Liquidus surface
The liquidus surface is the boundary in phase diagrams above which an alloy is fully liquid. Below it can be a mixed state or even solid.
Physical-Chemical Mechanism of Action
The liquidus surface marks the transition from a solid or mixed state to a fully liquid state in an alloy. It is defined by the temperature and pressure at which all components of the alloy exist in liquid form.
Metallurgical Relevance & Risks in Welding
The liquidus surface is crucial for understanding the melting behavior of alloys. If the temperature during welding is below the liquidus surface, incomplete melting or phase separation can occur, leading to faulty weld structure and low strength. It also influences the choice of the appropriate welding process and shielding gas atmosphere.
Workshop Practice & Action Instructions
To ensure that an alloy is fully melted, the temperature during welding must be at least as high as the liquidus surface of the alloy. This can be monitored using thermal cameras or other measuring devices. For certain alloys, it is important that the melting time is long enough to ensure homogeneous melting.