Aluminium carving on a CNC is not an easy task.
Speed and Feed rates must be lower and the risk of having a broken mill is not absent.
Different end-mills that cutting wood is required and lubrication is some time necessary to avoid friction when cutting.
If the speed is not adequate then the risk of having missing steps and consequently nasty cuts is big.
On the video below you can watch my first attempt to carve aluminium on my MPCNC.
I tried to cut on soft aluminium a note and the word Dark.
The result was not perfect but keep in mind was the 1st attempt.
Feedrates and end mill was a trial and error.