Aluminum alloys-Color etching

Material: Aluminum alloys
Type: Micro
Method: Chemical etching
Etchant (electrolyte): Acid mixture of 0.5% hydrofluoric acid plus 1.5% hydrochloric acid and 2.5% nitric acid in aqueous solution.
Procedure: Immersion at room temperature. Etching time approx 5-25 s.
Note: Color etching. Etching of cast aluminum alloys. Colors nickel-rich phases brown and heavily darkens the !vIg2Si phase. The aluminum matrix and silicon remain uncolorcd.
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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