Metallographic Aluminum Etchants
Aluminum alloys are designated as either wrought or cast. Wrought aluminum alloys are classified by the major alloying element
- 1000 series pure aluminum (1050, 1060, 1199)
- 2000 series aluminum copper alloys (2014. 2024, 2219)
- 3000 series aluminum ma managese alloys (3003, 3004, 3102)
- 4000 series aluminum silicon alloys (4041)
- 5000 series aluminum magnesium alloys (5005, 5052, 5083, 5086, 5154, 5356, 5154, 5356, 5454)
- 6000 series aluminum magnesium and silicon alloys (6060, 6061, 6063, 6066, 6070, 6082, 6105, 6162)
- 7000 series aluminum zinc alloys (7005, 7022, 7068, 7072, 7075, 7079, 7116, 7129, 7178)
- 8000 series aluminum lithium alloys
Cast aluminum alloys are classified similarly to wrought alloys, however, the 2nd and 3rd digit signify the percentage of aluminum
- 1xx.x series are minimum 99% aluminium
- 2xx.x series copper (201.0, 204.0, 242.0)
- 3xx.x series silicon, copper and/or magnesium (319.0, 328.0, 328.0, 355.0, 356.0)
- 4xx.x series silicon (433.3)
- 5xx.x series magnesium (512.0, 514.0, 520.0, 535.0)
- 7xx.x series zinc (705.0, 707.0, 710.0, 713.0, 771.0)
- 8xx.x series lithium
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:
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:
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 |
|
Wecks: 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 |
|
Wecks No. 1: Potassium Permanganate Sodium Hydroxide Distilled Water |
10 grams 1 gram 250 ml < |
10-60 seconds | Weck's No. 1 is a specific type of etchant used primarily for etching aluminum and its alloys to reveal the grain boundaries and other microstructural features. |
|
Krolls Reagent: Distilled water Nitric acid Hydrofluoric acid |
92 ml 6 ml 2 ml |
15 seconds | Aluminum-copper alloys |
 |
| Aluminum-Silicon Alloy, Kellers etch, 200X |
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