- Email: [email protected]
Chromium plating on aluminum
Heard on the Hotline by Ted Mooney, P.E.
Join us at http://www.finishing.com/letters
I
f you have anything to add to the following discussions, we’d prefer it if your reply was by E-mail to the inquirer with a copy to me when possible, or via a posting at the website. But substance comes before form, so we will appreciate all responses, even those in handwriting.
cobalt acetate, 8 g/L boric acid (in distilled water) for 15 to 20 min at 70 to 90°C and pH 5 to 6. Gary A. Nitowski, [email protected]
COATING TO PREVENT ALUMINUM
I am looking for information regarding the use of 7075-T6 Alodined fasteners with 5052 aluminum panels. Is there a possibility of galvanic corrosion over time between these two types of aluminum? The application is an electronics enclosure that will not see a particularly harsh environment. Pat Kelly, Penn Engineering, [email protected]
SEIZING
Can anyone tell me if there is a rule of thumb dealing with the proper procedure for connecting two threaded aluminum parts without the danger of having them seize? Joseph Anderson, [email protected] Huh! Good luck. I’ve spent hours carefully hacksawing aluminum hose fittings off of faucets, trying not to damage the threads on the faucets. I once bought a new garage door that had aluminum parts in the lock mechanism; my wife didn’t read the warning to use only brass keys. She had a duplicate aluminum key made, and stuck it in before the new door was two hours old. We’re still looking for the King Arthur who can pull this Excalibur from the lock. I know of no surface finish or assembly technique that makes an aluminum-to-aluminum screwed joint acceptable, but maybe I’m wrong. I’ve sent you via E-mail the name of a company that offers all sorts of slick, durable, specialty finishes for aluminum. If you find that one of them solves the problem, please update me. Ted Mooney, Finishing Technology, N.J., [email protected]
NICKEL ACETATE SEALS We currently warm seal anodized aluminum extrusions in water at approximately 100°C (212°F). I understand that appropriate quantities of nickel acetate will help the sealing process. Could someone explain how it works? How much nickel acetate should we add? Sanjay A. Bulchandani, Ajit India, sanjayb@giasbmOl .vsnl.net.in Nickel sealing is often used for dyed anodic oxides, since it is colorless. The corrosion resistance afforded by the process is generally not as good as boiling water or steam seal, unless the nickel acetate process is done at boiling temperature. Cobalt acetate may also be used. A practice found in Wemick, Pinner, and Sheasby’s Sq‘iice Treatment and Finishing of Aluminum is: 5 g/L nickel acetate, 1 g/L METAL FINISHING
l
JANUARY
1997
0 Copyright
Elsevier
GALVANIC CORROSION OF ALUMINUM
BETWEEN GRADES
I don’t know exactly how 7075 lines up against 5052 in the electrochemical series, and I don’t know of an activity chart that puts so fine a point on it as to distinguish between different alloys. Alodine is a proprietary name for a MILC-5541 chromate conversion coating; it will certainly retard corrosion rather than accelerate it. So I just can’t imagine galvanic corrosion between these two alloys being a problem in an electronics enclosure that will not see a harsh environment. Ted Mooney, Finishing Technology, N.J., [email protected]
CHROMIUM
PLATING ON ALUMINUM
I own a metal-finishing company in Florida and am looking into getting into chromium plating aluminum. A lot of people are telling me that it is a big thing. I’ve done chrome plating on steel and brass only. I’d appreciate any suggestions. Tony Pena, Miami Professional Polishing, mpp4925@aol,com Aluminum immediately forms a passive film onto which it is not possible to electroplate. The first step, therefore, is to apply a zincate coating, or a proprietary alternative. Once the zincate finish is in place you can copper-nickel-chromium; but there seems to be movement towards electroless nickel-nickel-chromium instead. A literature search will reveal numerous plant write-ups; the MFIS “Surface Finishing CD-ROM’ (available from Metal Finishing magazine) is a great tool for such literature searches. Ted Mooney, Finishing Technology, N.J., [email protected] Science
Inc.
65
Join us at http://www.finishing.com/letters
I
f you have anything to add to the following discussions, we’d prefer it if your reply was by E-mail to the inquirer with a copy to me when possible, or via a posting at the website. But substance comes before form, so we will appreciate all responses, even those in handwriting.
cobalt acetate, 8 g/L boric acid (in distilled water) for 15 to 20 min at 70 to 90°C and pH 5 to 6. Gary A. Nitowski, [email protected]
COATING TO PREVENT ALUMINUM
I am looking for information regarding the use of 7075-T6 Alodined fasteners with 5052 aluminum panels. Is there a possibility of galvanic corrosion over time between these two types of aluminum? The application is an electronics enclosure that will not see a particularly harsh environment. Pat Kelly, Penn Engineering, [email protected]
SEIZING
Can anyone tell me if there is a rule of thumb dealing with the proper procedure for connecting two threaded aluminum parts without the danger of having them seize? Joseph Anderson, [email protected] Huh! Good luck. I’ve spent hours carefully hacksawing aluminum hose fittings off of faucets, trying not to damage the threads on the faucets. I once bought a new garage door that had aluminum parts in the lock mechanism; my wife didn’t read the warning to use only brass keys. She had a duplicate aluminum key made, and stuck it in before the new door was two hours old. We’re still looking for the King Arthur who can pull this Excalibur from the lock. I know of no surface finish or assembly technique that makes an aluminum-to-aluminum screwed joint acceptable, but maybe I’m wrong. I’ve sent you via E-mail the name of a company that offers all sorts of slick, durable, specialty finishes for aluminum. If you find that one of them solves the problem, please update me. Ted Mooney, Finishing Technology, N.J., [email protected]
NICKEL ACETATE SEALS We currently warm seal anodized aluminum extrusions in water at approximately 100°C (212°F). I understand that appropriate quantities of nickel acetate will help the sealing process. Could someone explain how it works? How much nickel acetate should we add? Sanjay A. Bulchandani, Ajit India, sanjayb@giasbmOl .vsnl.net.in Nickel sealing is often used for dyed anodic oxides, since it is colorless. The corrosion resistance afforded by the process is generally not as good as boiling water or steam seal, unless the nickel acetate process is done at boiling temperature. Cobalt acetate may also be used. A practice found in Wemick, Pinner, and Sheasby’s Sq‘iice Treatment and Finishing of Aluminum is: 5 g/L nickel acetate, 1 g/L METAL FINISHING
l
JANUARY
1997
0 Copyright
Elsevier
GALVANIC CORROSION OF ALUMINUM
BETWEEN GRADES
I don’t know exactly how 7075 lines up against 5052 in the electrochemical series, and I don’t know of an activity chart that puts so fine a point on it as to distinguish between different alloys. Alodine is a proprietary name for a MILC-5541 chromate conversion coating; it will certainly retard corrosion rather than accelerate it. So I just can’t imagine galvanic corrosion between these two alloys being a problem in an electronics enclosure that will not see a harsh environment. Ted Mooney, Finishing Technology, N.J., [email protected]
CHROMIUM
PLATING ON ALUMINUM
I own a metal-finishing company in Florida and am looking into getting into chromium plating aluminum. A lot of people are telling me that it is a big thing. I’ve done chrome plating on steel and brass only. I’d appreciate any suggestions. Tony Pena, Miami Professional Polishing, mpp4925@aol,com Aluminum immediately forms a passive film onto which it is not possible to electroplate. The first step, therefore, is to apply a zincate coating, or a proprietary alternative. Once the zincate finish is in place you can copper-nickel-chromium; but there seems to be movement towards electroless nickel-nickel-chromium instead. A literature search will reveal numerous plant write-ups; the MFIS “Surface Finishing CD-ROM’ (available from Metal Finishing magazine) is a great tool for such literature searches. Ted Mooney, Finishing Technology, N.J., [email protected] Science
Inc.
65