No idea. I would guess the Al-Cu interface layer is brittle and can be prone to peeling apart, especially with corrosion (2000 series copper-based aluminum alloys are notoriously not very corrosion resistant). Thickness of the intermetallic layer will depend on how it was prepared in the first place, and how hot it's gotten, because diffusion. Also, solder is prone to creep, as is the soft aluminum core, making it difficult to secure.
Tim