Metallurgy
of
Braze
Welding - Studies of bond between copper alloys and cast iron have shown three sources of forces that bind brazewelded joints.
Wetting is the first action needed to accomplish bonding. Following this,
1. One is the atomic forces between metals at their interfaces in close contact. In this case, atomic diffusion takes place between the brazing filler metal and the base metal in a narrow zone at the interface.
2. A second is alloying with arises from diffusion of the metals in a narrow zone at the interface. In other words, constituents of filler metal (e.g., Cu, Zn, Sn, etc.) diffuse into the base metal (e.g., cast iron) and correspondingly base metal constituents diffuse into the filler metal in a narrow zone at the interface between the copper brazing alloy and the base metal.
3. The third is intergranular penetration. In this case the brazing alloy may slightly penetrate the grain boundaries of the base metal and contribute to bond strength.
