Electroless Plating of Zinc onto Copper in NaOH Solution
An explanation is provided in this reference. The idea is that the electrode reactions are

$\ce{Zn(s) + 4OH^- -&gt; [Zn(OH)_4]^{2-} + 2e-}$
and

$\ce{[Zn(OH)_4]^{2-} + 2e- -&gt; Zn(alloy) + 4OH^-}$

So the zinc powder remaining will go into solution and the zincate is reduced on the copper surface to form a form of zinc rich brass. Brass is an alloy and the atoms are held together via metallic bonding.