How to Braze Aluminum

Co-authored by Alvaro Mendoza, PhD and Eric McClure

Last Updated: February 24, 2025 References

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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Expert Source

Alvaro Mendoza, PhD
Metallurgist

Expert Interview} 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.

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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.
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Research source} This happens when the metal gets very hot. Once you apply a flux, it should change colors or turn clear throughout.
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Research source} 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.
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Research source} 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.
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Community Q&A

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Can I use acetylene to braze aluminum refrigeration pipes without flux using aluminum rods?

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This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

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For 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.

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Can you braze anodized aluminum?

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This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.

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Yes, 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.

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Is a high silver content in the rods better or worse for braising aluminum?

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Worse, as the temp required is too high for the aluminum. Use the correct rods for the job.

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Tips

Heat the entire piece of material and not just the repair area to avoid warping the aluminum.

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Add flux by dipping the filler rod into the flux when brazing aluminum.

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If the filler clumps, run the flame of the torch across the brazed area and remelt it and smooth with the rod.

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Warnings

Be careful to have good ventilation wherever you are brazing. Fumes from the brazing process can be harmful.

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Corrosion, must be use Fluoride Flux not Chloride Flux

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Flux becomes difficult to remove if the metal was overheated or if too little was applied.

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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.

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