The February issue of Sport Aviation has an article on how anodizing aluminum weakens fatigue resistance. Apparently other surface treatments of aluminum can do the same. This might be something to worry about when refinishing, for instance, lightweight dural drilling frames.

Good note But I think this is more for sheet aluminum then a block frame. Anodizing typically is only one or two thousandths thick.

Conventional anodizing is maybe 50 millionths to .0001 thick. It is actually measured in the US by miligrams per square foot. Hard anodize is typically .002 thick.
Anodizing is actually aluminum oxide - a ceramic.
Bend anodized material and you will hear it "cry" as the anodizing cracks. All the little cracks formed are tiny stress risers. That being said aluminum forms it's own layer of aluminum oxide naturally in contact with air.

When you talk about metal fatigue the design engineers are supposed to consider this when choosing a material.

Anodization process can vary greatly , depending upon who does it and what process is used .

Many metals are structurally weakened by the oxidation process, but not aluminum. Aluminum can actually be made stronger and more durable through a process called 'anodizing'. Anodizing involves placing a sheet of aluminum into a chemical acid bath, quite often acetone in laboratory experiments. The sheet of aluminum becomes the positive anode of a chemical battery and the acid bath becomes the negative. An electric current passes through the acid, causing the surface of the aluminum to oxidize (essentially rust). The oxidized aluminum forms a strong coating as it replaces the original aluminum on the surface. The result is an extremely hard substance called anodized aluminum.

Anodized aluminum can be nearly as hard as diamond under the right anodizing process. Many modern buildings use anodized aluminum in places where the metal framework is exposed to the elements. Anodized aluminum is also a popular material for making high-end cookware such as frying pans and pots. Heat is distributed evenly across anodized aluminum, and the process of anodizing provides a naturally protective finish. It is possible to use another electroplating process to make anodized aluminum look like copper or brass or other metals. Special dyes can also be used to color the anodized aluminum for decorative uses.


Now click on this link and learn about Hard Anodizing as well as other metal treatments .

http://www.nimet.com/?gclid=CL...SCy5gCFRxNagoduVZJ1w

Doc,

A hard surface treatment does not mean increased structural strength or fatigue resistance. In fact, quite the opposite can be true.

Hard more often than not equals "Brittle"

There are many characteristics that would be "good"
for aircraft skin.... Brittle isn't one that jumps to mind.

AD

Anodizing is a layer treatment, that usually will not adversely alter the strength of many component applications(depending on thickness of component & application)For Eg: Hobby/Kit Aircraft builders do not recommend anodizing the main spar.
The sulphuric acid creates micro poc marks on the surface in the TypeII anodizing process.
The other option is Chromic acid type I anodizing, which has less negative impact than type II.
Anodizing offers different levels of surface hardness.
Then theres;
Chromate conversion coating,which has no fatigue strength issues on alluminium.


with things like colourCase hardening on steel, If you repeatedly CC a receiver you progressively/accumulatively weaken it.

Thank You Trax !. It's obvious others don't read the post well !.



The February issue of Sport Aviation has an article on how anodizing aluminum weakens fatigue resistance. Apparently other surface treatments of aluminum can do the same. This might be something to worry about when refinishing, for instance, lightweight dural drilling frames.

Allan

I would just assume if vigillinus were speaking of Aircraft parts , perhaps he was

intelligent enough to post it in the AVIATION Section !. I failed to read Airframe

or skins in his posting . As I believe he was merrily making reference too an artical

he read in Sport Aviation . I also read the same article as it's one of 27 monthly

publications I receive . I also write articles for a few different publications

of the ACS group . In which I hold a PhD.



montea6b ; Thanks for sharing !. Back at you . I hold a M. in structural Eng.

I also worked for Scaled Composites for better than 20 years .


What was the first sentence of my posting !!.

The thing is yes anodizing creates a hard surface on the aluminum sub-straight. But to say that a block of aluminum is weakened by a thin layer on the outside is ridiculous. The surface may be ultra hard and conversely brittle but that buy no means will weaken the action.
A block of aluminum 2"X2" that has an anodize layer .001 thick is only .3% of the total volume of the block