around the web there are claims that the Military has found simple green to be destructive.
They show up on auto and bicycle and air craft forums.

The Military page they link to does not exist.
Whether it's because it's just old or never existed is anyone's guess

The claims insist that it's destructive to metal, and more specifically others say it's hard on aluminum.

Simple Green is a Sodium Metasilicate. water, and Limonene compound. Sodium metasilicate is a very harsh base. The company lists the ingredients as trade secrets on their MSDS sheet.

I got some powder sodium metasilicate that I got in a little 1 ounce bag from Ace Hardware sold as a paint brush cleaner. I used it as instructed on some natural bristle brushes that were well clogged with old paint.
It cleaned 'em up, got the pain out, and destroyed the brushes.

The bristles were partially dis-corporated by the harsh base. they went limp and never regained any of their original stiffness making the brushes useless. They were expensive brushes when new.