Method for increasing the strength and/or corrosion resistance of 7000 series Al aerospace alloy products

Abstract

This invention relates to a method for artificially aging 7000 Series A1 aerospace alloys to impart improved strength and/or corrosion resistance performance thereto. The method purposefully adds a second aging step or stage to a one-step tempering, or a third step/stage to a low-high, two-step aging operation. The added step/stage extends at about 225-275° F. for about 3-24 hours. More preferably, the added stage extends at about 250° F. for about 6 hours or more.

What is claimed is:  
     
         1 . A method for imparting improved strength at about the same corrosion resistance performance level to a 7000 Series, aluminum aerospace alloy product that has been artificially aged at one or more temperatures between about 290-330° F. for about 2-30 hours, said method comprising: 
 (a) performing an additional aging equivalent to about 225-275° F. for about 3-24 hours after the preceding, higher temperature artificial aging.  
 
     
     
         2 . The method of  claim 1  wherein said preceding, artificial aging includes heating the alloy product between about 295-310° F. for about 4-18 hours.  
     
     
         3 . The method of  claim 1  wherein said preceding, artificial aging includes a typical “T79” tempering.  
     
     
         4 . The method of  claim 1  wherein said preceding, artificial aging is, itself, preceded by a first heat treatment at about 225-275° F. for about 3 -28 hours.  
     
     
         5 . The method of  claim 4  wherein said first heat treatment is followed by an air or cold water quenching.  
     
     
         6 . The method of  claim 4  wherein said first heat treatment ramps up controllably through the artificial aging that precedes step (a) above.  
     
     
         7 . The method of  claim 1  wherein step (a) includes heating the alloy product for at least about 6 hours at about 250° F.  
     
     
         8 . The method of  claim 1  wherein step (a) is preceded by an air or cold water quenching.  
     
     
         9 . The method of  claim 1  wherein said preceding, artificial aging ramps down controllably through additional aging step (a).  
     
     
         10 . The method of  claim 1  wherein said alloy product is sheet or plate.  
     
     
         11 . The method of  claim 1  wherein said alloy product is an aerospace extrusion.  
     
     
         12 . The method of  claim 1  wherein said 7000 Series alloy is 7055 aluminum (Aluminum Association designation).  
     
     
         13 . The method of  claim 1  wherein step (a) is performed with the alloy product in a forming die.  
     
     
         14 . A method for imparting improved corrosion resistance performance at about the same strength level to a 7000 Series, aluminum aerospace alloy product artificially aged at one or more temperatures between about 290-330° F., said method comprising: 
 (a) performing an additional aging equivalent to about 225-275° F. for about 3-24 hours after the preceding, higher temperature artificial aging.  
 
     
     
         15 . The method of  claim 14  wherein the preceding, artificial aging includes heating the alloy product between about 295-310° F. for about 4-18 hours.  
     
     
         16 . The method of  claim 14  wherein the preceding, artificial aging is, itself, preceded by a first heat treatment at about 225-275° F. for about 4-28 hours.  
     
     
         17 . The method of  claim 16  wherein said first heat treatment ramps up controllably through the higher temperature, artificial aging that follows it.  
     
     
         18 . The method of  claim 14  wherein step (a) includes heating the alloy product for at least about 6 hours at about 250° F.  
     
     
         19 . The method of  claim 14  wherein said higher temperature, artificial aging step ramps gradually down and through said additional aging step (a).  
     
     
         20 . The method of  claim 14  whrein the preceding high temperature, artificial aging ramps down controllably through step (a).  
     
     
         21 . The method of  claim 14  wherein said 7000 Series alloy contains about 5-10 wt. % Zn, about 1-3 wt. % Mg and about 1-3 wt. % Cu.  
     
     
         22 . The method of  claim 21  wherein said 7000 Series alloy is 7055 aluminum (Aluminum Association designation).  
     
     
         23 . The method of  claim 14  wherein step (a) is performed in a forming die.  
     
     
         24 . In a method for artificially aging a 7000 Series aluminum aerospace alloy product to a “T79” type temper, the improvement for increasing the yield strength and/or corrosion resistance performance of said alloy comprises: 
 (a) performing an artificial aging equivalent to about 225-275° F. for about 3-24 hours after the last T79 type tempering step.  
 
     
     
         25 . The improvement of  claim 24  wherein step (a) includes heating the alloy product for at least about 6 hours at about 250° F.  
     
     
         26 . The improvement of  claim 24  wherein step (a) is affected by controllably ramping down from the last T79 type tempering step.  
     
     
         27 . The improvement of  claim 24  wherein said alloy product is sheet or plate.  
     
     
         28 . The improvement of  claim 27  wherein said alloy product is an aircraft wing component.  
     
     
         29 . The improvement of  claim 24  wherein said alloy product is made from 7055 aluminum (Aluminum Association designation).  
     
     
         30 . A method for improving the strength and/or corrosion resistance performance of a 7000 Series aluminum alloy plate product containing about 5-10 wt. % Zn, about 1-3 wt. % Mg and about 1-3 wt. % Cu, said method comprising: 
 (a) artificially aging said plate product at one or more temperatures between about 290-330° F. for about 2-30 hours, and    (b) performing an additional aging on said plate product equivalent to about 225-275° F. for about 3-24 hours.    
     
     
         31 . The method of  claim 30  wherein said 7000 Series alloy is 7055 aluminum (Aluminum Association designation).  
     
     
         32 . The method of  claim 30  wherein step (b) is performed in a forming die.  
     
     
         33 . The method of  claim 30  wherein step (b) includes heating the plate product for at least about 6 hours at about 250° F.  
     
     
         34 . The method of  claim 30  wherein step (a) includes heating the plate product between about 295-310° F. for about 4-18 hours.  
     
     
         35 . A method for improving the strength and/or corrosion resistance performance of a 7000 Series aluminum alloy plate product containing about 5-10 wt.% Zn, about 1-3 wt. % Mg and about 1-3 wt. % Cu, said method comprising: 
 (c) artificially aging said plate product to an equivalent of about 225-275° F. for at least about 6 hours;    (b) artificially aging said plate product at one or more temperatures between about 290-330° F. for about 2-30 hours, and    (c) performing a further artificial aging on said plate product equivalent to about 225-275° F. for about 3-24 hours.    
     
     
         36 . The method of  claim 35  wherein said 7000 Series alloy is 7055 aluminum (Aluminum Association designation).  
     
     
         37 . The method of  claim 35  wherein step (b) includes heating the plate product between about 295-310° F. for about 4-18 hours.  
     
     
         38 . The method of  claim 35  wherein step (c) is performed in a forming die.  
     
     
         39 . The method of  claim 35  wherein step (c) includes heating the plate product for at least about 6 hours at about 250° F.