Hard Chrome Plating on Aluminum

A. DEAR BRUCE:

NOT AN EASY JOB BUT THEORETICALLY HARD CHROMIUM CAN BE DEPOSITED OVER ALUMINUM THAT IS FIRST ZINCATED (THERE ARE A NUMBER OF SOURCES OF INFORMATION ABOUT ZINCATING, ONE OF THEM IS THE FINISHING HANDBOOK).

THE QUESTION IS IF YOU REALLY NEED A HARD CHROME PLATE, REMEMBER THAT HARD CHROME HAS TO BE THICK TO BE WEAR EFFECTIVE (AT LEAST 0.5 MILS), OTHERWISE ITS FUNCTION IS MARGINAL. THEN THE PROBLEM IS THAT CHROME IS TOO BRITTLE AND THE ALUMINUM TOO SOFT. YOU WILL END UP WITH A PIECE OF GLASS OVER YOUR LIVING ROOM COUCH. CAN'T SIT ON IT.

ON THE OTHER HAND, IF THE REASON TO LOOK FOR CHROME IS TO REDUCE WEAR, OR CORROSION, THERE ARE BETTER APPROACHES SUCH AS ELECTROLESS NICKEL PLATING.

HOPE I GAVE SOME LIGHT.

A. Hi Himmat. No single book covers the whole process exhaustively, but Hard Chromium Plating [suggestions on Amazon & AbeBooks --> affil links] by Guffie says aluminum is usually zinc or tin plated first, although castings are sometimes directly plated. Wernick, Pinner & Sheasby has a little over 3 pages on hard chrome plating of aluminum.

Hard chrome plating of aluminum is not a terribly common application because aluminum is so soft that you probably need a thick plating to exhibit hardness, and even then the item will be subject to easy eggshell cracking.

Regards,

A. Hi Hafiz. You may find our on-line articles "Introduction to Chrome Plating" and "Introduction to Anodizing" helpful if you are just starting out. Good luck with them.

After that, please spend a couple of paragraphs introducing yourself and your situation. People may be able to answer specific & limited questions for you, but the best known anodizing book is 1300 pages, so people would not know what answer of reasonable length they should give you vs. which 1299 pages they should skip if we don't know your situation :-)

You say that the aluminum is 10 foot long, but how wide is it? How thick is it? What alloy of aluminum is it? Why are you applying hard chrome plating to it? Do you know what thickness of plating you will need? Why are you anodizing these sheets? Do you know whether you want type 1, II, or III anoding? Thanks! Please hang in there and offer some details and we should be able to help! Good luck.

Regards,

A. Hi H.R.,

When Vikram said that chrome is blue and nickel is yellow, he didn't mean sky blue and canary yellow :-)
Rather, he was referring to a very faint cast to the silvery metallic color that "experienced platers" would probably recognize but others probably would not.

Please see thread 14252, "Chemical removal/stripping of chrome plating from aluminum parts". Stripping the chrome without affecting the aluminum will be a trick requiring a fair amount of skill, a little bit of luck, and favorable conditions of shape and thickness. Good luck.

Regards,

A. Hi Jingak. The first question is what do you mean by failure and remaining life? Are you considering those deep, full depth cracks as failures? And why exactly do they constitute failure ... corrosion, impressing a crack pattern on what they are rolling, flaking off?

I think three possible routes to those cracks are: 1). they were there from the beginning; 2). the much higher coefficient of expansion of aluminum caused the chrome layer to fail in tension; 3). 'eggshell' cracking developed because the underlying aluminum is too soft to support the load.

I am not a metallurgist and cannot claim any significant experience in evaluating such microphotographs for cause of failure, but it just looks like '2).' to me and, because chrome expands only less than half as much as steel whereas aluminum expands almost twice as much as steel, I would expect a significantly higher incidence of such failures on aluminum rollers than on steel rollers, and that 120 °C might be enough to do it.

Regards,

A. Hi Praneeth. Remember that it was you, not us, who claimed that aluminum alloy is a good alternate to QT steel :-)

Certainly aluminum can be hard chrome plated, electroless nickel plated, electroless nickel plated with occluded materials like tiny diamonds, electroless nickel plated with teflon additions, hard anodized, or anodized with teflon additives.

But any substitute of one material for another or one coating for another requires very careful evaluation -- there are no "drop in" substitutes. Please give us the full details of the component you are trying to build from aluminum. Hopefully it's not a hydraulic piston rod :-)

Regards,

A. Hi again. I'd stick with the hard chrome plating then and hope for the best, as it has proven itself for decades as the ideal surface for hydraulic piston rods.

Regards,

A. Electroless Nickel Low Phosphorus is a good alternative for hard chrome.

A. Hi Eduardo. Thanks! I'd agree that electroless nickel can often be a good substitute for hard chrome. But do you have experience in using it on hydraulic piston rods? I'm heard that the cracks associated with hard chrome are important for holding oil on hydraulic piston rods ... but I'd be happy to be told I'm misinformed :-)

Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Khamesra. Please introduce yourself and your situation to give us a starting point.

Guffie says "An interface of zinc or tin is almost always deposited on aluminum ... some cast aluminum alloys, however, are plated directly ..." and not much else. But see earlier postings above yours.

Luck & Regards,