When connecting copper to steel, what is the recommended brazing filler alloy?

When connecting copper to steel, the choice of brazing filler alloy is crucial for ensuring a strong and durable joint. A 15 percent silver alloy is recommended because it offers a good balance of melting point, flow characteristics, and bond strength between the two dissimilar metals.

Silver-containing brazing alloys have superior wetting properties, which allows them to flow into and fill the joint effectively. This is particularly important when joining metals with different thermal expansion characteristics, as is the case with copper and steel. The 15 percent silver alloy provides enough silver content to enhance the joint strength and create resistance against corrosion and thermal fatigue.

Other silver alloys with lower percentages, such as 10 percent or 5 percent, may not perform as well due to insufficient mechanical strength and corrosion resistance in the joint. Meanwhile, a 25 percent silver alloy, while it has high strength, can be more expensive and may not be necessary for most applications where 15 percent is adequate. Therefore, the 15 percent silver alloy strikes a favorable compromise for achieving reliability and effectiveness in the brazing process between copper and steel.