Abstract: A method is provided for zincating aluminum substrates for metal plating thereon wherein the plated aluminum product has smoothness, dimensional integrity and increased production yield of the plated products. The substrates also have enhanced paramagnetic thermal stability of ENP coatings used on memory disk products. A zincate bath contains as additives Fe.sup.+3 and NaNO.sub.3, and a chelator to chelate the iron, with a preferred iron chelator being Rochelle Salt and with the amount of Fe.sup.+3 being controlled at a preferred concentration of 0.2 to 0.3 g/l. A preferred zincating method employs an etchant composition comprising HNO.sub.3, H.sub.2 S0.sub.4 and H.sub.3 PO.sub.4 to etch the aluminum substrate prior to zincating. Use of this etchant composition, either alone or with the zincate bath of the invention, is particularly effective for aluminum substrates which have been ground to a smoothness of less than 100 .ANG..