Liquid metal’s low melting point

Fusible alloys’ low melting point makes them useful in a wide variety of applications

The melting point of aluminum is 1,220 degrees Fahrenheit. Carbon steel melts somewhere between 2,600 and 2,800 degrees Fahrenheit, and the temperature needs to rise all the way up to 6,150 degrees Fahrenheit to melt tungsten. Specialized furnaces are needed to achieve these temperatures, so when an alloy melts in boiling water or begins to liquefy at room temperature, it seems like magic.

Alloys with melting points below 450 degrees Fahrenheit are referred to as low-melting or fusible alloys. The most widely used fusible alloys contain high percentages of bismuth, combined with lead, tin, cadmium, indium and other metals. Bismuth has an impact on the melting point, as well as the growth and shrinkage characteristics of the alloys. Many of the bismuth-based alloys melt below the boiling point of water, and some of them melt below 150 degrees Fahrenheit.

Fusible alloys are stable and can either be classified as eutectic or non-eutectic. Eutectic alloys have the lowest melting point possible—the temperature at which the material is solid is equal to the temperature at which the material is liquid. Non-eutectic alloys begin to melt at one temperature and then enter a slushy state before they fully melt at a higher temperature. Low-melting alloys are available in a variety of forms: cake, ingot, bar, shot, wire, stick, strip and custom shapes.

Many of the low-melting alloys have good thermal conductivity, can be remelted and reused, and have combinations of elements that cause them to expand during solidification without contracting during cooling. These characteristics make fusible alloys versatile, allowing them to be used in a diverse amount of applications, including common everyday items such as fire sprinklers and pop-up turkey timers. In both cases, the alloys begin to melt at a specific temperature, triggering a mechanism that either opens a valve to let water flow or pops up a button to indicate the turkey is done.

Manufacturers can use fusible alloys to solve problems and save time and money. For instance, using a fusible alloy when bending thin-walled tubing can help prevent kinks or wrinkles. Tubes are lubricated, filled with a low-melting alloy and cooled so that the alloy solidifies inside, supporting the tube’s wall. Once bent, the tube is reheated to liquefy and remove the fusible alloy.

Along similar lines, fusible alloys can be used for manufacturing complex aerospace components that have internal cavities or as cores for forming fiberglass laminate or plastic parts. Fusible alloys also can be used to hold delicate or irregular-shaped work pieces, such as optical components, during manufacturing operations. After the component is polished or machined, the alloy is melted off and reused. Some fusible alloys are capable of sealing glass to glass or glass to ceramic in electronic devices, vacuum systems and laboratory equipment. They can even be used as master alloys to add lead, bismuth or tin to aluminum and other metals.

In addition to the common low-melting alloys with known temperature ranges, others can be formulated to meet specific temperature requirements. Inquire with a trusted alloy manufacturer for metallurgical assistance and technical support regarding standard and custom applications.