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Observing grain sizes in residual stress fields

What I am trying to do is measure the grain deformation that occurs after shot peening on the Aluminum 7050 and 7075 alloys. I tried Kellers reagent, for etching the 7050 alloy, but it did not bring out the differences I am hoping to see. If anyone has had the opportunity to observe grain boundaries in material that has residual stresses I would appreciate if they could direct me in the endeavor.

Brijesh Kumar
Research Scientist - Wichita , KS, USA
2004

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Keller's reagent is one of the recommended etchants for revealing cold working in 7xxx series Al alloys. Best results are obtained with the composition of 2 mL HF, 3 mL HCl, 5 mL HNO3, 190 mL water; immerse for 8-15 s, wash with warm water and then blow dry. Do not remove the etching products from the surface.

The other etchant that reveals cold working in these alloys consists of 2 g NaOH, 5 g NaF, and 93 mL water; immerse 2-3 minutes.

Toby Padfield
Automotive module supplier - Michigan
2004

I am interested to know what type of Aluminum alloys react to Keller's and Poulton reagent, to see it's microstructure.

Alexie Crespo Torres
Mayaguez College - Mayaguez, Puerto Rico
2004

I have the same problem on the Keller's reagent. I used Keller's reagent to examine grain boundaries of 7075 extrusion without T6 heat treatment.but the grain boundaries are not clear.

W. Chen
- China
2006