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Why is bismuth useful in low-melting fusible alloys?

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A labeled periodic table element box for bismuth shows atomic number 83, symbol Bi, atomic weight 208.9804, electron configuration, and properties including solid state, rhombohedral crystal structure, and weakly acidic oxides. — bismuth Properties of bismuth.

Bismuth is a valuable component in low-melting fusible alloys because it imparts its own special properties to these mixtures, specifically a low melting point and the tendency to expand upon solidification.1

Because these alloys can be formulated to melt at specific, relatively low temperatures—often between 90–100 °C (194–212 °F)—they are highly effective for applications requiring heat sensitivity. Their ability to melt reliably when exposed to heat makes them essential for safety equipment, such as automatic fire-detection sprinklers and electrical fuses designed to interrupt circuits when current becomes excessive. Additionally, the expansion of bismuth during solidification helps ensure that these alloys produce neat, clean castings.21