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topic 7041

Etching Aluminum to Reveal Microstructure


(2001)

Q. How can I see the microstructure of aluminium alloy? What is the etching solution for it ?

Ben [last name deleted for privacy by Editor]
- Malaysia


(2001)

A. In the metals lab, we use a freshly prepared mixture of 10 parts nitric acid, 1 part hydrofluoric acid, balance distilled water. Use a cotton swab or Q-tip to develop the grain structure on the surface of a highly polished specimen. Use a new swab each time to apply etchant for about 10 seconds only. Rinse and dry to examine. Repeat as necessary. You will develop improved technique with experience. Aluminum alloys will respond vastly different from relatively unalloyed aluminum, also.

W. Carl Erickson
- Rome, New York


(2001)

A. You etch aluminum in HF acid plus water. You can find in metals handbook (metallography).

Behnam Taki
anodizing - Teheran, Iran


(2002)

A. Each alloy of aluminum needs a special solution etch, for example I can see precipitate particles of 2024 by Kellers solution. For Kellers composition, reference a metals handbook.

HABIBOLAHY
- Isfahan-Iran


ASM Handbook: Volume 9: Metallography And Microstructures

April 12, 2008

A. Purer versions of aluminium alloys require electropolishing prior to electroetching to reveal the grain structure by developing an anodic film. ASTM Metals Handbook on Metallography =>
gives details on electropolishing & electroetching techniques.

Shankar Nayak
- Mumbai, India



Etchant for 7068 Aluminum to Reveal Grain Boundaries

(2006)

Q. I'm looking for a good solution to etch 7068 aluminum. I'm trying to do analysis of grain structure. I've tried many different solutions from the finishing manual I have, containing HF, HNO3, HCl, Acetic Acid, NaOH, and CrO3. Does anyone have experience with this alloy or anything similar?

Joe Barnhart
Research and Processing - State College, Pennsylvania, USA


August 2013

A. Hi Joe. I am not experienced in etching any aluminum, let alone Al7068, but Harry van der Zanden's advice on letter 55644, "Color Etching of Aluminum to Show Orientation of Grains" impressed me greatly.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Etching aluminum without HF

Metallography:
Principles and Practice

(2002)

Q. Does anyone know of an etching solution suitable for aluminium and its alloys that does not contain hydrofluoric acid?

Stephen Trippier
University of Central Lancashire. - U.K.


(2004)

A. You can use NaOH. A suitable reference is "Metallography: Principles and Practice" by Van der Voort =>

Yahwan Surnam
research - St Julien d'Hotman, Mauritius


April 4, 2011

Q. Hello to all,
My name is Shannon, and I am currently undertaking a final year project to complete me bachelor of engineering (Mechanical). My project is looking at the lubrication ability of an ionic liquid (for the chemistry fold P1444 DPP) on 3 aluminium alloys and to understand how microstructure effects performance.

The question I pose is, does anyone know of an etchant or etchants and process that will work on 5052, 6061, 7075 grade aluminium alloys. The catch is, I have been told these etchants must be HF-free.

I have scoured the internet, ASM handbook and other texts.

Your help is greatly appreciated.

Shannon

Shannon Biddulph
student and research assistant - Geelong, Victoria, Australia


April 5, 2011

A. There are some etchants for aluminum that don't use HF. Mix 1 g NaOH + 100 mL water, swab specimen for 5-15 seconds, then rinse with cold water. The other common etchant is Barker's reagent, which is an electrolytic method: 4-5 mL HBF4 (48%) + 200 mL water. Specimen is anode, use Al or Pb or stainless steel cathode, anodize for 40-80 seconds at 20 V dc. Microscopic examination requires crossed polarizers.

The last method is a color etchant detailed in a past issue of Struers Structure magazine: A Universal Method for the Mechanical Preparation of Aluminium Alloy Specimens with High Edge Retention and their Subsequent Colour Etching:
www.struers.com/resources/elements/12/2431/38art1.pdf

Toby Padfield
Automotive component & module supplier - Michigan, USA


March 14, 2015

Q. I want to know the best Etchant for 5052 Aluminum alloy, and its composition

Yogesha K K
Research - MYSORE, India


March 2015

Hi Yogesha. What exactly do you mean by "best"? Besides HF, and other earlier suggestions, Toby just finished offering 3 alternate etchants. Please help us move the discussion forward by trying to frame ongoing questions in terms of previous responses to this question rather than by starting over :-)

Thanks!

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



May 7, 2013

Q. Hi,
I am looking for aluminum plate which can reveal grain structure after anodizing. I need the grain as 1 mm in diameter. Does anyone know how to find this kind of material? Thanks in advance!

Frank Lee
Product designer - Tainan, Taiwan


July 12, 2013

Q. Keller is good reagent for etching Al 7075 and I have done it several times and I saw grain boundary and details clearly.
Now I'm trying to etch 6061 and 3105 to reveal boundaries but until now I could not do it ... is there anybody can help me?

morteza mortzai
- arak , markazi, iran


Etching Solutionized AA2024

October 30, 2017

Q. Hello dear masters,technicians and students!
I have a problem on etching my AA2024 samples that they are solutionized and air cooled. Although when the samples quench in water after solutionizing there isn't any problem in their etching. I have to mention I've used different etchants like keller, weck, barker and 5% HF

alireza torabi
- california,USA

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Ed. note: In addition to the excellent responses on this page, and the previously suggested letter 55644, readers may also be interested in letter 26269, "Metallographic Etching of Aluminum to See Grain".



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