Filler Solidus and Liquidus: A Melting Range Is Not One Sharp Temperature

Retain both boundaries

THESSCO defines solidus as the start of alloy melting and liquidus as the condition at which the alloy is fully molten. The interval between them is its melting range. Primary reference: THESSCO brazing principles, page 2.

These boundaries identify states, not a universal linear relationship between temperature and liquid fraction. Retain the actual composition and applicable phase information if a partly molten condition matters to the proposed process.

Read an invented interval

Assume a fictional alloy has solidus 500°C and liquidus 600°C. At 480°C it is below the stated onset; at 620°C it is above the stated fully molten boundary. At 550°C it lies inside the defined melting interval.

Calling that midpoint exactly fifty percent liquid would add an unsupported relation. The linear position within a temperature interval is not itself the phase fraction. These values are invented and do not identify a real filler alloy or prescribe a joining temperature.

Use a state worksheet

Make columns for alloy identity, solidus, liquidus, relevant temperature and the state conclusion supported by those boundaries. Add a separate phase-fraction field only when appropriate material information supports it.

Ask whether an offered single melting temperature represents onset, full melting or another working-temperature description. Restoring that identity can resolve an apparent disagreement between documents without changing the actual alloy or assuming every practical brazing route requires the same wholly liquid condition.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: THESSCO brazing principles, page 2