Detecting Anodize

weirdjim

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weirdjim
So, I've got this little sample 4x4" square of aluminum. Let's call it 5052H32 just for grins and giggles. I need to know that it is anodized without destroying the sample. I have no idea where it came from or any paperwork whatsoever.

How to do that?

Jim
 
The primary telling factor is the hardness of the surface. An anodized finish is very, very hard and very thin. Rub a piece of hardened steel carefully over the surface - if it doesn't leave a mark then the aluminum surface is probably anodized.
 
The primary telling factor is the hardness of the surface. An anodized finish is very, very hard and very thin. Rub a piece of hardened steel carefully over the surface - if it doesn't leave a mark then the aluminum surface is probably anodized.
But that ruins the surface of the part if it is NOT anodized. And what does rubbing a flat piece of steel over a flat surface prove?

Jim
 
Try a multimeter to measure resistance. Touch the two probes to the surface gently (not scratching into a coating if there is one). Aluminum is a conductor ( a few ohms) anodized surfaces are insulators
(Many megaohms).
 
Try a multimeter to measure resistance. Touch the two probes to the surface gently (not scratching into a coating if there is one). Aluminum is a conductor ( a few ohms) anodized surfaces are insulators
(Many megaohms).
I never knew this. Just pulled out a flashlight with an anodized finish and tried this.

Checks out!
 
Expect a Kiplanes article on how to anodize airplane parts using a 12 volt battery charger and vinegar as the acid anodize bath!!

Thanks, gang. That was my guess also and thanks for verifying my guess.

Jim
 
Lots of good home anodizing how-to videos on Youtube. My brake reservoirs are anodized blue using a cheap DC power supply and a couple of 5 gallon buckets.

One of my favs-
 
Hi,

Very good discussion of issue here -
https://www.eng-tips.com/viewthread.cfm?qid=43530

My concern with the multimeter method is that aluminium and many of its alloys rapidly create an oxide layer when exposed to air. Anodising increases the thickness of the layer substantially. Can it be guaranteed that the meter's probes will penetrate a natural layer?

There are many knowledgeable comments on the above page including from someone who says that testing with a simple continuity tester is sufficient.

https://www.checkline.com/product/6000AN-Series
6000AN SeriesAnodizing Thickness Gauge

$,1000 but someone can presumably test it for you.

Many hits on google -
detect anodising
anodizing thickness tester
 
With some experience, once can tell by looking with a high certainty. But the ohmmeter is a good test as well. We used to anodize motorcycle parts at home, with mixed results (good corrosion resistance, not so pretty dye distribution.)
 
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