Are there alternatives to zincate processes for preparing aluminum parts for plating?
Q. We just received a large contract to plate aluminum parts. Are there any other ways to prepare the aluminum for plating that do not involve the zincating process? –K.J.
A. There are alternatives to the classic zincating process used for preparing aluminum for plating. Two such processes are as follows:
1. Remove grease and oil using a suitable cleaner.
2. Alkaline clean.
3. Rinse thoroughly.
4. Acid dip for 25 - 35 seconds using a 30 percent nitric acid and 30 g/L ammonium bifluoride solution.
5. Rinse thoroughly.
6. Immerse for 30 seconds in an alkaline stannate solution (sodium or potassium stannate and sodium or potassium hydroxide with proprietary additives).
7. Strike in a bronze plating bath (proprietary bath).
8. Rinse well.
9. Plate in desired plating bath.
The second process is an anodizing process:
1. Clean parts thoroughly.
2. Thoroughly rinse.
3. Dip in nitric acid.
4. Thoroughly rinse.
5. Anodize in a phosphoric acid solution (20 - 60 percent phosphoric acid, 80 – 95°F, 5 - 30 volts, 5 - 15 min).
6. Thoroughly rinse.
7. Plate in desired plating bath.
As can be seen, neither of these processes are any less complicated than the zincating process, and hence are not seen that often in metal finishing operations. In addition, the first process uses proprietary materials that may or may not still be available.
The bottom line on this is that unless your customer requires a process without zinc, stay with the classic zincating process.