Aluminum alloys-Color etching

Material: Aluminum alloys
Type: Micro
Method: Chemical etching
Etchant (electrolyte): 0.5 ml hydrofluoric acid plus 100 rnl distilled water.
Procedure: Immersion at room temperature. Time required for color metallography is longer than for usual etching (15-60 s).
Note: Color etching. In cast aluminum alloys having a high Ni and Fe content, strong coloration occurs: pure iron is colored green, pure nickel is colored gray-brown, FeNiAl9 intermetallic compound is colored blue-violet. The aluminum matrix remains uncolored.
Source: E. Beraha and B. Sphigler, Color Metallography, American Society for Metals (ASM), Metals Park, Ohio 440073, USA, 1977. p. 87.

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