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Old 02-04-2016, 11:05 AM   #21
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[QUOTE=psneeld;411223]DGR Industrial Products, Inc. :: Specialty Coatings :: Conversion Coatings :: Alodine Chromate Conversion For Aluminum Alloys :: Henkel Alodine 1201 Chromate Conversion Coating


Applications in which temperatures can reach over 120║F can break down the corrosion resistance

of the coating. In comparison to anodizing, this chemical film is more fragile and

not generally recommended for high-use areas.


Wonder if my black window frames would be a candidate for Alodine as they easily go over 120 deg F in the summer.


Alodining





The temp limitations refer to Alodine applications that are not top coated, as the Alodine will dehydrate. I have used Alodine in many applications and results have been better than expected.



The temperature restrictions apply to unpainted Alodine«. The powder coating protects the chromate from dehydrating and cracking during the high temperature cure.

Adhesion problems due to improper chromating could be due to:
1) Poor aluminum pretreatment (e.g., over-etching, wrong deoxidizer for castings, dirty rinses),
2) Dirty post-chromate rinses; final rinsing in DI water is best (if not using a Deoxylyte« final rinse),
3) Excessively thick chromate; try Type II per ASTM B449-93 [link by ed. to spec at TechStreet] (twixt Classes 1A & 3 of Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil]).
4) Under-cured chromate (soft gel, lacking strength),
5) Over-cured chromate (powdered & cracked. Metal temperature shouldn't exceed 150 ░F).

See the appropriate Alodine product bulletin or Mil-HNDBK-509 [link by ed. to spec at TechStreet] CLEANING AND TREATMENT OF ALUMINUM PARTS PRIOR TO PAINTING for more info. Final rinsing in Deoxylyte« (rather than DI water) is given. Most Deoxylyte versions are dilute chromic acid solutions; Henkel likely has a non-hex. chromium version by now.

What adhesion & corrosion testing is currently performed? In letter 45803, Sheldon Taylor describes D-I-Y testing of X-scribed painted samples in boiling water, similar to ASTM D870 [link by ed. to spec at TechStreet]. Another quick test is adhesive tape testing of crosshatched samples, see ASTM D3359 [link by ed. to spec at TechStreet] or search this site. If successful with these, then do the more rigorous tests. E.g., have scribed samples tested by a lab per ASTM D2803 [link by ed. to spec at TechStreet], 'Standard Guide for Testing Filiform Corrosion Resistance of Organic Coatings on Metal,' either Procedure A or C (both are salt-fog followed by humidity). Letter 38976 "Specifications for Powder Coated Aluminum -- AAMA 2603, 2604, 2605" gives additional tests.
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Old 02-04-2016, 11:29 AM   #22
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Thanks...the second link I placed seemed to indicate issues about no top coating but wasn't exactly clear about it.
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Old 02-04-2016, 01:08 PM   #23
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This Adoline stuff is great info, but I'm not sure how I will etch my frames on the boat without it dripping all over my nice shiny gelcoat under the windows.

Guess I could try to tape off the gelcoat with plastic maybe.
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Old 02-04-2016, 02:32 PM   #24
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Are the frames fastened to the boat with stainless steel screws and is some of the peeling adjacent to the screws? If so, make sure you re-bed those with something like TefGel or you will have peeling all over again.
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Old 02-04-2016, 11:08 PM   #25
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CarDude- come on over about 4 slips for plenty of spots for you to practice on while you perfect the technique.

Seems this task keeps slipping down the to-do list.
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Old 02-04-2016, 11:28 PM   #26
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Quote:
Originally Posted by KneeDeep View Post
CarDude- come on over about 4 slips for plenty of spots for you to practice on while you perfect the technique.



Seems this task keeps slipping down the to-do list.

Ha! You don't me working on your boat!
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