Method for preparing rivets from cryomilled aluminum alloys and rivets produced thereby
View Patent ↗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.
1. A method of producing an aluminum alloy rivet comprising:
providing a metal powder comprising
0.9 to 10 weight % magnesium;
6 weight % to 9 weight % zinc;
about 2 weight % copper;
about 2 weight % cobalt;
about 0.2 weight % zirconium;
about 0.2 weight % nickel; and
balance aluminum;
processing the metal powder with a nanostructured material synthesis technique such that
at least 0.3 weight % nitrogen is added to the metal powder without introducing
substantially any refractory material during processing and wherein
the processed metal powder has a yield strength from about 67 to 126 ksi at −320° F.;
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.
2. The method of claim 1 , further comprising pre-alloying the provided metal powder prior to processing.
3. The method of claim 1 , 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.
4. The method of claim 3 , wherein the synthesis technique is cryomilling.
5. The method of claim 4 , 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.
6. The method of claim 5 , wherein the step of cryomilling is continued until the equilibrium grain size of the metal is reached.
7. The method of claim 6 , wherein the step of cryomilling is continued for between 6 and 10 hours.
8. The method of claim 7 , wherein the step of cryomilling is continued for about 8 hours.
9. The method of claim 1 , wherein the step of providing a metallic powder comprises providing a metallic powder substantially free of oxides.
10. The method of claim 9 , wherein the metal powder is provided in a substantially oxygen-free atmosphere.
11. The method of claim 1 , wherein the magnesium is present in an amount of 4 weight % to 10 weight % of the alloy.