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Corrosion Prevention: Alodine and Zinc Chromate

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messydeer(at)yahoo.com
Guest

Posted: Wed Feb 01, 2006 11:48 am Post subject: Corrosion Prevention: Alodine and Zinc Chromate

Hi!

   

  I've got seveal sheets of 6061. Some areas of most all the sheets got corroded from sitting stacked in the rain for the last several months. A great experiment, but I wish I wouldn't have done it with ALL the sheets. Just about ready to start bending metal. So I'm planning on getting some aluminum cleaner/etcher w/ phosphoric acid to clean them up. Prolly start with a manual scotchbrite (green) and the cleaner. Any residual left I'd take off with a Blendex drum and my angle grinder.

   

  Plan on treating all parts with Alodine, the gold kind. Larger parts I'll prolly brush on and may treat only the inside of the skins, leaving the outside to polish or paint. Faying surfaces I plan paint with zinc chromate. All other inside areas I may hit with a spray of zinc chromate, CorrosionX, or something like that. It would be nice to do this at the time of assembly, but could be done later.

   

  Could you refer me to some good sources for concentrated Alodine (Irridite?)?

   

  Let me know what you think of this plan. Oh! I live in Bellingham, WA. We've only had .3" of rain this month, but it rained 8" last month. Just north of Seattle. Plane will be tied down outside, most likely.

   

  Cheers,

  Dan Morehouse

   

   



		

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ding(at)tbscc.com
Guest

Posted: Wed Feb 01, 2006 2:10 pm Post subject: Corrosion Prevention: Alodine and Zinc Chromate

Dan,

        I recently researched the market for a source for these products,

and the winning vendor was Aircraft Spruce. They didn't charge $20 per jug

hazardous shipping, as some others wanted to, but $20 per order.  Huge

difference.  I wasn't able to find a cheaper source.

                                                                Lynn

                                                                Corry, PA

messydeer(at)yahoo.com
Guest

Posted: Wed Feb 01, 2006 3:41 pm Post subject: Corrosion Prevention: Alodine and Zinc Chromate

Thanks, Lynn.

   

  They're close to the bottom of the price list all right. I think they're around $17 per gallon before shipping. I asked them 2 days ago for a shipping w/ hazmat quote. They acknowledged they're working on that. Still no word, which sounds like Spruce. In my short experience Wicks is MUCH better organized if a little higher on most products. But they want something like $20 hazmat fee ontop of a higher than Spruce price.

   

  After calling around town, I found Alumiprep and Alodine for ~$20/gal each. Not a huge difference and no fees, except tax.

   

  Cheers,

  Dan



lynn dingfelder <ding(at)tbscc.com> wrote:

  



Dan,

I recently researched the market for a source for these products,

and the winning vendor was Aircraft Spruce. They didn't charge $20 per jug

hazardous shipping, as some others wanted to, but $20 per order. Huge

difference. I wasn't able to find a cheaper source.

Lynn

Corry, PA







  

		

---------------------------------

shilocom(at)mcmsys.com
Guest

Posted: Wed Feb 01, 2006 8:42 pm Post subject: Corrosion Prevention: Alodine and Zinc Chromate

Cory,  Have you tried your local automotive paint stores.  Here in the

Midwest the PPG and Dupont stores all have Alodine and Zinc Chromate or

epoxy primer.  Auto parts stores who mix paint's like O'Reiley's again in

the Midwest have it where you can walk in and pick it up with out hazardous

fees.  bob U.



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rjscep(at)yahoo.com
Guest

Posted: Thu Feb 02, 2006 6:02 am Post subject: Corrosion Prevention: Alodine and Zinc Chromate

 	  Quote: 	
		   I am also in a group building a Glastar and we had 

 just purchsed a gallon of etch and Alodine,  

 purchased locally and it cost double the price. We

 paid $40 a gallon for each. Guess we should have 

 ordered it from AC Spruce. thanks Lynn

 
	




--- lynn dingfelder <ding(at)tbscc.com> wrote:



 	  Quote: 	
		   

 <ding(at)tbscc.com>

 

 Dan,

         I recently researched the market for a

 source for these products,

 and the winning vendor was Aircraft Spruce. They

 didn't charge $20 per jug

 hazardous shipping, as some others wanted to, but

 $20 per order.  Huge

 difference.  I wasn't able to find a cheaper source.

                                                     

            Lynn

                                                     

            Corry, PA

 

 

 

 



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keithnorton(at)mac.com
Guest

Posted: Thu Feb 02, 2006 7:10 pm Post subject: Corrosion Prevention: Alodine and Zinc Chromate

 	  Quote: 	
		  Any residual left I'd take off with a Blendex drum and my angle grinder.


	


Be very careful using any power tools to remove corrosion.  It is very easy to remove too much material.  The FAA allows 10% on certified aircraft but I'm not sure what ZAC allows.  Most of the sheetmetal on these planes is very thin in the first place.



Another problem with using power tools this way is the possibility of heating the metal and changing its strength.



Good luck with it.



Keith Norton A&P



Zenith 701 - Tail completed

Cessna 170A - Major sheetmetal project due to corrosion

messydeer(at)yahoo.com
Guest

Posted: Sat Feb 04, 2006 3:48 pm Post subject: Corrosion Prevention: Alodine and Zinc Chromate

Thanks, Keith. I thought I replied earlier, but I think it got bounced.

   

  I've spent some time emailing and talking with people on the phone. Matt Clark of Henkel, makers of Alodine, talked with me for a good 15 minutes. Here's what he had to say:

   

  The corrosion that occurred in my stacked sheets of 6061 left outside in the rain will continue to occur, even though they are now dry and sitting indoors. He suggested cleaning them with Alumiprep and then immediately treating with Alodine. I asked if I couldn't just clean w/ Alumiprep and not Alodine. Then use Alumiprep again and then Alodine right after making the part. Sounded good to me.

   

  But he said corrosion would still occur, even after cleaning off the old corrosion. He mentioned mills put an anticorrosive finish on, which has now been degraded. That still sounds like overkill to me. What do you say?

   

  I also called Vic at MacDermid, makers of Iridite, which is a conversion coating similar to Alodine. He didn't think corrosion would continue after cleaning/etching, but was only going on personal experience.

   

  I hate to go through all the trouble of Alodining all 20 sheets, especially all at once. So I am thinking of a middle of the road approach: clean them all up now with Alumiprep then check every few months for corrosion. 

   

  I also had one person ask why not anodize. I've never heard anybody doing that in small airplane construction. I did a quick search and found one type (sulfuric?) weakens the aluminum substantially, while chromium doesn't do so near as much. I also would guess it's expensive?

   

  Take care,

  Dan



		

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Ron Lendon

Joined: 10 Jan 2006
Posts: 685
Location: Clinton Twp., MI

Posted: Sun Feb 05, 2006 10:57 am Post subject: Re: Corrosion Prevention: Alodine and Zinc Chromate

I work for GM in their Prototype Manfacturing Facility Press Room.  We get sheet metal in the flat on skids with a cover sheet on top and bottom.  Our guys don't use any material with rust (oxidation) when they make the stampings, the cover sheets are often thrown out.  It will provide incorrect test results when we crash test or endurance test the structure.



If it was me, I would replace the the oxidized metal and call it a learning experience.  You might have some areas of the sheets that can be used, if no oxidation is present.  Keep it clean and dry in a rack like this below:



Here is a link with a little more explanation of the rack.

http://www.kitlog.com/users/display_log.php?user=rlendon&project=113&category=1317&log=9945&row=1

100_0250.jpg

Description:

Material rack, holds 4' X 12' sheets

Filesize:

661.63 KB

Viewed:

594 Time(s)

_________________
Ron Lendon
WW Corvair with Roy's Garage 5th bearing
CH 601 XLB
N601LT - Flying
http://www.mykitlog.com/rlendon
Corvair Engine Prints:
https://sites.google.com/site/corvairenginedata/

messydeer(at)yahoo.com
Guest

Posted: Mon Feb 06, 2006 10:41 am Post subject: Corrosion Prevention: Alodine and Zinc Chromate

About my corrosion problem...

   

  I spoke with Sheldon Dean of Dean Corrosion Technology. He is also the editor of  the Journal of ASTM International. Heres what the Journal says about him: Leading the Editorial process of the Journal is Sheldon W. Dean, Jr., Sc.D., President of Dean Corrosion Technology, Inc. and formerly of Air Products and Chemicals, Inc. Dr. Dean has gained worldwide recognition for his outstanding contributions in corrosion testing, standardization and leadership in the voluntary standards system within both ASTM and the International Organization for Standardization (ISO). Dr. Dean has been an ASTM member since 1965. He has authored more than 95 publications, is primary author of six standards, and has assisted with 20 others. He has also edited seven books. A large number of these standards and publications are used throughout the world in materials and corrosion technology.

   

  This is a water stain, a type of corrosion. It starts out blackish then over time it turns white. This is aluminum hydroxide, which forms instead of the oxide. A protective layer of aluminum oxide is formed from the oxygen in the air. The hydroxide is formed when it is exposed to water.

   

  Once the corrosion is removed, a feint stain pattern might remain or recur at a later time. This could be easily removed by polishing. The surface could be primed and painted, in which case there would be no further evidence of the corrosion. There are no damaging physical or chemical changes made by a superficial layer of this corrosion. If the stained sheets are dry now and remain so, there will be no further corrosion even when stored this way for a few years.

   

  Acid etching also does not promote corrosion. The protective oxide layer will form. Aluminum may be acid etched and stored dry without a conversion coating. There is no benefit to applying a conversion coating when the sheets will remain dry afterwards.

   

  Removing the stain/corrosion could be done with an acid etch and scotchbrite, or possibly with scotchbrite alone. The latter method would not require eye and skin protection needed with the acid etch method.

   

  I also spoke with David Burleigh, Ph.D. (from MIT) of the Materials and Metallurgical Engineering department at the New Mexico Institute of Mining and Technology. He agreed with Dr. Dean, but added a couple items: 

   

  1. Corrosion could continue if there were road salts deposited on the aluminum 

  2. The sheets should be inspected for signs of pitting: pimples of powder above the surface.

   

  I think now Ill inspect the corrosion to make sure there is no pitting. At that time I could try removing the corrosion with scotchbrite alone. Most sheets have the stain on one side only. Ill mark this side so I can avoid the potential of recurring stain on the exterior.

   

  I give thanks to Dr. George Totten, author of  the Handbook of Aluminum and past president of the International Federation of Heat Treating and SurfaceEngineering (IFHTSE).  Dr. Totten referred me to Drs. Dean and Burleigh.

   

  Take care,

  Dan

   



		

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pmoore505(at)msn.com
Guest

Posted: Mon Feb 06, 2006 11:41 am Post subject: Corrosion Prevention: Alodine and Zinc Chromate

Thanks Dan for the well presented information. I really like this sort of 

objectively obtained, informed study of the issues, risks, and mitigation. 

This helps us all alot. Well done.



Paul

XL-O200



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