During an axle removal i stumbled upon superficial corrosion.
Is there a way to minimize/treat this corrosion ? What kind of products do you guys use ?

 

You have to grind/sand as much rust as possible until shiny metal shows. Apply some rust converter to remaining rust spots (like Naval Jelly or similar).
Then sand again and then paint over it. If there was a tiny bit of rust left untreated and got painted over - you will see it in few months. I had little success with things like POR-15 or Rust Bullet. Best course is mechanically getting rid of rust and quality paint over (few coats of primer, few coats of paint, few coats of clear coat). Since in your case the paint job won't be visible, you don't need to make it look perfect/blend which is plus.

​​​​​​That arch rust in the last photo. It is not surface. It is rusting from within that seam formed by two sheet metal pieces. You remove the surface rust, paint over only to discover rust showing up again there.