Regarding aluminum and the cleaning of aluminum:
As a young engineer, I was a product application specialist and die designer in an aluminum plant for some years.
When typical aluminum is extruded, cast, or forged and machined, it always contains surface pores.
To seal the aluminum, before Anodizing, it is boiled in water, and this causes the surface of the aluminum to seal up by shrinking the pores. Anodizing or hard coating seals it further, and for a lasting finish parts are usually clear coated or painted.
Any cleaning method, whether a chemical, abrasive, or otherwise, which breaks into the surface of the aluminum even a little bit, opens the pores.
In the open oxygen-rich atmosphere, these miscroscopic pores immediately fill with soft aluminum oxide, and soon you will actually see blooms of oxide on your aluminum parts.
The other thing to note is that die marks were removed before boiling etc, by a caustic etch process.
Lye is used and it eats aluminum fast, but any cleaner with caustic properties will eat aluminum.
To test this, mix a bit of cleaner with a drop of vinegar. Any caustic will cause immediate foam as gases release. The more vigorous the reaction the more caustic is the cleaner.
Caustics do the same thing on Steel by the way. But they eat aluminum maybe 100x as fast.
When I was working my way through school, I worked at a shop that had a "hot tank". Keeping it hot meant the chemical reactions were more vigorous, and your parts came clean quickly.
One mechanic was working on an old boat & put an aluminum porthole frame in the hot tank.
The next morning he was running around trying to find out who took his antique porthole.
Well it was taken completely, by hot boiling lye, and turned to grey sludge at the bottom of the tank.