Aluminum Etchants

2% HF (Alpha Case) — ASTM formula 11, attacks FeAl3, other constituents outlined. It contains hydrofluoric acid as the name implies.
AWS D1.2 Basic Etchant — A macro etchant for visual inspection of aluminum, listed in AWS welding code D1.2. It does NOT contain hydrofluoric acid.
Barker’s Reagent — ASTM formula 5, an electrolyte for electrolytic etching pure aluminum, 1000, 3000, 5000, 6000 and 7000 series. Need a polarized light microscope to see the result.
Keller’s Reagent — ASTM formula 3, the most popular general-purpose micro etchant for aluminum alloys, shows microstructure and grains. It contains hydrofluoric acid.