Method for preparing rivets from cryomilled aluminum alloys and rivets produced thereby

• US 20040140019A1
• Filed: 01/22/2003
• Published: 07/22/2004
• Est. Priority Date: 01/22/2003
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Bampton, Clifford C., Wooten, John R.
• Granted Patent: US 7,435,306 B2
• Time in Patent Office: Days
• US Class Current: 148/437
• CPC Class Codes: B21C 23/00 Extruding metal; Impact extrusion
• CPC Class Codes: B21K 1/58 rivets
• CPC Class Codes: B21K 1/60 hollow or semi-hollow rivets
• CPC Class Codes: B22F 1/07 Metallic powder characterised by particles having a nanoscale microstructure nanosized particles B22F1/054
• CPC Class Codes: B22F 2009/041 by mechanical alloying, e.g. blending, milling
• CPC Class Codes: B22F 2202/03 Treatment under cryogenic or supercritical conditions
• CPC Class Codes: B22F 2999/00 Aspects linked to processes or compositions used in powder metallurgy
• CPC Class Codes: B22F 9/04 starting from solid material, e.g. by crushing, grinding or milling C22C1/1084 takes precedence; crushing, grinding or milling, in general, see the relevant subclasses, e.g. B02C
• CPC Class Codes: C22C 1/0416 Aluminium-based alloys
• CPC Class Codes: F16B 19/04 Rivets; Spigots or the like fastened by riveting lead seals G09F3/00

Abstract

High strength aluminum alloy rivets are provided in which the aluminum alloys exhibit high strength at atmospheric temperatures and maintain high strength and ductility at extremely low temperatures. The rivets are produced from an alloy which is made by blending about 89 atomic % to 99 atomic % aluminum, 1 atomic % to 11 atomic % of a secondary metal selected from the group consisting of magnesium, lithium, silicon, titanium, zirconium, and combinations thereof, and up to about 10 atomic % of a tertiary metal selected from the group consisting of Be, Ca, Sr, Ba, Ra, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, and combinations thereof. The alloy is produced by nanostructure material synthesis, such as cryomilling, in the absence of extrinsically added refractory dispersoids. The synthesized alloy is then consolidated and formed into a solid or blind rivet. Grain size within the rivet is less than 0.5 μm, and the rivet has exceptional thermal stability, resistance to strain localization cracking during rivet head upsetting, and resistance to stress corrosion cracking during service.

Claims

1. An aluminum alloy rivet comprising:

a head portion having a maximum diameter; and

a body portion, axially aligned with the head portion, having an outside diameter which is less than said maximum diameter;

wherein the rivet is formed from an aluminum alloy comprising

89 atomic % to 99 atomic % aluminum;

1 atomic % to 11 atomic % of a secondary metal selected from the group consisting of magnesium, lithium, silicon, titanium, zirconium, and combinations thereof; and

wherein the alloy comprises at least 0.3% nitrogen by weight,

wherein the alloy has an average grain size of less than 0.5 μ

m, and

wherein the alloy is substantially free of extrinsically added refractory materials.

2. The rivet of claim 1, further comprising up to about 10 atomic % of a tertiary metal selected from the group consisting of Be, Ca, Sr, Ba, Ra, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, and combinations thereof.

3. The rivet of claim 1, wherein the secondary metal is magnesium.

4. The rivet of claim 3, wherein the magnesium is present in an amount of 4 weight % to 10 weight % of the alloy.

5. The rivet of claim 4, wherein aluminum is present in an amount of 82 weight % to 96 weight %, and the tertiary metals are selected from the group consisting of zinc, copper, cobalt, zirconium, and nickel.

6. The rivet alloy of claim 5, comprising 6 weight % to 9 weight % zinc, less than 2 weight % copper, less than 2 weight % cobalt, less than about 0.2 weight % zirconium, and less than about 0.2 weight % nickel.

7. The rivet of claim 1, wherein the alloy has a stable grain structure up to at least 850°

F.

8. The rivet of claim 1, wherein the rivet is a solid rivet.

9. The rivet of claim 1, wherein rivet is a blind rivet.

10. The rivet of claim 1, wherein the alloy comprises less than about 0.5 volume % of a refractory material.

11. An aluminum alloy rivet comprising:

a head portion having a maximum diameter; and

a body portion, axially aligned with the head portion, having an outside diameter which is less than said maximum diameter;

wherein the rivet is formed from an aluminum alloy consisting essentially of;

89 atomic % to 99 atomic % aluminum;

1 atomic % to 11 atomic % of a secondary metal selected from the group consisting of magnesium, lithium, silicon, titanium, zirconium, and combinations thereof; and

up to about 10 atomic % of a tertiary metal selected from the group consisting of Be, Ca, Sr, Ba, Ra, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, and combinations thereof; and

,

at least 0.3% nitrogen by weight.

12. The rivet of claim 11 wherein the alloy has an average grain size of less than 0.5 μ

m.

13. A method of producing an aluminum alloy rivet comprising

providing a metal powder comprising atomic % to 99 atomic % aluminum, and

1 atomic % to 11 atomic % of a secondary metal selected from the group consisting of magnesium, lithium, silicon, titanium, zirconium, and combinations thereof;

processing the metal powder with a nanostructured material synthesis technique such that at least 0.3 weight % nitrogen is added to the metal without introducing substantially any refractory material to the metal during recessing;

consolidating the processed metal powder; and

forming the consolidated metal into the form of a rivet having at least a head portion and a body portion.

14. The method of claim 13, wherein the metal powder further comprises up to about 10 atomic % of a tertiary metal selected from the group consisting of Be, Ca, Sr, Ba, Ra, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, and combinations thereof;

and,

15. The method of claim 13, further comprising the step of pre-alloying the provided metal powder prior to processing.

16. The method of claim 13, wherein the synthesis technique is selected from the group consisting of cryomilling, gas condensation, chemical vapor deposition, plasma synthesis, rapid solidification, and severe plastic deformation, whereby a limited and controlled amount of nitrogen may be introduced into the alloy.

17. The method of claim 16, wherein the synthesis technique is cryomilling.

18. The method of claim 17, wherein the step of cryomilling comprises:

supplying the metal powder to a ball mill attritor;

maintaining the supply of metal powder in a liquid nitrogen medium;

activating the attritor, whereby the metal powder is repeatedly impinged between metal balls within the attritor;

deactivating the attritor; and

,

removing the cryomilled metal powder from the attritor.

19. The method of claim 18, wherein the step of cryomilling is continued until the equilibrium grain size of the metal is reached.

20. The method of claim 19, wherein the step of cryomilling is continued for between 6 and 10 hours.

21. The method of claim 20, wherein the step of cryomilling is continued for about 8 hours.

22. The method of claim 13, wherein the step of providing a metallic powder comprises providing a metallic powder substantially free of oxides.

23. The method of claim 22, wherein the metal powder is provided in a substantially oxygen-free atmosphere.

24. The method of claim 13, wherein the secondary metal is magnesium.

25. The method of claim 24, wherein the magnesium is present in an amount of 4 weight % to 10 weight % of the alloy.

26. The method of claim 25, wherein aluminum is present in an amount of 82 weight % to 96 weight %, and the tertiary metals are selected from the group consisting of zinc, copper, cobalt, zirconium, and nickel.

27. The method of claim 26, comprising 6 weight % to 9 weight % zinc, less than 2 weight % copper, less than 2 weight % cobalt, less than about 0.2 weight % zirconium, and less than about 0.2 weight % nickel.