Secondary Phase Precipitation
Secondary phase precipitation is the process where fine particles drop out of a supersaturated solution and increase strength. These particles block dislocation movement in the crystal lattice.
Physico-chemical mechanism of action
During secondary phase precipitation, a new phase forms in a supersaturated solution, finely dispersed. This new phase has a different crystal lattice than the original solution and is held together by chemical bonds.
Metallurgical relevance & risks in welding
Secondary phase precipitation increases material strength by blocking dislocation movement in the crystal lattice. However, it can also lead to cracks and hardness issues if the particles are too large or not well distributed. Uneven precipitation can also cause local stresses and thus hot cracks.
Workshop practice & instructions
To ensure optimal secondary phase precipitation, it is important to control welding parameters like temperature and time precisely. Too fast cooling can mean the particles don't have enough time to form and distribute properly. Too slow cooling, on the other hand, can lead to uneven precipitation and thus hardness problems. It's recommended to cool the weld in a protected environment to ensure even cooling.