Electroless Nickel Plating over Aluminum
May 20, 2010
Optimizing Adhesion
Heatbath® Corporation offers the following guide for the pretreatment of aluminum substrates prior to electroless nickel plating. Following these guidelines will result in improved adhesion as well as extended life of the electroless nickel plating bath. For specific product recommendations, based on your specific performance requirements and processing capabilities, please contact one of our Technical Service Specialists.
CLEANING
- Remove soils with a non-etch alkaline cleaner
- If processing castings, consider baking the parts at 270°F for 4-8 hours to bake soils out of the pores prior to the cleaning step
ALKALINE ETCH
- Dissolves oxide layer on surface of the part
- Do not over etch parts
- Do not use on castings
- Acid etchants can be used when less aggressive etch is required, for instance when surface smoothness is critical
DESMUT
- Removes alloying elements that have been brought to the surface by alkaline cleaning
- Type dependent on alloy being processed. Most common is a mix of nitric and sulfuric acids with fluoride
- Heavy copper smut may require a second desmut of 50% nitric acid
- Should be used after each alkaline cleaning and etching step
- Should not be used to strip zincate or other coatings
- Should be replaced regularly
ZINCATE
- Coats the surface of the part with a thin film of zinc, preventing oxidation of the surface
- Coating should be uniform, dark gray
- Monitor bath concentration – Excessive gassing may indicate low zinc level
NITRIC ACID STRIPPING
- 50% Nitric Acid used to strip first zincate layer along with surface impurities
- Do not leave parts in longer than necessary, typically 15-30 seconds