Specifications for indicate that "Solujet is inhibited for Aluminum. Corrosion testing is advisable." What does this mean?
Solujet contains sodium metasilicate which acts as a corrosion inhibitor to stop alkaline attack on aluminum. Solujet would not cause alkaline attack on aluminum as long as the bath is not overused and the metasilicate depleted.
There are galvanic (forming a battery) attacks on aluminum that involve interactions with other metals that may be dissolved in the cleaning solution from prior use, or that may be present as metal in the tank or part being cleaned, and this form of attack will happen with just about any detergent solution including Solujet. Ideally you should not clean other metals in baths used to clean aluminum and should not have other metals that have significantly different galvanic potential than aluminum present in the cleaning solution. If there is any concern that there may be other metals involved, then some testing may be advisable. If the aluminum parts being cleaned are very high value parts, then some testing would be advisable.
Certainly Solujet is designed to clean aluminum safely. Aluminum is a reactive metal, especially if it has been recently machined, cut or tooled so that there is exposed, freshly cut aluminum that has not had a chance to form a protective passive layer of alumninum oxide, which happens naturally with exposure to air. If the protective passive layer is not formed then you can get all sorts of strange galvanic reactions that are not technically corrosion, but which will result in discoloration due to deposits of whatever the other metal or metal oxide on the surface of the aluminum.