Cadmium Plating 1

[Viroos]

Hi,
In order to provide long-term galvanic corrosion protection for steel parts contacting other aluminum parts we'd like to plate steel parts with cadmium (already having alodine coating on aluminum). Also, these steel parts are of high precision and must withstand very high loads, so originally we make them from SS 17-4PH Condition H900.
1. Is it OK to plate 17-4PH with Cadmium?
2. Could you recommend on other high-performance steel with low distortion during heat treatment which is better for Cadmium plating?
Thanks in advance,
Max

 

[dik]

For environmental reasons, you should not use cadmium. With very few exceptions it is banned in Europe... With the election of the Donald, cadmium may find its way into baby food cans...

Dik

 

[Viroos]

Hi Dik,
We know that, but for some applications, like aviation, it's still widely used.
Anyway, I'd be thankful for any advice regarding alternative plating (like IVD) as well.

 

[dik]

Even electrical aviation components are being restricted.

Dik

 

[dik]

Is the area wet or dry, indoors, outdoors and/or near the oceans or other 'salty' environment? Can the surfaces be electrically isolated? Cadmium may be the only alternative.

Dik

 

[Viroos]

It may be wet, outdoors, and the surfaces cannot be isolated.

 

[EdStainless]

Plating of any high strength material is problematic, and 71-4 at peek strength is no exception.
Care in preparation, plating, and baking after are all required.
There are documents covering this, AMS specs and NASA studies. I am sure that there are MIL and USAF docs as well, but I have never used those.
You do know that 17-4 H900 is susceptible to SCC and other forms of environmentally assisted cracking and has restriction on usage?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Viroos]

EdStainless,
Sorry, haven't got it... what kind of restrictions?
Could you advise on a better steel? I think having the plating it shouldn't be stainless steel, am I right?

 

[mrfailure]

Cad plating is the very last alternative you should consider due to the safety concerns already raised. I suggest you actually contract an appropriate materials engineering consultant with experience in your system to help you select these materials.

 

[israelkk]

From ar-mmpds-01 (MIL-HDBK-5J) here is a quote:
"The impact strength of 17-4PH, especially large size bar in the H900 and H925 conditions, may be very low at subzero temperatures; consequently, the use of 17-4PH for critical applications at low temperatures should be avoided. For non-impact applications, such as valve seats, parts in the H925 condition have
performed satisfactorily down to -320EF. The H1100 and H1150 conditions have improved impact strength so that parts made from small diameter bar can be used down to -100EF with low risk. For critical low temperature applications, a similar alloy, 15-5PH (consumable electrode vacuum melted), should be used instead of 17-4PH because of its superior impact strength at low temperature."

You mentioned outdoor use. The "alodine coating on aluminum" is not enough for outdoor use it has to be Aluminum anodize (Sulfuric acid anodizing or Chromic acid anodizing. See MIL-A8625) depends on the Aluminum alloy. It is also requires a specific minimum coating thickness.

 

[EdStainless]

Thanks IS, was more concerned about SCC and other stress cracking issues.
I have NASA documents that prohibit the use of aging temps below 1025F if the part is in an open environment. If it is inside a sealed unit then they would allow it.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[WKTaylor]

Not having a clear understanding of exactly WHAT you are doing, with what alloy-spec, with what heat treatment process, in what kind of environment, for how long, etc...

17-4PH H900 per MIL-HDBK-1587 Table 1 Restricted Materials this is prohibited from use in MIL aerospace vehicles [SCC prone and low fracture toughness]

Per MMPDS-10, Table 2.6.9.0(e) 17-4PH H900 => Ftu = 190-KSI min, Fty = 170-KSI Min, Fcy = 170-KSI, Fsu = 123-KSI, FBru2.0 = 380-KSI, FBry = 280-KSI

Recommended replacement...

PH18-8Mo AMS5934 Steel, Extra High Toughness, Corrosion-Resistant, Bars, Wire, Forgings, Rings, and Extrusions.... Rough machine to W/in ~0.1-0.2-inch of finished contour, then PHT to condition H1000 per AMS2759/3. After finish machining, stress relieve per AMS2759/11. Mechanical allowables equal or =or-better and defined fairly high KIc, etc... relative to 17-4PH.

Apply Zinc-Nickel alloy plating AMS2417 [0.0003--0.0005] Type 2 [with post plating chromate treatment]. Hydrogen embrittlement relief bake plated part W/in 4-hrs after plating [before application of chromate treatment] per AMS2759/9.

Also apply Epoxy primer [MIL-PRF-23377 type I class C1, C2 or N [0.0008--0.0016 DFT] or 'other' epoxy primer [W/WO Special capabilities, IE: very high temp] per MIL-DTL-18264.

IF PRACTICAL, in-lieu of chromate conversion coating [CCC, 'alodine'], anodize the aluminum surface in contact W CRES per MIL-A-8625 Class IA, 1C or IIB + apply epoxy primer [noted].

Also. Assemble parts and install fasteners 'wet' with sealant MIL-PRF-81733 [type/class/time TBD by YOU]... or equiv.

Just saying... typical structural assy.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[tbuelna]

The EU has a general prohibition on importing products using Cd plating, conversion coatings using chromates, or chromic acid anodizing. But at one time there were exemptions allowed for some aerospace products. If this product will be exported to an EU member nation, this RoHS compliance is something you might want to look into.

 

[WKTaylor]

Viroos...FYI

Zinc-Nickel alloy plating AMS2417 Type 2 chromate treatment options...
Grade A Hexavalent chromate treatment, service temperature 250 °F (121 °C) max. [VERY Bad]
Grade B Trivalent chromium treatment, service temperature 375 °F (191 °C) max. [sorta bad]

Zinc-Nickel alloy plating AMS2417 Type 3 has a post plating phosphate treatment for improved paint/primer adhesion.

MIL-A-8625 Type IIB is a thin film sulfuric acid anodic [TFSAA] coating.

MIL-PRF-23377 Ty I Class N is non-chromated is [low VOC] solvent-borne.
MIL-PRF-85582 Ty I Class N is non-chromated is water-borne

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Viroos]

Sorry, I've been away for a long time...
Thank you very much for your answers, they're very helpful!
Regarding the design-I'm talking about Coke can size electro-mechanical munition subsystem, with motors, levers, lead screws and controller PCB inside, which has to be stored for 20 years at -40...+85 degC temperatures and still has to operate, only once, for a short period of time (the munition isn't not reusable, of course). The system is a kind of a closed box, but it's not hermetically sealed.
When it's taken out of a storage facility, it may be outside for a couple of weeks until it's used.
The mechanism is built of 7075 aluminum case, some 7075 aluminum parts and some high-precision high-strength steel parts, and we haven't finally decided regarding the materials. Because of the required precision, the parts cannot be coated in any coating which is thicker then several microns.
Our main fear is the galvanic corrosion. We've found an alternative coating of the steel with aluminum, called IVD - Ion Vapor Deposition, but it seems to be unavailable in my country. What would you recommend, having this additional info?
Thanks in advance.

 

[Viroos]

...this is a part of the mechanism. All these items are made of steel, but they contact aluminum parts which I cannot show here. The bore in the slotted cylinder is 5.5 mm dia., its length is 30 mm.

 

[WKTaylor]

Viroos... Perhaps...

Titanium Nitride [TiN] coating...

AMS2444 Coating, Titanium Nitride Physical Vapor Deposition

SAE AMS03-28 PART 3 Physical Vapor Deposition of Metals: Physical Vapor Deposition of Titanium Nitride for Surface Protection

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[EdStainless]

They really want 20 year shelf life and they are not sealing it?
Best of luck to you.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[mfgenggear]

any time a coating or plating is involved it makes it a nightmare to maintain precision tight assembly. maintaining precision tolerance of the loose parts.. it is better to obtain a material that does not require plating or coating if possible. I would suggest a stainless like Will Taylor suggested. would dry film lube work? to help isolate the parts. or maybe a thick coat of lube that can be easily cleaned off or removed prior to use. since it is only for storing.

 

[WKTaylor]

viroos... fud-4-thot...

MIL-STD-331 FUZE AND FUZE COMPONENTS, ENVIRONMENTAL AND PERFORMANCE TESTS FOR

MIL-HDBK-1455 DISPENSER AND SUB-MUNITION, AIR DELIVERED, SAFETY DESIGN AND SAFETY QUAUFICATION CRITERIA FOR

MIL-STD-1466 SAFETY CRITERIA AND QUALIFICATION REQUIREMENTS FOR PYROTECHNIC INITIATED EXPLOSIVE (PIE) AMMUNITION

MIL-STD-1512 ELECTROEXPLOSIVE, SUBSYSTEMS, ELECTRICALLY INITIATED, DESIGN REQUIREMENTS AND TEST METHODS

MIL-STD-1751 SAFETY AND PERFORMANCE TESTS FOR QUALIFICATION OF EXPLOSIVES

MIL-STD-1911 HAND-EMPLACED ORDNANCE DESIGN, SAFETY CRITERIA FOR

NATO AASTP-1 NATO GUIDELINES FOR THE STORAGE OF MILITARY AMMUNITION AND EXPLOSIVES

SAE AIR1412 DESIGNING FOR LONG-LIFE WITH ELASTOMERS

SAE ARP1833 SEALING TECHNIQUES FOR MISSILE APPLICATIONS

NOTE.
A trick for long-term storage where loss of environmental sealing is required: Pressurize the component with dry nitrogen or argon... and have a small pressure gage or port to which a dial indicator or perhaps electronic indicator is attached. IF positive-pressure seal is lost [IE: due to leakage of any kind], then the gage/electronics will report loss of seal integrity. This system must be robust to survive extreme temperature and storage environment... then survive delivery to combat and final flight/delivery to target.

NOTE.
Helicopter rotor blades are often pressurized and an electronic sensor reports when pressure is breached due to any reason [cracks, corrosion impact damage, penetration, etc]. When this happens it is wise to land ASAP.

MIL-PRF-32014 GREASE, AIRCRAFT AND INSTRUMENT

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]