Our metal shop grinder has a prominent sign that states that you shouldn’t use aluminum on it. This is because aluminum will actually gum up the wheels. Someone ignored the sign and rather thoroughly gummed up both grinding wheels.
It is fixable, but I had to remove a lot of wheel material to do so, far more than you would wear off in normal use. (I also broke one of our dressing tools doing so, but they’re cheap.)
Please pay attention to any signs on a machine. If you need to remove material on aluminum, copper, or brass, you will have to use the belt sander. It’s more versatile anyway, and is often a better choice than the grinder even for steel parts.