Compositions and methods for darkening and imparting corrosion-resistant properties to zinc or other active metals
Methods and compositions that serve to both darken a zinc or other active! metal surface and impart corrosion-resistant properties thereto, are disclosed. The compositions include an aqueous solution containing about 0.1 percent to about 5 percent ammonium chloride and about 0.1 percent to about 5 percent ammonium molybdate. The compositions utilize particular ratios of concentrations of ammonium chloride and ammonium molybdate.
1. A coated metallic substrate comprising:
a metal substrate having an outer surface, wherein said metal is selected from the group consisting of zinc, magnesium, manganese, and alloys and intermetallic mixtures thereof; and
a darkening coating disposed on said substrate, said coating formed from an aqueous composition consisting essentially of (i) from about 0.1 percent to about 5 percent by weight ammonium chloride, and (ii) from about 0.1 percent to about 5 percent by weight ammonium molybdate, wherein the weight ratio of ammonium chloride to ammonium molybdate is from about 1:2 to about 2:1.
2. The coated substrate of claim 1 further comprising:
a corrosion-resistant coating disposed on said darkening coating, wherein said corrosion-resistant coating comprises zinc flakes and aluminum flakes dispersed in an inorganic binder.
3. The coated substrate of claim 1 wherein said ratio is about 1:1.
4. The coated substrate of claim 1 wherein the concentration of ammonium chloride is from about 0.5 percent to about 3 percent by weight.
5. The coated substrate of claim 1 wherein the concentration of ammonium chloride is about 2.5 percent by weight.
6. The coated substrate of claim 1 wherein the concentration of ammonium molybdate is from about 0.5 percent to about 3 percent by weight.
7. The coated substrate of claim 1 wherein the concentration of ammonium molybdate is about 2.5 percent by weight.
8. The coated substrate of claim 1 wherein the concentration of ammonium chloride is about 2.5 percent by weight and the concentration of ammonium molybdate is about 2.5 percent by weight.
9. The coated substrate of claim 1 further comprising;
a corrosion-resistant coating disposed between said outer surface of said metal substrate and said darkening coating, wherein said corrosion-resistant coating comprises zinc flakes and aluminum flakes dispersed in an inorganic binder.
10. The coated substrate of claim 1 wherein the metal is zinc.
11. The coated substrate of claim 1 wherein the metal is magnesium.
12. The coated substrate of claim 1 wherein the metal is manganese.