Almost certainly ceramic, concrete, or some kind of painted metal to resist rust. Just a standard metal would be a mess of rust in that kind of environment.
The scaling definitely got better, but from what I see there are still a few parts that could be proportioned better. The robotic arm looks a lot bigger in the reference than what you have; be sure to check all your props with something else. Nothing else looks funkier than unproportional objects because viewers need to…