Taking aluminum parts as an example, aluminum parts will quickly form oxide films in the air. Abrasive (polishing paste) during polishing will first throw off the oxide film on the protruding part, but the concave part will not be thrown, then the matrix will oxidize quickly after being exposed, and then it will be thrown away, and it will be repeated until it is thrown into Bright so far.
Polishing is not actually the cutting of aluminum itself, but just the process of continuously throwing off the oxide film, but due to repeated polishing, the throwing speed of the later aluminum material itself is still very fast.
Some researchers also believe that polishing is the result of metal moving from the convex to the concave, thus forming an amorphous layer. It was also observed from an electron microscope that the outer surface of the mechanically polished surface was crushed into an irregular, very fine crystalline state. Which statement is more correct is still to be further discussed.