And now for something…completely different.
If you could bring some AL sheet metal through a time machine, go back 500 years ago and hand it to an armorer, he might work with it for an hour and promptly declare it to be of the devil. Other armorers might rule it must be blessed by God. Cursed or enchanted…it’s just not normal stuff.
Aluminim plate armor has some distinct advantages. It is far lighter than sheet steel, like half or less. It virtually does not rust (it does oxidize), and it is very easy to bring to a high polish. It holds its polish well, and all of these things make it the perfect material for walking around the ren faire showing off a bit.
Disadvantages include cost and weird/low maliability.