All heat sinks with fins is extruded alluminum.
I have to disagree there. On this last load I had a big heatsink with a big flat plate and fins, but when you looked at it close the fins were thin sheet bent and pinned to the plate with alum pins. That one went as old sheet. The yard resorted my load while they were weighing it and the majority went as the MCL, and I'm still not 100% sure what they classify MCL as.