You can proceed with Keller's reagent i.e. Distilled water (95%)+ Nitric acid (2.5%) + Hydrochloric acid (1.5%) + Hydrofluoric acid (1%) to your polished specimen for 20 to 25 seconds.
personally for Aluminum alloys, such as etching solution, I generally use Keller's solution, as suggested by Dr. Priyaranjan Samal , but in the following technical notes you can also try valid alternatives and specific characteristics.
-Metallographic Aluminum Etchants by Pace Technologies
Available at: https://www.metallographic.com/Metallographic-Etchants/Metallography-Aluminum-etchants.htm
-Metallographic preparation of aluminium and aluminium alloys by Struers
Available at: https://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjtqJmThuztAhUNGewKHRxaCHUQFjADegQIAxAC&url=https%3A%2F%2Fwww.struers.com%2F-%2Fmedia%2FStruers-media-library%2FMaterials%2FApplication-reports%2FAN-11_Aluminium_2015_ENG.pdf&usg=AOvVaw3ih5sXXOUyWS02X86zDYky
-Etching In Metallography by Kemet
Available at: https://www.kemet.co.uk/blog/metallography/etching-in-metallography
Dear all, the general standard etching for aluminium alloy is Keller's solution as mentioned in the reference I suggested above, but specifically for this alloy, methanol solution was recommended as reported in the reference. With thanks.
I tried the keller solution but its not clearly wiev grain boundry for AA6082. But the keller solution is not fresh preparation. İs it effect the fresh or not.
it is certainly better to use an etching fresh solution and, if necessary, you can try to immerse a sample for a few five-ten of seconds more ... then eventually, depending on the result, set a standardized time for all your samples.
Yes , the freshness of some etching solution has a great effect. Also for electrolyte polishing special precautions are needed because of the existence of many phases such as Mg2Si , Al2Cu and Al6Mn