The solidification temperature is the temperature at which a material changes from the liquid into the solid state. Above the liquidus temperature, a material is completely liquid. The material is completely solid only once the solidus temperature is reached. The range in between is called the solidification interval.
Liquidus, solidus and the solidification interval
Once the melt cools below the liquidus temperature, solidification starts: the first solid crystals form while the rest of the melt is still liquid. For a pure metal such as iron or copper, liquidus and solidus temperature coincide: the material solidifies at a single temperature, the same way water freezes at 0 °C. For an alloy, the two temperatures are usually apart, because the composition of the remaining melt keeps shifting throughout solidification. Only at eutectic compositions, for example eutectic cast iron with about 4.3% carbon, do liquidus and solidus temperature converge to a single point again.[1] The solidification interval, the gap between the two temperatures, largely determines the flow and feeding behaviour of a casting alloy: a narrow interval solidifies shell-like from the outside in, while a wide interval solidifies mushy across the whole cross-section, which makes feeding harder and increases the risk of shrinkage porosity.
Practical use: why foundry engineers need liquidus and solidus temperature
For the engineer, the liquidus temperature is first of all the minimum temperature an alloy must reach in the furnace before it is castable at all; in practice the melt is superheated somewhat above it so it does not solidify prematurely while filling the mould. The solidus temperature marks the point from which a casting is dimensionally stable enough to be shaken out or unmoulded without any liquid melt still escaping. Together, both values also determine whether an alloy is suitable for semi-solid casting (rheocasting, thixocasting), and they underpin riser design: the wider the solidification interval, the larger the riser must be sized to avoid shrinkage porosity in the last region to solidify.
Liquidus and solidus temperatures of common foundry materials
The following values are rounded reference figures and vary with the exact alloy composition.
| Material | Liquidus temperature | Solidus temperature | Solidification interval |
|---|---|---|---|
| Pure iron | 1536 °C[1] | 1536 °C[1] | 0 K (pure metal) |
| Eutectic cast iron (~4.3% C) | ~1153 °C[1] | ~1153 °C[1] | ~0 K (eutectic) |
| Hypoeutectic cast iron (~3.2% C) | ~1200 °C[1] | ~1150 °C[1] | ~50 K |
| Aluminium casting alloy AlSi12 (near-eutectic) | ~577–590 °C[2] | ~577 °C[2] | narrow |
| Brass CuZn37 | 920 °C[3] | 902 °C[3] | 18 K |
Frequently asked questions about liquidus and solidus temperature
What is the solidus temperature?
The solidus temperature is the temperature at which an alloy’s solidification is complete. Below this temperature, the material is fully solid.
How are liquidus and solidus temperature measured?
The common method is thermal analysis: a sample of the melt is cooled under controlled conditions while its temperature is recorded over time. The start and end of solidification show up as kinks or plateaus in the cooling curve, because latent heat is released during the phase change.
Why is a narrow solidification interval an advantage for the foundry engineer?
A narrow interval leads to directional, shell-like solidification from the mould wall inward. This can be fed well with risers and produces a denser casting with fewer shrinkage defects than mushy solidification with a wide interval.
Standard reference
DIN 51007 describes the fundamentals of thermal analysis (including differential thermal analysis), the method used in operational and laboratory practice to determine liquidus and solidus temperatures.
References
- maschinenbau-wissen.de: Eisen-Kohlenstoff-Diagramm (iron-carbon phase diagram), liquidus line and eutectic point. German-language source, no English edition available. Accessed 27 August 2026.
- materialmagazin.com: Aluminium-Gusslegierungen (aluminium casting alloys), Al-Si eutectic at 577 °C. German-language source, no English edition available. Accessed 27 August 2026.
- Deutsches Kupferinstitut (German Copper Institute): Werkstoff-Datenblätter CuZn37 (material data sheet), section 3.2, solidus and liquidus temperature. German-language source, no English edition available. Accessed 27 August 2026.