Corrosion due to manufacturer's markings

Jeff R · #1 02-09-2012, 05:11 PM

I have noticed that on my aluminum skins I have gotten corrosion where the markings applied by Alcoa were printed.

Any suggestions for dealing with this? I suppose I need to lightly sand the corrosion off and treat it with some kind of primer or corrosion inhibitor. Any suggestions? I am not planning on painting the surfaces anytime soon, but am getting close to a first flight and streaks of rattle can zinc chromate would really look strange.

Thanks.

bird · #2 02-09-2012, 05:41 PM

are you sure it is corrosion? Try wiping it with mek. If in fact it is corrosion then you will have to scuff it with scotcbrite and treat it with alodine or self-etching primer. I have never seen anything like that. If you are planning on painting in the near future, you may not have to do anything and take care of that at painting time.

bird

aturner · #3 02-09-2012, 08:45 PM

Some time before I began my project I built one of Van's practice toolboxes and tossed it into a corner of my garage. As I geared up to build I fetched the toolbox and was surprised to find that the marking ink had promoted corrosion under the ink. I believe it is absorbing water from the atmosphere. So, I was careful from day 1 to clean all that ink off my airplane parts.

rv9av8tr · #4 02-09-2012, 09:04 PM

I know that inks can be corrosive. For example, some pens have chlorides in them and can not be used on stainless steel, else they cause chloride stress corrision cracking. The nuclear industry is very particular what marking pens can be used/not used.

N208ET · #5 02-10-2012, 07:37 AM

On some of my parts, the blue ink was causing corrosion. Early on in my build I wasn't worrying about wiping off the ink until I found this out. After I made sure to wipe off all the ink.

Randy
8A flying

az_gila · #6 02-10-2012, 09:14 AM

I've noticed the opposite.

A very light tarnish on the sheets, but still shiny under the blue markings when the ink is removed with acetone...

Don Jones · #7 02-10-2012, 10:14 AM

Quote:

Originally Posted by az_gila

I've noticed the opposite.

A very light tarnish on the sheets, but still shiny under the blue markings when the ink is removed with acetone...

I don't think you or I know what corrosion is....... living in the desert southwest like we do

My experience is just like yours, shiny underneath when cleaning off the blue markings.

az_gila · #8 02-10-2012, 12:51 PM

Quote:

Originally Posted by Don Jones

I don't think you or I know what corrosion is....... living in the desert southwest like we do

My experience is just like yours, shiny underneath when cleaning off the blue markings.

Yep... but I saw the same when I lived in Los Angeles a mile inland from Marina del Rey. It just happened a lot quicker...

smiller · #9 02-11-2012, 07:02 PM

I've experienced the same thing, Jeff. Many of my parts which were stored for 2+ years with the blue plastic still on revealed "corrosion" where the lettering was. That is, I'd remove the blue plastic, clean off the ink with lacquer thinner, and find the lettering still there, in the form of a different shade of aluminum color (not as shiny)! It almost looks like the top layer of (pure) aluminum of the alclad is gone, but I wouldn't know. I took a sample to a couple of local A&Ps for their assessment. They said they didn't think it was corrosion, but rather etching. Neither thought it was anything to be alarmed about, said it shouldn't get any worse now that the ink is removed, and I can ScotchBrite and prime those areas if I'm particularly bothered by it.

I believe Van's recommends removing the blue plastic immediately upon receipt of the parts. Maybe for this reason?