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plating processes, procedures & solutions

UPDATE ON ALTERNATIVES FOR

CADMIUM COATINGS ON MILITARY

ELECTRICAL CONNECTORS

BY ROB MASON, CEF, MARGO NEIDBALSON, AND MELISSA KLINGENBERG,

PHD, CONCURRENT TECHNOLOGIES CORPORATION (CTC), JOHNSTOWN,

PA., AND LARGO, FLA., AND PARMINDER KHABRA AND CARL HANDSY,

UNITED STATES ARMY TANK-AUTOMOTIVE RESEARCH DEVELOPMENT AND

ENGINEERING CENTER (TARDEC), WARREN, MICH.

The metal finishing industry has been impacted by numerous regulatory actionsrelated to the hazardous materials that are used in decorative and functionalcoating processes. These environmental regulations are applicable to both commercialand government facilities. In addition, Executive Order (EO) 13423,Strengthening Federal Environmental, Energy, and Transportation Management, and EO13514, Federal Leadership in Environmental, Energy, and Economic Performance, wererecently enacted. These EOs require government agencies to reduce the quantityof toxic and hazardous chemicals and materials acquired, used, or disposed.Cadmium and hexavalent chromium are very toxic and carcinogenic materialsheavily regulated by the Environmental Protection Agency (EPA) and theOccupational Safety and Health Administration (OSHA). In addition, hexavalentchromium is among the three hazardous materials that the Department ofDefense (DoD) has targeted for reduction to meet the requirements of the EO13423. Due to the toxicity and carcinogenicity, as well as the numerous regulatoryactions related to these materials, the U.S. Army Tank-automotive ResearchDevelopment and Engineering Center (TARDEC) has been working to eliminateor reduce the use of cadmium and hexavalent chromium in ground vehiclesand related systems. The National Defense Center for Energy and Environment(NDCEE), operated by Concurrent Technologies Corporation (CTC), has beentasked to support TARDEC’s activities in this area.Specifically, the protective shells of electrical connectors currently used inmilitary ground systems are cadmium plated and then chromated with chromateconversion coatings (CCCs) to provide additional corrosion protection.Theaforementioned regulatory concerns underscore a need to find alternativesto the currently used coating processes to reduceenvironmental and safety risks.However, the replacement of cadmium for any application is not a trivialtask. Cadmium has been used as a protective coating for electrical connectorsfor many years because of the numerous properties that it imparts to the overallcomponent. Key properties that cadmium coatings impart to electrical connectorshells include: 1,2

• Ease of manufacturing

• Ease of repair

• Electrical conductivity

• Electromagnetic compatibility (EMC)/electromagnetic interference (EMI)

effectiveness

• Environmental resistance, particularly corrosion resistance

• Galvanic coupling

• Inhibition of algae growth

• Low cost

• Lubricity (meets established torque/tension requirements)

• Shock resistance

• Solderability

• Temperature resistance

• Vibration resistance

CCCs are applied over cadmium coatings to provide additional properties,the most important of which are:

• Enhanced corrosion resistance

• Paintability (meets requirements for paint adhesion to coating)

• Color

As seen above, the synergistic benefits provided by this coating system havemade its replacement challenging. One example of the unique protective propertiesthat are imparted by cadmium and hexavalent chromium is corrosionresistance. Cadmium coatings provide galvanic corrosion protection to electricalconnector shells, and very few metals can provide a similar level of corrosionprotection in this application. This is demonstrated by the position of cadmiumin the galvanic series, shown in Figure 1. 1Figure 1 demonstrates that zinc and zinc alloys, beryllium, magnesium, andaluminum alloys are generally the most active metals in corrosive environmentsand, therefore, are the onlymaterials that can provide sacrificial corrosionprotection similar to cadmium in this application. However, beryllium is morehazardous than cadmium, and magnesium and pure zinc both corrode toorapidly for many engineering applications.Other examples of the unique properties that are imparted by cadmium toconnector shells involve electrical properties, specifically EMC and EMI effectiveness.Connector mating resistances must be kept to a minimum (e.g. lessthan 2.5 milliohms) for EMC, because greater mating resistances can lead tohigh voltages (and subsequent failures) when induced by sudden surge currents(such as a lightning strike). Cadmium-plated connectors meet this requirementthroughout the life of the connector (i.e., the corrosion products of cadmiumare generally non-insulating). Other plated coatings, such as electroless nickel(EN), meet this requirement initially, but lose effectiveness over time due to theresistances that are generated by corrosion products.

VIABLE ALTERNATIVES TO CADMIUM

The DoD has been interested in cadmium replacement for many years, andnumerous potential replacements have been identified and explored in pastwork conducted by Brooman2,3,4, Gaydos5, Klingenberg3, 4, 6, Legg1; and Shahin7,among many others. It is the intent of this paper to summarize past work thathas been accomplished in this area, with the intent of providing a rationale forthe selection of the mostpromising candidates for further study under futurephases of this current effort.Based on the many previous studies related to cadmium replacement, andthe available data on candidate technologies, a number of promising candidatesfor cadmium replacement were identified. Due to the particular focus of thisproject, candidates were limited to commercially available or near-commercialtechnologies. These include:

• Advanced materials

• Alloys deposited by chemical vapor deposition (CVD)

• Alloys deposited by molten salt bath processes

• Alloys deposited by ionic liquid processes

• Electrodeposited aluminum and alloys

• Electroless nickel technologies

• Electroplated tin alloys

• Electroplated zinc-cobalt

• Electroplated zinc-nickel

• Ion vapor deposited (IVD) aluminum and alloys

• Metal-filled paints and ceramics

• Sputtered aluminum and alloys

The viability of each of these processes in the context of the specific application—electrical connector shells—is discussed herein. Where data is available,issues such as compatibility of the alternatives with existing cadmium-platedconnectors will be addressed.

ADVANCED MATERIALS

The use of advanced materials as a replacement for cadmium-plated parts hasbeen considered mostly for larger aerospace components. Stainless steel is themost likely candidate to replace cadmium on larger, non-electric components. Acorrosion-resistant stainless steel, S53, was developed under a project funded bythe Strategic Environment Research and Development Program (SERDP). Thiseffort1, 5, 8 focused on providing corrosion protection and resistance to stresscorrosion cracking on aircraft landing gear. Stainless steel alloys would providemany of the necessary properties needed for electrical connector shells and maybe acceptable for some applications. However, these materials generally exhibita high mating resistance and also may not be cost-effective. Likewise, titaniumalloys and Inconel¨ have been found to be adequate as substrate substitutesfor cadmium plated fasteners5, but these may also be cost prohibitive for usein electrical connectors. Polymer composite materials (such as polyetheretherketone)are already in use in some commercial applications. However, militaryusage appears to be minimal (at least for ground vehicle applications), andconsideration of this material introduces issues related to cost, conductivity,and mechanical wear for some applications. Overall, it is evident that additionalresearch and development is required to use advanced materials to replace thestandard shells in newer models of electrical connectors.

ALLOYS DEPOSITED BY CHEMICAL VAPOR DEPOSITION

The Air Force Research Laboratory (AFRL) evaluated aluminum coatingsapplied through Atmospheric Pressure Chemical Vapor Deposition (APCVD).9Environmentally benign CVD processes using triethylaluminum as a precursorfor producing high-quality aluminum coatings was explored. While promising, this process involves special high-cost, equipment. Considerable further devel-

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Figure 1. Galvanic series, showing position of cadmium and viable

alternative metals. (Circled area: materials providing sacrificial

protection.) 1

opment from a processstandpoint would likelybe necessary to implementthis process forhigh-volume applicationssuch as electricalconnector shells.

ALLOYS DEPOSITEDBY MOLTEN SALTBATH PROCESSES

An aluminum-manganesemolten salt platingprocess was exploredunder funding fromthe EnvironmentalSecurity TechnologyCertification Program(ESTCP), but the processwas plagued byinconsistent bathcomposition, visiblefumes, and excessivecrust formation [Ref.10]. In addition, thisprocess operated at avery high temperature,which is likely to affectthe properties of aluminumshells. While thistechnology is promising,considerable furtherdevelopment froma process standpointwould be necessary toimplement this processfor electrical connectorshells.

ALLOYS DEPOSITED BY IONIC LIQUID PROCESSES

As an alternative to the molten salt bath process mentioned above, the use ofionic liquids as an electrolyte to plate aluminum is under investigation. 5,11 Ionicliquids are salts with a low melting point, which originates in their chemicalstructure (a mix of anions and large organic cations). These liquid salts haveunique properties that allow easy dissolution of normally insoluble chemicals,such as cellulose. Ionic liquids enable electrochemical plating of metals likealuminum; deposition rates of one micron per minute at low temperatures (60to 100°C) have been reported.11 These deposition rates are significantly superiorto other low-temperature aluminum coating methods. While this processis not yet mature enough to enable the plating of commodity items such aselectrical connector shells, work is progressing rapidly and promising resultswill be forthcoming.

ELECTRODEPOSITED ALUMINUM AND ALLOYS

AlumiPlate¨ is a proprietary process in which a pure aluminum coating iselectrolytically deposited onto a substrate that has been immersed into a nonaqueous,fully enclosed solution in an inert atmosphere. The resulting coatingis highly versatile. It can be anodized or topcoated with the standard CCC posttreatment, trivalent chromium post-treatments (TCPs), or non-chrome posttreatments(NCPs). TCPs are much less hazardous than CCCs and meet requirementsunder the European Union’s Reduction of Hazardous Substances (RoHS)Directive—although this substance is still regulated under U.S. requirements.Additionally, the AlumiPlate¨ process does not appear to impart hydrogenembrittlement—a concern with cadmium plating.5AlumiPlate¨ is one of the more promising new processes for cadmiumreplacement on electrical connectors. Researchers at the Naval Air SystemsCommand (NAVAIR) conducted 2,000 hours of salt spray corrosion testingon electroplated aluminum electrical connectors with TCP12,13, in accordancewith ASTM B117.14. NAVAIR found that all connectors performed equal to orbetter than the cadmium-plated controls with respect to visual appearance ofcorrosion. A plated connector is shown after 2,000 hours of B117 exposure inFigure 2.12.From a functionality standpoint, all tested connectors met the requirementfor shell-to-shell conductivity, with the exception of the AA6061 AlumiPlate¨coating with TCP at 25% concentration (the most dilute). The AA6061AlumiPlate¨ coating with Class III post-treatment was the top performer.Other projects involving this process include a partnership betweenLockheed, Alcoa, and the U.S. Air Force, which is evaluating several coatings,including AlumiPlate¨, to replace cadmium for military and commercialfasteners.15Based on the results from both the NAVAIR testing and thispartnership, the AlumiPlate¨ coating is currently being qualified for electricalconnectors under MIL-DTL-38999L as well as relevant internal manufacturers’specifications. Specifically, qualification and approval of the AlumiPlate¨ coatingis anticipated for Model 38999 electrical connectors with spring fingers,which will be used on the Lockheed Martin F-35 Lightning II (also known asthe Joint Strike Fighter) program.Despite the good performance of this candidate and its recent qualification,several drawbacks remain with the use of AlumiPlate¨. Due to the use of thenon-aqueous electrolyte, it is unlikely that this process could meet the environmentalrequirements that would allow its use in a DoD facility.1 Furthermore,the process requires the use of highly specialized equipment (e.g. high start-upcost). Finally, there are questions regarding whether the plated coating can berepaired, although initial work has found that it may be possible to use brushplatedtin-zinc to repair this coating.1,5

ELECTROLESS NICKEL TECHNOLOGIES

A number of new EN-based coating systems continue to be considered for electricalconnector shells. However, as mentioned previously, the corrosion propertiesof nickel—and subsequent electrical properties—are considerably differentthan those of cadmium.2 Further testing would be required to fully assess thiscandidate for military electrical connectorshells. Despite these concerns,at least one leading manufacturer ofelectrical connectors is investigatingthe use of EN with occluded particles(polytetrafluoroethylene, or PTFE)as a cadmium replacement.16 Whilethe inclusion of these particles willprovide lubricity, the corrosion characteristicsand electrical propertiesimparted to the connector shell must be considered and are being evaluated

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Figure 2. AlumiPlate-coated electrical connector,

After 2,000 hours B117exposure.12

ELECTROPLATED TIN ALLOYS

Among the most mature and promising tin alloy coatings for electrical connectorshells are tin-zinc coatings. Tin-zinc electroplating processes are mature,commercially available systems that can deposit alloys of 20–30% zinc (balancetin) from an aqueous solution. Tin-zinc coatings have been considered promisingfor cadmium replacement 2,7,17, and this finish was found to be a topperformer in past studies. 18 However, more recent studies have derived lesspositive results. An extensive study on potential cadmium replacements conductedby the NDCEE19 found that a proprietary tin-zinc coating failed bothcyclic corrosion and wet notch environmentally influenced cracking (EIC) testsyet passed hydrogen embrittlement and cooked EIC. A summary of test resultsfrom this effort can be found in Table 1.19In this study, itwas noted that the deposited tin-zinc coating was found tohave an insufficient amount of zinc in the deposit to provide adequate corrosionprotection (less than 1% zinc, versus the anticipated >20% zinc concentrationfound in more corrosion-resistant coatings that had been tested underrelated projects). This implies that, while tin-zinc does show promise for someapplications, some bath chemistries may not be robust enough to provide aconsistent coating composition (and, hence, sufficient corrosion resistance) forthe harsh environments to which military electrical connectors are routinelysubmitted. Promising results under past studies imply that this candidate couldprovide comparable performance to cadmium if the deposit composition couldbe made more consistent.It is noted that other tin alloys, specifically tin-indium coatings, are beingconsidered for both commercial and military applications, but these wouldtake considerable development to be considered for electrical connector shells.

ELECTROPLATED ZINC-COBALT

Zinc-cobalt plating is typically used to finish relatively inexpensive parts thatrequire a high level of abrasion and corrosion resistance. This coating is reportedto demonstrate particularly high resistance to corrosion in sulfur dioxide environments.Several suppliers of commercial electrical connectors offer connectorshells coated with zinc-cobalt as a replacement for cadmium to meet RoHScriteria. Zinc-cobalt alloys are not commonly used in applications requiringheat treatment because these alloys have been reported to demonstrate reducedcorrosion resistance when exposed to high temperatures. In one study20, aftersalt spray corrosion testing in accordance with ASTM B11714, zinc-cobalt-platedsleeves showed considerably less corrosion resistance after one hour heat treatmentat 250°F as compared to the as-plated condition. While this process wasinitially considered as being a worthy cadmium replacement, the questionablecharacteristics under high-temperature environments excluded its considerationunder further review.

ELECTROPLATED ZINC-NICKEL

Zinc-nickel electroplating processes are mature, commercially available systemsthat can deposit alloys of 5–15% nickel (balance zinc) from an aqueous solution.Zinc-nickel alloys can be deposited from both acid and alkaline processes.Boeing has found that the alkaline process is easier to maintain and providesa more consistent coating composition.5 From a performance standpoint, theNDCEE found that a proprietary acid zinc-nickel coating with CCC passedbend adhesion, paint adhesion, and hydrogen embrittlement tests, but displayedonly marginal EIC performance19 (see Table 1). The corrosion resistance wassignificantly less than the cadmium baselines, but increased coating thicknessand selecting a suitable conversion coating may improve those results—althoughthe implications of these changes to the form, fit, and function of the electricalconnector would need to be identified. The proprietary alkaline zinc-nickelcoating with a CCC performed similarly to the acid zinc-nickel in this study19(see Table 1). Previous TARDEC work also found alkaline zinc-nickel coatingswith a CCC to be promising for some electrical connector designs, particularlyon MIL-C-83513 microminiature D-subminiature connectors, but less promisingon other connector designs.Based on these promising results, zinc-nickel has seen implementation as acadmium replacement process in several areas. The NDCEE work19 providedinformation that assisted Rolls Royce Defense Aerospace in qualifying zincnickelas an acceptable alternative to cadmium on the T56 engine system. Boeingalso found that zinc-nickel plating is an acceptable coating to replace cadmiumon component parts made of low strength steel (less than 200 ksi), stainless steel,aluminum, and copper alloys.1Other ongoing projects involving this process include the aforementionedpartnership between Lockheed-Martin, Alcoa, and the U.S. Air Force, whichis evaluating several coatings, including both acid and alkaline zinc-nickel, toreplace cadmium for military and commercial fasteners.15It is recognized that both acid and alkaline zinc-nickel processes may providean acceptable alternative coating for cadmium in many applications. Acid zincnickelprocesses have traditionally been used; however, some embrittlementissues have been related to this process.1 For this reason, Boeing restricts theuse of acid zinc-nickel to steels with ultimate tensile strength of 220 ksi or less.While these issues may not be relevant for electrical connectors, a post-processbake has been found to both relieve hydrogen embrittlement and enhance corrosionproperties.2 In any case, alkaline zinc-nickel appears to be the stronger candidatefor this application, due to the reduction in required maintenance of thebath and the aforementioned current interest in the properties of this coating.

ION VAPOR DEPOSITED ALUMINUM AND ALLOYSIon vapor deposited (IVD) aluminum is a physical vapor deposition (PVD) processn which a part is placed in a vacuum chamber and glow discharge cleaned.Pure aluminum is then melted in heated ceramic boats until it evaporates andcondenses on the part to form a coating. Concurrently, ions from the dischargebombard the forming coating to enhance its density.IVD aluminum is a mature process that has been used successfully to deposita variety of coatings for many years, and has traditionally been one of the mostpromising technologies for cadmium replacement. It is non-embrittling andgalvanically compatible with aluminum substrates. In addition, it has excellenthigh temperature properties and can be conversion coated. Corrosion resistancehas been reported to be comparable to, or better than, cadmium in someenvironments.2,21 Alloying the IVD aluminum coating is reported to provideeven better corrosion protection; IVD aluminum-magnesium alloys with 10%magnesium have demonstrated significant pitting corrosion protection.17 PastNDCEE work found that aluminum-tungsten and aluminum-molybdenum alsodemonstrated improved passivation over pure aluminum.6As mentioned previously, Boeing has qualified IVD aluminum to replacecadmium on component parts made of low strength steel (less than 200 ksi),stainless steel, aluminum, and copper alloys. In a past TARDEC study, IVDaluminum demonstrated the best overall performance on aluminum connectors.Specifically, on MIL-C-38999 circular connectors, IVD aluminum performedsimilar to or better than cadmium, with lower shell-to-shell resistance,but slightly less corrosion resistance. It was noted that, on MIL-PRF-24308D-subminiature connectors, cadmium demonstrated the best overall performance,with IVD aluminum being the best performing alternative. It was alsonoted that on MIL-C-83513 microminiature D-subminiature connectors, IVDaluminum was reported to have a significant drawback for use on these connectors.During the IVD process, aluminum coated the entire connector surface(including the phenolic material), causing the pins to be electrically continuouswith each other and the connector shell, resulting in shorts and eventualconnector failure.As seen above, there are numerous drawbacks to using IVD aluminum forelectrical connector shells. These include the aforementioned overcoating issues,as well as high start-up and operations costs because the equipment that is usedto apply this finish is expensive. Also, while IVD aluminum is not completelylimited to line-of-sight coverage, the conventional process cannot “throw” intodeep recesses on some parts—particularly holes.1, 5 There are some coating performanceconcerns as well. IVD aluminum coatings display a columnar structurewith a high degree of porosity. As a result, the coatings must usually beglass-bead peened to densify the coating and alleviate porosity and corrosionconcerns. The NDCEE found that IVD aluminum coatings, even with CCC,provide only marginal cyclic corrosion results19 (see Table 1), underscoring theimportance of a dense aluminum coating. Also, like many pure aluminum coatings,IVD aluminum has also been reported to have poor wear resistance, and hasdemonstrated galling issues. The latter is a particular concern for electrical connectors;an aluminum-to-aluminum interface could result in excessive matingforces, or even unmateable connectors1 (the incorporation of dry film lubricantshave been proposed to resolve this issue, but this would have an adverse effecton electrical connectivity).In summary, while IVD aluminum may be viable to replace cadmium in manyapplications, it is not anticipated to be a direct replacement for electrical connectors.In fact, an Air Force study has recognized that IVD aluminum will noteasily replace more than about 50% of cadmium plating requirements.17

METAL-FILLED PAINTS AND CERAMICS

Organic paint systems that are loaded with sacrificial metals (generally aluminumand zinc metal powders) have demonstrated significant corrosion resistancein several applications. However, they are generally not considered forcadmium replacement due to poor galvanic corrosion performance and pooradhesion (compared to electroplating).5Metal-filled ceramic coatings are being considered for some cadmium-replacementefforts. One supplier offers a coating that incorporates aluminum flakesin a ceramic matrix. The coating can be applied via brush or spray. It is usedprimarily for larger components in aircraft such as landing gear (specifically theF-22), as well as for high-temperature applications. Drawbacks to this candidateinclude sole source (only one supplier provides the coating, and they only licenseto major users), high cost, limited available data, and the requirement to heattreatthe coating before use.1,5 Also, coating conductivity has apparently not beendetermined. As such, this candidate is likely not feasible for electrical connectors.

SPUTTERED ALUMINUM AND ALLOYS

Sputtering, or magnetron sputtering, is another PVD process. In this process,a part is placed in a vacuum chamber, where it is glow discharge cleaned afterthe system is evacuated. The ionized gas (typically argon) is attracted to thebiased aluminum target, and aluminum atoms are ejected from the target andcondense on the substrate to form a coating. The “Plug and Coat” method ofsputtering allows both inner diameters (IDs) and outer diameters (ODs) to becoated within the same chamber.Recent work conducted by Boeing 1, 5 found that sputtering provides a betterquality aluminum coating than IVD, with lower porosity. Through the “Plug andCoat” process, parts can be 100% PVD aluminum-coated (IVD Al on OD, sputterAl on ID). In addition, the process is non-hazardous as compared to cadmiumplating (no air emissions, water emissions, or solid waste).Sputtered aluminum alloys have also showed promise to replace cadmium.They include aluminum magnesium, aluminum-molybdenum, aluminumtungsten,aluminum-manganese, aluminum-zinc, and aluminum-magnesium-zinc.5, 6While promising, magnetron sputtered aluminum is still under developmentfor coating aircraft parts. Susceptibility to environmental embrittlementhas yet to be determined, and more recent work has generated mixedresults.22 Also, while technically acceptable, this process involves high startupand operational costs, and may not be cost-effective for smaller parts suchas electrical connector shells.5, 22

OTHER DEPOSITION TECHNOLOGIES

Aluminum and its alloys can be readily deposited with thermal spray processes,such as flame spray, but these coatings are usually very thick—typically 76 to127 microns (0.003’’ to 0.005’’)—and exhibit high roughness and porosity inthe as-deposited state. The process also imparts a high degree of heat to thesubstrate. The latter issue can be partly alleviated by utilizing “cold spray” processes;however, the former issues restrict the use of this technology for electricalconnectors.As mentioned previously, the use of ionic liquids (salt mixtures that meltbelow room temperature) as an electrolyte to plate aluminum is currently underinvestigation. This technology is a relatively new development, and while someinformation is available5,10, the ability to adapt this process to coat electricalconnector shells in mass quantities has yet to be determined.

VIABLE ALTERNATIVES TO HEX CHROME TOPCOATS

The most promising alternatives to standard CCCs at this time are TCPs.Specific applicability for electrical connectors, when used in conjunction withthe AlumiPlate¨ process, has been promising.5,12,13 Further work is necessary tofully qualify TCPs as a replacement for CCCs.NCPs are also becoming available, but these have been far less studied inthis application. NAVAIR is currently continuing studies on the effectivenessof their NCPs, and AlumiPlate¨ offers a proprietary non-chromated topcoatover its coating system. An NDCEE Task is currently being conducted with theobjective of evaluating NCPs for TARDEC.

SUMMARY

The most promising candidate coating processes to replace cadmium andhexavalent chromium in electrical connector applications are technologies thatare already being used on electrical connectors to some extent, or demonstrateboth considerable promise for the application and sufficient maturity. Theseinclude:

• Electroplated aluminum (AlumiPlate¨)

• Electroplated alkaline zinc-nickel (5-15% nickel in the deposit)

• Electroplated tin-zinc (at least 20% zinc in the deposit)

Future efforts will focus on these three most promising candidates. In addition,to support efforts being undertaken by electrical connector manufacturers,two EN-based technologies, both incorporating occluded particles, will also beevaluated. Coatings with both CCCs and TCPs will be considered, as available,and cadmium with CCC will be used as the control.The most promising candidate coating processes from emerging alternativeswere also identified. These are technologies that show promise for electricalconnector applications, but require further development for the electrical connectorsemployed by TARDEC. These include:

• Alloys deposited from ionic liquids

• Magnetron sputtered aluminum alloys

• Tin-indium alloys

Future efforts may consider these candidates as the technology matures andbecomes more feasible for electrical connectors.

REFERENCES

1. K. Legg, “Cadmium Replacement Options,” presentation to The WeldingInstitute, Cambridge, UK, October 2003.

2. E. Brooman, “Alternatives to Cadmium Coatings for Electrical/Electronic Applications,” Plating and Surface Finishing Journal, AmericanElectroplaters and Surface Finishers Society, Orlando, FL, February 1993.

3. E. Brooman, D. Schario, M. Klingenberg, “Environmentally PreferredAlternatives to Cadmium Coatings for Electrical/Electronic Applications,”Electrochemical Society Proceedings 96-21, Electrochemical Society,Pennington, NJ, 1997, pp. 219-235.

4. E. Brooman, M. Klingenberg, M. Pavlik, “Alloy Deposition of Alternativesto Chromium and Cadmium”, Sur/Fin ’99 Conference Proceedings,American Electroplaters and Surface Finishers Society, Orlando, FL, 2000,pp. 163-176.

5. S. Gaydos, “Cadmium Plating Alternatives for High Strength Steel AircraftParts,” Proceedings of the Surface Engineering for Aerospace and DefenseConference, Orlando, FL, January 2008.

6. M. Klingenberg, “Evaluation of Magnetron Sputtered Aluminum Coatingsas a Replacement for Cadmium Coatings,” presentation at SUR/FIN ’07,Cleveland, OH, August, 2007.

7. G. Shahin, “Alloys are Promising as Chromium or Cadmium Substitutes,”Plating and Surface Finishing Journal, American Electroplaters and SurfaceFinishers Society, Orlando, FL, August 1998.

8. “Corrosion Resistant Steels for Structural Applications in Aircraft,” FinalTechnical Report, SERDP Pollution Project PP-1224, February 28, 2005.SERDP website: http://www.serdp.org/Research/upload/PP-1224-FR-01.pdf

9. “Investigation of Chemically Deposited Aluminum as a ReplacementCoating for Cadmium,” SERDP website:http://www.serdp.org/Research/upload/PP_FS_1405.PDF

10. “Aluminum Manganese Molten Salt Plating,” Final Technical Report,ESTCP Project WP-9903, June 2006.

11. M. O’Meara et al, “Deposition of Aluminum Using Ionic liquids,” MetalFinishing, Elsevier, Inc., New York, July/August 2009, pp. 38 – 39.

12. A. Schwartz, “Corrosion Performance of AlumiPlate Coated ElectricalConnectors with Trivalent Cr Post-Treatment,” presentation to the JointCadmium Alternatives Team, New Orleans, January 2007.

13. G. Vallejo, “RoHS Compliant Electroplated Aluminum for AerospaceApplications,” Proceedings of the Surface Engineering for Aerospace andDefense Conference, Orlando, FL, January 2008.

14. ASTM B117, “Standard Practice for Operating Salt Spray (Fog)Apparatus,” ASTM International, West Conshohocken, Pennsylvania, 2002.

15. L. Haylock, “Fasteners for Military and Commercial Systems,” SERDP andESTCP’s Partners in Environmental Technology Technical Symposium &Workshop, Washington, D.C., November 2006.

16. E. Fey and M. Barnes, “Amphenol Cd free Cr VI free Finishes,”ASETSDefense 2009: Sustainable Surface Engineering for Aerospace andDefense Workshop, September 3, 2009. ASETSDefense website: http://www.asetsdefense.org/SustainableSurfaceEngineering2009.aspx

17. B. Navinsek, et al., “PVD Coatings as an Environmentally Clean Alternativeto Electroplating and Electroless Processes,” Surface and CoatingsTechnology, Elsevier, 116-119, (1999), pp 476-487.

18. P. Decker, J. Repp, and J. Travaglini, “Finding Alternatives to Cadmiumon Mil-Spec Electrical Connectors,” Corrosion 2000, NACE International,Houston, TX, 2000.

19. “NDCEE Demonstration Projects: Task No. 000-02, Subtask 7 –Alloy Plating to Replace Cadmium on High-Strength Steels, FinalReport,” Contact No. DAAE30-98-C-1050, National Defense Center forEnvironmental Excellence, April 1, 2003.

20. N. Zaki, “Zinc Alloy Plating,” Products Finishing, Gardner Publications,Inc http://www.pfonline.com/articles/pfd0019.html

21. G. Legge, “Ion-Vapor-Deposited Coatings for Improved CorrosionProtection,” Products Finishing, Gardner Publications, Inc, 1995.

22. “Joint Service Initiative Project AF5: Evaluation of Magnetron SputteredCoatings – Phase II,” Final Technical Report to the NDCEE under ContractNo. W74V8H-04-D-0005, Task No. 0429, Project AF5, December 19, 2006.