Choosing the Right Braze Alloy

Braze Alloy Characteristics and Applications

Selection Considerations for Brazing Alloys

Use an alloy that melts at a temperature at least 100 F below the point at which the two materials being brazed are effected. This definitely includes phase changes in steels leading to embrittlement.

The alloy must be able to wet the two materials or the material(s) must be treated to make it (them) wettable.

For wide joints it is best to use a viscous brazing alloy.

Cadmium and Zinc fume and can seriously contaminate brazing furnaces

Mechanical Strength Of Braze Joints

If brazing is done reasonably well with joint thickness in the range of 0.003” to 0.005” then it is fairly safe to assume the following strengths.

Tensile strength: 30,000 psi.

Shearing strength: 15,000 psi.

With proper material preparation and good techniques strengths somewhere between double and triple these figures are possible.

Three Most Popular Choices For Brazing Carbide Saw Tips

56% Silver with Tin – Cadmium free

• This is popular because it is low temp and seems to be easiest to use.

• It works very well in gentle applications such as cutting widow blind slats in clear wood

• It can also work well in applications with really big tips such as slasher tips

• Of the three alloys it has the weakest bond and least impact protection

50% Silver- cadmium free – (often referred to simply as ‘Cad Free’) middle for temperature range and performance

New standard since health regulations on cadmium got tightened so much

49% Silver with Manganese - Cadmium free

• It is a bit harder to use than the others because it requires more heat and has a sluggish flow.

• Pretinned tips have a rough surface

• The performance is exceptional good especially in impact situations with smaller tips. In Weyerhaeuser tests it showed about 40% better on tip loss and break age than the standard 50% Cadmium free and about 100% better than 56% with Tin on tip loss and breakage

Most Common Alloys for Brazing Carbide

                                                  Solidus   Liquidus

BAg-3        50% with Cadmium    1170    -    1270                                      

BAg-22      High Impact                1260    -    1290                 

BAg-24      50% Cadmium free     1220    -    1305                                  

Bag-8         56% with tin                1145    -    1205

All Silver Brazing Alloys We Offer

BAg Classifications (‘B’ for Brazing and ‘Ag’ from the chemical symbol for Silver)

Brazing filler metals of the BAg classifications are used for joining most ferrous and nonferrous metals, except aluminum and magnesium. These filler metals have good brazing properties and are suitable for preplacement in the joint, or for manual feeding into the joint. Although lap joints are generally used, butt joints may be used if requirements are less stringent.

Joint clearances of 0.00 1 to 0.005 in. (0.025 to 0.13 mm) are recommended for proper capillary action. Flux is generally required, however, on most metals. When furnace brazing in a protective atmosphere, flux is generally not required. If filler metals containing zinc or cadmium are used in a protective atmosphere furnace, the zinc or cadmium is vaporized changing chemical composition as well as the solidus and liquidus. Therefore, filler metals free of cadmium or zinc are recommended for furnace brazing in a protective atmosphere.

BAg-1 brazing filler metal has the lowest brazing temperature range of the BAg filler metals. It also flows most freely into narrow clearance capillary joints. Its narrow melting range is suitable for rapid or slow methods of heating. This filler metal contains cadmium. The special precautions of the warning label in 11.4 should be followed. BAg-1 is more economical (less silver) than BAg-la.

BAg-la brazing filler metal has properties similar to BAg-l. BAg-1a has a narrower melting range than BAg-l making it slightly more free-flowing. It also has a higher silver plus copper: zinc plus cadmium ratio resulting in a slight increase in its resistance to corrosion in chlorine, sulfur, and steam environments. Either composition may be used where low-temperature, free-flowing filler metals are desired. This filler metal contains cadmium. The special precautions of the warning label in 17.4 should be followed.

BAg-2 brazing filler metal, like BAg-1, is free-flowing and suited for general-purpose work. Its broader melting range is helpful where clearances are wide or are not uniform. Unless heating is rapid, care must be taken that the lower melting constituents do not separate out by liquation. This filler metal contains cadmium, and the special precautions of the warning label in 11.4, should be followed.

BAg-2a brazing filler metal is similar to BAg-2, but is more economical than BAg-2, since it contains five percent less silver. This filler metal contains cadmium. The special precautions of the warning label in 17.4 should be followed.

BAg-3 brazing filler metal is a modification of BAg-1 a, i.e., nickel is added. It has good corrosion resistance in marine environment and caustic media. When used on stainless steel, it will inhibit crevice (interface) corrosion. Because its nickel content improves wettability on tungsten carbide tool tips, the largest use is to braze carbide tool assemblies. Melting range and low fluidity make BAg-3 suitable for forming larger fillets or filling wide joint clearances. This filler metal contains cadmium. The special precautions of the warning label in 17.4 should be followed.

BAg-4 brazing filler metal, like BAg-3, is used extensively for carbide tip brazing, but flows less freely than BAg-3. This filler metal does not contain cadmium.

BAg-5 and -6 brazing filler metals are used especially for brazing in the electrical industry. They are also used, along with BAg-7 and -24, in the dairy and food industries where the use of cadmium-containing filler metals is prohibited. BAg-5 is an excellent filler metal for brazing brass parts (such as in ships piping, band instruments, lamps, etc.). Since BAg-6 has a broad melting range and is not so free-flowing as BAg-1 and -2, it is a better filler metal for filling wide joint clearances or forming large fillets.

BAg-7 brazing filler metal, a cadmium-free substitute for BAg-l, is low-melting with good flow and wetting properties. Typical applications include the following:

(1) For food equipment where cadmium must be avoided

(2) To minimize stress corrosion cracking of nickel or nickel-base alloys at low brazing temperatures

(3) Where the white color will improve color match with the base metal

BAg-8 brazing filler metal is suitable, for furnace brazing in a protective atmosphere without the use of a flux, as well as for brazing procedures requiring a flux. It is usually used on copper or copper alloys. When molten, BAg-8 is very fluid and may flow out over the workpiece surfaces during some furnace brazing applications. It can also be used on stainless steel, nickel-base alloys and carbon steel, although its wetting action on these metals is slow. Higher brazing temperatures will improve flow and wetting.

BAg-8a brazing filler metal is used for brazing in a protective atmosphere and is advantageous when brazing precipitation-hardening and other stainless steels in the 1400 to 1600° F (760 to 870° C) range. The lithium content serves to promote wetting and to increase the flow of the filler metal on difficult-to-braze metals and alloys. Lithium is particularly helpful on base metals containing minor amounts of titanium or aluminum.

BAg-9 and -10 filler metals are used particularly for joining sterling silver. These filler metals have different brazing temperatures and so can be used for step brazing of successive joints. The color, after brazing, approximates the color of sterling silver.

BAg-13 brazing filler metal is used for service temperatures up to 700° F (370° C). Its low zinc content makes it suitable for furnace brazing.

BAg-13a brazing filler metal is similar to BAg-13, except that it contains no zinc, which is advantageous where volatilization is objectionable in furnace brazing.

BAg-18 brazing filler metal is similar to BAg-8 in its applications. Its tin content helps promote wetting on stainless steel, nickel-base alloys, and carbon steel. BAg-18 has a lower liquidus than BAg-8 and is used in step brazing applications where fluxless brazing is important.

BAg-19 brazing filler metal is used for the same applications as BAg-8a. BAg-l9 is often used in higher brazing temperature applications where precipitation-hardening heat treatment and brazing are combined.

BAg-20 brazing filler metal possesses good wetting and flow characteristics, and has a brazing temperature range higher than the popular Ag-Cu-Zn-Cd compositions. Due to its good brazing properties, freedom from cadmium, and more economical silver content, new uses for this filler metal are being developed.

BAg-21 brazing filler metal is used in brazing AIS1 300 and 400 series stainless steels, as well as the precipitation hardening nickel and steel alloys. BAg-21 is particularly suited to furnace brazing in a protective atmosphere because of the absence of zinc and cadmium. It does not require a flux for proper brazing when the temperature is 1850 oF (1010 oC) or above. It requires a high brazing temperature, and it flows in a sluggish manner. The nickel-rich layer (halo) formed along the fillet edges during melting and flow of the filler metal prevent crevice (interface) corrosion of stainless steels. This is particularly important for the 400 series steels that do not contain nickel and are, therefore, more susceptible to crevice (interface) corrosion. BAg-21 has been used for brazing stainless steel vanes of aircraft gas turbine engines.

BAg-22 is a low-temperature, cadmium-free filler metal with improved brazing characteristics over BAg-3, particularly in brazing tungsten carbide tools.

BAg-23 is a high-temperature, free-flowing filler metal usable both for torch brazing and furnace brazing in a protective atmosphere. This filler metal is mainly used in brazing stainless steel, nickel-base and cobalt-base alloys for high-temperature applications. If this filler metal is used in a hard vacuum atmosphere, a loss of manganese will occur due to its high vapor pressure. Thus, a soft vacuum, produced by inert gas back filling a hard vacuum, is desirable when brazing with this filler metal.

BAg-24 brazing filter metal is low-melting, free-flowing, cadmium-free, and suitable for use in joining "300" series stainless steels (particularly food-handling equipment and hospital utensils), and small tungsten carbide inserts in cutting tools.

BAg-26 brazing filler metal is a low-silver, cadmium-free filler metal suitable for carbide and stainless steel brazing. The filler metal is characterized by its low brazing temperature, good wetting and flow, and moderate-strength joints when used with these base metals.

BAg-27 brazing filler metal is similar to BAg-2 but has lower silver and is somewhat more subject to liquation, due to a wider melting range. This filler metal contains cadmium. The special precautions of the warning label in 17.4 should be followed.

BAg-28 brazing filler metal has a lower brazing temperature with a narrower melting range than other cadmium-free classifications with similar silver content. BAg-28 also has free-flowing characteristics.

BAg-33 brazing filler metal was developed to minimize brazing temperature for filler metal containing 25 percent silver. It has a lower liquidus and, therefore, a narrower melting range than BAg-27. Its higher total zinc plus cadmium content may require more care during brazing. The special precautions of the warning label in 17.4 should be followed.

BAg-34 brazing filler metal is a cadmium-free filler metal with free-flowing characteristics. The brazing temperature range is similar to that of BAg-2 and BAg-2a, making it an ideal substitute for these filler metals.

BAg-35 is a cadmium-free filler metal used for brazing ferrous and nonferrous base metals. It is a moderate temperature filler metal frequently used for production brazing applications.

BAg-36 is a low temperature, cadmium-free, filler metal suitable for brazing ferrous and nonferrous base metals. The lower brazing temperature makes it a useful replacement for several of the cadmium-bearing classifications.