Method for preparing high-temperature nanophase aluminum-alloy sheets and aluminum-alloy sheets prepared thereby
View Patent ↗An aluminum or aluminum-alloy material sheet comprised of an aluminum material having an ultra-fine, submicron grain structure. The strength and physical properties of the aluminum or aluminum-alloy material sheet are improved over previous aluminum and aluminum-alloy material sheets because the aluminum is produced by cryomilling the aluminum or aluminum-alloy materials into a metal powder with ultra-fine, submicron grain structure. The powder is consolidated and rolled into the form of a sheet.
1. A method of producing an aluminum or aluminum-alloy material sheet comprising
providing an aluminum or aluminum-alloy metal powder having ultra-fine, submicron grain size by cryomilling an aluminum or aluminum-alloy raw material, agglomerating the aluminum or aluminum-alloy metal powder following the cryomilling and degassing the aluminum or aluminum-alloy metal powder following the agglomerating;
consolidating the metal powder following the degassing; and
cold-forming the consolidated metal into a sheet comprising:
initially cold-forming the consolidated metal into an intermediate form;
heating the intermediate form to a temperature between 600° F. and 700° F. following initial cold-forming of the consolidated metal to reduce cold work hardening and to improve ductility, wherein heating the intermediate form to reduce cold work hardening and to improve ductility comprises maintaining the workpiece substantially free of recrystallization or grain growth; and
further cold-forming the consolidated metal after heating the intermediate form.
2. The method of claim 1 , wherein the step of further cold-forming is performed without subsequent thermal processing.
3. The method of claim 1 , further comprising the step of thermal processing after further cold-forming the consolidated metal.
4. The method of claim 1 , further comprising the step of extruding the consolidated metal powder prior to cold-forming the sheet.
5. The method of claim 1 , wherein the step of providing metal powder comprises
providing an aluminum or aluminum-alloy metal powder;
and wherein cryomilling an aluminum or aluminum-alloy raw material comprises cryomilling the metal powder such that the resultant metal powder has an average grain size of less than 500 nanometers.
6. The method of claim 5 , wherein the grain size of the material is sized to between about 100 and about 500 nanometers.
7. The method of claim 5 , 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.
8. The method of claim 7 , wherein the step of cryomilling is continued until the equilibrium grain size of the metal is reached.
9. The method of claim 1 , wherein the metal powder is commercially pure aluminum or an aluminum-alloy material composed of at least 50% aluminum by weight in combination with alloying elements selected from the group consisting of magnesium, titanium, molybdenum, vanadium, tungsten, iron, nickel, cobalt, manganese, copper, niobium, zinc, lithium, silicon, titanium, chromium, and combinations thereof.
10. The method of claim 7 , wherein the step of providing a metallic powder comprises providing a metallic powder substantially free of oxides.
11. The method of claim 1 , wherein the step of consolidating the ultra-fine, submicron grain material to form a densified ultra-fine, submicron grain material comprises hot isostatic pressing the ultra-fine, submicron grain material to form a densified ultra-fine, submicron grain material.
12. The method of claim 1 , wherein the step of consolidating the ultra-fine, submicron grain material to form a densified ultra-fine, submicron grain material comprises Ceracon-type forge consolidating the ultra-fine, submicron grain material to form a densified ultra-fine, submicron grain material.
13. The method of claim 1 wherein initially cold-forming comprises initially cold rolling the consolidated metal into the intermediate form, and wherein further cold-forming comprises further cold rolling the consolidated metal after heating the intermediate form.
14. The method of claim 1 wherein heating the intermediate form comprises heating the intermediate form to a temperature between 600° F. and 700° F. and thereafter permitting the intermediate form to air cool.
15. The method of claim 1 , wherein the step of forming is performed without water quenching.