Sodium HydroxideNaOH
Al-NaOH Etchant
Material Specific
Composition
10-20g NaOH, 100ml H₂O
10-20%
Method
Immersion (warm)
Time
30–60 s at 50–70 °C
Alternative Names
Tags
Reveals
Macroscopic grain structure; forging flow lines; segregation; weld fusion zone and HAZ in aluminum
Typical Results
Sodium-hydroxide caustic macroetch for aluminum. Reveals grain structure on as-cast and forged sections, weld fusion / HAZ outlines, and as-rolled flow patterns. Not for micro grain-boundary work; use Keller's or 0.5% HF there.
Application Method
Method:Immersion (warm)
Typical Time:30–60 s at 50–70 °C
Preparation Notes
CAUTION: NaOH is caustic. Dissolve 10-20g NaOH in 100ml water. Use at 50°C.
Application Notes
Heat to 50–70 °C in PE container. Immerse 30–60 s. Rinse with water, then dip briefly in 25% HNO3 to desmut (removes the black film), then rinse again and air-dry.
Troubleshooting
Black smut on surface is expected; that's what the desmut step removes. Pitting on edges: solution too hot or time too long.
Storage Notes
PE or PP bottle. Stable indefinitely. Heat in the same container; do not heat in glass.
Alternative Etchants
- Tucker's Reagent (macro)
- Keller's Reagent (micro)
Similar Etchants
- NaOH macroetch variants