NEVER use aluminum. If you look at the rail under my pics, that's made of aluminum. it doesn't slide at all, even with 20 coats of wax. Your edges cut up the sides, making them jagged and very sharp, and it hurts to touch it, and cuts you and your clothing if you fall on it. It wears very easy, and you almost always catch an edge. The one under my pics, we ended up putting HDPE on the top of it, so it is just like a very skinny box, or a HDPE'd rail.
DON'T USE ALUMINUM