[villagetinker]

I have concerns about using aluminum screws, everytime I have tried to use these they have sheared or broken off, they do not have the strength of steel or stainless steel. While I am not an expert in metal corrosion I have never seen stainless steel corrode when in contact with aluminum. In any case, I would ask an expert in birdcage design if aluminum screws would be acceptable from a load bearing consideration. Stainless steel screws are available from all of the big box stores in Phillips head, not sure I have seen hex head type. If you are doing a DIY here is what I would do: take existing steel screws out one row at a time, clean any rust stain off (try sno-cap), then dry the area and install new stainless-steel screws. Vinegar or similar weak acid MAY clean the calcium buildup, however if the original anodizing has failed some paint may be required.
I have had very poor luck with painting aluminum that has had a corrosion problem, I would suggest going to a boat repair facility to find out how they repair the paint on aluminum boats. DO NOT EVER use a STEEL tool on aluminum if you intend to paint the aluminum, the paint will fail.
Hope this helps.