Aluminum and Copper Bar Attach

I would worry if you wanted the "3600Amps rated aluminum bars" to carry 5200 Amps.

I don't think corrosion would be a problem at that point.

Sometimes it's easy to get carried away with over-specing a system design when planning for the future.

Assuming your current is less than the lowest current rated joint in your system (in this case say the 3600A bus bar) there are a number of options to ensure a good and tight connection between these metals.

A good place to start is a search of CR4 for busbars (or similar) as this question has been answered a few times.

There are conditions that one can safely connect 3600A aluminum bus bars to 5200A copper bus bars. There are also conditions that one should never connect these two bus bars together. I do not have the time nor patience to list all of the conditions required to identify if this is safe or dangerous. Consult the electrical standards and documents for your location.

Could you make a drawing to show the proposed setup with typical loads...Generally speaking you can connect copper to aluminum with a conductive grease to protect from corrosion...

Tin plate the joint area and you will be fine. No need for us to see drawings etc. This is fairly common, especially in transformer connections where the transformer LV windings tend to be aluminium (cast resign type)

I'm still amazed that a group of people that consider themselves Engineers still fall for and promote anecdotal fallacies. Just because you have safely connected these two bus bars together without a problem, does not mean that every joint of these two bus bars is correct.

Use a bimetallic connector,if approved.

This may add to the confusion http://cr4.globalspec.com/thread/70944

Use an approved conductive grease between the two contact surfaces after these surfaces have been sanded with 400 grit silicon carbide paper or cleaned with an abrasive pad and solvent wiped. Bolt the bus bars together and check the bolt tightness periodically. Corrosion won't be a problem if the connection remains dry.