Comment

Comment by Brent Cameron on September 25, 2015 at 3:38pm

I guess I really do need to visit their aviation section!  Thanks!

Comment by Carlos Sa on September 25, 2015 at 11:50am

I use Mothers.

I also tried one of these conventional polishing process (Nuvite), with different grades of abrasiveness.

Not impressed. Results were about the same, but the mess it makes is unbelievable.

To have an idea, after a polishing session, I had to undress before getting into the house.

Mother's, on the other hand, is quite civilized. It even smell good - reminds me of cleaning products (as opposed to petroleum derivatives).

http://www.canadiantire.ca/en/pdp/mothers-mag-and-aluminum-polish-0...

Comment by Brent Cameron on September 22, 2015 at 10:46pm

Ah...  I've seen the Home Depot, the Princess Auto and the West Marine aviation sections but I'll have to go find the Canadian Tire one.  I was special ordering in spray bombs of the Zinc Chromate through West Marine but they are going out of business in Canada so I'll have to check out Canadian Tire.    I noticed what a great job you were doing of polishing the aluminum.  What are you using for that?   

Comment by Carlos Sa on September 22, 2015 at 11:48am

Hello, Brent

You are correct regarding the corrosion: raw material that I leave in the garage shows signs of light corrosion after a while.

I have been using zinc chromate (from Canadian Tire, the aviation section) on all parts, except where I polish the aluminum (which seems to make it more corrosion proof! ?!)

Comment by Brent Cameron on September 22, 2015 at 11:24am

Ernest, numerous studies have proven the efficacy of Alodine on T6061 and I've seen the results first hand in my garage.  Treated parts can sit on concrete unprimed without any signs of corrosion while untreated parts quickly get that white dust.  I suspect you are right in that it won't go much farther than that because of the self oxidizing nature of it but the fact that the certification authorities require T6061 to be corrosion protected in areas of high corrosion is enough for me to be concerned by it.  As to the Alumaprep, I neglected to mention the rinse phase between the Alumaprep and the Alodine.   Water dilutes the phosphoric acid down to harmless levels even in those nooks and crannies.  Aircraft repair shops and factories have been doing this for years and it is accepted practice for Mil Spec.  The real problem is that the Alodine is very nasty stuff (highly carcinogenic so you don't want it going into the local water table and you need a mechanism to gather it all up and then lock it away so it can't leech into the septic systems or water table.  I've been told that a good way is to use it as the liquid required for making concrete. Apparently it binds with the lime and can be disposed of that way.   

Comment by Ernest Christley on September 22, 2015 at 8:25am

You don't think you want to do that, Brent.

Alumaprep is an acid (phosphoric is memory serves).  It is necessary to eat through that "light dusting" you refer to. If you spray the whole plane, it will seep into every crack, crevice and rivet gap, never to be extricated.

The Alodine lays down a chromium layer that bonds with the aluminum.  When oxygen reacts with the chromium, it forms chromate which is insoluable in water, locking out further reactions with oxygen.  Left alone, 6061 does the same. The outside layer reacts with oxygen, forming a protective layer that protects everything underneath.

The problem with the other types of aluminum is that the alloys either make the protective layer to soft to be useful, or allow/enable other types of corrosion to bypass the protective layer.

Comment by Brent Cameron on September 21, 2015 at 11:38pm

Looking good Carlos!    What are you using for Primer?  Looks like you are shooting it as you go?  I've been using Zinc Chromate between the surfaces but have left mine bare for the most part yet - the big pieces at least.  I've dipped all the parts less than 3' long and 2' wide into an acid bath (after thoroughly cleaning first) called Alumaprep and then a quick rinse in water and into an Alodine solution to "plate them" with Chromium.  They come out a nice shade of gold.  Problem is that it doesn't work for big parts like the skins or wing ribs/main spar.  I was going to spray the whole thing once I'm done with Alumaprep and then give it a bath in Alodine before shooting the primer.

I don't know why they say that the T6061 doesn't corrode as it seems to form a light dusting if left to its own devices.  I guess that's probably as far as it goes but I'm going to scrub it all off and corrosion protect/prime the whole thing once I'm ready to close her up.