Download ArticleDownload ArticleThis article was co-authored by Alvaro Mendoza, PhD and by How.com.vn staff writer, Eric McClure. Alvaro Mendoza, Ph.D., is a Metallurgist and the Owner of Mendoza Metallurgy in Portland, Oregon. With over 15 years of professional and research experience, Dr. Mendoza has worked in the aerospace industry in forging, casting, metal-making, and additive manufacturing primarily with nickel-based superalloys, titanium and steels. He currently runs a metallurgical consulting and education business that focuses on providing technical expertise to businesses of any size. He was recently featured on a podcast about why metallurgy matters. Dr. Mendoza received his B.S. and M.S. and Ph.D in Materials Science and Engineering, focus on Metallurgy from the University of Florida.
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Knowing how to braze aluminum can be a useful skill for anyone who is faced with a variety of at-home repairs. Brazing aluminum is a quick and inexpensive option for repairing leaks, cracks, or holes in aluminum and is often found in air-conditioning repairs. When compared to welding equipment, aluminum brazing equipment is inexpensive, portable, and does not require high amounts of voltage.
Things You Should Know
- Put on non-flammable gear and clear all dirt, oil, and grease from the area, then clamp the piece to be brazed and use a brush to apply an all-purpose flux.
- Heat the repaired area with a propane or acetylene torch, and apply the filler metal with a brazing rod.
- Remove the flux with hot water and polish the area with emery cloth once cooled; finish by applying a rust-resistant coating.
Steps
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Wear non-flammable clothing, gloves, and safety goggles before you begin the brazing process.
Clean all dirt, oil, paint, or other residue from the area to be repaired by aluminum brazing. Use a degreasing solvent to get rid of oil and grease. Depending on the size of the repaired area, you may need to sandblast the area or use an emery cloth, grinding wheel, or file.Advertisement
Clamp or support the piece to be brazed.
Use a brush to apply the flux appropriate to the temperatures and the metal. An all-purpose flux covers a wide range of temperatures and is beneficial to have on hand for general purpose brazing. Add flux by dipping the filler rod into the flux. You may also use flux-coated rods to eliminate this step. The flux-coated rods apply the flux during the aluminum brazing process.
Heat the repaired area with a propane or acetylene torch until the aluminum shows an orange bloom.[1] This happens when the metal gets very hot. Once you apply a flux, it should change colors or turn clear throughout.
Apply the filler metal by running a brazing rod along the crack or the joint.[2] The heat of the metal will melt the filler into the area needing the repair. Move the flame of the torch on and off as needed to melt the rod.
Remove the flux after the filler material has solidified by dipping the part or pouring hot water on the repair.[3] The flux will flake off. If it does not come off, use a wire brush to gently scrub the brazed area while wet or still in the hot water.
Polish the area with an emery cloth after the metal has cooled completely.
Coat the area with a rust-resistant coating if you are not immediately finished with the area.[4]
Community Q&A
- QuestionCan I use acetylene to braze aluminum refrigeration pipes without flux using aluminum rods?
How.com.vn Staff EditorThis answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.
Staff AnswerHow.com.vn Staff EditorStaff AnswerFor refrigeration pipes, it's best to fit another pipe with a larger diameter between the 2 pieces of copper to create a sleeve. You do need to use flux with copper pipes. Apply the flux along the joint where the larger pipe meets the 2 thinner pipes, and use a silver welding or brazing rod to seal the 2 joints. - QuestionCan you braze anodized aluminum?How.com.vn Staff EditorThis answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.
Staff AnswerHow.com.vn Staff EditorStaff AnswerYes, but you need a really strong brazing rod that will heat through the anodized layer. Anodized aluminum is essentially aluminum with another layer of metal on it, so the rod has to be strong enough to heat through the anodized layer and reach the aluminum. It's usually safer to weld anodized aluminum at a higher temperature to ensure that you penetrate the anodized layer. - QuestionIs a high silver content in the rods better or worse for braising aluminum?
Community AnswerWorse, as the temp required is too high for the aluminum. Use the correct rods for the job.
Tips
- Heat the entire piece of material and not just the repair area to avoid warping the aluminum.Thanks
- Add flux by dipping the filler rod into the flux when brazing aluminum.Thanks
- If the filler clumps, run the flame of the torch across the brazed area and remelt it and smooth with the rod.Thanks
Warnings
- Flux becomes difficult to remove if the metal was overheated or if too little was applied.Thanks
- Corrosion, must be use Fluoride Flux not Chloride FluxThanks
- Do not apply heat directly to the joint area. Because brazing works by capillary action, heat must be applied uniformly to a broad area surrounding the joint, allowing braze alloy to become fluid and be drawn into the joint area.Thanks
- Be careful to have good ventilation wherever you are brazing. Fumes from the brazing process can be harmful.Thanks
Things You'll Need
- Non-flammable clothing
- Gloves
- Safety goggles
- Degreasing solvent
- Sandpaper, emery cloth, grinding wheel, or file
- Brazing rod and flux paste or flux-coated rods
- Brush
- Torch
- Wire brush
- Rust-resistant coating (optional)
Expert Interview
Thanks for reading our article! If you’d like to learn more about brazing aluminum, check out our in-depth interview with Alvaro Mendoza, PhD.
References
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