How to Brazing Aluminum – A Technical Guide

You can actually use Aluminum brazing to repair cracks, holes, leaks, rivets, broken ears, threads, or fabricate aluminum, cast aluminum, and cast iron quickly, easily, and stronger than new. It’s not hard at all.

Many aluminum alloys can be brazed. Aluminum brazing alloys are used to provide an all-aluminum structure with excellent corrosion resistance and good strength and appearance.

The melting point of the brazing filler metal is relatively close to that of the material being joined. However, the base metal should not be melted; as a result, close temperate control is necessary. The brazing temperature required for aluminum assemblies is determined by the melting points of the base metal and the brazing filler metal.

How to Brazing Aluminum?

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.

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  1. Wear non-flammable clothing, gloves, and safety goggles before you begin the brazing process.
  2. 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.
  3. Clamp or support the piece to be brazed.
  4. 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.
  5. Heat the repaired area with a propane or acetylene torch until the aluminum shows an orange bloom. This happens when the metal gets very hot. Once you apply a flux, it should change colors or turn clear throughout.
  6. Apply the filler metal by running a brazing rod along the crack or the joint. 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.
  7. Remove the flux after the filler material has solidified by dipping the part or pouring hot water on the repair. 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.
  8. Polish the area with an emery cloth after the metal has cooled completely.
  9. Coat the area with a rust-resistant coating if you are not immediately finished with the area.
Aluminum brazing use to repair cracks, holes, leaks, rivets, broken ears, threads, or fabricate aluminum, cast aluminum, and cast iron quickly, easily, and stronger than new. It’s not hard at all.

Aluminum Braze Instructions

Start by making sure that you have a safe environment to braze aluminum. This includes proper ventilation and a welding helmet. Next, purchase a small piece of carbon steel pipe.

Place the pipe between 2 fire bricks, laid about 3/4″ from each other. Get your oxyacetylene torch and set it to neutral

Start on the side of the steel pipe that is most comfortable for you (e.g; right-handed people start on the right side). Use the torch to melt off a piece of the filler rod onto the end of the pipe.

Note: After placing an initial amount of melted rod on the end of the steel pipe, use the molten metal itself to melt more of the rod. Do not use the torch flame.  If you see white smoke rising from the molten metal, it means that you may get a poor weld

If you want to cool the pipe and try again, pick up with a tool and place in the water a process called quenching a weld (water will weaken a weld, but for practice it is fine).

Aluminum Brazing Filler Metals

Commercial brazing filler metals for aluminum alloys are aluminum bases. These filler metals are available as wire or shim stock.

A convenient method of preplacing filler metal is by using a brazing sheet (an aluminum alloy base metal coated on one or both sides). Heat treatable or core alloys composed mainly of manganese or magnesium are also used.

A third method of applying brazing filler metal is to use a paste mixture of flux and filler metal powder. Common aluminum brazing metals contain silicon as the melting point depressant with or without additions of zinc, copper, and magnesium.

Aluminum Brazing Flux

Aluminum braze flux is required in all-aluminum brazing operations.

Aluminum brazing fluxes consist of various combinations of fluorides and chlorides and are supplied as a dry powder. For torch and furnace brazing, the flux is mixed with water to make a paste. This paste is brushed, sprayed, dipped, or flowed onto the entire area of the joint and brazing filler metal.

Torch and furnace brazing fluxes are quite active, may severely attack thin aluminum, and must be used with care. In dip brazing, the bath consists of molten flux. Less active fluxes can be used in this application and thin components can be safely brazed.

Braze Aluminum Welding Basics

The process of brazing refers to the use of gas-generated heat (800 degrees F), and an iron-free filler such as aluminum to join different metals. The aluminum itself can also be used to replace a part of another metal that might have cracked or fallen off.

  • Cost of Equipment: No argon gas, wire spool, gloves, shield, or electricity required.
  • Portability: Stores easily, along with small torch.
  • Skills Needed: Simple instructions virtually anyone can use. No flux, chemicals, or special cleaners required. 100% guaranteed.
  • Danger: No high voltage electricity used.
  • Oily Aluminum: Heli-arc boils aluminum and any impurities below the surface must be brought to the top and cleaned off.
  • Thin Aluminum: Melts 500 degrees before aluminum.
  • Different Alloys: Works with any alloy of aluminum or cast aluminum.
  • Time Involved: Makes many repairs much quicker than conventional methods.
  • Filling Holes: Instantly fills any size hole for threads much stronger than the original threads.
  • Versatility: One product fill cracks or holes, rebuilds ears, seals leaks, or permanently bonds flat pieces.

Heat sources include a propane or MAPP gas, a turbo tip, or oxy-acetylene torch, and special material.

Advantages Of Brazing Over Welding

Many new and used parts can be repaired with braze aluminum and be made stronger than the original form. Examples include:

  • Aluminum heads
  • Cast iron heads
  • A/C lines
  • Timing covers manifolds
  • Fuel tanks
  • Wheels
  • Aluminum Boats etc.

Brazing is a group of welding processes in which materials are joined by heating to a suitable temperature and by using a filler metal with a melting point above 840°F (449°C), but below that of the base metal.

The filler metal is distributed to the closely fitted surfaces of the joint by capillary action. The various brazing processes are described below.