What must be done to D and DD series rivets if they are not driven within the prescribed time after heat treatment?

D and DD series rivets, which are often made from aluminum alloys, undergo a heat treatment process to enhance their mechanical properties and strength. This heat treatment is time-sensitive, as it affects the rivets’ ability to achieve the desired performance characteristics. If these rivets are not utilized within the specified timeframe after the heat treatment, they may lose their integrity and strength due to natural aging or other factors.

Reheating these rivets restores their properties and ensures they will perform as intended in their final application. This process typically involves bringing the rivets back to a specified temperature for a particular duration, which allows them to regain their mechanical characteristics. The need for this reheating emphasizes the importance of timing in the handling and application of heat-treated rivets.

Other options may suggest discarding or using the rivets as-is, which would risk the structural integrity of the assembly they are part of. Refrigeration could be a method to temporarily slow down aging, but it does not replace the need for proper heat treatment. Thus, reheating is the essential action to take if the rivets are not used in time.