A fusible alloy is a metal alloy capable of being easily fused, i.e. easily meltable, at relatively low temperatures. Fusible alloys are commonly, but not necessarily, eutectic alloys.
Sometimes the term "fusible alloy" is used to describe alloys with a melting point below 183 °C (361 °F; 456 K). Fusible alloys in this sense are used for solder.
Low-melting alloys can be divided into the following categories:
1. Mercury-containing alloys
2. Only alkali metal-containing alloys
3. Gallium-containing alloys (but neither alkali metal nor mercury)
4. Only bismuth, lead, tin, cadmium, zinc, indium, and sometimes thallium-containing alloys
5. Other alloys (rarely used)
6. Some reasonably well-known fusible alloys are Wood's metal, Field's metal, Rose metal, Galinstan, and NaK.
Melted fusible alloys can be used as coolants as they are stable under heating and can give much higher thermal conductivity than most other coolants; particularly with alloys made with a high thermal conductivity metal such as indium or sodium. Metals with low neutron cross-section are used for cooling nuclear reactors.