Amorphous brazing foil

An amorphous brazing foil (ABF) is a form of eutectic amorphous metal that serves as a filler metal in brazing operations. Various transition metals such as nickel, iron, and copper blend with metalloids like silicon, boron, and phosphorus to form ABFs. By carefully adjusting the amount of these metalloids to reach or get close to the eutectic point, these alloys can quickly harden into an ductile amorphous foil. This process allows the ABF to effectively bond materials in the brazing process, providing a strong and seamless joint.

Production
You can produce an amorphous metal by rapidly cooling the liquid alloy to prevent the formation of a crystal structure. Melt spinning, a traditional method, produces a 0.5–125 mm wide strip with a thickness of 20–50 m. Cutting, stamping, etching, or other methods can transform the cooled metal into parts or preforms.

Properties
A key characteristic of amorphous brazing foils (ABFs) is their relatively low melting points, which typically range from 830 to 1200°C. This characteristic is critical for their use as brazing filler metals. Due to their ductility and flexibility, ABFs present a viable alternative to filler metals in paste or powder form. This substitution offers notable advantages, such as the elimination of soot formation, a common drawback associated with residual organic solvents in paste-based fillers. ABFs also help stop surface oxides from forming, which is a problem that often happens with gas-atomized powder fillers. This makes the brazed joint better and stronger.

Usage
Brazing, a metallurgy process that joins two pieces of metal by melting and cooling a third "fill metal" at their joint, typically uses amorphous brazing foils. Preforms enhance the industrial scale capabilities of ABFs, enabling machine assembly.