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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.



From practical view, low melting alloys can be divided up into:

  • Mercury-containing alloys
  • Only alkali metal-containing alloys
  • Gallium-containing alloys (but neither alkali metal nor mercury)
  • Only bismuth, lead, tin, cadmium, zinc, indium and sometimes thallium-containing alloys
  • Other alloys (rarely used)

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.

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.[1]

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.[2]

Low melting alloys and metallic elementsEdit

Well known alloysEdit

Alloy Melting point Eutectic? Bismuth Lead Tin Indium Cadmium Thallium Gallium Antimony
Rose's metal 98 °C (208 °F) no 50% 25% 25%
Cerrosafe 74 °C (165 °F) no 42.5% 37.7% 11.3% 8.5%
Wood's metal 70 °C (158 °F) yes 50% 26.7% 13.3% 10%
Field's metal 62 °C (144 °F) yes 32.5% 16.5% 51%
Cerrolow 136 58 °C (136 °F) yes 49% 18% 12% 21%
Cerrolow 117 47.2 °C (117 °F) yes 44.7% 22.6% 8.3% 19.1% 5.3%
Bi-Pb-Sn-Cd-In-Tl 41.5 °C (107 °F) yes 40.3% 22.2% 10.7% 17.7% 8.1% 1.1%
Galinstan −19 °C (−2 °F) yes <1.5% 9.5-10.5% 21-22% 68-69% <1.5%

Other alloysEdit

(see also solder alloys)

Low melting alloys and metallic elements
Composition in weight-percent Melting point Eutectic? Name or remark
Cs 73.71, K 22.14, Na 4.14 [3] −78.2 °C yes
Hg 91.5, Tl 8.5 −58 °C yes used in low readings thermometers
Hg 100 −38.8 °C (yes)
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 (yes)
Ga 100 29.8 °C (yes)
Rb 100 39.30 °C (yes)
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.[4]
Bi 49, Pb 18, In 21, Sn 12 58 °C ChipQuik desoldering alloy.[5] Cerrolow 136. Slightly expands on cooling, later shows slight shrinkage in couple hours afterwards. Used as a solder in low-temperature physics.[4] Lens Alloy 136, used for mounting lenses and other optical components for grinding.[6] Used for mounting small delicate oddly-shaped components for machining.
Bi 32.5, In 51.0, Sn 16.5 60.5 °C yes Field's metal
K 100 63.5 °C (yes)
Bi 50, Pb 26.7, Sn 13.3, Cd 10 70 °C yes Cerrobend. Used in low-temperature physics as a solder.[4]
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 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,[7] also called Onions' Fusible Alloy[8]
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.[9]
Bi 50.0, Pb 31.2, Sn 18.8 97 °C no Newton's metal
Na 100 97.8 (yes)
Bi 50.0, Pb 28.0, Sn 22.0 94–98 °C no Rose's metal
Bi 56.5, Pb 43.5 125 °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.[9] Low-temperature eutectic solder with high strength.[10] Particularly strong, very brittle.[11] 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.[12] Sensitive to shear rate. Good for electronics. Used in thermoelectric applications. Good thermal fatigue performance. Yield strength 7,119 psi (49.08 MPa), tensile strength 5,400 psi (37 MPa).[13]
Bi 57, Sn 43[14] 139 yes
In 100 157 °C (yes) 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.[15] 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.[4]
Li 100 180.5 °C (yes)
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.[10] 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.[16]

Yield strength 3,950 psi (27.2 MPa), tensile strength 4,442 psi (30.63 MPa).[17]

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.[18] UNS#: L91090
Sn 92.0, Zn 8.0 199 °C no Tin foil
Sn 100 231.9 °C (yes) Sn99. Good strength, non-dulling. Use in food processing equipment, wire tinning, and alloying.[19] Susceptible to tin pest.
Bi 100 271.5 °C (yes) Used as a non-superconducting solder in low-temperature physics. Does not wet metals well, forms a mechanically weak joint.[4]
Tl 100 304 °C (yes)
Cd 100 321.1 °C (yes)
Pb 100 327.5 °C (yes)
Zn 100 419.5 °C (yes) For soldering aluminium. Good wettability of aluminium, relatively good corrosion resistance.[20]

See alsoEdit


  1. ^   Chisholm, Hugh, ed. (1911). "Fusible Metal" . Encyclopædia Britannica (11th ed.). Cambridge University Press.
  2. ^
  3. ^ Oshe, Ed. R.W., "Handbook of Thermodynamic and Transport Properties of Alkali Metals", Oxford. UK, Blackwell Scientific Publications Ltd, 1985, p. 987
  4. ^ a b c d e Guy Kendall White; Philip J. Meeson (2002). Experimental techniques in low-temperature physics. Clarendon. pp. 207–. ISBN 978-0-19-851428-2. Retrieved 14 May 2011.
  5. ^ Johnson Manufacturing Co, MSDS for Chip Quik Alloy w/Lead. Retrieved on February 6, 2015.
  6. ^
  7. ^ François Cardarelli (2008-03-19). Materials Handbook: A Concise Desktop Reference. Springer Science & Business Media. pp. 210–. ISBN 978-1-84628-669-8.
  8. ^ Jenson, W.B. "Ask the Historian - Onion's fusible alloy", J. Chem. Educ., 2010, 87, 1050-1051.
  9. ^ a b John H. Lau (1991). Solder joint reliability: theory and applications. Springer. p. 178. ISBN 0-442-00260-2.
  10. ^ a b Ray P. Prasad (1997). Surface mount technology: principles and practice. Springer. p. 385. ISBN 0-412-12921-3.
  11. ^ Charles A. Harper (2003). Electronic materials and processes. McGraw-Hill Professional. pp. 5–8. ISBN 0-07-140214-4.
  12. ^ Karl J. Puttlitz, Kathleen A. Stalter (2004). Handbook of lead-free solder technology for microelectronic assemblies. CRC Press. ISBN 0-8247-4870-0.
  13. ^ Qualitek. Technical Data Sheet Sn42/Bi58 Solid Wire Rev.A 03/14 (PDF). Retrieved 3 May 2018.
  14. ^ See phase diagram for the tin-bismuth binary system here:
  15. ^ T.Q. Collier (May–Jun 2008). "Choosing the best bumb for the buck". Advanced Packaging. 17 (4): 24. ISSN 1065-0555.
  16. ^ msl747.PDF. (PDF). Retrieved 2010-07-06.
  17. ^ Qualitek. Technical Data Sheet Sn42/Bi58 Solid Wire Rev.A 03/14 (PDF). Retrieved 3 May 2018.
  18. ^ "Tin-Zinc Solders for Aluminium to Aluminium and Copper". Kapp Alloy & Wire, Inc. Retrieved 23 October 2012.
  19. ^ Madara Ogot, Gul Okudan-Kremer (2004). Engineering design: a practical guide. Trafford Publishing. p. 445. ISBN 1-4120-3850-2.
  20. ^ Howard H. Manko (8 February 2001). Solders and soldering: materials, design, production, and analysis for reliable bonding. McGraw-Hill Professional. pp. 396–. ISBN 978-0-07-134417-3. Retrieved 17 April 2011.

Further readingEdit

  • "ASTM B774—Standard Specification for Low Melting Point Alloys". ASTM International. 1900. doi:10.1520/B0774.
  • Weast, R.C., "CRC Handbook of Chemistry and Physics", 55th ed, CRC Press, Cleveland, 1974, p. F-22

External linksEdit