It's impossible to tell what metal is used from the photographs. It might be aluminium but it's far more likely to be steel. Steel is cheaper and stronger and with such heavy compnents inside the unit, using aluminium to make it lighter would have a negligible effect.
The standard paint surfaces are powder coated for best appearance although I've seen dip and spray painting being used as well. The black case may be anodized instead of being painted. A clue is to look where the screws were fitted. Anodizing bonds well with the underlying metal so the screw would only scratch it, paint would be thicker and more likely to flake away under the compression of the screw head.
Brian.