Overaging of Precipitates
Overaging of precipitates: At too long holding times at elevated temperature, the precipitate structure grows and coarsens, reducing the strength of the material.
Physico-Chemical Mechanism of Action
In overaged precipitates, the grain in the weld grows. This happens through continuous diffusion of atoms between the precipitate phases and the matrix lattice. The reduction of phase boundary area leads to lower toughness of the material.
Metallurgical Relevance & Welding Risks
Overaged precipitates can lead to a significant reduction in the strength and toughness of the material. This increases the risk of cracking and failure under mechanical stress. Furthermore, the material may become less machinable, which can cause problems in further processing steps.
Workshop Practice & Action Instructions
To avoid overaging, the time the weldment is held at elevated temperature should be minimized. This can be achieved by:
• Using stable shielding gases such as argon or helium
• Optimizing welding parameters (voltage, current)
• Regular inspection and replacement of the precipitate lattice
• Short holding times at elevated temperature