Silver

Silver brazing alloys and the fluxes that make them work, for copper, brass, bronze, steel and dissimilar-metal joints.

Choosing the alloy

• BCuP-5, 15% silver. A phosphorus-bearing copper alloy. On copper-to-copper joints the phosphorus acts as its own flux, which is why this alloy dominates refrigeration and plumbing work. Critical limitation: never use phosphorus-bearing alloys on ferrous metals or nickel alloys - the joint forms brittle phosphides and fails.
• BAg-5, 45% silver. Flows at a lower temperature, wets a far wider range of base metals, and gives a stronger, more ductile joint. The alloy for steel, stainless, brass and mixed-metal work. More expensive per stick and usually cheaper per job, because it flows where the cheaper alloy will not.

Cadmium-free, and that matters

The alloys stocked here are cadmium-free. Cadmium-bearing brazing filler releases acutely toxic fume at brazing temperature, and no realistic shop ventilation makes it a sensible choice today.

Flux is not optional

Flux dissolves the oxide layer so the filler can wet the joint. Without it - on anything other than a self-fluxing copper-to-copper joint - the alloy balls up and sits on the surface instead of drawing in.

Match the flux temperature range to the alloy. High-temp paste for the silver alloys; low-temp for lower-flowing work. Using the wrong one means the flux burns off before the filler flows, or never activates at all.

The gap does the work

Brazing joins by capillary action. Too tight and the filler cannot draw in; too loose and it cannot bridge. Get the gap right and a brazed joint is frequently stronger than the base metal beside it.

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