Fusibility

Fusibility is the property of a material that describes how readily it can be fused, melted, or softened by heat. It involves the temperature at which fusion occurs and the behavior of the molten material, including viscosity and flow, which determine how easily it can join with another substance or be shaped by fusion. Fusibility is important in soldering, brazing, welding, glassmaking, and the use of fusible alloys in safety devices.

Fusibility is commonly characterized by a fusion temperature or softening point, and may be inferred from phase diagrams or measured with calorimetric techniques. Impurities, crystal structure, and microstructure strongly influence fusibility: small amounts of a low-melting-phase can reduce fusion temperature, while alloying can raise or lower it. Heating rate and pressure can also affect the effective fusibility, particularly for materials with polymorphic transitions.

Materials with low melting points, such as tin, lead, and certain solder alloys, are highly fusible, whereas refractory metals like tungsten and many ceramics exhibit low fusibility. In glass science, fusibility relates to softening and flow at high temperatures and is critical for glaze and frit development. Fusible alloys are deliberately engineered to melt at specified temperatures for use in fuses and temperature-sensing devices.

Understanding fusibility informs material selection and process design across electronics, metallurgy, glassmaking, and geology, affecting joining quality, processing control, and safety considerations.