[WWI] aluminium and corrosion was SPAD 13 Internal fitting

dr-i.417.17 at cox.net dr-i.417.17 at cox.net
Wed Apr 18 10:22:53 EDT 2007


Andy writes:
 Japanese aircraft for instance corroded very badly and relatively quickly even though they were constructed of duraluminium. Even in the harsh environment of the Pacific theatre the material allied aircraft were constructed from fared far better.


My 2C on this.  A distinction must be made between pure aluminum and alloyed alluminum.

It is the pure aluminum mentioned in an earlier post that forms aluminum oxide on the outside.  And because of its chemical properties it developes an increadibly high resisance to any corrosive compound.

On the other hand alloyed aluminum with bits of copper and other metals form galvanic cells, that in the presence of just plain old moisture start robbing and swapping electrons, and they cause the alloy to break down and corrode.

ALCLAD is an application of a 5% thick layer of pure aluminum on any alloyed aluminum.  This outer pure layer forms the aluminum oxide and prevents moisture from reaching the other molecules in the alloy that wil start the breakdown.  

Now the problem with pure AL is that it is very soft, it is the alloying that gives it the strength to be useable in aviation aplications.  So we run a constant compromise between strenght and corrosion simply due to the internal composition of the metal.

In light of the thread, my OPINION, based on other military practices, to preserve and protect those expensive compointents, alloyd aluminum products more than likely had a protective paint finish on them.

MTC YMMV MrT


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