What does the liquidus line indicate in a thermal equilibrium diagram?

The liquidus line in a thermal equilibrium diagram represents the threshold for liquid phase formation. At any temperature below the liquidus line, the material will start to solidify, meaning that a mixture of solid and liquid phases will be present. As the temperature decreases, the material cools down and reaches the point along the liquidus line where it transitions from being completely liquid to a mixture of liquid and solid. This transition is critical in understanding phase changes within materials, especially in processes like melting and solidification.

In thermal equilibrium diagrams, the liquidus line specifically delineates the conditions under which a material begins to form a liquid phase as it is heated or reaches an appropriate temperature threshold. This makes it a vital reference point for predicting behavior during material processing.