Anodizing Automotive Brightwork Q&A's

A. 1. Your aluminum alloy is about 4.5 % Magnesium. All inorganic salts of Magnesium are white. Anodizing only control oxidizes pure aluminum, and leaves the magnesium on the surface probably in your case as Magnesium sulphate, and Epson Salts are white.

2. The last time I saw white specs under clear powder paint in South Carolina, I stopped by the grocery store and picked up some distilled water and a squirt bottle. Then I sprayed the parts at the end of the line with pure water. Guess what, the white spots were gone. Then we learned that the local water authority had switched lakes and at the same time our D.I. unit went down -- the calcium and magnesium were coming thru and both make white salt.

3. Go to Section 4 of finishing.com and locate my paper on "White Spots". Let us hear from you.

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby

(note: this book is two volumes)

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A. Based on the limited info, my suggestion is to try anodizing at a faster rate. Brightness decreases with time in the tank, and 10 minutes sounds excessive. Work near the upper current density limit given by the anodize additive vendor. Typically, anodic coatings of 0.3-0.5 mils (7.7-12.7 microns) are used for exterior trim. Less may be acceptable for a restorer who keeps things well waxed.

You may wish to begin by experimenting on bright anodizing alloys such as 5252, 5457, 5657 and 6463 in cold rolled or extruded condition (not annealed).

A. The type of aluminium you want to use for anodising is probably 5 or 6 series (i.e., 5052, 5252, 6061 or 6101. These alloys are inherently strong and ductile. Series 1 is generally classified as very soft, whilst 2 is very strong and hard. Series 3 is also strong and 4 is strong and fluid. Series 7 is very strong.

A. Far from my area of expertise, but have you tried any of the 3000 series? If I recall, that series brightens up quite well.

ASM Metal Handbook
9th Edition, Vol. 5
"Surface Cleaning, Finishing & Coating"

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A. Hi Shaun. I would certainly expect that one out of three anodizing shops, at the least, would be technically proficient enough to solve the problem if it was solvable. Based on that -- and the previous input on this thread which we appended your inquiry to, and several related threads -- I think you may be trying to achieve the finish on an alloy which can't support it.

I am not an alloy expert but my understanding from the ASM Metals Handbook is that hard tempered 5457, 5357, 6463 and 6063 would be best, in order of decreasing quality. Good luck.

Regards,

----
P.S. June 9: Prompted by Willie Alexander's posting, I reread yours ... and it seems that all of these samples are your customers' from their Porsches ... so my response about you perhaps needing a different alloy sounds off track.

Q. Thank you Ted, I appreciate the quick posting. I think the solution lies in the ALZAK process. Do you or does anyone know of an anodizer on the East Coast who is offering this process?

I remember when the plating supply company I was with was offering acid zinc plating plus clear-coating as an alternative to chrome plating for bicycle rims. I thought they looked darned good! ... until somebody got a chrome plated wheel and put it next to them, that is, and you had to admit there was just no comparison at all :-)

That's life -- I loved Gillette Castle until I saw Falling Water; Scarlett Johansson was gorgeous until I saw a Grace Kelly re-run. It just might be that you can't get the 1970 Porsche clarity with any process that is environmentally acceptable in 2016 (nor can you get the full look of cadmium plating on classic car restorations). Best of luck with the journey though!

Regards,

How's that for a wide variety of answers? All are good, but Harry's strikes me as the most likely description of the overall situation. Things tend to look fine until they're compared to something which looks better :-)

A. Shaun

If I read you post correctly, you are trying to re-anodize the original window frames. I would think the pretreatment is effective, the buffing and bright-dip, but the anodize is what is causing the hazy finish. I believe you will need to alter the operating conditions to achieve a 'clearer' anodize. I would try a cooler bath temperature 63 - 65 °F, 15 - 18% by weight acid, and 9 - 10 ASF current density.

A. To add to what Willie Alexander said, I've red this exact thing in one of the anodizing related books or publications, can't recall where though

About the "streaks", they look to me not to be related to extrusion at all, but rather sanding marks from the early grits used to remove scratches (some rotary "witness marks" are visible also), thus I would recommend, after stripping the old anodizing from the parts (I would use 5% phosphoric acid + chrome oxide at ~95 degrees C instead of caustic so as not to deepen the scratches), then use no coarser that 600 grit wet paper and some type of lubricant other than water (I've successfully used WD-40 ⇦this on eBay or Amazon [affil links] , I simply had this at hand) to sand the deep scratches out, and do this "across" the part, then use 800, and 1000, and maybe even 1500, each time go across previous sanding direction (otherwise you will not notice that you haven't sanded out marks left by previous grit), after last paper you can start to polish the part, and use at least 2 grits to do that aswell - all these steps are required on aluminum, since it is so soft, going from, lets say 320/400 to 800 and then paste, there is a high chance you will simply "smudge" and level deep scratches left by coarse grits, and this is exactly the reason you see those marks later after anodizing - because the smudged/mirror-polished top layer is being converted to oxide revealing your early sanding marks.

Restoring something like this is quite difficult and laboursome, much more than when the new parts were made at he factory - simply because they didn't have to deal with such defects and required less polishing, mechanical or (electro)chemical.

"It looks like I will have build my own bright dip and anodizing solution in-house."

Not wanting to rain on your parade, but the investment in time, technical knowledge, equipment, permits and environmental compliance to set up a bright dip and anodizing operation, even at a minimal level would cost as much as a trailer load of restored Porches.

A. Good day Shaun.

Very interesting situation.
I like the thought of using acetone instead of MEK.
Are you using a mild alkaline soak and checking for water break?
Can you inspect the frames directly after anodize, before sealing/drying?
What is the TDS, silica and chloride concentration of the seal?
What is the compressed air quality, if used used to assist in drying?
I have found 15 ppm in RO water to cause some grief.
Sometimes I can't see the forest because the trees are in the way!
Hope this helps.

Regards,

A. ` Hi Brian.

Forgive me for being a smart ass, but saying that things are different but unchanged is a hard point to start from.

Brightness around titanium contacts is due to local electropolishing caused by the current generated by the Al/Ti couple. It is always there to some degree but normally not noticeable. When the brightener gets out of balance, especially with respect to nitric acid, the chemical brightening generally becomes poorer (slight etching) and the electropolished area stands out.

Generally, look for anything which might pull down the chemical brightening and increases the contrast between the two.

Things on my list would be:
Nitric acid
Water content
Aluminum content
The aluminum metal - Do you have parts from previous batches to compare?
An open mind!

 Ted, Thank you very much. Harry Parkes gave me some excellent advice that we tried immediately. It took TWO shifts of no nitric adds to our Bright Dip but by golly the lower nitric concentration totally took care of our problem. Thanks again. Great website.