I'm guessing coated steel bolts as well as a coupling between Al and Cu. It looks like some rusting on the bolts.
The objective of anodizing is to put a 'protective' oxide on the surface of the metal, which acts as a barrier to electrical conduction, which is the cause of galvanic corrosion, which is probably what one has here. Galvanic corrosion occurs when two dissimilar metals are in contact and one is reduced while the other oxidizes. One has to electrically isolate (insulate) the metals.
As Gokul mentioned find an alternative to steel bolts.