Copied directly from the Simple Green website FAQ section:
"Aluminum - Is it safe to use Simple Green® on aluminum?
...The aqueous-base and alkalinity of Simple Green All-Purpose Cleaner can accelerate the corrosion process. Therefore, contact times for unprotected or unpainted aluminum surfaces should be kept as brief as the job will allow - never for more than 10 minutes."
"Simple Green has also developed break-through water based cleaners that are safe for use on metals, plastics, rubber and high tech alloys. Extreme Simple Green® Aircraft & Precision Cleaner and Simple Green® Pro HD are available on both the industrial and retail markets, respectively. These products were initially developed for the aircraft industry and extensive testing shows that they are safe and effective on a variety of metals and other sensitive surfaces even in the most extreme circumstances. "