Yes, heatsinks are considered Extrusion, Although there is a dictionary-type definition of extrusion, most yards will not pay extrusion for thinner manufactured aluminum frames (usually window). Last one I asked, said he didn't have an exact thickness, but knew extrusion when he saw it. Best advise is take several samples to your yard and ask them. Then keep the samples for comparison.

General examples of "Extrusion" are door and window frames.