Most of my wheels have aluminum alloy freehubs bodies. Some people worry about cassette sprocket notchng. This concern is misplaced. Notching occurs for very specific and avoidable reasons. 

First riders are not strong enough to cause notching. Regardless of how strong you think you are you can't notch a freehub that has a properly installed lockring.

The pic is of one of my freehub. Notching should not get any worse than this. Its barely notched.

First notching can only occur if the cassette lockring does not provide enough preload to the cassette. Thay preload stops the sprocket slipping and notching the freehub.

Grease freehub splines lubricates them. Dont do it. It is likely to make notching more of a problem. 

Recommended lockring torque is 40 to 50 Nm.

Not all torque wrenches tell the truth. A good mechanic has feel. The tool and feel tell you if your getting tight enough. 

Due to manufacturing tollerances there  an be a range of preload applied to the cassette hence feel is important. So the correct torque  can be aplllied but the correct preload not. Don't be a torque wrench slave. Lubricating lockring threads does reduce the variation in preload applied but also increases it and could result in stripped threads. There we fit lockrings without greasing them. We ensure the threads are sharp and clean.This way the correct preload is applied to cassette when the lockring is at 40 Nm. 

Most lockring tigheneing effort is used to over come friction so dirty or damaged threads mean notching is more likely.

If you get a freehub that notches, file the burrs and thick about what could have caused it. Its not the freehubs fault you just need to be a better mechanic.

One of my alloy freehubs is pictured after a few thousand km. No notching because i avoid the errors above.