Fusible alloy
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. Fusible alloys in this sense are used for solder.
Introduction
From a practical view, low-melting alloys can be divided into the following categories:- Mercury-containing alloys
- Only alkali metal-containing alloys
- Gallium-containing alloys
- Only bismuth, lead, tin, cadmium, zinc, indium, and sometimes thallium-containing alloys
- Other alloys
Applications
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.Such alloys are used for making the fusible plugs inserted in the furnace crowns of steam boilers, as a safeguard in the event of the water level being allowed to fall too low. When this happens the plug, being no longer covered with water, is heated to such a temperature that it melts and allows the contents of the boiler to escape into the furnace. In automatic fire sprinklers the orifices of each sprinkler is closed with a plug that is held in place by fusible metal, which melts and liberates the water when, owing to an outbreak of fire in the room, the temperature rises above a predetermined limit.
Bismuth on cooling expands by about 3.3% by volume. Alloys with at least half of bismuth display this property too. This can be used for mounting of small parts, e.g. for machining, as they will be tightly held.
Low melting alloys and metallic elements
Well known alloys
Other alloys
| Composition in weight-percent | Melting point | Eutectic? | Name or remark |
| Cs 73.71, K 22.14, Na 4.14 | −78.2 °C | yes | - |
| Hg 91.5, Tl 8.5 | −58 °C | yes | used in low readings thermometers |
| Hg 100 | −38.8 °C | - | |
| Cs 77.0, K 23.0 | −37.5 °C | - | |
| K 76.7, Na 23.3 | −12.7 °C | yes | - |
| K 78.0, Na 22.0 | −11 °C | no | NaK |
| Ga 61, In 25, Sn 13, Zn 1 | 8.5 °C | yes | - |
| Ga 62.5, In 21.5, Sn 16.0 | 10.7 °C | yes | galinstan alloy |
| Ga 69.8, In 17.6, Sn 12.5 | 10.8 °C | no | galinstan alloy |
| Ga 68.5, In 21.5, Sn 10 | 11 °C | no | galinstan alloy |
| Ga 75.5, In 24.5 | 15.7 °C | yes | - |
| Cs 100 | 28.6 °C | - | |
| Ga 100 | 29.8 °C | - | |
| Rb 100 | 39.30 °C | - | |
| Bi 40.3, Pb 22.2, In 17.2, Sn 10.7, Cd 8.1, Tl 1.1 | 41.5 °C | yes | - |
| Bi 40.63, Pb 22.1, In 18.1, Sn 10.65, Cd 8.2 | 46.5 °C | - | |
| Bi 44.7, Pb 22.6, In 19.1, Cd 5.3, Sn 8.3 | 47 °C | yes | Cerrolow 117. Used as a solder in low-temperature physics. |
| Bi 49, Pb 18, In 21, Sn 12 | 58 °C | ChipQuik desoldering alloy. Cerrolow 136. Slightly expands on cooling, later shows slight shrinkage in couple hours afterwards. Used as a solder in low-temperature physics. Lens Alloy 136, used for mounting lenses and other optical components for grinding. Used for mounting small delicate oddly-shaped components for machining. | |
| Bi 32.5, In 51.0, Sn 16.5 | 60.5 °C | - | |
| Bi 50, Pb 26.7, Sn 13.3, Cd 10 | 70 °C | yes | Cerrobend. Used in low-temperature physics as a solder. |
| Bi 49.5, Pb 27.3, Sn 13.1, Cd 10.1 | 70.9 °C | yes | Lipowitz's alloy |
| Bi 50.0, Pb 25.0, Sn 12.5, Cd 12.5 | 71 °C | yes | Wood's metal |
| In 66.3, Bi 33.7 | 72 °C | yes | - |
| Bi 42.5, Pb 37.7, Sn 11.3, Cd 8.5 | 74 °C | no | Cerrosafe |
| Bi 56, Sn 30, In 14 | 79-91 °C | no | ChipQuik desoldering alloy, lead-free |
| Bi 50, Pb 30, Sn 20, Impurities | 92 °C | no | Lichtenberg's alloy, also called Onions' Fusible Alloy |
| Bi 52.5, Pb 32.0, Sn 15.5 | 95 °C | yes | - |
| Bi 52, Pb 32.0, Sn 16 | 96 °C | yes | Bi52. Good fatigue resistance combined with low melting point. Reasonable shear strength and fatigue properties. Combination with lead-tin solder may dramatically lower melting point and lead to joint failure. |
| Bi 50.0, Pb 31.2, Sn 18.8 | 97 °C | no | Newton's metal |
| Na 100 | 97.8 | - | |
| Bi 50.0, Pb 28.0, Sn 22.0 | 94–98 °C | no | Rose's metal |
| Bi 55.5, Pb 44.5 | 125 °C | yes | - |
| Bi 58, Sn 42 | 138 °C | yes | Bi58. Reasonable shear strength and fatigue properties. Combination with lead-tin solder may dramatically lower melting point and lead to joint failure. Low-temperature eutectic solder with high strength. Particularly strong, very brittle. Used extensively in through-hole technology assemblies in IBM mainframe computers where low soldering temperature was required. Can be used as a coating of copper particles to facilitate their bonding under pressure/heat and creating a conductive metallurgical joint. Sensitive to shear rate. Good for electronics. Used in thermoelectric applications. Good thermal fatigue performance. Yield strength, tensile strength. |
| Bi 57, Sn 43 | 139 | yes | - |
| In 100 | 157 °C | In99. Used for die attachment of some chips. More suitable for soldering gold, dissolution rate of gold is 17 times slower than in tin-based solders and up to 20% of gold can be tolerated without significant embrittlement. Good performance at cryogenic temperatures. Wets many surfaces incl. quartz, glass, and many ceramics. Deforms indefinitely under load. Does not become brittle even at low temperatures. Used as a solder in low-temperature physics, will bond to aluminium. Can be used for soldering to thin metal films or glass with an ultrasonic soldering iron. | |
| Li 100 | 180.5 °C | - | |
| Sn 62.3, Pb 37.7 | 183 °C | yes | - |
| Sn 63.0, Pb 37.0 | 183 °C | no | Eutectic solder. Sn63, ASTM63A, ASTM63B. Common in electronics; exceptional tinning and wetting properties, also good for stainless steel. One of the most common solders. Low cost and good bonding properties. Used in both SMT and through-hole electronics. Rapidly dissolves gold and silver, not recommended for those. Sn60Pb40 is slightly cheaper and is often used instead for cost reasons, as the melting point difference is insignificant in practice. On slow cooling gives slightly brighter joints than Sn60Pb40. Yield strength, tensile strength. |
| Sn 91.0, Zn 9.0 | 198 °C | yes | KappAloy9 Designed specifically for Aluminum-to-Aluminum and Aluminum-to-Copper soldering. It has good corrosion resistance and tensile strength. Lies between soft solder and silver brazing alloys, thereby avoiding damage to critical electronics and substrate deformation and segregation. Best solder for Aluminum wire to Copper busses or Copper wire to Aluminum busses or contacts. UNS#: L91090 |
| Sn 92.0, Zn 8.0 | 199 °C | no | Tin foil |
| Sn 100 | 231.9 °C | Sn99. Good strength, non-dulling. Use in food processing equipment, wire tinning, and alloying. Susceptible to tin pest. | |
| Bi 100 | 271.5 °C | Used as a non-superconducting solder in low-temperature physics. Does not wet metals well, forms a mechanically weak joint. | |
| Tl 100 | 304 °C | - | |
| Cd 100 | 321.1 °C | - | |
| Pb 100 | 327.5 °C | - | |
| Zn 100 | 419.5 °C | For soldering aluminium. Good wettability of aluminium, relatively good corrosion resistance. |