Surface treatment for improved bonding in bi-metallic casting

1. A method of forming a bi-metallic casting, the method comprising:

providing a metal preform of a desired base shape defining a substrate surface;

subsequently removing a natural oxide layer from the substrate surface by degreasing, yielding a cleaned metal preform;

subsequently forming a thin metallic film on at least a portion of the substrate surface of the cleaned metal preform via a zincate immersion treatment comprising subjecting the cleaned metal preform to a bath comprising NaOH, ZnO, KNaC 4 H 4 O 6 .4H 2 O, and FeCl 3 .6H 2 O for about 60 seconds at a temperature of about 18° to about 25° C.; and

subsequently metallurgically bonding the portion of the metal preform having the metallic film with an overcast metal to form a bi-metallic casting, wherein the metallic film promotes a metallurgical bond between the metal preform and the overcast metal.

2. The method of claim 1 , further comprising preheating the metal preform prior to metallurgically bonding the metal preform with the overcast metal.

3. The method of claim 1 , comprising providing the metallic film having a thickness sufficient to prevent re-formation of the natural oxide layer, wherein the metallic film has a thickness of less than about 250 μm.

4. The method of claim 1 , wherein the metallic film has a melting point lower than a melting point of the metal preform.

5. The method of claim 1 , wherein removing the natural oxide layer from the substrate surface comprises:

treating the substrate surface with an alkali etching solution; and

pickling the substrate surface after degreasing the substrate surface and before forming a thin metallic film on at least a portion of the substrate surface of the cleaned metal preform.

6. The method of claim 1 , wherein forming the metallic film on at least a portion of the substrate surface of the cleaned metal preform further comprises incorporating a zinc galvanizing treatment.

7. The method of claim 1 , wherein metallurgically bonding the portion of the metal preform having the metallic film with the overcast metal comprises a metal casting process using a molten metal.

8. The method of claim 1 , wherein the metal preform comprises a metal selected from the group consisting of: aluminum (Al), magnesium (Mg), iron (Fe), copper (Cu), and alloys and mixtures thereof.

9. The method of claim 1 , wherein the metallic film comprises a metal selected from the group consisting of zinc (Zn), tin (Sn), indium (In), bismuth (Bi), antimony (Sb), lead (Pb), rare earth (RE) metals, metal phosphides, and mixtures thereof.

10. The method of claim 1 , wherein the overcast metal comprises one of an aluminum alloy, a magnesium alloy, or both.

11. The method of claim 1 , wherein the metallic film is formed on an entirety of the substrate surface, and the overcast metal is metallurgically bonded to an entirety of the metal preform.

12. The method of claim 1 , wherein the bath comprises about 360 g/L NaOH, 60 g/L ZnO, 15 g/L KNaC 4 H 4 O 6 .4H 2 O, and 1.5 g/L FeCl 3 .6H 2 O.

13. A method of forming a bi-metallic casting with improved bonding between metal components, the method comprising:

providing a metal preform of a desired base shape defining a substrate surface;

subsequently removing a natural oxide layer from the substrate surface;

subsequently etching the substrate surface;

subsequently forming a thin metallic film on the substrate surface, the metallic film having a melting point lower than a melting point of the metal preform;

subsequently preheating the metal preform; and

subsequently forming a metallurgical bond between at least a portion of the metal preform and an overcast metal having a composition different from both the metal preform and the metallic film, wherein the metallic film promotes the metallurgical bond between the metal preform and the overcast metal.

14. The method of claim 13 , wherein the metal preform comprises aluminum (Al) and the metallic film comprises zinc (Zn).

15. The method of claim 13 , wherein the metallic film is formed having a thickness of less than about 250 μm.

16. The method of claim 13 , wherein removing the natural oxide layer from the substrate surface comprises degreasing the substrate surface prior to etching the substrate surface.

17. The method of claim 16 , wherein etching the substrate surface comprises treating the substrate surface with an alkali etching solution followed by pickling the substrate surface.

18. The method of claim 13 , wherein forming the metallic film on the substrate surface comprises incorporating at least one or both of a zincate immersion treatment and a zinc galvanizing treatment.

19. The method of claim 13 , wherein the metal preform is one of a casting, a forging, an extrusion, and a stamping, and forming the metallurgical bond between at least a portion of the metal preform and the overcast metal comprises a die casting or sand casting technique.

20. A method of forming a bi-metallic casting with an aluminum preform, the method comprising:

removing a natural oxide layer from a surface of an aluminum preform;

subsequently etching the surface of the aluminum preform;

subsequently immersing the aluminum preform into a galvanizing bath and forming a thin metallic film having a thickness of less than about 250 μm on the surface of the aluminum preform;

subsequently preheating the aluminum preform; and

subsequently contacting at least a portion of the aluminum preform with a molten metal to form a bi-metallic casting, wherein the metallic film substantially remains on the surface of the aluminum preform as an interface promoting a metallurgical bond between the aluminum preform and the molten metal.