A low melting point alloy might also be referred to as a fusible alloy. It is a metal alloy that can be easily fused, and as such can be melted at a low temperature. For an alloy to fit into this category its melting point would need to be below 183 °C, although they are usually lower than this. They are also commonly eutectic alloys, which means they melt at a single temperature like a pure metal. These alloys typically contain either indium or bismuth but can also be made up from tin, lead and cadmium.
Fusible, or low melting point alloys are also commonly good thermal conductors with high liquid fluidity and low vapour pressure. They have controlled thermal dimensional properties that mean they can be made with minimal solidification shrinkage. Bismuth, which is commonly used in fusible alloys, can expand 3.3% of volume when it changes from liquid to solid. As a result of this, alloys with over 55% of bismuth expand on solidification, whilst those with less than 48% contract.
Once a fusible alloy is melted it can be used as a coolant. They are stable under heating and unlike other coolants can give a high level of thermal conductivity, particularly if they are made with indium or sodium.