Etching of Aluminium alloys

[darkelf]

I am made to understand that you are meant to use different etching agents for different aluminum alloys. How does one find which etching agent is the right one for each alloy?

Does anyone know what etching agent I can use for Al 3104?

Thank you

 

[Mapes]

Try Samuels' Metallographic Polishing by Mechanical Methods, whence comes the following information:

LIGHT METALS - Aluminum and Alloys
Composition Comments

1. 
   95 mL water, 2.5 mL HNO3, 1.5 mL HCI, 1.0 mL HF: Keller’s reagent, very popular general purpose reagent for Al and Al alloys, except high-Si alloys. Immerse sample 10-20 seconds, wash in warm water. Can follow with a dip in conc. HNO3. Outlines all common constituents, reveals grain structure in certain alloys when used by immersion.
2. 90-100 mL water, 0.1-10 mL HF: General-purpose reagent. Attacks FeAl3, other constituents outlined. The 0.5% concentration of HF is very popular.
3. 84 mL water,15.5 mL HNO3, 0.5 mL HF, 3 g CrO3: Graff and Sargent’s etchant, for grain size of 2XXX, 3XXX, 6XXX, and 7XXX wrought alloys. Immerse specimen 20-60 seconds with mild agitation.
4. 1.8% fluoboric acid in water Barker’s anodizing method for grain structure. Use 0.5-1.5 A/in2, 30-45 V dc. For most alloys and tempers, 20 seconds at 1 A/in2 and 30 V dc at 20 °C is sufficient. Stirring not needed. Rinse in warm water, dry. Use polarized light; sensitive tint helpful.

A fume hood and personal protective equipment is mandatory. Don't go near HF unless you fully understand the associated hazards, are fully protected, and have calcium gluconate on hand.