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.

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.

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

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.