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Etchant for recrystallized zone of FSW AA2219

2007

Dear All,

I am not able to see the Grain Boundaries the Nugget (Dynamically Recrystallized) region of Friction Stir Welded AA2219 (Al-6.3%Cu). The etchants simply do not highlight them, I can't see any demarcations except a dark region. Grain boundaries are etched to a relatively OK status (they are not as well defined to see clearly) in TMAZ, HAZ and BM. I have already tried the following reagents in step os 10 sec (starting from 20-30 seconds to 90 maximum after which its totally dark !)

The etchants which have been used are:
1. 1% NaoH
2. 10% NaOH
3. Keller Reagent
4. Kroll Reagent
5. Dix and Keller
6. 0.5 vol% HF
7. H20*HNO3+HF+HCl
8. H20*HNO3+H2SO4+CrO3

Dynamically Recrystallized Grain size is generally reported as too small in order of 5-20 micrometer.

Kanwar Singh Arora
Research Scholar IIT Delhi - present address: Institute of Material Research, TU Dresden, Germany

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Hi Kanwar,

I am not very sure but you may try Barker's etchant and then examine under cross polarised light.
Barker's etching : The specimen to be anodised in an electrolyte e.g. 4 - 5 mls of HBF4 in 200 mls D.I.water; use lead strip as cathode at voltage 20 d.c. for 1 - 2 minutes. Always make sure that a gap between the micr-sample and the lead cathode is maintained around 1 inch. Hope you may get better result.
Good luck.

Basu

Srimay Basu
- Dubai, U.A.E
2007