.25 Marauder packs a wallop

On the way home from the farmers market on our bikes my son found a piece of mystery metal on the ground. It's light and thin but REALLY strong. We tested it with a magnet and it is non-ferrous. It might be an aluminum alloy but it definitely isn't standard aluminum. The boy asked me to try shooting it. I couldn't bend it at all so I didn't expect the airgun to make a dent. Boy was I wrong.