Copper colored "scum" over my alodine --- ???

[fairchild]

Tested my new alodine (PPG DX-503)
I seem to be getting a very rapis color change when the part goes into the alodine bucket. (brand new alodine)
I left a test piece in for on;y 30 sec. and it came out a deeper golden-brown about the color of a tarnished penny.
The darker part seems to be like a "scum" or loose film laying on top of the chromate conversion layer. i can
take my wet gloved finger and rub it gently and it slides/rubs off --- leaving the converted surface showing below.

Never seen it do this before------ called PPG tech line---- they never heard of it.

I am using a water rince between the acid cleaner and the alodine----- that rinse is running tap water which would be
chlorinated. Could the chlorinated water be doing that ? I tried a whole nose rib and the brown "scum" was very uniform over the whole part.
If it is some byproduct thats just laying there loose on the surface---- I certainly cant epoxy prime over THAT ..........

As an experiment I tried diluting the alodine with some distilled water----- that didnt seem to make the brown film--- but it was much slower
overall. and the chromate color was not as dark looking.

As prep----wiped with alcohol,,,, scrubbed with white scotchbrite and dawn soapy water. water rinse---- acid/cleaner bath.....
running tap water rinse---- dip in alodine. ..... water rinse---- (wipe off brown scum)

see anything I am doing thats not correct ?

Tim

[fairchild]

These are my test pieces. The 2 little ones: left- full strength in for 30 sec. only
Right : the sx-503 was diluted about 100% ---- about 3 to 4 minutes in.
Then I did the rib---- It looked like the left sample when I took it out---- the darker film seemed to mostly wipe off with my finger.
I wiped it off under running water--- and this is how it looks now......
Am I supposed to let the darker slimey film dry on it ?
I let them dry overnight on the samples-- and today -- a white scotchbrite didnt wipe it off too easily---- I didnt rub hard though.....
This color seems WWAAYYY darker than any alodine I have ever seen in the past......
Did I wipe off the alodine on the rib or just some kind of unwanted layer ??????
Tim

[BTAZ]

Much darker than it needs to be.

It should be light and "Iridescent gold" (I.E. color changing with rainbow hues).

Even the smallest hint of gold is enough. Note what I have shown below is still darker than it needs to be. Just a "hint" is sufficient to show the conversion has taken place.

For most things you need to dilute it with distilled water. As you process parts, the mix gets weaker and weaker and you adjust your soak time as required. I expect you have seen my wings build log and the approach I used.

Etch, rinse in DI water Alodine, then rinse again(can use tap water at that point if you want)

When using it full strength most of the time you will etch, rinse, then wipe it on full strength and rinse it off after perhaps 40 seconds.

Did you get the application sheets from Henkel? They give typical application techniques

20140112_103604.jpg

[BTAZ]

I believe what you are wiping off is Alodine that has not actually reacted with the Aluminum. It is a "conversion coat" so only a very thin layer actually reacts.

You can actually buy it as an "Iridite" powder. The liquid you buy is just a pre-diluted prep of the powder plus DI.

Dawn soap wash(handle with rubber gloves to avoid skin oils starting there) etch, rinse with DI, then Alodine. Adjust the soak time for the color you want. Anything more than a light "hint" is more than required. Note the soak time will change as the Alodine gets weaker.

Note the "Gold" version is a Chromate base and should not be allowed to soak on your skin. It is no longer allowed in Europe as it doens't meet RoHS requirements. I don't believe the clear phosphate version is actually better but is now the industry standard.

[fairchild]

Thanks Taz------
I just now found a PDF guide from Henkel companny (locktite) that makes the other brand ( I have PPG)

https://emeraldcoatings.com/wp-content/uploads/2018/02/1201-Alodine-Technical-Process-Bulletin.pdf

It says use full strength for brush on and dilute for dipping/submerge application.
Im not quite sure why may first tiny test piece was so blasted dark. I had it in a tiny disposable pill cup and the test piece
was less than 1 inch square. 30 sec. only. It was going way fast. Tried another test piece in may big plastic bin (nose rib
fits down inside it) and it looked pretty much a lot lighter at 3 min. submerge time. Maybe a little darker than your rib. But I have
not diluted it yet. Out to be about right once diluted.

I see you did double fluts in those difficult areas. I thought about doing that but I wasnt sure if it might eat up too much
of that flat area where the rivet wanted to be.

i will do another rib tomorrow once I get more distilled water to dilute with. will post a pic ! :_)
I guess I should prime them the day after I alodine them so they dont get dirty. Or even morning/evening.

Thanks for the help ! Thats a beautiful rib !
Tim