Indium Blog

Indium and Bismuth Alloys for Mechanical Uses (Fusible Alloys)

  • Bismuth
  • Indium
  • Indium Alloy

  • We tend to think of Indium Corporation as a “solder company”, but some of the alloys we offer are not used just for soldering (which is joining two surfaces with a filler metal, typically below 300° Celsius). Some of the non-joining or temporary-joining mechanical uses of our alloys are quite interesting. In this post I’d like to describe some uses of low temperature alloys that are not considered soldering applications, with the hope that this sparks your curiosity.

    1. Pipe Bending: If you have ever bent a pipe you will recall that an unsupported pipe will wrinkle and kink when it is formed. It is fairly common to fill a pipe with a low temperature alloy before bending to support the pipe from within. When the pipe is successfully bent, the low temperature alloy can be dipped into warm water to liquefy the alloy and remove it from the pipe.
    2. Blocking / Fixturing: A temporary mounting point is sometimes needed to hold a part while it is machined. Low temperature alloys can be cast onto a part and removed after processing with low heat, perhaps in the form of a heat gun or hot water.
    3. Compressible Thermal Interface: Some components do not need an actual solder joint to connect them thermally to a heat spreader or heat-sink. If the device and passive radiator are already mechanically coupled with a clamp, a piece of indium can proved thermal transfer. The material is not melted in a compression interface, so it is not a solder application.
    4. Thermal Fuses: As the name suggests, these lower melting point alloys turn to a liquid at specific temperatures, which make them great fuses. Imagine a plug for an oil pan made from an alloy that melts at 118°C. If the oil in the pan reaches 118°C (which may be a safety threshold), the alloy would melt and let the oil escape from the pan. It could also be used to trigger other events. Once popular uses for thermal fuses include turkey timers and sprinkler heads.
    5. Liquid at Operating Temperature: When selecting a liquid metal for use at room temperature, there are two categories: mercury and gallium/indium alloys. If the application calls for a liquid metal, and it is not compatible with gallium (uncoated aluminum for instance), AND the operational temperature will be sufficiently high, some of the fusible alloys may work for the application. I know this is a strange set of conditions, but we see a lot of strange applications!
    6. Low Temperature Casting: These alloys can be re-casted and very low temperatures, making them very easy to work with. In addition, most fusible alloys have interesting growth/shrinkage patterns.

    I am quite sure I barely scratched the surface with this list, since I didn’t even mention alloys that are liquid at room temperature. If you have other ideas for uses of fusible alloys, contact me at


    Authored by previous Indium Application Manager Jim Hisert