Method for increasing the strength and/or corrosion resistance of 7000 Series AI aerospace alloy products

Abstract

This invention relates to a method for artificially aging 7000 Series Al 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.

1 . A method for imparting improved strength at about the same corrosion resistance performance level to an aluminum aerospace alloy product selected from the group consisting of 7050, 7055, 7075, 7085, and 7150 (Aluminum Association designation) 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,    wherein the crystal grain size that is substantially larger than about 50 μm.    
   
   
       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 3 , wherein the majority of grains are from about 50 μm to 200 μm at the surface of the alloy product.  
   
   
       5 . The method of  claim 2 , wherein the majority of the grains range in size from about 200 μm to about 500 μm in the interior (T/2).  
   
   
       6 . An aluminum alloy product produced by the method of  claim 1 .  
   
   
       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 3  wherein said alloy product is an aerospace extrusion.  
   
   
       12 . An alloy product produced by the method of  claim 3 .  
   
   
       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 an aluminum aerospace alloy product of the 7XXX series of alloys (Aluminum Association designation) 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,    wherein, the aspect ratios of crystals in the alloy product are substantially larger than 4:1 in the recrystallized grain in the surface layer to predominantly on the order of about 50:1 for the unrecrystallized interior of the product.    
   
   
       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 . An aluminum alloy product produced by the method of  claim 14 .  
   
   
       17 . The method of  claim 14 , wherein the crystal grains range in size from about 200 μm to about 500 μm in the interior (T/2).  
   
   
       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 . A method for improving the strength and/or corrosion resistance performance of aluminum alloy plate product comprising about 5 to 10 wt. % Zn, about 1 to 3 wt. % Mg and about 1 to 3 wt. % Cu, said method comprising: 
 (a) artificially aging and die forming 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,    wherein the crystal grains range in size from about 200 μm to about 500 μm in the interior (T/2) and the aspect ratios of crystals in the alloy product are substantially larger than 4:1 in the recrystallized grain in the surface layer to predominantly on the order of about 50:1 for the unrecrystallized interior of the product.