Arrest temperatures such as liquidus and solidus in a cooling curve as well as cooling rates during various phases of the solidification can be used as metallurgical attributes to classify a melt and to correlate it to the behavior when poured in a mould. Fig 1 shows a phase diagram for two metals, A and B, soluble in each other. When the liquidus temperature is reached the first solid phase is precipitated. This explains why the cooling curve is less steep until solidus is reached. In this case the temperature will drop until the liquidus temperature is reached and stay at that temperature until all is solid.
Commercial alloys consist of a mixture of two or more metals and in some cases metalloids.
Metals are often soluble in each other or form compounds or phases during the solidification process. Different compounds can also be formed between metalloids and gases present in the liquid. In such cases the alloy usually solidifies over a temperature range and different phases are precipitated from the liquid. The released latent heat is different for the different phases, which will influence the slope of the cooling curve. In some cases the temperature stays at a certain constant value until all the liquid has been transformed into solid state.