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Metallographic Aluminum Etchants

Aluminum alloys are designated as either wrought or cast. Wrought aluminum alloys are classified by the major alloying element

Cast aluminum alloys are classified similarly to wrought alloys, however, the 2nd and 3rd digit signify the percentage of aluminum

The most common etchants for aluminum are Kellers etch and Kroll's reagent, however, there are hundreds of more specific etchants. A good resouce for additional etchants can be found with the etchant database provided by PACE Technologies:

PACE Technologies Etchant Database Click here to get order

CAUTION: Safety is very important when etching. Be sure to wear the appropriate protective clothing and observe all WARNINGS on chemical manufacuters SDS (Safety Data Sheets). Also review the COMMENTS and CONDITIONS Section for each etchant.


Sample Preparation:
Aluminum alloys must be properly prepared to reveal the true metallographic microstructure. A number of recommended procedures can be found at the following links:

PACE Technologies Recommended Preparation for Aluminum PACE Technologies Metallographic MET-MANUAL Link

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Recommended Etchants
Etchant Conc. Conditions Comments
Kellers Etch:
Distilled water
Nitric acid
Hydrochloric acid
Hydrofluoric acid

190 ml
5 ml
3 ml
2 ml
10-30 second immersion
Use fresh
For most aluminum and aluminum alloys
Methanol
Hydrochloric acid
Nitric acid
Hydrofluoric acid
25 ml
25 ml
25 ml
1 drop
10-60 seconds Pure aluminum, aluminum-magnesium, and aluminum-magnesium-silicon alloys
Krolls Reagent:
Distilled water
Nitric acid
Hydrofluoric acid

92 ml
6 ml
2 ml
15 seconds Aluminum-copper alloys

Metallographic micrograph for Aluminum-silicon alloys
Aluminum-Silicon Alloy, Kellers etch, 200X

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