I've had great results with oven cleaner. Use the nasty stuff, though it needs to contain lye. The sissy-fied ones won't cut it. Spread some old newspaper out, lay out your part and give it a good heavy coating, then let it sit for a few minutes, then use fine steel wool to remove anything left. If you have to work up a sweat, you either didn't use strong enough oven cleaner or you didn't let it sit long enough. I've used this stuff to remove all manner of anodizing and it leaves a really nice finish, since most aluminum is polished prior to anodizing.