Aluminum can be plated quite nicely provided it's done properly. Must be prepped then the first coat that goes on is copper. It fills imperfections, It sticks to the aluminum. The second coat that goes on is nickel which sticks to the copper. Finally the chrome coat is last. It needs the nickel to adhere properly. If any of these steps are skipped then the adherence will not work properly and it will peel. I have a 30+ year 3 step chromed old rocker cover that Brown's did for me when I lived down the street from them back in my old Paducah days. Still very nice. No peel. I have a newly chromed cover that they did with their newer 7 step (haven't really studied that process) and it's nothing short of amazing. Get what you pay for with Brown's. I had some aluminum wheels done for my Fat Boy by a place in Michigan that peeled. More "reasonably" priced but Brown's doesn't do wheels from what I've seen. I see copper and chrome layers in the peelings. Can't say there is nickel involved. Totally amazed at the thickness thinness of the layers! Shocked actually. Thinner than a sheet of notebook paper for both. And to think the shine looks amazingly deep. I sent the wheel to Meclec in s. CA. for rechroming. Right up there with Brown's as far as the eye can tell. You could consider them also.
Yes, you are correct on most accounts. Chrome is put over aluminum all the time. The aluminum must first be zincated, then it gets underplated with a variety of platings. The traditional way of doing it was a copper-nickel-chrome process like you described, however more and more places are going to a nickel-nickel-chrome process that uses a very very thin layer of nickel to activate the part, then a slightly thicker layer of slightly different nickel over it, then chrome on top.
It's funny, in the metal finishing industry decorative chrome and nickel are some of the thickest platings there are. They are still typically less than half the thickness of a sheet of computer paper, but this is still 4-5 times thicker than most other platings and coatings (not counting paint and powdercoat). The layers of copper and nickel under the chrome layer are often .0004"-.0005" thick while the chrome layer is often more like .0010"-.0015" thick.
What would you recommend?
It depends on the part, the alloy, and the result you are after. The plater you go with should be able to help you with the best solution for your application. There are different methods of nickel plating, one is electrolytic (typically sulfamate nickel), the other electroless. Electroless has more advantages, but tends to be more expensive. Where I work we do a lot more electroless nickel than sulfamate nickel do to the advantages it holds in industrial applications. A midphos bright electroless nickel with between 6-9% phosphorus gives a nice shiny bright finish that is very corrosion resistant when applied to a nicely finished part.
