Primer / corrosion experiment

Since my first investigation about primers in September 2016 I still have some questions about the different kind of primers and prepping the aluminium. Therefore I started a small experiment with different kind of aluminium, degreasers, primers and a final 2K paint.

I started with 16 pieces aluminium 6061-T6 (the material where the Sling is made of) and 5 pieces anodized aluminium from the local hardware store. Since the wing spars are anodized I wanted to test several ways of prepping the spars before priming.

3 ways of prepping were used:

Skotch brite pad + Thinner + Silicone remover	Skotch brite pad + Waterbased degreaser	Skotch brite pad + AluPrep33 + Alodine 1201

2 different kind of primers were used:

Wash primer Kristal Coatings	Epoxy primer Mipa

Some samples were finished with a 2K PU paint from Mipa, type OC420.

This is the test setup:

The paint cures very fast but before testing the adhesion I waited 3 days.
After 3 days I tested the adhesion with the cross hatch test and tested the resistance against thinner with a swab.

Here a photo of the actual result:

Conclusion after the cross hatch and thinner test:
– both wash primer and epoxy primer have good adhesion to aluminium
– wash primer is a thinner layer of paint which saves weight but epoxy primer has better scratch and chemical resistance
– prepping 6061-T6 doesn’t make a big difference between thinner / silicone remover / waterbased degreaser, Alodine seems a bit better but not worth all the effort
– prepping anodized aluminium seems better with thinner and silicone remover compared with the waterbased degreaser
– epoxy primer can be sprayed over wash primer with good adhesion
– the white PU paint adhesion to the primers is not that good on these test samples, but on another older sample that was sprayed with wash primer some month ago the same white PU paint had good adhesion

I moved the samples to the outside where they will face the Dutch winter and I will spray the samples with salt water every day. I’m curious if and how severe they corrode.