Cadmium vs. Zinc

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Cadmium vs. Zinc vs. Nickel PlatingComparison

Q. We are currently looking for an alternative to cadmium plated parts. The argument for an"equivalent" to cadmium plate has been going round and round. The parts are threadedassemblies and maintaining tight dimensions is critical to the operation of the assembly.

We were getting a .2 Cadmium plate (commercial grade). The alternatives appear to be Zincplating or Nickel Plating. Tin-Zinc plating is not an option with our current vendor.

With Zinc, the interaction with metals and the sacrificial nature are issues. The corrosiveby-products may cause operation issues in the threads and other tight areas. The base material is

SA-1983-B7 Steel.

Can anyone offer any insight to this? The consensus opinion is that Nickel plating offers bettercorrosion resistance than Zinc. The plater says the Zinc doesn't offer any less protection than theCadmium plate. I'm just shooting for something comparable to the Cadmium. Any advice/opinionsare greatly appreciated.

Brian Bukoski- Erie, Pennsylvania, USA

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A. Here are two opposites to ponder, Brian:1). there is no true substitute for cadmium plate because it offers sacrificial protection,malleability, freedom from sticky and bulky corrosion products, galvanic compatibility withaluminum, softness, and reliable torqueing through freedom from stick-slip, which no othermetal or alloy offers.2). the overwhelming volume of hardware worldwide is zinc plated rather than cad plated.

In many cases just switching to zinc will do fine; in other cases it could be a disaster. Itdepends on how critical the issues I mentioned are.

Nickel does not offer sacrificial protection, but sacrifical protection may not be required foryour application. Please try to describe it. Thanks!

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mium vs. Zinc vs. Nickel Plating Comparison http://www.finishing.com/130/89.shtml

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Ted Mooney, P.E. RETfinishing.com

Brick, New Jersey

A. First, there is no direct equivalent of cadmium. If you have to go away from it, youneed to decide what properties you need and in what order or amount of preference. Zincand cadmium have similar but not equal corrosion resistances. One is better in industrialsettings and the other is better in maritime settings. Tin-zinc is the accepted bestsubstitute by most. Nickel offer better corrosion resistance, but has far less lubricity and isnot as malleable. You might want to look into some of the other zinc alloys like zinc-nickel,zinc-iron, zinc-cobalt to see if one of those might work as there are a lot more platingshops with those than with tin-zinc.

James Watts- Navarre, Florida

A.

You would not get the corrosion protection you are looking for from Barrel plated Nickel;

your best alternative would be Zinc plate to approx. 4 /10th of a thou and finish with ayellow / iridescent chromate; if the fasteners are any harder than about 28 Rockwell "C"then you might need to consider Mechanical Plating , or plating from a Chloride Zinc

solution if the surface is high in carbon & Carbides In most cases Zinc is a betterperformer than Cadmium in practice however this is not shown in accelerated corrosiontesting .

Regards,

John Tenison - Woods- Victoria Australia

A. Brian,

You said that Tin / Zinc is out of the question. How some of the other alloy depositssuch as Zinc / Nickel which seems to be the best of your two worlds, will give you someof the best of both zinc and nickel deposits.

In my opinion Zinc is not as good as Cadmium for corrosion although the chromate are.The nickel deposit will give you superior corrosion but will loose lubricity, nickel depositstend to be much harder.

It is impossible to replace all the properties of Cadmium with one deposit, but with


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some research you can get what you have need for.

Chris Snyderplater - Charlotte, North Carolina

A. The finish that will work well for you is Alkaline Zn/Ni 12-16% Ni. This process witha yellow chromate will give at least 1000 hours NSS to white rust and 2500 hours to redrust (assuming 8 microns minimum). The product produces very little in the way ofwhite corrosion products and has excellent slip properties.

Hope that helps.

Regards,

Jonathan Timms

- Hong Kong

A. The topic of Cadmium replacement finishes has been ongoing since '95, when thefinal regulations in the automotive came to light. Many finishes were tested, and veryfew offer all of the benefits of Cadmium. We just completed a Cad Replacement Studywith the US Army, in which our coatings (both chrome-containing and chrome-freeversions) were chosen as the best performing alternatives for Cad. They offer most, ifnot all, of the benefits of Cad, but they are water-based and environmentally friendly.

The areas looked at were: cosmetic corrosion, galvanic corrosion (including pit depth

and pitted volume), torque-tension (including clampload at 90 ft-lbs, break-loose torque,and torque range), thickness, conductivity and cost. Tin Zinc and Zinc + Yellow weretested in this study and did not compare to the Dacromet(r) and Geomet(r) products.They showed excessive white/red corrosion very early in testing, and there was a largeamount of pitting caused by the bimetallic cell (the bolts were tested assembled to an Alfixture). Also, the Army didn't consider Zn Nickel for this study because it did notperform well in their preliminary studies. At the very base of the results of this study

was to not consider Zinc Plating + Yellow Chromate as an alternative to Cadmium.

Andrew R. Pfeifer- Chardon, Ohio, USA

i. Hi Andrew.

Yes, zinc-rich dip-spin coatings (there are several other suppliers including Magni andDorken) are an excellent alternative finish for many applications in both automotive and

military. They may be the best choice 3 out of ten times or even 7 out of ten times ... butI am very surprised that the Army called them the "best performing alternative for Cad"since most professionals feel that nothing should ever be substituted for cadmium

plating except on a case-by-case basis after design review. Is the army implying thatdip-spin coated fasteners are the best performing alternative for cadmium platedfasteners on aluminum aircraft? I think that would be a horrible mistake. Substitutionwithout a design review is a bad idea.


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Regards,

Ted Mooney, P.E. RETfinishing.comBrick, New Jersey

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A. Cadmium is a great corrosion inhibitor, however we're finding that a properlyplated piece of iron with tin-zinc outperforms the best cadmium plating job.

Tin-zinc is malleable, offers great ductility and torque characteristics without chipping or

flaking off the plated steel part. It offers excellent secondary processing withoutcracking.

Nickel is terrible for all of the above characteristics and offers poor corrosioncharacteristics when even compared to plain old zinc.

Remember, for wear protection, hard chrome and nickel are the best. For corrosionprotection, zinc and cadmium are the best. If you want ultimate corrosion protection, go

with tin-zinc. Zinc-Nickel is okay for corrosion protection but is lacks in secondaryprocessing characteristics. The plating cracks when torquing is applied to the metalpart. Tin-zinc usually doesn't.

Roger Fasting- Sacramento, California, USA

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Q. I would like to know which coating is better Zinc Coating or Nickel Coating. Which one of thetwo will provide better corrosion resistance, surface finish.

Bhavneet Singhbuyer - Shanghai, China

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A. If one coating were just plain better than the other, nobody would ever use theother, Bhavneet. As mentioned above, the corrosion resistance of zinc will be better inmany instances. That's because zinc is anodic to steel and can sacrificially protect it,whereas nickel is not anodic to steel but cathodic. But nickel is self-leveling and willcertainly give a better "surface finish". Please describe the actual component you arethinking about plating, and then people may be able to give you an assessment basedon the function and the environment it will be exposed to. Thanks!

Ted Mooney, P.E. RET

finishing.comBrick, New Jersey

February 26, 2008


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Q. We are looking for a suitable replacement for the zinc coating found on some of our parts.The reason being is zinc's reaction with Polyamides 6 or 66 (reference GM's Worldwide standard-GMW3044). Would nickel plating act as a suitable replacement as far as friction properties areconcerned?

Rick LeslieAutomotive - Troy, Michigan

January 22, 2009

Q. I have a '98 Cadillac Deville...I'm looking to replace all rotors. It's just for daily driving andNOT very aggressive driving. Which plating is better for this application? zinc or cadmium?

Brian johnson

auto repair - Lancaster Texas

January 28, 2009

A. Hi, Brian. Cadmium is a cumulative biotoxin much like Lead and Mercury. It's useis forbidden in many countries, and it should only be used where it's uniquecombination of properties (most of which are listed above) is required.

Because rotors can be satisfactory without cadmium plating, they should not (in myopinion) be cadmium plated.

Regards,


August 9, 2010

Q. I was wondering what would be better concerning self drilling fasteners (Zinc Nickel or Zinc) -both would come with a top coat, but in your opinion which would serve as a more corrosiveresistant undercoat?

many thanks

Donnie Peterson- Melbourne Australia

August 10, 2010

A. Hi, Donnie

Nickel is primarily a decorative finish. It is a "barrier layer" finish: once compromised byporosity or a scratch, it accelerates the rusting of the fastener. Zinc-nickel is a cathodicprotection coating intended as a replacement for cadmium or an improvement uponplain zinc. If you are going to topcoat the fastener, zinc-nickel is almost surely the better

choice and may even be a bit less expensive.


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Regards,

Ted Mooney, P.E. RETfinishing.com

Brick, New Jersey

April 18, 2012

Q. Which plating would be a good alternative to cad plating suspension bolts for a classic carrestoration?The car won't be driven much, just basically need a plating that looks like cad zinc, and will be safeto use.

Mitch Frego- Seattle Washington USA

April 19, 2012

A. Hi Mitch.

Zinc plating is probably okay, and is very widely available. But make sure the platerknows that these are suspension bolts (probably high strength that will requirehydrogen de-embrittlement baking).

Regards,

Ted Mooney, P.E. RET

finishing.comBrick, New Jersey

December 17, 2012

Q. I'm looking for a suitable plating for the steel housing of an E85 compatible fuel pump. Highethanol means the potential for attracting water and the susceptibility to corrosion. The housing isbasically tube steel which is crimped at the top and bottom holding the inlet and outlet caps inplace. Are either of the plating options in this discussion suitable for this application?

Todd Wilson- Jupiter, Florida, USA

April 20, 2013

Q. I am looking for intelligent opinions on plating hardware of all kind on a Porsche road/racecar. This includes engine studs, nuts and bolts vital for engine operation, engine mounting bolts,

etc. Also I am replating all fuel hard lines.I have a selection of zinc platers and one cadmium locally, among others.I have had cad plated in the past and some decorative nickel.Please help if you can. It's greatly appreciated.


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Marcus Herman- Grain Valley, Missouri, USA

April 23, 2013

A. Hi. Even critical jetliner parts are no longer cadmium plated despite its

advantages, so cadmium should not even be considered. Nickel is a decorative finish,not intended primarily for underhood components. Zinc plating should be good. Aplating of zinc alloy like zinc-cobalt, zinc-iron, zinc-nickel, or my preference tin-zincshould be even better.

Regards,


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