Metal Finishing Guide Book

2013

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opment from a process standpoint would likely be necessary to implement this process for high-volume applications such as electrical connector shells. ALLOYS DEPOSITED BY MOLTEN SALT BATH PROCESSES Figure 1. Galvanic series, showing position of cadmium and viable alternative metals. (Circled area: materials providing sacrificial protection.) 1 An aluminum-manganese molten salt plating process was explored under funding from the Environmental Security Technology Certification Program (ESTCP), but the process was plagued by inconsistent bath composition, visible fumes, and excessive crust formation [Ref. 10]. In addition, this process operated at a very high temperature, which is likely to affect the properties of aluminum shells. While this technology is promising, considerable further development from a process standpoint would be necessary to implement this process for electrical connector shells. ALLOYS DEPOSITED BY IONIC LIQUID PROCESSES As an alternative to the molten salt bath process mentioned above, the use of ionic liquids as an electrolyte to plate aluminum is under investigation. 5,11 Ionic liquids are salts with a low melting point, which originates in their chemical structure (a mix of anions and large organic cations). These liquid salts have unique properties that allow easy dissolution of normally insoluble chemicals, such as cellulose. Ionic liquids enable electrochemical plating of metals like aluminum; deposition rates of one micron per minute at low temperatures (60 to 100°C) have been reported.11 These deposition rates are significantly superior to other low-temperature aluminum coating methods. While this process is not yet mature enough to enable the plating of commodity items such as 353

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