How are certain aluminum alloy rivets stored to remain soft after heat treating?

Aluminum alloy rivets are stored in a refrigerator below 32 degrees F to maintain their soft state after heat treatment. This cold storage practice is essential because certain aluminum alloys can undergo aging or hardening if kept at room temperature or warmer.

When heat-treated, these alloys are often in a solutionized state, which means they can be formed into rivets while still soft. However, if they are allowed to sit at higher temperatures, they may begin to age and harden, making them more difficult to work with and less effective for assembly purposes. By keeping them in a cold environment, the aging process is significantly slowed, preserving their softness and malleability until they are ready to be used.

The other storage methods listed would not be effective; for example, storing rivets outdoors under sunlight or at room temperature would risk premature hardening. Thus, the refrigeration method is crucial for maintaining the desired properties of the rivets prior to installation in airframe structures.