Aerospace Plating and Cadmium Alternatives: Specs and Callouts
Cadmium plating is bought to SAE AMS-QQ-P-416 by type (supplementary treatment) and class (minimum thickness); its main alternatives are zinc-nickel to AMS 2417 and high purity aluminum such as IVD to MIL-DTL-83488. Nickel and chromium are bought to AMS specs that replaced the cancelled federal QQ documents, and every electroplate on high strength steel needs an embrittlement plan.
Updated
Spec map: what replaced what
Most legacy plating callouts still cite federal QQ specs that were cancelled around 2001 and 2002 and moved to SAE as AMS-QQ documents. Several have since been replaced again by native AMS specs. Check the status before you copy an old callout onto a new drawing.
| Spec | 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 | Active, revision G, September 2022 |
| SAE AMS 2417 | Electrodeposited zinc-nickel alloy | Active, revision K, May 2020 (first issued 1960) |
| MIL-DTL-83488 | High purity aluminum coating (IVD, sputtered or organic electrolyte electroplate) | Revision D, 1 April 1999 reviewed here; confirm current revision on ASSIST |
| QQ-N-290A | Electrodeposited nickel | Cancelled 3 May 2001; future acquisition to SAE AMS-QQ-N-290 |
| SAE AMS-QQ-N-290 | Electrodeposited nickel on steel, copper and zinc alloys | Active, revision D, October 2021 |
| SAE AMS 2423 | Nickel plating, hard deposit | Active, revision F, July 2022 |
| QQ-C-320B | Electrodeposited chromium | Cancelled 3 May 2001; future acquisition to SAE AMS-QQ-C-320 |
| SAE AMS-QQ-C-320 | Electrodeposited chromium | Listed by SAE as cancelled (July 2007, January 2008) |
| SAE AMS 2460 | Plating, chromium | Active, issued July 2007, revision B February 2023 |
| SAE AMS 2404 | Electroless nickel | Active, revision K, October 2024 |
| SAE AMS-C-26074 | Electroless nickel coatings | Revision D stabilized June 2013 (earlier cancelled 2011, noncurrent 2005) |
AMS 2460 was issued the same month SAE first cancelled AMS-QQ-C-320, and it is the SAE chromium plating spec in current use; if an old drawing still says QQ-C-320, ask engineering to choose the AMS 2460 class and type explicitly rather than letting the plater map it. The electroless nickel classes are summarized on our surface finishing page and are not repeated here. AMS-C-26074D is stabilized, so for new designs ask engineering whether AMS 2404 should be called out instead.
Cadmium: types, classes and defaults
Cadmium plating is called out by type and class. The definitions below are from the federal QQ-P-416F text that SAE adopted as AMS-QQ-P-416; confirm them against revision G, since SAE has revised the document several times.
| Designation | Meaning |
|---|---|
| Type I | As plated |
| Type II | With supplementary chromate treatment (iridescent bronze to brown, olive drab, yellow or forest green) |
| Type III | With supplementary phosphate treatment |
| Class 1 | 0.00050 in minimum on surfaces a 0.75 in ball can touch; 0.00030 in on surfaces it cannot |
| Class 2 | 0.00030 in minimum; 0.00020 in where the ball cannot reach |
| Class 3 | 0.00020 in minimum; 0.00015 in where the ball cannot reach |
The defaults matter. If no class is given, the plating is Class 2. If no maximum is given, the maximum is the minimum plus 0.0003 in. Unless the order says otherwise, parts that will not be completely painted get Type II and parts that will be completely painted get Type III. Internal surfaces, including internal threads, are exempt from thickness requirements, so if a bore needs protection the drawing must say how. If the contract restricts hexavalent chromium, ask whether the plater's Type II chromate is hexavalent; the DFARS clause is discussed on our chem film page.
The QQ-P-416F text also sets limits that drive part design: parts above 200 ksi ultimate tensile strength (about HRC 43) are not plated to the spec unless the order allows it, and brighteners are prohibited on parts at 160 ksi (HRC 36) or higher. Type II salt spray acceptance was 96 hours without white cadmium corrosion, pitting or base metal corrosion. OSHA's cadmium standard, 29 CFR 1910.1027, sets a permissible exposure limit of 5 micrograms per cubic meter and an action level of 2.5, both as 8 hour averages.
Have a part like this?Send it in under a minute. A person replies within 1 business day.Hydrogen embrittlement relief and testing
Every electroplate on high strength steel can trap hydrogen, and the bake has to be scheduled, not remembered. The heat treat page covers AMS 2759/9 relief baking in general; these are the plating specific rules buyers trip over.
- Timing. QQ-P-416F required the bake within 4 hours after plating, and plated springs and other flexing parts may not be flexed before the bake.
- Order of operations. On Type II and III cadmium the bake comes before the supplementary chromate or phosphate. Cadmium passivated by the bake must be reactivated before chromating.
- Stress relief first. Parts machined, ground, cold formed or straightened after heat treatment get a stress relief before plating. Rolled threads and cold worked fillets on fasteners are exempt because the work leaves compressive stress.
- Cleaning. Fasteners at 160 ksi or higher are abrasive cleaned for scale; pickling is not permitted, and cathodic electrocleaning is not used.
- Proof testing. Embrittlement testing applies to parts heat treated to 160 ksi (HRC 36) or above. The QQ-P-416F method plated four notched round specimens of 4340 steel with the lot, at the same or higher strength than the parts, and held them at 75 percent of notched ultimate strength for at least 200 hours with no cracking or fracture.
Stripping counts as well. MIL-DTL-83488D requires steel parts at HRC 40 or above that are stripped in caustic to be baked afterward. Put the part's material, heat treat condition and hardness on the PO for every plating job on steel, and ask for the bake time and temperature on the cert.
IVD aluminum and other high purity aluminum coatings
MIL-DTL-83488 covers coating low alloy steel, stainless, aluminum, copper and titanium alloys with aluminum of at least 99.0 percent purity. Ion vapor deposition (IVD), sputtering and electroplating from an organic electrolyte all qualify, and MIL-DTL-5541F describes IVD aluminum as used on many military platforms as a cadmium alternative or galvanic corrosion inhibitor.
| Class | Minimum thickness | Salt spray, Type I | Salt spray, Type II |
|---|---|---|---|
| 1 | 0.0010 in | 504 h | 672 h |
| 2 | 0.0005 in | 336 h | 504 h |
| 3 | 0.0003 in | 168 h | 336 h |
Type I is as coated and Type II adds a MIL-DTL-5541 Class 1A chromate, and Type II is the default. Parts that need electrical conductivity get a chromate that meets both Class 1A and Class 3. Use Class 1 where tolerance permits, Class 2 where Class 1 is too thick, and Class 3 for close tolerance and finely threaded parts such as bushings, pins and fasteners. Appearance of white corrosion products on the aluminum layer during salt spray is not a rejection; base metal corrosion is.
The spec's notes list the reasons engineers choose it: no hydrogen embrittlement on high strength steel, service up to 925 °F, use in lieu of anodize on fatigue critical aluminum structure, and galvanic compatibility for copper, titanium and stainless parts in aluminum structure. The same notes warn that process control is critical because the coating can change fatigue life or strength on aluminum substrates.
Zinc-nickel and choosing a replacement
SAE AMS 2417 covers the electrodeposition of a zinc-nickel alloy and the properties of the deposit; it has been revised many times since 1960 and is at revision K (May 2020). Because zinc-nickel is electroplated, the same hydrogen embrittlement controls apply to high strength steel as for cadmium, and the bake requirements should be on the order. Read the current AMS 2417 for its alloy composition range, types and supplementary treatments rather than relying on a vendor summary.
Swapping cadmium for zinc-nickel or IVD aluminum on an existing part is an engineering change, not a purchasing substitution. The questions that decide it:
- Fastener torque and preload, if the new coating behaves differently in friction
- Galvanic compatibility with the mating structure, usually aluminum
- Electrical bonding and conductivity requirements
- Embrittlement risk: IVD avoids hydrogen charging; electroplates do not
- Coverage and thickness distribution in bores, threads and recesses
- Paint adhesion over the new coating and its supplementary treatment
- Whether the supplementary chromate is hexavalent, given DFARS 252.223-7008
Plated hardware on a parts list carries its own spec, often a fastener standard that names the plating; our fasteners section covers buying those with traceability.
Measuring plating thickness
Plating thickness is measured on the parts, at the locations the spec or drawing defines, and the measurement method should be agreed before a dispute. The QQ-P-416F text named these methods, and they remain the common toolkit:
| Method | Standard | Notes |
|---|---|---|
| Magnetic | ASTM B499 | Nonmagnetic coating on magnetic steel; nondestructive |
| Eddy current | ASTM B244 | Nonconductive coatings on nonmagnetic bases; also used for anodize and paint |
| Beta backscatter | ASTM B567 | Nondestructive |
| X-ray fluorescence | ASTM B568 | Nondestructive |
| Microscopic cross section | ASTM B487 | Destructive |
| Coulometric | ASTM B504 | Destructive; strip the chromate or phosphate first |
For Types II and III cadmium, the minimum thickness is met after the supplementary treatment. Fastener measurement locations follow MIL-STD-1312-12. QQ-P-416F rejected a part if any single reading fell below the minimum, sampled lots at inspection level II with an AQL of 1.5 percent, and did not allow separate test specimens to stand in for thickness checks on parts. Our receiving inspection page covers how to check certs and readings when plated parts arrive.
What to call out on the drawing or PO
- Current spec and revision (AMS-QQ-P-416G, AMS 2417K, MIL-DTL-83488, AMS 2460B, AMS-QQ-N-290D, AMS 2404K), not the cancelled QQ number
- Type and class, or the thickness range, and whether the dimension applies before or after plating
- Supplementary treatment, and whether it must be free of hexavalent chromium
- Base material, heat treat condition and hardness or strength
- Stress relief before plating and embrittlement relief bake after, with the bake recorded on the cert
- Embrittlement test requirement and sampling, for parts at 160 ksi and above
- Masked areas and protection required on internal surfaces and threads
- Thickness measurement method and locations
- Prime approved source or Nadcap chemical processing requirement
- One cert per lot from the plater, separate from the machining cert
How plating fits into a routing with heat treat, NDT and paint is on our special processes page, and the cost drivers are on the special process cost page. Back to the coatings library.
Get plating sourced with the embrittlement plan in place
Send the drawing, material and heat treat condition through the special process request form. Those three details decide which platers can take the job and which bake and test apply. We source plating from qualified processors, flow down the spec, class, supplementary treatment and embrittlement requirements, check each cert against the drawing before parts ship, and a person replies within one business day. Controlled drawings follow our controlled programs process.
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Questions
What does Class 2 mean in a cadmium plating callout?
Class sets minimum thickness. In the QQ-P-416F text adopted as AMS-QQ-P-416, Class 2 is 0.00030 inch minimum on surfaces a 0.75 inch ball can touch and 0.00020 inch where it cannot. Class 1 is thicker and Class 3 thinner. If the drawing gives no class, Class 2 applies, and if no maximum is given, the maximum is the minimum plus 0.0003 inch. Confirm values against the current revision G.
Is QQ-P-416 still a valid spec?
No. QQ-P-416F was cancelled on 28 March 2002, and the cancellation notice directs future acquisition to SAE AMS-QQ-P-416, which SAE revised to revision G in September 2022. Old drawings and fastener standards still cite QQ-P-416, and platers normally process to the AMS version. Put the AMS document and revision on new purchase orders so the cert matches what was ordered.
Does IVD aluminum cause hydrogen embrittlement?
No, according to MIL-DTL-83488D, which says high purity aluminum coating can be used on high strength steel without causing hydrogen embrittlement. That is one of its main advantages over cadmium and zinc-nickel electroplates. Stripping is different: steel parts at HRC 40 or above that are stripped in caustic must be baked afterward. Confirm with the coater how it will cover deep bores, threads and blind holes on your geometry.
How soon after plating must the bake happen?
The QQ-P-416F text required the hydrogen embrittlement relief bake within 4 hours after plating, before any chromate or phosphate supplementary treatment, and plated springs must not be flexed before baking. AMS 2759/9 sets bake requirements by steel strength or hardness. Give the plater the material and heat treat condition on the PO, and require the bake time and temperature on the cert.
What replaced QQ-C-320 chrome plating?
QQ-C-320B was cancelled on 3 May 2001 in favor of SAE AMS-QQ-C-320. SAE now lists AMS-QQ-C-320 as cancelled, and AMS 2460, Plating, Chromium, issued in July 2007 and at revision B since February 2023, is the SAE chromium plating spec in current use. Have engineering pick the AMS 2460 type and class rather than letting the plater interpret an old QQ callout.
Can zinc-nickel replace cadmium without a drawing change?
Treat it as an engineering change. AMS 2417 covers electrodeposited zinc-nickel, but its friction behavior may differ from cadmium, which can change fastener torque and preload, and it is still an electroplate with hydrogen embrittlement risk on high strength steel. Galvanic behavior against aluminum, conductivity and paint adhesion also need review. The design authority, not the buyer or plater, should approve the substitution.
Related
Sources
- EverySpec: QQ-P-416F, Plating, Cadmium (Electrodeposited) (1 October 1991)
- EverySpec: QQ-P-416F Notice 1, cancellation in favor of SAE AMS-QQ-P-416 (28 March 2002)
- SAE Mobilus: AMS-QQ-P-416G, Plating, Cadmium (Electrodeposited) (September 2022)
- EverySpec: MIL-DTL-83488D, Coating, Aluminum, High Purity (1 April 1999)
- SAE Mobilus: AMS2417 nickel-zinc alloy plating (revision history)
- SAE Mobilus: AMS2404 electroless nickel plating (revision history)
- SAE Mobilus: AMS-C-26074D electroless nickel coatings, stabilized June 2013
- EverySpec: QQ-N-290A Notice 1, cancellation in favor of SAE AMS-QQ-N-290 (3 May 2001)
- EverySpec: QQ-C-320B Notice 1, cancellation in favor of SAE AMS-QQ-C-320 (3 May 2001)
- SAE Mobilus: AMS-QQ-C-320B status (cancelled)
- SAE Mobilus: AMS2460 Plating, Chromium (revision history)
- OSHA: 29 CFR 1910.1027 Cadmium
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