Metal Finishing Guide Book


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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 to 127 microns (0.003'' to 0.005'')���and exhibit high roughness and porosity in the asdeposited state. The process also imparts a high degree of heat to the substrate. The latter issue can be partly alleviated by utilizing ���cold spray��� processes; however, the former issues restrict the use of this technology for electrical connectors. As mentioned previously, the use of ionic liquids (salt mixtures that melt below room temperature) as an electrolyte to plate aluminum is currently under investigation. This technology is a relatively new development, and while some information is available5,10, the ability to adapt this process to coat electrical connector 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 with the AlumiPlate�� process, has been promising.5,12,13 Further work is necessary to fully qualify TCPs as a replacement for CCCs. NCPs are also becoming available, but these have been far less studied in this application. NAVAIR is currently continuing studies on the effectiveness of their NCPs, and AlumiPlate�� offers a proprietary non-chromated topcoat over its coating system. An NDCEE Task is currently being conducted with the objective of evaluating NCPs for TARDEC. SUMMARY The most promising candidate coating processes to replace cadmium and hexavalent chromium in electrical connector applications are technologies that are already being used on electrical connectors to some extent, or demonstrate both considerable promise for the application and sufficient maturity. These include: ��� 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 be evaluated. 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 alternatives were also identified. These are technologies that show promise for electrical connector applications, but require further development for the electrical connectors employed by TARDEC. These include: ��� Alloys deposited from ionic liquids ��� Magnetron sputtered aluminum alloys ��� Tin-indium alloys 414

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