alloys.
One other and rather common method of adding your brazing filler is to rely on either a paste or a metal powder. These methods are a little more messy and require you to be a bit more pedantic about where the filler is going to go, though being a lot more versatile than a metal sheet, these remain quite popular.
You’ll be able to find these powders and pastes with silicon integrated within them, which means that the melting point is going to be reduced without the need of copper, zinc or magnesium — again this may be a requirement for you depending on the project you’re working with.
The Aluminium Brazing Flux Process
As you may have already expected, when working with braze aluminium you’re going to need to work on an aluminium brazing flux. This will be what allows your brazing to melt more effectively and provide a better result.
You’ll find that there are two combinations of fluxes, which rely on both chloride and fluoride offered as a powder.
If you’re working with the torch brazing we mentioned above, or a furnace brazing, you’ll need to mix this flux with water to ensure you’re turning this flux into a paste and better able to coat the area where you’re looking to join or repair.
The more common ways of adding this paste are to either brush, dip, spray or pour it over the area. It’s imperative to make sure that you’re coating the entire area here as you’ll want to be sure that there aren’t any gaps or holes in the brazing that could compromise the strength of a join or a repair.
To add, both furnace brazing and torch brazing are a little active or lively, so to speak, and that means you’ll need to ensure you’re taking this process with a lot of care. This is down to the fact that thinner aluminium may be affected negatively by this process, so be as pedantic and careful as possible.
For the dip brazing processes, you will essentially be working to create a bath of molten flux — which is created in the same was we outlined above.
This is the more delicate brazing process, and that means you’re able to more easily braze thinner aluminium without the risk of damaging or attacking it too severely.
Getting Your Brazing Practice In
With all of our points out of the way above, the actual task of brazing may seem a little complex and rather daunting for those new to doing it.
However, it’s good to note that because the process is rather affordable — and not overly complicated despite the fact it seems to be — you can work to practice your brazing before going all-out on a project.
We’ve outlined some pointers below for you which will help you better understand and build your confidence in brazing aluminium and have you on track to repairing these materials on your own.
Here’s What You’ll Need
Off the top, there are just a few things you’ll need to get started when it comes to practising your aluminium brazing.
- A Carbon Steel Tube or Pipe
- An Automatic Welding Helmet — Auto-darkening
- A Brazing Aluminium Rod
With those materials on hand, you can then follow our step by step guide to brazing aluminium and getting some essential practice in.
Before we begin, it’s important to make sure you’re in a safe environment. You’ll want to make sure you have your helmet on-hand and you’re in a well-ventilated space for the process. This is going to ensure you’re not at risk of inhaling fumes and other toxic substances.
From here, get your hands on the carbon steel tube or piping that we mentioned above.
Place this tube between two bricks or something that can cling and grip to the pipe, giving you a free hand and a good vantage point for our next step.
Once you’ve placed your tubing in a safe place, work on getting your oxyacetylene torch and firing it up to neutral.
Start by choosing a side of the rod that’s most easily accessible to you and comfortable to braze and work on using your torch to melt some of the brazing rod to the pipe. Once you’ve started this process, you might find that the molten metal is hot enough to continue melting the brazing rod on its own, so continue to use this and melt more of the rod on to the tube.
It’s far safer and more effective to use the molten steel to continue to melt the rod, so be sure not to use the torch to continue melting the rod.
Work to continue melting the rod on to and around the tube and you’ll be on your way to better understanding how to braze aluminium.
We suggest restarting a few times to get the hang of the process and that means cooling down the pipe and starting over. You can use your welding gloves or a tool large enough to grab the pipe and dip it in water to cool things off and start again.
In real world situations, dipping your pipe or the tube in water with the weld is going to majorly weaken the weld — though for practicing your brazing this isn’t an issue.
With that practice task out of the way, you’ll be on the way to better understanding and perfecting your aluminium brazing. It’s always good to keep in mind that confidence is key here and you’re going to want to keep practicing and perfecting your craft until you’re feeling most comfortable and confident with this.
Once you’re really getting the hang of it, you can then move on to working with your joins and repairs, which we will go over in a little more detail below.
Brazing in the Real World
After you’ve completed a few practice rounds over the day or a few weeks, you’ll likely feel a little more confident and be ready to move on to some professional or hobbyist brazing activities.
We have some information below for you about working on perfecting joint designs and repairs along with fixtures and some other brazing essentials, so continue reading if you’re looking for a little more assistance here.
Brazed Joint Design Essentials
To kick things off, when it comes to the design of your brazed joints, you’re going to want to stick to a few different types.
This isn’t a free for all and you’ll certainly want to make sure you’re following a brazing-friendly type of joint, especially when it comes to the repair of highly important materials, structures or vehicles.
With a poorly designed joint, you could reduce structural and material integrity which could lead to an accident.
The more common joints for brazed aluminium include either a flange, tee, lock seam or a lap. You can research these join type for some more information.
The scarf and butt joints are not something you’ll want to undertake when brazing, even though these are common welding joint types.
For some added information on the joint types, we have some pointers for you below.
The Tee Joints are your best bet for ensuring capillary flow that we talked about above. These types of joints will essentially be working to strengthen and create reinforcement fillets on either side of the joint or the metal you’re working to join or repair.
The Lap Joints are the better option if you’re simply looking for the fastest and most efficient way to join sheets together. You’ll want to make sure that there is an overlap here for around two times the thickness of your joint member, however.
On top of this, if you’re creating an overlap of around 6.4mm you’ll be creating voids or issues with flux inclusion — this will be where you should work to use straight grooves or a knurl that follows the direction of your brazing.
A few other things to keep in mind are that your lap joins, or the longer lap joins, rather, should flow in the same direction. You shouldn’t be changing the direction or the angle of these joints in relation to themselves otherwise you’re going to damage or cause issues with the strength of your brazing. You should also make sure that your lap joints, and almost all joint types, enable space for your flux removal after your brazing is complete.
To end, all of your closed assemblies or materials will need to have a large enough gap to allow for the brazing gas to escape as well as for you to drain or remove the flux from the joins.
Fixing Your Brazing
As with most welding activities, brazing should also be designed and undertaken in a way that is self-jigging. This will mean that you’re working with materials, sheets or a vehicle that is designed in such a way that you’re not needing to add extra assembly or pieces to your final materials.
If you do add or incorporate other materials to your brazed materials, there runs the risk of expansion which means there could be a distortion or a total failure of your brazing depending on how severe this distortion or expansion is.
It is common for either Inconel springs or stainless steel to be made use of when there is the potential for expansion. You can utilise either a stainless or a mild steel here, as a fixture material, though if you’re working with a furnace brazing technique, you’re going to want to rely more on aluminium-coated steels or a nickel material to achieve the outcomes you’re after.
The Pre-cleaning Process
As we mentioned earlier in the article, pre-cleaning is sometimes integral to ensuring that you’re getting the best brazed joints possible.
For a leak-tight and strong brazed joint you’re going to want to make sure that you make use of a cleaning solvent or a vapour to strip your materials and alloys of any impurities that could damage or affect the brazing you’re looking to undertake.
Keep in mind that solvent and vapours will be your best option for cleaning non-heat treatable materials, though you may want to consider manual cleaning and chemicals for cleaning materials that are heat treatable. Getting our your wire brush or even some sand paper might be a better option here.
The Other Brazing Types
As we mentioned above, there are a few brazing types that are common and rather simple to undertake. We already outlined the torch brazing process, though there are a few more to consider and we’ve described these briefly below.
Keep in mind that not one single brazing activity is ideal for all of the materials in a single project and you may need to rely on multiple to achieve your desired result.
The brazing type that relies on either oil, electricity or gas-heated furnace is aptly named furnace brazing and this is the technology that you’ll want to rely on for the more uniform brazing outcome.
In the furnace, you’ll want to make sure that temperature ranges don’t range any further than 2.8 degrees Celsius or 5 degrees Fahrenheit. This will ensure that your brazing is as consistent in appearance and strength as possible.
One other important factors to consider is the atmosphere in the furnace. Typically, you won’t need to make any changes here, though keeping the atmosphere as stable as possible will mean you’re able to more efficiently braze your aluminium.
As we mentioned above, it’s important to consider the durability and the melting point of the materials you’re looking to braze and making sure they are suitable for furnace brazing. Thinner aluminium may become an issue.
As we briefly touched on above, the torch brazing process is quite simple and the one you’re most likely to undertake.
This type of brazing works differently due to the fact that the head is more localised or directional, which means you’ll need to keep your torch and brazing moving at a consistent rate to ensure you get a good level of finish.
If you’re confident in welding or are a boilermaker, this is the type of brazing that is going to seem most familiar in that it follows a very similar process. You’re essentially moving your brazing down the join line you’re looking to create, however, the filler metal is a little more fluid and free-flowing than a weld will be.
In most cases, you will notice that torch brazing is most common in workflows that require the attachment of materials to a sheet or material rather than in the creation of joints alone.
You can also find torch brazing to be a suitable workflow for repairing cracks or holes in metals.
The Dip Brazing Process
To one of the more complex and potentially more dangerous types of brazing, we have dip brazing. This process a little more dangerous in that you’re using a rather hefty amount of molten flux.
This will be stored in a ceramic pot and maintained at the temperature required to braze the material.
One way this process is made a little safer is in the fact that you’ll find the brazing pots now being heated by an internal heating element, rather than having to heat them in a furnace or via another method.
You’ll be able to rely on high current transformers running at a low voltage to keep your molten flux sustained at the temperature required. From here you’ll be able to bathe your materials.
It’s imperative to keep in mind that the solutions here are quite toxic and corrosive and the material or solution you’ll be working to use to strip your welding and brazing are quite dangerous.
The use of a range of PPE equipment such as aprons, gloves, goggles and suitable footwear is essential here to ensure you’re not coming into contact with these substances.
It’s also important to ensure you’re utilising a face mask to ensure there is no chance of inhaling the fumes coming from these chemicals.
To end, these materials should never come into contact with water from a pour-over, but rather the acid should be poured over the water. When mixing acid and water, you must also mix this slowly and only in an area that offers suitable ventilation.
Your Final Post-braze Clean
Once you’ve completed all of the above activities or processes and are ready to move forward with wrapping up your braze aluminium project, there is then a cleaning process you’ll need to undertake.
As we mentioned, brazing will increase the level of corrosion on your materials so it’s important to clean all of this off and the accompanying substances too.
Our biggest tip here is to simply move your freshly-brazed materials from your work bench into a tub of boiling water as soon as possible — only after your brazing alloy or material has become solid.
This will make sure that you’re removing as much of the flux as possible and keeping your base material as free from corrosion as possible.
Given that you’re moving your material into hot or boiling water, you’ll find that the temperature change will be what strips a good portion of the flux here. If you’re worried about quenching, or the material becoming less sturdy, you can also allow the alloy and the metal to sit and cool for a moment before submerging it.
Once you’ve submerged your material in the water, there’s another step you might want to consider — the nitric acid.
We suggest that after you bathe your material in boiling water that you also move it to be dipped in a bath of concentrated nitric acid. It’s best to let the flux sit in here for around 15 minutes to ensure that you’re getting as much of the substance off as possible — then finish this process with a quick boiling water rinse.
Now that you have essentially all you need to know about working with brazing aluminium, you’ll be free to go ahead and work on your repairs at home or in your workshop.
Be sure to follow all of our safety instructions and to do your research based on the exact materials and project you’re looking to undertake. It’s always better to be safe than sorry and this means checking the brazing requirements for your material’s thicknesses and more.
You don’t want to damage or reduce your metal’s integrity, so always make certain you’re following guidelines.