Fusible alloy

A metal alloy formulated to melt at a relatively low temperature. Fusible alloys serve in casting, joining, thermal control, and temporary support.

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Eutectic system: A mixture of components with a composition that melts and solidifies at one fixed temperature, lower than nearby compositions. Many fusible alloys exploit a eutectic composition to achieve a sharp, low melting point.
Lost-wax casting: A casting process in which a wax pattern is replaced by molten metal inside a refractory mold. Low-melting alloys can be cast into detailed parts with less heat than conventional casting metals.
Solder: A filler metal used to join components by melting it below the melting temperatures of the joined materials. Solder is defined by its joining role, while fusible alloy describes a broader low-melting material class.
Darcet's alloy: A low-melting alloy of bismuth, lead, and tin, named after the French chemist Jean Darcet. Its early use established a practical family of alloys designed to melt below boiling-water temperature.
Phase diagram: A graph showing which phases of a material are stable at different temperatures, pressures, and compositions. Phase diagrams identify compositions and temperatures where fusible alloys begin to melt.
Soldering: A joining process that melts a filler metal without melting the parts being joined. Fusible alloys can act as low-temperature filler metals for heat-sensitive assemblies.
Brazing: A joining process that melts filler metal above 450 °C while keeping the base materials solid. Brazing uses higher-temperature fillers than the low-melting alloys considered here.
Rose's metal: A bismuth-lead-tin alloy that melts at about 94 °C. This lead-containing formulation became a familiar example of an alloy melting below 100 °C.
Solidus: The boundary below which an alloy is entirely solid at a specified pressure and composition. It marks the lower edge of the melting interval in non-eutectic fusible alloys.
Thermal fuse: A safety device that interrupts an electrical circuit when excessive temperature melts or releases its element. A fusible alloy can provide the temperature-sensitive element that opens the circuit.