Metal Finishing Guide Book


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Table XIX. Suggested Watts Nickel Strike Formulation Component Nickel metal Concentration (oz/gal) 10-12 Nickel chloride 8-10 Nickel sulfate 32-37 Boric acid 5-6 2. Conventional alloy zincate. Similar to the conventional zincate but differs as follows: contains iron, which forms an Fe-Zn alloy immersion deposit. Chemistry and operation as previous plus 0.2-0.4 oz/gal ferric chloride 3. Modified alloy zincate. Similar to conventional alloy zincate but differing as follows: contains several metals (commonly from among copper, iron, nickel and zinc, forming a unique alloy immersion deposit. Copper and nickel control rate of zincate formation and enhance its tight, cross-linked structure. Gluconate complexors (small amounts of cyanide are optional) used in place of tartrates, and much less sodium hydroxide. The working solution is much less viscous, providing improved rinsing characteristics. In each zincate described, the type and concentration of complexors are critical to maintain solubility of the alloying metals. Which zincate to use? The conventional zincate is a good process when applied to high-purity aluminum alloys. But, it doesn't provide as strong adhesion over 5000 and 6000 series alloys as do conventional alloy and modified alloy zincates. The latter provide a far stronger bonding to a wider range of aluminum alloys. This is due to formation of less porous, denser, uniform films. They also protect sharpened corners and edges of zincated parts from being worn and abraded in barrel plating. Tips on zincating include: • Rinse well before the zincate bath to prevent drag in of desmut acid solution. For example, fluorides will detrimentally affect the zincate film. • The zincate should be an even gray or blue-gray color. Splotchiness may indicate zincate solution components are out of balance. • Poor adhesion of zincate to basis aluminum may be due to bath temperature out of range or poor cleaning and surface preparation. • Spongy zincate (thickened) is usually a result of excess immersion time or too high bath temperature. • A good, adherent zincate film will pass a Scotch tape pull. Strikes Copper This bath is designed to coat the zincated surface with a strong bond, while not attacking it in the process. (See Table XVIII.) The deposit serves as an active site for reception of subsequent electrodeposits, some of which might be highly aggressive toward the unprotected zincate. Both formulas operate at 4 A/ft2 for 5 minutes or at 25 A/ft2 for 10 seconds, 110-125°F (43-52°C). pH of first bath at 10-10.5. pH of second bath at 11.5-12.0. A proprietary grain refiner and anode corroder may also be added. 150

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