[Horshu]

I think we got caught up in semantecs. I'm speaking of surface strength (a facet of its hardness), whereas I think others are speaking of structural strength. I do believe that a hard, diamond-like (aluminum oxide is what is in rubies and sapphires) coating over a metal will increase its rigidity, although the loss of malleability leads to a loss of flexibility/"give" such that while harder to bend than plain aluminum alloy, once it starts bending, it cracks (kinda like tungsten vs. titanium, although tungsten will flat-out break rather than just crack)