Solvent to remove carbon deposits, rusting, scaling, etc.

Well, it depends upon what is important to you. It is most efficient cleaning processes, speed, economy, etc.

First off, aluminum and cast iron are best cleaned (carbon, grease, dirt) with different chemicals. Cast iron/steel can be cleaned with sodium hydroxide (used in solution with water and heated, of course). Aluminum requires alternate chemicals for this process; basically, a heated detergent. Some chemicals like mineral spirits or so forth can also be used.

Rust and scale are entirely different matters. Iron/Steel, muriatic acid will work. Also, mechanical cleaning may be something to look at: glass bead or organic material (ex., walnut shells). Blasting Aluminum, mechanical cleaning may be your best bet, but with very soft media.

Your best bet is to hook up with an automotive machine shop supplies company: these folks usually have complete lines of the correct products-one stop shopping, you could say.

Agreed about different chemicals being required: DO NOT BRING SODIUM HYDROXIDE NEAR ALUMINIUM!

If in contact with finely-divided aluminium, a violent exothermic reaction takes place, resulting in the formation of sodium aluminate, and a lot of heat!

And hydrogen gas!