For aluminum, especially for a beginner, I would recommend using a single flute super "O" bit as they work really well in that material. Typical speeds with a super O are 12-14k and 6 ips. For a two flute end mill, I'd use 6000 RPM (slowest your machine can produce) and a fast speed, like 6 ips. A straight end mill is likely a risky choice as it has no way to eject the chips, which will lead to the kerf being clogged and that can cause all sorts of problems, especially with cut quality.
Corian is pretty easy to cut. I suggest doing some test cuts on a waste area to see which works best with your choice of end mills.
Regardless of the material, the best results are obtained when the chips are the right size. I like to see chips that are about the size of large sand grains. The chips take the heat away from the cut so larger chips take away more heat than small chips. If your chips are the size of dust, you're moving too slow and/or have a too high RPM. Try looking at a chip load calculator for some guidance.
I suggest reading a number of past posts in regard to cut quality and chip load to get a better idea of what are best practices.
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