Those pads are not makinfg full contact!
There should be
NO rust on the swept part of the disk!
(I am amazed at what seems to be able to pass an MOT these days. I have seen disks with only 10mm of "shiny" metal visible and yet if it passes on the rollers it is just an advisory!

)
The hub section can be painted with any heat resistant paint, Washing it first with a phosphoric acid based de-ruster will remove any trace corrosion and prolong the life of the finished surface.