Believe me, I´m quite able to distinguish grease spots from aluminium corrosion!
Hi Barry,galewarning wrote: ↑Wed Jun 13, 2018 11:12 pmThe raised white crust usually occurs above pitting and is a hydrated form of the alumina, itself quite insoluble in water and to an extent protective. But it wouldn't be there so soon if the anodization was done correctly. In the interim, consider getting in a habit of wiping all the aluminum with something like Boeshield T9.
Yes, I'm a better materials science tech weenie than a kiter.
Though I am not a corrosion engineer nor a metallurgist I have a fair amount of corrosion experience in the aircraft and oil and gas industries. From your explanation, it does sound like the beginning of crevice corrosion. Your diagnosis of a breakdown in the protective coating seems entirely feasible. In the crevice between fuse/wings/screws, seawater can be trapped and deprive the crevice of oxygen. This leaves localized chemistry becoming increasingly reactive. As the passive oxide layer breaks down and cannot regenerate (due to oxygen deprivation)the voltage potential difference between the Cathodic anodized surface and the anodic pit in the crevice increased until a galvanic cell is produced. As the localized chemistry becomes increasing reactive and the voltage potential difference increases from anode to cathode the pit in corrosion increases at an accelerated rate.Onda wrote: ↑Tue Jun 12, 2018 9:30 pmHi all,
after having ridden my Moses foil in North Sea water for less than 3 hours during its first use I´ve been irritated to see clear signs of corrosion on the fuselage.
The shiny black (anodized) surface was covered with numerous elevated white spots of Al2O3 (alumina). These corrosion spots were centered around the screw holes for the mast and two areas where the wings are mounted.
I´ve put Li-grease on all screws before first water contact and have never left any parts assembled in wet condition (how could I - before first use).
The lapidary response from Moses (having received detailed pictures of the fuselage via my dealer) is: Send it in for analysis (2-3 weeks) or simply keep it and wipe it clean.
I´m kind of an expert for metal surface coatings... This is a clear quality issue from defective anodization. And any expert would be able to see it from my pictures. No need for "analysis"... if you´d like to call yourself a customer centric company. Needless to mention that this cannot be "wiped clean"! I´d have to sand it away, further thinning that anodized surface and worsening the issue.
What do you think?
Will post the pictures here when I´ve managed to upload them.
Onda wrote: ↑Thu Jun 14, 2018 7:11 amHi Barry,
thanks, this sounds helpful. Never came across this T9 stuff. I can buy a tiny bottle on German amazon for USD40 But will probably try it. Any special version of the T9 you would recommend?
I hope that Moses sees their fault and replace my fuselage without starting a mess about it.
Yeah man I agree. Looking at the photo's you have a breakdown of the passive oxide layer outside of the crevice. That means pitting corrosion most likely due to a poor or improper anodizing process. I would expect to see this sort of corrosion on an anodized foil after 1 to 3 years depending on the environment. Getting this type of corrosion in a matter of hours from new is clearly a manufacturing fault or material defect! The only way to fix this now is a) warrantee claim, B) sand back and remove all corrosion and apply a protective coating. IE etch primed and painted with high grade aluminium paint. To be honest that will be a workaround as the painted surface will at some point become scratched and corrosion will commence again rapidly!Onda wrote: ↑Thu Jun 14, 2018 3:59 pmExcellent, plummet. I studied electro chemistry and know a bit about electrochemical cells
The corrosion will always happen as soon as you bring Aluminium and carbon into electrically conductive contact and add an electrolyte (sea water). No crevice is neededf or this. However, a crevice - which stays wet for prolonged time - increases the issue.
Carbon has a much more positive electrochemical potential than aluminium, which means the Al gets oxidized by the carbon when brought into contact with each other plus electrolyte. The only means to protect the Al is to apply a protective (passive) layer on top of the raw Al. This is why you anodize the Al (= forming a thick and hopefully dense / tight layer of Al2O3 on the surface). Al2O3 btw has very desireable mechanical properties (stable, hard, robust) you will never be able to reach with any kind of paint or varnish.
BUT: Producing a dense, thick layer of Al2O3 is kind of an art and needs very deep understanding of the anodization process. One of the very tricky details is to "reach" into holes and cavities with the anodization. Holes are intrinsically shielded from the electric field in the acid (electrolyte) into which the Al part is immersed during anodization. No electric field, no anodization. This problem is particularly valid for anodization due to the very high current densities needed here (much higher than for any other "galvanic" coatings). So you have to take measures to get the electric field into every cavity, which is usually done by positioning separate electrodes right within the cavities - without touching the metal surface. This causes a lot of effort and cost for the anodization (manual work, needs a lot of attention to avoid short-circuiting during anodization). Another issue occurs with / near sharp edges of the Al part.... OK, it gets boring now
And certainly, the surface of the Al part has to absolutely perfectly cleaned before the actual anodization process (several steps of immersion into various detergents, acids, caustics, rinsing....). Even the slightest traces of fat / grease, silicone etc ruin the coating process. One touch by human skin: Ruined.
I always dismantle the whole foil after every use asap and rinse every single part (even the screws) with fresh water and dry it with a cloth, right after use before everything goes into my car.
But as I said, the corrosion signs became visible after 2 hours of use (the first ever use of the brand new foil) right at the beach!
Will post some pictures later.
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