Electroless Nickel
| Callout | Requirement |
| Class 1 | 350-400°F for 3+ hr embrittlement only for steel > Rockwell C40 no treatment for other material |
| Class 2 | 550 °F for 2+ hr 650 °F for 1-1.5 hr hardness must be > 800 HK100 |
| Class 3 | 360 to 390°F for 1-1.5 hr for non heat-treatable aluminum |
| Class 4 | 240 to 260°F for 1-1.5 hr for heat-treatable aluminum |
| Grade A | 1.0 mil minimum thickness |
| Grade B | 0.5 mil minimum thickness |
| Grade C | 1.5 mil minimum thickness |
| (thickness order does not match grade order best to specify on print) | |
This specification was discontinued for years and then reinstated at MIL-C-26074E then superseded by AMS-C-26074E which is virtually identical to the MIL-C-26074E specification. Depending on the print date, "MIL-C-26074", "AMS-C-26074" or "AMS2404" may be referenced - scroll down to investigate these various specifications.
Correct callouts for aluminum are Electroless Nickel per MIL-C-26074 Class 3 or Electroless Nickel per MIL-C-26074 Class 4 depending on whether the alloy will be affected by the higher temperature of the Class 3 bake. AA6061-T6, for example, would normally require a MIL-C-26074 Class 4 processing, since T6 will lose its temper (ha!) well below 360°F. Other basis materials should specify Electroless Nickel per MIL-C-26074 Class 1, if no heat treatment is required other than the embrittlement bake for hardened steel (> Rockwell C40). If a bake to increase hardness is desired, specify Electroless Nickel per MIL-C-26074 Class 2, which specifies baking to achieve a hardness greater than 800 Knoop: the specification shows a table of time and temperature that should achieve this result.
Purchasing due diligence should include a look at the shop’s bath testing records, acceptance test records, and quarterly test results. Be sure to specify phosphorus content on your purchase order if it is not specified on the print. Note also that your supplier is required to bake hardened steels for embrittlement relief; however, he is not required to do embrittlement testing unless specified on your print or by contract or purchase order. If embrittlement testing is required, you should supply test specimens fabricated from your alloy per ASTM F519 diagrams. Hardened steels and titanium are candidates for hydrogen embrittlement.
Note to engineer: A common weakness of the AMS/MIL-C-26074 and AMS2404 specifications is that deposited phosphorus content is not specified. Phosphorus content in the deposit affects corrosion resistance, brightness and hardness of the plating. If you are working on a new application, you should consider the ASTM B733 specification. If you decide to use the MIL-C-26074 or AMS2404 specification, consider specifying phosphorus content in the print notes: you may specify as low-phos, mid-phos or high-phos, or you may nail down you requirements with a specific percent phosphorus in deposit. Use the ASTM B733 specification for guidance, since specifying a non-standard percentage range may cause procurement problems or price increases.
Note to supplier: See complexing titrations for analysis instructions for nickel metal in electroless nickel baths.
Bath Testing
¶ 3.3.1.2: test plan to be established by supplier and approved by customer
Coupon Testing - monthly
¶ 4.4.2: embrittlement
¶ 4.4.4: plating hardness
Coupon Testing - quarterly
¶ 4.4.1: destructive adhesion
¶ 4.4.5: destructive thickness
¶ 3.3.4: corrosion resistance
Coupon/Part Testing - per lot
¶ 4.4.1.2: coating thickness
¶ 4.4.3: adhesion bend test
ASTM B733
| Callout | Requirement |
| Type I | xxx% phosphorus |
| Type II | 1-3% phosphorus |
| Type III | 2-4% phosphorus |
| Type IV | 5-9% phosphorus |
| Type V | 10+% phosphorus |
| Class 1 | No heat treatment |
| Class 2 | 260 to 400°C for 2-4 hr hardness must be > 850 HK100 |
| Class 3 | 180 to 200°C for 1 hr min embrittlement bake for steels |
| Class 4 | 120 to 130°C for 1 hr min for heat-treatable alloys |
| Class 5 | 140 to 150°C for 1 hr min for non heat-treatable alloys |
| Class 6 | 300 to 320°C for 1 hr min adhesion bake for titanium alloys |
The active specification is ASTM B733-04 and is available from ASTM International. We believe ASTM B733 is the best specification to use for electroless nickel, principally because it requires specification of phosphorus content the deposited nickel. Higher phosphorus content improves corrosion resistance and microhardness while reducing the brightness and electrical conductivity. ASTM B733 lets a purchaser nail down his requirements in the specification callouts, thereby ensuring consistent results and improving chances that alternate sources will deliver similar product.
Notice that the heat treatment classes do not align with the AMS2404/MIL-C-26074 specification. Correct callouts for aluminum are Electroless Nickel per ASTM B733 Class 4 or Electroless Nickel per ASTM B733 Class 5 depending on whether the alloy will be affected by the higher temperature of the Class 5 bake. ASTM B733 Class 1 gets no heat treatment, and ASTM B733 Class 3 has been added to specify an embrittlement bake for hardened steel. ASTM B733 Class 2 is the only one of the class call outs that aligns with the more familiar MIL-C-26074; however, the target hardness is 850 HK100.
The purchaser should include Type and Class in print note or purchase order, and should not expect a plating supplier to know whether 304 Stainless should receive an embrittlement bake or not. As always, the purchaser should ensure specification compliance with regular inspection of bath test records and periodic test results, and should also encourage use of an independent lab.
Note to supplier: ASTM B733 requires routine testing, including setting of control limits for SPC of the ENi bath used to plate parts that are certified to the specification. It does not specifically require testing of prep baths, but soap, acid and zincate baths are just as important as the ENi bath to ensure plating adhesion. See complexing titrations for analysis instructions for nickel metal in electroless nickel baths.
Bath Testing
¶ 6.5.1: temperature & pH
¶ 6.5.1: nickel -10% +0%
¶ 6.5.1: hypo -10% +0%
¶ 6.5.1: SPC to set control limits
Coupon Testing - monthly
¶ 7.3.1: phosphorus content
¶ 7.3.2: plating microhardness
Coupon/Part Testing - per lot
¶ 7.2.2: coating thickness
¶ 7.2.3: adhesion bend test
¶ 7.2.4: porosity
AMS-C-26074
| Callout | Requirement |
| Class 1 | 350-400°F for 3+ hr embrittlement only for steel > Rockwell C40 no treatment for other material |
| Class 2 | 550 °F for 2+ hr 650 °F for 1-1.5 hr hardness must be > 800 HK100 |
| Class 3 | 360 to 390°F for 1-1.5 hr for non heat-treatable aluminum |
| Class 4 | 240 to 260°F for 1-1.5 hr for heat-treatable aluminum |
| Grade A | 1.0 mil minimum thickness |
| Grade B | 0.5 mil minimum thickness |
| Grade C | 1.5 mil minimum thickness |
| (thickness order does not match grade order best to specify on print) | |
AMS-C-26074 has been cancelled at AMS-C-26074E as of July 2011. The AMS specification is virtually identical to MIL-C-26074E. Correct callouts for aluminum are Electroless Nickel per AMS-C-26074 Class 3 or Electroless Nickel per AMS-C-26074 Class 4 depending on whether the alloy will be affected by the higher temperature of the Class 3 bake. AMS-C-26074 Class 1 gets no heat treatment unless the basis material is hardened steel (> Rockwell C40) which always gets an embrittlement bake. AMS-C-26074 Class 2 must be baked to achieve a hardness greater than 800 Knoop, and the specification shows a table of time and temperature that should achieve this result.
Purchasing due diligence should include periodic inspection of the shop’s bath testing records, acceptance test records, and quarterly test results. Bath records should include soap and etch tanks, as well as deox and zincate tanks for aluminum material. If a purchaser is receiving a cert to the AMS specification, he should ensure that the plater has a current copy of the specification.
The AMS/MIL-C-26074 specification does not specify phosphorus content in the deposit, although phosphorus content affects corrosion resistance, brightness and hardness of the plating. If you are working on a new application, you should consider the ASTM B733 specification. If you are purchasing to an existing print, you should specify the phosphorus content on your purchase order. You should not leave this specification in doubt.
Bath Testing
¶ 3.3.1.2: test plan to be established by supplier and approved by customer
Coupon Testing - monthly
¶ 4.4.2: embrittlement
¶ 4.4.4: plating hardness
Coupon Testing - quarterly
¶ 4.4.1: destructive adhesion
¶ 4.4.5: destructive thickness
¶ 3.3.4: corrosion resistance
Coupon/Part Testing - per lot
¶ 4.4.1.2: coating thickness
¶ 4.4.3: adhesion bend test
AMS2404
| Callout | Requirement |
| Class 1 | 350-400°F for 3+ hr embrittlement only for steel > Rockwell C40 no treatment for other material |
| Class 2 | 450 °F for 4+ hr hardness must be > 800 HK100 |
| Class 3 | 360 to 390°F for 1-1.5 hr adhesion non heat-treatable aluminum |
| Class 4 | 240 to 260°F for 1-1.5 hr adhesion heat-treatable aluminum |
| All Classes 1-13% phosphorus by weight | |
AMS2404 is the successor to the AMS/MIL-C-26074 specifications. The monthly coupon test regimen is more rigorous than the previous specifications. The latest revision, AMS2404F, is available from SAE International. Correct callouts for aluminum are Electroless Nickel per AMS2404 Class 3 or Electroless Nickel per AMS2404 Class 4 depending on whether the alloy will be affected by the higher temperature of the Class 3 bake. Tempered aluminum (AA6061-T6 for example) should not be baked above 260°F. AMS2404 Class 1 gets no heat treatment unless the basis material is hardened steel (> Rockwell C40) which always gets an embrittlement bake. AMS2404 Class 2 must be baked to achieve a hardness greater than 800 HK100, and the specification shows a table of time and temperature that should achieve this result.
As with the older AMS/MIL-C-26074 specs, the phosphorus content should be specified by percentage on either print or purchase order, and monthly test results, preferably from an independent test lab, should be checked to ensure that the supplier is hitting the number. Results from salt spray testing are also important since this is the validation of phosphorus content and plating porosity. As always, purchasing due diligence should include periodic checking of the supplier’s bath records, including prep baths. A bit of inexpensive due diligence may save a very expensive field failure. Don’t rely on a certificate of conformance without due diligence.
Bath Testing
¶ 4.4.3: Control factors must include: surface preparation (including strike), plating bath composition and control limits, plating bath temperature limits and controls, thermal post treatment times and temperatures, test methods, and periodic test plan.
Coupon Testing - monthly
¶ 3.4.3: corrosion resistance
¶ 3.4.4: plating hardness
¶ 3.4.5: embrittlement
¶ 3.4.6: internal stress
¶ 3.4.7: phosphorus content
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.2: adhesion bend test
AMS2405
| Specification | Requirement |
| "low" phosphorus | Less than 8% by weight |
| Specification non-current | |
AMS2405C has been discontinued.
Bath Testing
periodic testing of cleaning and
plating solutions is specified
Coupon Testing - periodic
¶ 3.4.1: phosphorus content
¶ 3.4.3: adhesion
¶ 3.4.4: corrosion resistance
Coupon/Part Testing - per lot
¶ 3.4.2: coating thickness
FED QQ-N-290
| Callout | Requirement |
| Class 1 | Corrosion protection |
| Class 2 | Engineering plating (for wear and/or lubricity) |
| SB | Single layer - Bright |
| SD | Single layer - Dull |
| M | Multi layer |
| Grade A | 1.6 mil plate thickness |
| Grade C | 1.0 mil plate thickness |
| Grade E | 0.6 mil plate thickness |
| Grade F | 0.4 mil plate thickness |
(Note: See complexing titrations for analysis instructions for nickel sulfate and nickel chloride concentrations in Watts nickel baths.) Newer prints may reference the superseding AMS QQ-N-290 specification. The QQ-N-290 is required reading for any shop doing nickel electroplating. The print note for the high corrosion resistance is Nickel Plate per QQ-N-290 Class 1 (Grade A through C). When plated on steel, this requires a duplex nickel process with careful control of the sulfur content. This multi-layer plating has been shown to increase corrosion resistance over a single plating material of the same thickness. Similar multi-layer nickel plating is required to meet the ASTM B456 specification for chrome over nickel plating, and this ASTM specification has a lot of good information about the process and methods of testing sulfur content in nickel plating.
Nickel Plate per QQ-N-290 Class 1 or Nickel Plate per QQ-N-290 Class 2 can be achieved with either a Watts or sulfamate bath, but the properties of the deposit (e.g. internal stress, brightness, corrosion resistance), are significantly different for these two types of plating. If the bath is not specified, a careful plater will confirm with the purchaser. Ideally, the bath type will be mentioned on the cert. As always, a purchaser must ensure that a supplier is doing the required testing of all process baths, including cleaning, prep and strike baths. If plating hardened steel, the purchaser should check the monthly embrittlement test results. Don’t rely on a certificate of conformance without due diligence.
Bath Testing
¶ 4.3.1: processor to keep
records of all chemical
concentrations and additions
Coupon Testing - monthly
¶ 4.5.3: embrittlement
Coupon/Part Testing - per lot
¶ 4.5.1: coating thickness
¶ 4.5.2: adhesion bend/knife test
AMS QQ-N-290
| Callout | Requirement |
| Class 1 | Corrosion protection |
| Class 2 | Engineering plating (for wear and/or lubricity) |
| SB | Single layer - Bright |
| SD | Single layer - Dull |
| M | Multi layer |
| Grade A | 1.6 mil plate thickness |
| Grade C | 1.0 mil plate thickness |
| Grade E | 0.6 mil plate thickness |
| Grade F | 0.4 mil plate thickness |
Many plating shops offer certification to one of the variations of the QQ-N-290 specification - AMS is the current custodian, and the spec has been recently updated to AMS QQ-N-290B. The specification can be met with either a Watts or a sulfamate bath, but the properties of the deposit (e.g. internal stress, brightness, corrosion resistance) are different for these two types of plating. A Watts bath uses nickel sulfate as the metal salt, while the sulfamate bath uses nickel sulfamate. Purchaser and plater should agree on the type of bath to be used. As always, the purchaser must ensure that the supplier is doing the required testing of all process baths, including cleaning and prep baths.
The typical process for aluminum includes a zincate or double zincate ENi process for underplating, and the prep and strike baths (soap, nitric acid, zincate, ENi strike, Woods strike) will be more important than the electrolytic nickel bath for final plate adhesion. Prep and strike baths are also crucial for other materials; however, the prep process on steels, copper, etc. is less tedious than for aluminum or magnesium. If the material is hardened steel, the purchaser should check the monthly embrittlement test results. Don’t rely on a certificate of conformance without due diligence.
Bath Testing
¶ 4.3.1: processor to keep
records of all chemical
concentrations and additions
Coupon Testing - monthly
¶ 4.5.3: embrittlement
Coupon/Part Testing - per lot
¶ 4.5.1: coating thickness
¶ 4.5.2: adhesion bend/knife test
AMS2403
| Specification | Requirement |
| Thickness | Must be on print |
AMS2403L is the current revision available from SAE International. AMS2423 and AMS2424 are similar specifications targeting specific coating properties. This family of specifications does not specify bath type, and platers routinely certify to this specification using both Watts and sulfamate baths, with significantly different plate properties resulting. As was true with the QQ-N-290, the safest way to guarantee consistent results would be to include a bath specification in the form: ("Sulfamate Nickel per AMS2403" or "Watts Nickel per AMS2403"). As always, a purchaser must ensure that a supplier is doing the required testing of all process baths, including cleaning, prep and strike baths. If plating hardened steel, the purchaser should check the monthly embrittlement test results. Don’t rely on a certificate of conformance without due diligence.
Bath Testing
¶ 4.4.3: Control factors must include: activation; plating bath composition, control limits and testing frequency; plating bath temperature limits and controls; plating current (or voltage) limits; time in cleaning, activation and plating solutions; and periodic test plan.
Coupon Testing - periodic
¶ 3.4.3: heat resistance
¶ 3.4.4: corrosion resistance
¶ 3.4.5: embrittlement
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.2: adhesion bend test
¶ 3.5: general quality
AMS2423
| Specification | Requirement |
| Thickness | Must be on print |
AMS2423D is available from SAE International. See notes on AMS2403. The correct print callout would be "Nickel Plate per AMS2423". Woods, Watts, sulfamate, or other bath may be used. Hardening agents may be used. (Note: See complexing titrations for analysis instructions for Watts nickel baths. The basic method can also be used for sulfamate and nickel chloride concentrations in sulfamate nickel baths.)
Bath Testing
¶ 4.2.2: periodic testing of
cleaning and plating solutions to
ensure specification conformance
Coupon Testing - periodic
¶ 3.4.3: stress testing
¶ 3.4.5: embrittlement
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.2: hardness
¶ 3.4.4: adhesion test
¶ 3.5: general quality
AMS2424
| Specification | Requirement |
| Thickness | Must be on print |
AMS2424F is available from SAE International. See notes on AMS2403. The correct print callout would be "Nickel Plate per AMS2424". The low-stress requirements are normally met using a sulfamate nickel bath with no additives (brighteners, stress-reducers, etc.) that could increase internal stress or reduce the corrosion resistance of the coating. (Note: See complexing titrations for analysis instructions for Watts nickel that can also be used for sulfamate and nickel chloride concentrations in sulfamate nickel baths.)
Bath Testing
¶ 4.2.2: periodic testing of
cleaning and plating solutions to
ensure specification conformance
Coupon Testing - periodic
¶ 3.4.2: hardness
¶ 3.4.3: residual stress
¶ 3.4.5: heat resistance
¶ 3.4.6: corrosion resistance
¶ 3.4.7: embrittlement
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.4: adhesion test
¶ 3.5: general quality