Why should 2017 and 2024 aluminum alloy rivets be refrigerated after heat treatment?

Refrigerating 2017 and 2024 aluminum alloy rivets after heat treatment is crucial for retarding the aging process, also known as age hardening. These alloys are known for their exceptional strength-to-weight ratio, and their optimal mechanical properties are developed through careful heat treatment and subsequent aging.

When aluminum alloys undergo heat treatment (solution heat treatment), they are placed in a supersaturated solid solution; however, once they are removed from the heat, they begin to age at room temperature. This aging process leads to the precipitation of fine particles within the aluminum matrix, which increases hardness and strength over time. If the rivets are refrigerated immediately after heat treatment, the lower temperature slows down this aging process significantly. As a result, the mechanical properties can be optimized further, and there is a reduction in the risk of premature hardening before they are formed or installed.

This practice ensures that the rivets maintain their workability while still possessing the desired strength characteristics when ultimately used in applications, especially in aircraft and aerospace structures where precision and material properties are critical. The options regarding improving tensile strength or enhancing corrosion resistance do not directly relate to the purpose of refrigeration in this context, and while making them easier to handle is a consideration, it is