Blue Demon Triple Play Low Temp Aluminum-Zinc Brazing Rod 1/8" x 18" 1 Lb Tube #BDTP12501T

This very thin layer of aluminum oxide is what must be removed. When you puncture this layer it breaks up into a fine powder and floats to the surface of the puddle. You can actually see it appear on the surface. Draw the abrading tool through the puddle several times to remove oxides and promote fusion with the base metal. A few strokes are usually enough-.004 to .005 deep gives maximum strength. Get rid of the oxides' barrier by going down through the molten coating and abrading the oxides away. A thin layer of insoluble oxide begins to form on the surface even before you lay the brush down.

As the base metal is heated, oxides form even more quickly but become stretched under tension. The oxide must be removed or penetration will not occur. Localizing of heat techniques can also be utilized to improve the shape of the fillets.

If you are joining two pieces of different sizes you will want to apply most of the heat to the larger piece so that they both arrive at the working temperature at about the same time. A short stub can be fused to a new rod with the torch flame if you control temperatures carefully. The repair will harden in a few seconds and can be worked immediately. Do not immerse in water to speed the cooling.

The material will be quite hard. It will grind, machine, drill, tap, and paint much like mild steel. Yet when fused with aluminum it is not brittle unless it is cooled too quickly. For most jobs, an LP gas torch is enough. Make sure to reach 730°F. Use the general-purpose tip. For heavy pieces, you will need a fuel-oxygen torch. If so, use a large tip with a neutral flame to spread the heat evenly. Only heat with the middle or outer cones of the flame.