-- [ From: Bob McKechnie * EMC.Ver #2.10P ] --
Graham Singleton writes: "In the case of aluminium, eventually
corosion will creep between the resin and the metal and separate the
two. I always etch any aluminium parts to be embedded with Alodine.
Anodising is even better. In the case of anodised parts it is only
necessary to solvent clean/degrease."
Andrew C. Marshall, in his book "Composite Basics" (4th Ed., 1994)
cites a 1975 study by a Boeing employee which reports problems in
achieving a reliable high strength bond with aluminum and composites.
Though he acknowledges anodizing with a chromic or sulfuric acid
process results "in a relatively permanent bond that rarely
deteriorates with age," he states such methods "do not result in the
high strengths possible with some of the better surface preparation
methods."
He lists "FPL etch," a sulfuric acid-dichromate etch, and Phosphoric
Acid Anodizing (PAA) as two of these methods. Whichever is used, it is
followed by priming with a corrosive inhibiting adhesive primer.
Specifically mentioned are American Cyanimid BR-127 and Hysol EA-9228.
Reportedly, parts so treated may be kept almost indefinitely without
loss of bond durability. The downside is that this is not a do-it-
yourself project. He recommends contacting aircraft manufacturer
subcontractors and lists one whom he had dealt with: Panel-Air
Corporation, 1571 MacArthur Boulevard, Costa Mesa, California 92626;
Telephone (714) 549-0311. Treated parts are returned with
certification they have been treated per Boeing spec BAC 5555. The
minimum charge is quite high (US$500) and he recommends builders submit
parts together because of this.
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