Originally Posted by
PixMan
PCD (Poly Crystalline Diamond) seems to work just fine too, as that's what the automotive guys use in a lot of applications. Of course I can appreciate that what you (K&Y) make and sell is the best (certainly from the K&Y seat), it can be cost-prohibitive for a short run jobs.
The OP is asking about turning, not fly-cut milling.
For turning, consider PCD inserts from any of a wide variety of sources. Whose products do you buy now, or whose do you have a good distributor for? PCD inserts are sold by Kennametal, (Walter) Valenite, Sumitomo, NTK, Sandvik Coromant, Iscar, the list is long.
Tell me what insert holders and/or shape your lathe uses, I'll make a suggestion.
You may not even have the speed to run PCD or MCD tools, and a highly-polished uncoated carbide would probably be fine. Fair warning, 2011 aluminum is called "Microchip" for a reason. It's very granular structure helps prevent long stringy chips, and that also results in grainy-looking finish even when its very smooth from high-speed/low-feed rates.
Again, tell me what insert size you have in holders for the trigon, and I can recommend from there.