What happens to clad aluminum alloy when subjected to repeated heat treatment?

When clad aluminum alloy is subjected to repeated heat treatment, the material can indeed become brittle. This brittleness arises from the interaction of the aluminum alloy with the heat treatment process, which can lead to the formation of precipitates and changes in the microstructure.

Repeated heat treatment can enhance the effects of aging or overaging, which can result in the reduction of ductility and toughness. As these important mechanical properties deteriorate, the likelihood of cracking or failure under stress increases, leading to a material that is less reliable in performance.

In contrast, the other options present varying characteristics that clad aluminum alloy does not typically exhibit after heat treatment. While improved strength might occur with optimal heat treatment, excessive heating can lead to opposite effects, such as weakness and reduced performance. Similarly, while reshaping might be possible with some materials, repeated heat treatment generally affects the material integrity, making it less malleable. Lastly, retaining original properties is unlikely since the repeated application of heat imparts significant changes to the material structure and properties.