You may want to check: https://www.researchgate.net/post/What_is_the_suitable_etchant_required_to_visualize_the_grain_boundaries_of_an_aluminium_5083_alloy

Hossein:

Revealing GBs in Al and its alloys is not simple. I am attaching a pdf of a PPP I made on etching GBs in Al and its alloys. 5083 is included. Weck's color reagent for Al is the best overall etch for revealing GBs.  In the example shown for 5083, the grain size was very small and at 500X, does not show up easily in the picture. But, it was the only etch that worked of the 4 tried. Hope this helps!  You can find more PPPs on my web site, www.georgevandervoort.com (free!).

George Vander Voort

Thanks for the help,guys