Natural Aging
Cold aging is the process where precipitation forms in a solution-annealed alloy over an extended period at room temperature. This increases strength and coarsens the microstructure.
Physical-Chemical Mechanism of Action
During cold aging, precipitates form in the alloy over a longer period at room temperature. This happens through the formation of metal crystals that slowly crystallize from the solution-annealed phase.
Metallurgical Relevance & Risks in Welding
Cold aging increases the strength and toughness of the alloy by coarsening the microstructure. However, this can also lead to an increased susceptibility to cracks and grain growth if not properly controlled. Too fast cold aging can lead to glass-hard martensite, which increases hardness but at the same time reduces durability.
Workshop Practice & Action Instructions
To successfully initiate and control cold aging, it is important to cool the weld slowly. This can be achieved by using cooling water or special cooling dies. The cooling time should be set so that the microstructure has enough time to coarsen without cooling too quickly, which could lead to glass-hard martensite. Recommended cooling times vary depending on the alloy, but generally should be between 10 and 30 minutes.