The cover is definitely aluminium. The inner part however does look like it has plastic mold lines on the back so it must be plastic, but it looks so similar to the aluminium shell. Could you elaborate on what part of the material needs work? What seems off? I've been looking at this for too long so any fresh opinions…
Looks cool but I think you should play with the values a bit more. Right now it lacks contrast which makes it look pretty bland. A 2 second (slightly overboard) contrast tweak I did; Makes a great difference and shouldn't take too long to do. Also, I'm still not a fan of those mud splotches. They look more or less okay…