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

 

[mfgenggear]

even stainless steel will corrode if there is moisture in the bags. vacuum sealed with gas works as long as there is no leakage.

 

[Viroos]

I wish we could change storage conditions as we want. They were set by our client who integrates our mechanism into his system. Actually, the munition is stored in an outer case with silica gel bag, but the munition itself isn't sealed.
Anyway, what we got is a spec which explicitly requires galvanic potential difference less than 0.25 V or a "proper coating", regardless of storage conditions. We can't just say: "there is a silica gel bag, don't worry, it won't corrode".
Moreover, the outer shell, which is made of aluminum, is also a part of the client's system and its material virtually cannot be changed. On the other hand, our parts cannot be made of aluminum because of strength requirements...

BTW, what's wrong with tin plating? Its galvanic index is -0.65, aluminum is -0.75. Why the tin coating cannot replace cadmium?

 

[WKTaylor]

Viroos...

Tin-plating or TiN coating?

Under certain circumstances, tin-plating can lead to tin-whiskers SAE AIR5444 Investigation of Whisker Formation on Tin Plated Conductors.

Unsealed long-term storage in a less-than-optimum environment] has a high probability of inadvertent moisture intrusion. Packaging that is not physically robust is likely to degrade [thermal, solar, moisture absorption, tear/puncture, etc exposure] regardless of how good it executed at the factory.

100% sealed metal or plastic packaging that must be destructively opened with significant force, such as a 'pop-open can-lid' or 'sardine can tear-strip' [etc, like an aluminum can or plastic bottle], might be a better answer. IF the packaging can survive 10-m water depth pressure variations and handling/transportation shock then unprotected components might survive.

Otherwise, the 'object' needs good individual sealing [resin-seals and paint finishes, CPC, etc] for high reliability moisture exclusion + basic protect.

some Fud-4-Thot...

SAE AIR867 LONG TERM STORAGE FOR MISSILE HYDRAULIC CONTROL SYSTEMS - DESIGN AND OPERATIONAL PRACTICES GUIDE

SAE AIR974 Long-Term Storage of Missile Hydraulic Systems

SAE AIR4725 Long-Term Storage Reliability of High Pressure Gas Containers for Pneumatic Actuation Systems

SAE GEIA-STD-0003 Long Term Storage of Electronic Devices


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]

 

[WKTaylor]

Also...

IN-LIEU OF permanent sealing...

MIL-PRF-6799 COATINGS, SPRAYABLE, STRIPPABLE, PROTECTIVE, WATER EMULSION


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]

Well... we can't require certain storage conditions. Anyway, the munition, of course, will be stored in a controlled environment facility, but it's for sure not hermetically sealed or filled with argon.
Also, we can't seal the device because it must have openings towards client's part of the mechanism, and it's not hermetically sealed for sure.
Sorry, I know it's complicated and far from being optimal, that's why I'm looking for your advice (which doesn't come from the science of logistics haha)