Anodizing is an interesting field and it is an electrolytic passivation process to increase the thickness of the natural oxide layer. When aluminum is exposed to air it will form a natural oxide layer.
It is the anodized oxide layer that can be colored with different dies after the anode cathode electrolytic passivation. This is my own understanding of the process used so let me know if I am wrong.
Anodizing increase corrosion resistance and wear resistance. Victorinox has used handles of aluminum for over 40 year and to increase the quality of the handles they are anodized.
the dividing layers of a SAK may be anodized depending on the application and functionality. Not all dividing layers are anodized.
Some Swiss Army Knives has been exposed to elements and substances
that have caused damage to the surface on the aluminum dividing layers. If a SAK get maintenance it will last for a very long time without any damages.
On the picture you can see a side plate
and a dividing layer made of aluminum from a rather hard used Victorinox 91mm knife. All the discoloration you can see on the surface is caused by scratching. This from sand or other materials that’s been in the mechanism. Some discoloration will probably
always happen. The surface got no buildup of corrosion or other malformations and it is this that is important.
Victorinox changed to aluminum dividing layers in 1951 this because of weight and excellent
Galvanic corrosion or this is the term collectors and users use on the buildup of the surface on the dividing layers or side plates. This buildup is not good because it will affect
the functionality of the SAK. The functions will not be possible to open depending on the extent of damage or buildup.
If a SAK that is used get some maintenance and oil it will not happen.