[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.
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.