I have done a few of the Sig 22 cal 1911's Which have Have alloy tops and bottoms. The one thing I noticed was the alloy tended to chip away instesd of roll like steel. But both came out nice in the end. ZZ
I have never had any problems engraving aluminum alloy handgun frames. Just like any time you are cutting aluminum you should use some lube. Not because it is hard to cut but because you will get some loading on your tip and some Break Free or kerosene will reduce the build up.