Cadmium vs Zinc-Nickel Plating: When to Switch and How
Keep cadmium to AMS-QQ-P-416 where a qualified drawing, fastener standard or connector class requires it and no alternative is approved. Choose zinc-nickel to AMS 2417, or a low hydrogen embrittlement version qualified for DoD use, for new designs and approved substitutions, after torque, galvanic, embrittlement and finish code questions are closed.
Updated
The short answer, side by side
Cadmium is still the benchmark for sacrificial protection, lubricity and steel in aluminum structure, which is why it survives on qualified aerospace drawings. Zinc-nickel is the most common electroplated replacement, but it is an engineering change with its own test burden, not a drop-in purchasing swap.
| Question | Cadmium | Zinc-nickel |
|---|---|---|
| Main specification | SAE AMS-QQ-P-416, revision G (September 2022); QQ-P-416F cancelled 2002 | SAE AMS 2417, revision K (26 May 2020), first issued 1960 |
| Low hydrogen embrittlement version for DoD aerospace use | Not applicable | MIL-PRF-32660 (10 November 2020) covers LHE alkaline zinc-nickel with 12 to 15 percent nickel; an ESTCP project page says USAF and NAVAIR approvals are limited to LHE zinc-nickel per MIL-DTL-32648 |
| Worker exposure rule | OSHA 29 CFR 1910.1027: PEL 5 µg/m3, action level 2.5 µg/m3 (8 hour TWA) | No cadmium; chromate post-treatments, if hexavalent, fall under OSHA's separate chromium (VI) standard, 29 CFR 1910.1026 |
| EU REACH | Cadmium plating restricted by Annex XVII entry 23; aeronautical and aerospace use with high safety standards is exempted | Not restricted by entry 23 |
| Hexavalent chromium on DoD deliverables | Olive drab and yellow Type II chromates raise the DFARS 252.223-7008 question | Same question if the passivate is hexavalent; trivalent passivates avoid it |
| Hydrogen embrittlement | Electroplate; bake and test required on high strength steel | Electroplate; same controls unless an LHE process is qualified for the part |
| Torque-tension | Industry benchmark for lubricity | Close to cadmium in Alcoa and Lockheed Martin tests, with higher values in some multi-cycle tests |
| NASA EEE parts | Prohibited without project waiver | NASA's zinc prohibition names zinc plating; zinc-nickel is not named, so ask project materials engineering |
| Connector finish | D38999 Class W; Glenair code NF | D38999 Class Z (black); Glenair codes ZR (black) and ZN (olive drab) |
Cadmium types, classes, defaults and thickness methods are on our aerospace plating reference. This page goes into the replacement decision itself.
Why cadmium is being replaced
No single rule bans aerospace cadmium in the United States; the pressure comes from worker exposure rules, European restrictions, the DoD hexavalent chromium clause and service-funded replacement programs acting together.
- OSHA. 29 CFR 1910.1027 limits airborne cadmium to 5 micrograms per cubic meter as an 8 hour average, with an action level of 2.5. Plating, stripping, grinding and touch-up all create exposure, which shrinks the pool of shops willing to keep cadmium lines.
- REACH. Annex XVII entry 23 defines cadmium plating as any deposit or coating of metallic cadmium on a metallic surface and prohibits it for listed equipment and machinery sectors, then exempts articles used in the aeronautical, aerospace, mining, offshore and nuclear sectors whose applications require high safety standards, plus certain safety devices and electrical contacts. That is the consolidated text as of 31 January 2020; check the current EU text for later amendments. Aerospace cadmium is therefore exempted, not banned, but the exemption is scoped, and EU customers and supply chains ask about it.
- DFARS 252.223-7008 (January 2023). Unless the contracting officer specifies otherwise, deliverables may not contain more than 0.1 percent hexavalent chromium by weight in any homogeneous material, and may not require hexavalent chromium materials to be removed or reapplied during sustainment. The clause addresses chromium, not cadmium, but Type II cadmium is cadmium plus a chromate, so the post-treatment is where the clause bites.
- Service programs. The DoD's ESTCP program lists a project, WP26-9089, validating low embrittling zinc-nickel on aerospace fasteners, with completion anticipated in 2029. Its page states that Navy gravelometer coupon data showed five times better corrosion performance for zinc-nickel than cadmium, and that LHE zinc-nickel has not yet been approved by the USAF and Navy for high strength aerospace fasteners.
The DFARS definition is worth reading closely. It counts surface coatings as homogeneous materials but excludes conversion coatings that chemically modify the substrate. Whether a chromate passivate over cadmium or zinc-nickel plate falls inside that carve-out is a question for your contracting officer, not your plater. Our chem film page covers the clause's exemptions and authorization levels.
Have a part like this?Send it in under a minute. A person replies within 1 business day.Corrosion and galvanic behavior with aluminum
The reason cadmium persists is the steel fastener in aluminum structure: the coating has to protect the steel sacrificially without driving attack on the aluminum around it. Zinc-nickel can do that, but published results vary with formulation, passivate and test, so ask for data on your actual couple.
Two sources point in different directions, and both are useful to an engineer:
- Newer Navy data. The ESTCP project page cites Navy gravelometer coupon testing showing five times better corrosion performance for zinc-nickel than cadmium.
- An older Army assembly test. A 1999 Products Finishing article by an engineer at the U.S. Army Tank-Automotive and Armaments Command reported zinc-nickel at about -0.80 V against -0.87 V for aluminum alloy 5083, which predicted minimal galvanic interaction. In fastened assemblies, though, zinc-nickel was the only finish attacked on both the inside and outside diameter under the flange nut, and nickel at corrosion sites rose from about 11 percent to 29 percent as zinc was removed preferentially. Deepest average pits grew from 0.19 mm at 80 cycles to 1.4 mm at 120 cycles, against 0.16 and 0.3 mm for cadmium with olive drab chromate. The author warned that material loss at a bearing surface means loss of preload over time.
That test used a yellow chromated commercial zinc-nickel bought to an automotive spec, so it does not describe current aerospace processes. What it does show is the failure mode to test for: dezincification under a clamped joint that leaves a nickel rich, more cathodic surface against aluminum. Check the coupling against the current MIL-STD-889 revision on ASSIST and require a coupled corrosion test on the joint, not just flat panels in salt spray.
For copper, titanium or stainless parts in aluminum structure, IVD aluminum is the other alternative; its classes and limits are on the plating reference.
Lubricity and torque-tension
Cadmium smears under load and acts as a thread lubricant, so torque tables written around cadmium can deliver different preload on zinc-nickel. Published fastener tests show zinc-nickel close to cadmium, not identical.
- A 2006 SAE paper by Alcoa Fastening Systems and Lockheed Martin Aeronautics (2006-01-3169) found that in torque-tension tests zinc-nickel performed nearly as well as cadmium, judged it the coating that best mimicked cadmium overall, and concluded that no single coating offered cadmium's broad range of properties.
- The third paper in that series (2009-01-3228) found all candidates needed similar torque to reach the required tension because of surface lubrication, but zinc-nickel showed increased values, especially on NAS1580 fasteners, in multi-cycle run-on and breakaway tests.
- The 1999 Army article reported a 17 percent rise in break-loose torque for zinc-nickel in its assembly test.
Practical rule: if the joint is preload critical, re-establish the torque-tension relationship with the new coating, the actual lubricant or anti-seize, and the mating nut or insert finish before changing the callout. If the assembly will be reused, include multi-cycle tests, because that is where the published results diverged. Fastener buying with traceability is covered in our bolts and screws section.
Hydrogen embrittlement and bake
Both coatings are electroplates, so both can embrittle high strength steel, and switching to zinc-nickel does not remove the bake or the test. The difference is that zinc-nickel has dedicated low hydrogen embrittlement (LHE) process specifications aimed at high strength steel.
- Cadmium. The QQ-P-416F text adopted by SAE required the relief bake within 4 hours of plating and barred plating parts above 200 ksi unless the order allowed it; the details are on our plating reference.
- AMS 2417 zinc-nickel. Treat it like any electroplate on steel: stress relieve before, bake after, record the bake on the cert, and read the current AMS 2417 for its own requirements rather than a vendor summary.
- LHE zinc-nickel. MIL-PRF-32660 covers alkaline LHE zinc-nickel with 12 to 15 percent nickel as a cadmium alternative. The ESTCP project page refers to approvals under MIL-DTL-32648. Confirm the current document, its qualified products list and whether your part's strength level is within its approved scope on ASSIST before you write it on a drawing.
- Proof testing. ASTM F519 is the common mechanical test for showing a plating or coating process does not cause hydrogen embrittlement, used both to qualify a new process and as a periodic audit. A new zinc-nickel line, a new passivate or a new pretreatment is a process change that should be requalified.
Give the plater the steel, heat treat condition and hardness on every order. Relief bake practice in general is on our heat treatment page.
AMS-QQ-P-416 vs AMS 2417: the specification map
| Document | What it covers | Status as checked October 2026 |
|---|---|---|
| QQ-P-416F | Electrodeposited cadmium | Cancelled 28 March 2002; future acquisition to SAE AMS-QQ-P-416 |
| SAE AMS-QQ-P-416 | Electrodeposited cadmium, Types I to III, Classes 1 to 3 | Revision G, September 2022 |
| SAE AMS 2417 | Nickel-zinc alloy plating | Revision K, 26 May 2020; prior revisions 2013, 2010, 2004 |
| MIL-PRF-32660 | LHE alkaline zinc-nickel, 12 to 15 percent nickel | Listed active by EverySpec, 10 November 2020; confirm the current revision on ASSIST |
| MIL-DTL-32648 | LHE zinc-nickel, named on the ESTCP project page as the basis of USAF and NAVAIR approvals | Confirm the current revision and QPL on ASSIST |
| ASTM B841 | Electrodeposited zinc-nickel, cited by Glenair for its connector finishes (Grade 5 over electroless nickel) | Confirm the current revision with ASTM |
| DFARS 252.223-7008 | Hexavalent chromium in deliverables | January 2023 |
The practical difference between the two SAE documents is the callout structure. AMS-QQ-P-416 uses type for the supplementary treatment and class for thickness, with defaults that apply if the drawing is silent. AMS 2417 has its own structure; do not translate a cadmium type and class into zinc-nickel terms by analogy. Have engineering write the zinc-nickel callout from the current AMS 2417 or LHE document.
Connector finish codes
On connectors and backshells the plating is part of the part number, so changing from cadmium to zinc-nickel means ordering a different part. The MIL-DTL-38999 classes (W for olive drab cadmium, Z for black zinc-nickel) and their temperature and salt spray ratings are covered on our circular connectors page. Manufacturer codes add another layer. In Glenair's 2013 materials and finish appendix:
| Glenair code | Base | Finish as Glenair states it |
|---|---|---|
| NF | Aluminum | Olive drab cadmium, AMS-QQ-P-416 Type II Class 2 over electroless nickel |
| XW | Composite | Olive drab cadmium, AMS-QQ-P-416 Type II Class 3 over electroless nickel |
| ZN | Aluminum | Olive drab zinc-nickel, ASTM B841 Grade 5 over electroless nickel |
| ZR | Aluminum | Black zinc-nickel, ASTM B841 Grade 5 over electroless nickel, described as RoHS compliant |
| ZU | Stainless steel | Black cadmium, AMS-QQ-P-416 Type II |
- Olive drab zinc-nickel (ZN) exists for programs that want the familiar color; the D38999 Class Z finish is black. Check which one your drawing or harness spec actually allows.
- Keep the connector, backshell and accessories on a consistent finish, or have engineering accept the mixed couple, since the coupled metals at the interface change.
- Olive drab cadmium is a chromate over cadmium. On contracts with DFARS 252.223-7008, get the hexavalent chromium question answered for the specific finish before release.
Approval and qualification steps
A cadmium to zinc-nickel change is owned by the design authority. The buyer's job is to make sure each of these steps has an owner and a record before parts are ordered.
- Find who owns the callout. A drawing note, a fastener standard, a connector slash sheet or a QPL can each fix the finish. You cannot change a standard part's finish by PO note.
- Open an engineering change. State the reason: DFARS, supplier availability, REACH, or a program decision.
- Define the test matrix. Coupled corrosion on the real joint, hydrogen embrittlement per ASTM F519 on the actual process, torque-tension and multi-cycle run-on and breakaway with the actual lubricant, electrical bonding resistance where the joint is a bond path, and paint adhesion if the part is painted.
- Pick the passivate deliberately. Trivalent or hexavalent, with the DFARS determination on file.
- Qualify the processor. Customer approved source, Nadcap chemical processing if flowed down, and QPL listing where the governing document has one.
- Run a first article. Thickness, adhesion and bake records on the first production lot, per your AS9102 practice.
- Update downstream documents. Torque tables, repair and touch-up instructions (the DFARS sustainment wording matters here) and the parts list.
Choose cadmium when, choose zinc-nickel when
| Keep cadmium when | Choose zinc-nickel when |
|---|---|
| A qualified drawing, fastener standard or connector class requires it and no alternative is approved | The design is new, or the design authority has approved the substitution |
| Preload critical joints have torque data only for cadmium | Torque-tension has been re-established on the new coating |
| A legacy sustainment contract already authorizes the finish | The contract carries DFARS 252.223-7008 and a trivalent passivate is acceptable |
| The part is high strength steel and no LHE zinc-nickel approval covers its strength level | An LHE process qualified to the governing document covers the part |
| Mating hardware is cadmium and mixed finishes are not accepted | REACH, customer policy or plater availability rule out cadmium |
For space EEE hardware, neither may be the answer: NASA's parts selection list prohibits cadmium and zinc plating without a project waiver, citing sublimation in vacuum and whisker growth, and electroless nickel finishes are the usual route.
Callout examples
Example formats only; engineering must confirm each document's current revision on ASSIST or SAE and the approved type, class and passivate.
- Cadmium: CADMIUM PLATE PER AMS-QQ-P-416G, TYPE II, CLASS 2. MATERIAL 4340, HEAT TREATED TO [strength]. STRESS RELIEVE BEFORE PLATING; HYDROGEN EMBRITTLEMENT RELIEF BAKE AFTER PLATING, RECORD ON CERT.
- Zinc-nickel to AMS 2417: ZINC-NICKEL PLATE PER AMS 2417K, [type, thickness and supplementary treatment as defined in AMS 2417K]. SUPPLEMENTARY TREATMENT SHALL BE FREE OF HEXAVALENT CHROMIUM. BAKE AND RECORD AS ABOVE.
- LHE zinc-nickel: LHE ZINC-NICKEL PLATE PER [MIL-PRF-32660 or MIL-DTL-32648, current revision], FROM A QUALIFIED SOURCE. HYDROGEN EMBRITTLEMENT TEST PER ASTM F519 AS REQUIRED BY THE GOVERNING DOCUMENT.
- Connector: order the manufacturer part number with the approved finish code (for example a D38999 Class Z part, or the approved Glenair code), never "equivalent finish".
What to put on the PO
- Coating spec and revision, with type, class or grade, and the passivate
- Whether the passivate must be free of hexavalent chromium, and whether the contract carries DFARS 252.223-7008
- Base material, heat treat condition and hardness, and the bake requirement
- Hydrogen embrittlement test frequency per the governing document
- Masking and protection of internal threads and bores
- Approved source, Nadcap or QPL requirement
- The engineering change or deviation number that authorizes a zinc-nickel substitution, if one applies
- A plating cert per lot, separate from the machining cert, with bake time and temperature
Routing with heat treat and paint is on our special processes page and cost drivers are on the special process cost page. For aluminum parts the parallel decision is Type II vs Type III anodize; the rest is in the coatings library.
Get cadmium or zinc-nickel plating sourced with the approvals in place
Send the drawing, base material, heat treat condition and any engineering change through the special process request form. We source platers that hold the approvals your callout needs, flow down the spec, passivate, bake and embrittlement test requirements, and check each plating cert against the drawing before parts ship. A person replies within one business day. Defense drawings and export controlled data follow our controlled programs process, never the website.
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Questions
Is zinc-nickel a drop-in replacement for cadmium plating?
No. It is the closest electroplated match in published fastener tests, but torque-tension, galvanic behavior with aluminum, hydrogen embrittlement controls, conductivity and paint adhesion all need review. Alcoa and Lockheed Martin concluded no single coating matched cadmium across all properties. The design authority must approve the change, and standard parts and connectors need a different part number, not a PO note.
Is cadmium plating banned for aerospace?
Not under the documents reviewed here. OSHA regulates worker exposure under 29 CFR 1910.1027 rather than banning the process. REACH Annex XVII entry 23 restricts cadmium plating in listed sectors but exempts aeronautical and aerospace articles whose applications require high safety standards. NASA prohibits cadmium on EEE parts without a project waiver, and DFARS 252.223-7008 limits the hexavalent chromate often applied over cadmium.
Does DFARS 252.223-7008 apply to olive drab cadmium?
It can. Olive drab and yellow cadmium finishes use a chromate supplementary treatment. The January 2023 clause limits hexavalent chromium to 0.1 percent by weight in any homogeneous material unless the contracting officer specifies otherwise, and it excludes conversion coatings that chemically modify the substrate. Whether that exclusion covers a chromate over plating is a contracting officer decision, so get it in writing.
Does zinc-nickel still need a hydrogen embrittlement bake?
Yes, on high strength steel, unless a low hydrogen embrittlement process qualified to the governing document says otherwise. Zinc-nickel is an electroplate like cadmium. MIL-PRF-32660 covers an alkaline LHE zinc-nickel, and the ESTCP project page says USAF and Navy approval for high strength aerospace fasteners was still pending. Require the bake record and ASTM F519 testing as the document directs.
What is the difference between D38999 Class W and Class Z?
Class W is olive drab cadmium over electroless nickel on an aluminum shell; Class Z is black zinc-nickel on an aluminum shell, sold as the cadmium free option. They are different part numbers, and swapping them is a configuration change. Manufacturer codes also differ: Glenair lists NF for olive drab cadmium and ZR for black zinc-nickel, plus ZN for olive drab zinc-nickel.
Will zinc-nickel change my fastener torque values?
Possibly. A 2006 Alcoa and Lockheed Martin SAE paper found zinc-nickel performed nearly as well as cadmium in torque-tension tests, but their 2009 follow-up saw higher values in multi-cycle run-on and breakaway tests, and a 1999 Army test reported a 17 percent rise in break-loose torque. Re-establish torque-tension with your actual lubricant and mating hardware before changing a preload critical joint.
Related
Sources
- OSHA: 29 CFR 1910.1027 Cadmium
- legislation.gov.uk: REACH Regulation (EC) 1907/2006 Annex XVII, entry 23 cadmium (version of 31 January 2020)
- Acquisition.gov: DFARS 252.223-7008 Prohibition of Hexavalent Chromium (January 2023)
- SERDP and ESTCP: WP26-9089 Validation Testing of Low Embrittling Zn-Ni Plating of Aerospace Fasteners
- EverySpec: MIL-PRF-32660, Plating, Zinc-Nickel Alloy, Low Hydrogen Embrittlement, Alkaline Electro-Deposited (10 November 2020)
- SAE Mobilus: AMS2417 Nickel-Zinc Alloy Plating (revision history)
- SAE Mobilus: AMS-QQ-P-416G, Plating, Cadmium (Electrodeposited) (September 2022)
- SAE Technical Paper 2006-01-3169: Evaluation of Alternatives to Electrodeposited Cadmium for Threaded Fastener Applications (Alcoa Fastening Systems, Lockheed Martin Aeronautics)
- SAE Technical Paper 2009-01-3228: Evaluation of Alternatives to Electrodeposited Cadmium for Threaded Fasteners Applications (III)
- Products Finishing (February 1999): Long-Term Performance of Cadmium Alternatives, U.S. Army TACOM
- Glenair (2013): Selected material and finish options for Glenair connectors and backshells
- NASA NEPP Parts Selection List: zinc plating prohibition
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