The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Caustic etch grain refiners

 

Does anybody out there have any experience with home-brew (simple) grain refiners to add to a caustic etch for aluminum? We find that we are expanding the grain boundaries on some re-work to the point the parts are unusable. Any help would be appreciated.

Victor Waldman
- Naugatuck, Connecticut

---

Your etch is cutting into the grain boundary, the grain size is what comes with the part. What conditions, temperature, concentration formulation are you using now? What alloy, wrought, cast, etc, are you processing?

  
Tom Pullizzi
Falls Township, Pennsylvania
 

---

Hi Victor,

As far as I know, grain refiners are only added to the molten aluminium during the casting process.

If the grains are opening up, it is likely due to over-etching during the early phases of the anodising process. Maybe it only happens after repeated (excessive) re-work?

The grain boundaries are areas of metallurgical weakness and will always be preferentially etched. This is not generally a problem as long as the metal is only re-worked one maybe two times.

What alloy and product form are you experiencing problems with?

Best regards,

Martin Webb
New Zealand