I've tried Acetic-Picral (5 mL Acetic Acid, 6 g Picric Acid, 10 mL Water, 100 mL Ethanol) and also a solution of 5ml acetic acid, 6g picric acid, 10ml water, 100ml ethanol, 5 ml HCl and 7 ml nitric acid for 1–2s, But it didn't work....
Any suggestions?
Composition (1)
25 mL water
75 mL 3-5 ethylene glycol
1 mL HNO3
Comments: Glycol etch, general purpose etch for pure Mg and alloys. Swab specimen seconds for F and T6 temper alloys, 1-2 minutes for T4 and 0 temper alloys.
Composition (2)
19 mL water
60 mL ethylene glycol
20 mL acetic acid
1 mL HNO3
Comments: Acetic glycol etchant for pure Mg and alloys. Swab specimen 1-3 seconds for F and T6 temper alloys, 10 seconds for T4 and 0 temper alloys. Reveals grain boundaries in solution-treated castings and most wrought alloys.
Composition (3)
100 mL ethanol
10 mL water
5 g picric acid
(Cimments): For Mg and alloys. Use fresh. Immerse specimen for 15-30 seconds. Produces grain contrast
Magnesium and its alloys, regardless of the processing procedures employed, are among the most difficult metallic specimens to prepare for microstructural examination.
In my opinion immersion time is quite important. Please read attached article with its conclusion.
The Picric acid concentration of your solution is high. You should decrease it.
It's best to polish your samples water free and finish with electro polishing. Otherwise you will always have a scratched surface.
Than you apply the Picric acid solutio, while the time depends on your sample state as well as on the acid concentration.
- Nital 1-5 are common reagents for Mg alloys. They can be useful for observe general micro structure.
Strongly depends on the alloy you are trying to etch. More aluminum easier to etch. 4.2g Picric acid, 10ml DISTILED water, 10ml acetic acid and 70ml ethanol works fine. use fresh etchant (not more than 3 hours old for best results), polish without water and electro polish for best results.
Goodluck
Hello.
I follow ASTM Standard Practice for Microetching Metals and Alloys (E407-07)
There are a number of different etchants available for different magnesium alloys. I work on Mg-RE alloys and acetic-picral (5 mL acetic acid, 10 mL water, 6 g picric acid, 100 mL ethanol (95% [immerse with gentle agitation, 10-60s] ) for phase identification.
You can also try ( 1 mL HNO3, 75 mL ethylene glycol, 25 mL water [swab 35- s for F and T6, 1-2 min for T4 and O temper])
I have good results for AZ91 and WE43 alloys using etching agent 11 g of picric acid, 11 ml of acetic acid, 100 ml of ethanol.
One of the best solutions for etching:
Alcohol ethanol 96%, 150 ml
Acetic acid, 10 ml
Distilled water, 10 ml
Picric acid powder, 4.26 g.
The etching time is between 40-70 seconds.
Devadas Bhat Panemangalore dear what about ZK61 extruded magnesium alloy? and please mention the time. additionaly after etching i got black dots or corrosive surface, i am using ethanol during polishing and finishing, is their any other liquid that i can use before polishing?
Always prepare fresh etchant solution for better results.
The etching process and conditions vary for every sample. As-cast samples can get etched faster than as-extruded ones.
If the concentration of the solution is high then it could be the reason to get black dots.
The secondary phases could get attacked faster.
Please try to dilute the solution with ethanol (if you are using acetic picral).
Use cotton swab to etch gently or if you are using dip method then make sure to wash it with ethanol immediately (tilt the sample to ensure the ethanol gets drained easily).
For magnesium based materials, I always finish upto 4000 grit paper in water, and use diamond paste 6, 3, 1 upto 0.25 micron. DP-Lubricant (Struers), Red, a lubricant with high viscosity, is used with the diamond abrasive.
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