Effect of Solution Composition on Double Zincate Process of Aluminum

The double-zincate processing of aluminum in three different zincate solutions was examined to evaluate the effect of solution composition. Higher concentrations of NaOH and ZnO in zincate solution dissolve both the Al oxide layer and Al substrate more rapidly. This leads to faster Zn deposition. In a solution containing Fe3+ions, Fe codeposition resulted in the growth of rather small, nonhexagonal Zn particles during the first zincate process. In the second zincate process, a stratiform Zn layer grows to cover the Al substrate in a zincate solution without Fe3+ions. Granular Zn is deposited due to Zn growth suppressed laterally by the codeposition of Fe in a solution containing Fe3+ions. Such granular Zn deposition provides a sufficient anchor effect for subsequent electroless Ni plating.