Chroming aluminium ?

Hi,
I'm a sucker for old car and bike building programs and was watching American Chopper the other day. It was the one where they built a bike for the Yankees
baseball team and Vinney was clearly shown turning the handlebars from solid aluminium bar. My curiosity was piqued by the fact these bars were shown chromed at the end of the program and I'd always understood aluminium to be hard or impossible to chrome, is that not true ? Where can you get ally chromed in the UK ?
Thanks,
Boo
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Have you met Mr Google? http://www.reevemetalfinishing.co.uk/nickel-and-chrome.htm
I've had machined aluminum microwave circuit enclosures nickel plated cheaply enough. It's easier when they don't need a polished finish. Nickel keeps the EMI gasket surfaces conductive longer.
jsw
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On 05/08/12 12:19, Boo wrote:

Plating another metal like chromium onto aluminium is a little tricky, but it's done routinely in many plating shops.
It is a bit specialised, and not all plating shops offer it, but it is not that uncommon.
The process is a bit different to plating steel or brass, especially the preparation stages, and many companies do not have or routinely operate the many extra tanks needed - for instance, the process described below will need 19 or 20 baths, only about 7 of which would be used in plating more usual substrates.
Most often the surface is cleaned, stripped, polished, cleaned, stripped, zincated, stripped, zincated again, a thin cyanide copper or electroless nickel strike is plated on the zincated layer, then electrical copper and/or nickel, then chrome.
It's not a job for the amateur, as you need hydrofluoric acid, cyanide and chrome VI baths for best results (though it can be done without, and electroless nickel can be substituted for cyanide copper with reasonable results, but otherwise the result is not usually very good).
Note that cast aluminium alloys do not usually plate well unless they are a special plateable grade. The same is true of some other aluminium alloys. There are a few shops which specialise in plating these alloys, but they are usually more expensive.
This can cause some uncertainty and distress for the plater, as some cast aluminium alloys can wreck a very expensive electroless nickel bath - it also means that some shops will not plate random objects which could be made of troublesome alloys.
All this means that chrome plating aluminium is usually quite a bit more expensive than chrome plating steel or copper alloys.
I can't recommend anyone from personal experience unless you are talking about the large end of industrial scale (and I'm not entirely sure I'd recommend my old firm), but most good shops should either be able to do it themselves or know a man-who-can.
Plating aluminium onto another metal is another matter, and very difficult and expensive. But you weren't asking about that :)
-- Peter Fairbrother
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Boo wrote:

Just smooth it and buff it.
Look into Young's Modulus - the srength of the bar/tube doesn't vary with the amount of material in it - up to a point...
--
Old Nick

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That's a strange assertion; also unclear. When you say "strength", do you mean ultimate tensile strength in tension, yield point in bending, or stiffness under reversible load. From your reference to Young's modulus, I assume you mean the latter, as YM has no relevance to the first two.
Deflection s of, say, a tubular section cantilever is given by
s = WL^3/3EI,
where W is the applied load, L is the length, E is Young's modulus of the material, and I the moment of inertia of the cross section of the beam.
For a tubular beam, I = 0.049(D^4-d^4),
where D is the outside diameter and d is the inside diameter.
Now tell me how that means that stiffness is not dependent on wall thickness.
Similar factors apply to failure modes, though I don't have the details to hand.
David
--
David Littlewood

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I should of course have specified that this is for the case where weight W is applied at the unsupported end of the beam, rather than evenly distributed along it.
David
--
David Littlewood

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