I'll take a crack at these Q's --
> i) Am I correct to alodyne the parts that I will subsequently bond to
> the airframe?
Yes (and all other aluminum to be later painted).
> Does alodyne affect the bond strength with the epoxy?
It may be nominally beneficial. Its primary purpose is corrosion inhibiting.
> ii) Am I correct in NOT using Zinc Chromate primer on parts which will
> be bonded to the airframe?
Oh, indeed. Its most remarkable property is it doesn't adhere well
to aluminum. The bonding part should be thoroughly roughened with
sandpaper per manual. Alumiprep and alodine. For the painted portion,
consider epoxy chromate (e.g., Poly-Fiber EP-420). It adheres tenaciously
(I hear similar stuff is used by McDonnell-Douglas, now Boeing).
> iii) What should I use to clean the aluminum parts prior to alodyning?
Dupont Alumiprep; it is an acid cleaner. You can first use MEK or acetone
to remove any oil, but make sure it is chemically pure (most retail stuff
is "recovered," meaning possible oils and contaminants therein). Dupont says
its Alumiprep removes oils, though. How well, who knows.
> iv) How much alodyne crystals to dissolve in how much water?
Mix to taste; garnish with a lemon slice. Really, no directions
supplied? Well, the liquid stuff (Dupont 1001, e.g.) is mixed 50/50
with water. A pure guess would be mix to saturation and cut 50/50.
> v) How long should the parts be left in the solution.
Dupont again says 1-3 minutes; rinse BEFORE it evaporates. Can retreat
if desired. For the bonded parts, I don't think distilled water rinse is
too conservative.
Note that some builders have commercially anodized the aluminum parts. I
can't say how much better this is; they may add to this thread. But aluminum
corrosion is an electrolytic process, and can occur buried in resin and thus
in the absence of air (but latter also promotes it -- e.g., acid or salty
atmosphere). A clean, rough surface is probably the most important thing to
have.
Regards,
Fred Fillinger, A063
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