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Anodizing of A357 sample for metallograpy

Anodizing of A357 sample for metallograpy

Anodizing of A357 sample for metallograpy

(OP)
Hi all,

I tired to anodize an A357 sample for metallographic observation usng perpendicular polarized light. I used Barkers solution (195 ml H2O + 5 ml HBF4) at room tempearture with 20V supply using Al cathode for 80 sec. But I was not able to get any contrast between the grains. I also tried a wrought alloy and pure Al but failed to get ay contrast. The samples were mechanically polished before anodizing. I also checked whether the surface is anodized or not using a multimeter and there was no current across the samples.
Can any body help me in this regard.

Thanks

Kamran

RE: Anodizing of A357 sample for metallograpy

Weird.  Try a bit longer?  According to the latest Microscopy Today (November) Vander Voort has an article on color etching that uses just that:  Barker's, 30V dc for 2 minutes.

Another option Vander Voort presents is 100 ml H20, 4g KMnO4 and 1 g NaOH [Weck's reagent for Al].  Whether this will work on your grade of aluminum is unknown.  Let me know.

I've used 10% Molybdic acid on pure aluminum, but had difficulty getting a decent photograph due to the fact that you've got to have almost 90° cross-polarized light, which didn't give me a lot of light to work with for the photograph.

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