Citric acid is the primary ingredient in most dishwasher cleaners. Of course, not a good idea to use it in every load. However, my DW manufacture suggests up to 10% citric acid solution as an alternative to rinse aid.

I haven’t seen any aluminum in a dishwasher, and I have noted that if I send any aluminum through it tarnishes like crazy and pits on repeat offenses. I don’t think that hot caustic water is any environment in which to design an aluminum part.

That said, again, dishwasher detergent is basic, so you’re right in that adding acid probably won’t improve the efficacy of the wash cycle.