Ok, just to be perverse, I'm going to ask people how you'd put that back together.
I'm interested because apart from silver-loaded epoxy I don't know how a strong thermal and physical bond between aluminium and copper plates can be made. I tried messing with stuff called HTS2000, a 'brazing' alloy that can bond them, but the mess is terrible because the resultant aluminium alloy has a lower melting point that the aluminium substrate so the whole thing collapses like a hot wet sponge! It's not easy to make HTS2000 meld either, you have to literally scrub it onto the surface, so when the substrate collapses, great gouges result in the surface. I had hopes that a fast heating of powdered HTS2000 alloy with a flux might allow a bond to form before the surface of the aluminium dissolved the alloy and collapsed, but I never found a flux that worked.
The reason for putting Cu onto Al is that a thin Cu layer can be easily used to mount other parts by solders of varying melting points onto a cheap Al heatsink or other form to make cheap and stable small optics systems. Big ones would suffer from thermal bimetallic action but a thin Cu on thick Al ought to be ok for many small DIY projects like beam combining.