alodine questions
alodine questions
(OP)
I recently started alodining parts so any advice would be apreciated. My process now is as follows:
1. clean parts with diswasher.
2. acid dip 3-4 min.
3. spray with hot water.
4. soak parts in room temp water 3-4 min
5. dip parts in alodine for 3.5-6 min
6. let parts air dry 30 sec.
7. dip in room temp water for 10-15 sec.
8. air dry
I'm having mixed results some problems i'm having are:
Parts have white streaking from holes.
light coloring.
a few parts don't plate usually in the middle of the rack.
staining around holes and bottom of part. this is better when blotting is done before total drying.
Any help/advice would be great.
Thanks,
Chris
1. clean parts with diswasher.
2. acid dip 3-4 min.
3. spray with hot water.
4. soak parts in room temp water 3-4 min
5. dip parts in alodine for 3.5-6 min
6. let parts air dry 30 sec.
7. dip in room temp water for 10-15 sec.
8. air dry
I'm having mixed results some problems i'm having are:
Parts have white streaking from holes.
light coloring.
a few parts don't plate usually in the middle of the rack.
staining around holes and bottom of part. this is better when blotting is done before total drying.
Any help/advice would be great.
Thanks,
Chris





RE: alodine questions
Paint/coatings engineering Forum
forum332
What Al alloy & what is pre-existing surface condition?
Through or blind holes? Threaded?
Which Alodine solution? pH & concentration, too.
What acid & concentration?
Re: Spraying with hot water and soaking in water 3-4 mins. Why? This just gives the deoxidized surface more time to re-passivate. Better to dip rinse up & down several times quickly, spray rinse out the holes, rinse in DI water, then Alodine.
"white streaking from holes" indicates inadequate draining & rinsing. At each step, lift & tilt the rack with parts to drain holes, then submerge & tilt to fill holes. Especially, do so in the Alodine to get the holes filled with the solution.
"let parts air dry 30 sec." Usually lift from the Alodine, tilt a few directions to drain holes, then rinse w/o drying. Up & down rinsing, tilting at different angles, to drain & rinse holes.
RE: alodine questions
Thanks,
Chris
RE: alodine questions
Tapwater contaminants can precipitate on the aluminum surface and interfere with the Alodine coating. Any idea of your water's TDS?
Get Technical Process Bulletin for Alodine 600 here:
h
pH range should be 1.5 to 2.0; aim for 1.7-1.8.
Too low pH usually gives no coating, too high gives powdery.
RE: alodine questions
Thanks,
Chris
RE: alodine questions
Any pH tester will cover the range of 1 - 14!
Orenda
RE: alodine questions
The longer you etch (more than needed to remove surface oxide), the worse the results. On a machined surface, just degrease & 30 seconds acid deox. Maybe even skip (unless the aluminum still has heat treat scale) -- the Alodine will just take longer.
Don't like the phosphoric acid (what concentration & temperature??), it is difficult to rinse & cause phosphate contamination of the Alodine. Phosphate on the aluminum surface interferes with Alodining; it also uses up the acidity of the Alodine solution which has to dissolve it. Suggest only using 5% phosphoric & warm water rinsing to help get it off. Nitric acid is far better and is needed to lower the pH of the Alodine.
If you don't want to buy a pH tester (& pH 4 & pH 7 calibration solutions & DI water), there is pH paper available for range 1-2.5 (a bit crude, only indicates pH's of 1, 1.5, 2, 2.5):
http://www.mcmaster.com P/N 1434T14
RE: alodine questions
The acid is 2 to 1 and is hard to get off. The hot stray does help but I was told that the parts should be rinsed in cool water for the best results. The main problem I'm having is parts turn out to light. 2024 doesn't seem to color at all but if you get the part wet it shows up gold then fades back to purple/silver color when dry. From what I've heard in practice most people just add more alodine to solution to get better color.
Chris
RE: alodine questions
Is this 2 parts by volume phosphoric (75 or 85 wwt%?) to 1 part water??? -- more appropriate for rusty steel; it will leave a phosphate film.
Suggest cleaning the 2024 with a ScotchBrite pad & DI or distilled water (grocery stores sell), then Alodine.
Or, as with out-of-the way places on airplanes that can't be dipped, clean the surface with ScotchBrite pad & DI water, then apply the Alodine while rubbing with ScotchBrite pad, leaving the surface wet, dripping on more Alodine as needed, until the color takes.
Of course, Alodine has hex. Cr & acids, so wear appropriate PPE & use plastic dropcloths.
RE: alodine questions
Thanks,
Chris