Whilst mechanical treatments often remove the bulk of surface damage, they often add further complications and hide underlying problems.
Metals are crystalline structures and when looking closely at such surfaces, the crystal structure should be easily seen. Once again, going back to how the original material is formed, this group of materials easily plasticize at 500ºC, allowing the upper layer to be pushed over damaged sites and for inclusions, debris and contaminates to be trapped within the upper surface layer
Mechanical treatments can also induce heat that far exceeds the phase changes of the material, taking them into the molten stages at local sites and enables cold quenching to take place with the material behind the local sites that remains within the stable phase, leading to local phase changes to take place.
Below details a typical phase change and oxide generation with applying various mechanical treatments