High Strength, Better Fatigue Crack Deviation Performance, and High Anisotropic Ductility 7xxx Aluminum Alloy Products and Methods of Making Such Products

Abstract

The high strength 7xxx aluminum alloy products and methods of making such products are disclosed resulting in better fatigue crack deviation performance, and high anisotropic ductility. The 7xxx aluminum alloy product comprises 7.0 to 7.8 wt. % Zn, 1.1 to 2.2 wt. % Cu, and 1.1 to 2.1 wt. % Mg. This 7xxx aluminum alloy product can be fabricated to produce plate, extrusion or forging products, and is especially suitable for aerospace structural components, especially large commercial airplane wing structure applications. The minimum tensile yield strength (TYS) along rolling (LT) direction is higher than 65 ksi for 4 to 5 inch plate. The minimum K max at crack deviation point is higher than 31 ksi*in 1/2 for 4 to 5 inch plate. The minimum elongation is 1.4% for all tensile orientations including lowest orientations of ST-22.5 to ST-45. The 7xxx aluminum alloy product provides high damage tolerance performance as well as better corrosion resistance performance suitable for aerospace application.

1 - 27 . (canceled) 
     
     
         28 . A high strength 7xxx aluminum alloy product comprising,
 7.0 to 7.8 wt. % Zn,   1.1 to 2.2 wt. % Cu,   1.1 to 2.1 wt. % Mg,   one or more elements selected from the group consisting of up to 0.2 wt. % Zr, up to 0.2% wt. Sc, and up to 0.2 wt. % Hf,   with the balance Al, and incidental impurities,   wherein the tensile yield strength (TYS) along the rolling (LT) direction is higher than 65ksi for 4 to 5 inch plate, the K max-dev  at crack deviation is higher than 31 ksi*in 1/2  for 4 to 5 inch plate, and the minimum elongation is 1.4% for all orientations including lowest orientations of ST-22.5 to ST-45 is 4 to 5 inch plate.   
     
     
         29 . The high strength 7xxx aluminum alloy product of  claim 28  consisting essential of:
 7.3 to 7.6 wt. % Zn, 
 1.2 to 1.7 wt. % Cu, 
 1.2 to 1.7 wt. % Mg, 
 one or more elements selected from the group consisting of up to 0.2 wt. % Zr, up to 0.2 wt. % Sc, and up to 0.2 wt. % Hf, 
 ≤0.12 wt. % Si, 
 ≤0.15 wt. % Fe, 
 with the balance Al, and incidental impurities. 
 
     
     
         30 . A method of manufacturing a high strength 7xxx aluminum alloy comprising the steps of
 a. casting stock of an ingot comprising the 7xxx aluminum alloy product of  claim 28 ;   b. homogenizing the cast stock;   c. hot working the homogenized stock by one or more methods selected from the group consisting of rolling, extrusion, and forging;   d. solution heat treating (SHT) of the hot worked stock;   e. cold water quenching said SHT stock;   f. optionally stretching the SHT stock; and   h. ageing of the SHT, cold water quenched and optionally stretched stock to a desired temper.   
     
     
         31 . The method of  claim 30 , wherein said step of homogenizing includes homogenizing at temperatures from 454 to 491° C. (849 to 916° F.). 
     
     
         32 . The method of  claim 30 , wherein said step of hot working includes hot rolling at a temperature of 385 to 450° C. (725 to 842° F.). 
     
     
         33 . The method of  claim 30 , wherein said step of solution heat treating includes solution heat treated at temperature range from 454 to 491° C. (849 to 916° F.). 
     
     
         34 . The method of  claim 30 , wherein said step of optionally stretching includes stretching at about 1.5 to 3%. 
     
     
         35 . The method of  claim 30 , wherein said step of ageing includes a two-step T7651 ageing process wherein a first stage temperature ranges from 100 to MO ° C. (212 to 284° F.) for 4 to 24 hours and a second stage temperature ranges from 135 to 200° C. (275 to 392° F.) for 5 to 20 hours. 
     
     
         36 . The method of  claim 30 , wherein
 a. said step of homogenizing includes homogenizing at temperatures from 454 to 491° C. (849 to 916° F.);   b. said step of hot working includes hot rolling at a temperature of 385 to 450° C. (725 to 842° F.);   c. said step of solution heat treating includes solution heat treated at temperature range from 454 to 491° C. (849 to 916° F.);   d. said step of cold water quenching includes cold water quenching to room temperature;   e. said step of optionally stretching includes stretching at about 1.5 to 3%;   f. said step of ageing includes a two-step T7651 ageing process wherein a first stage temperature ranges from 100 to 140° C. (212 to 284° F.) for 4 to 24 hours and a second stage temperature ranges from 135 to 200° C. (275 to 392° F.) for 5 to 20 hours.   
     
     
         37 . The method of  claim 30 , wherein said step of ageing includes a two-step T7651 ageing process wherein a first stage temperature ranges from 100 to 140° C. (212 to 284° F.) for 4 to 24 hours and a second stage temperature ranges from 135 to 152° C. (275 to 305° F.) for 5 to 20 hours. 
     
     
         38 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises 7.46-7.8 wt. % Zn. 
     
     
         39 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises 1.2-1.55 wt. % Cu. 
     
     
         40 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises 1.1-1.4 wt. % Mg. 
     
     
         41 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises 1.55-2.14 wt. % Mg. 
     
     
         42 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises ≤0.12 wt. % Si. 
     
     
         43 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises ≤0.05 wt. % Si. 
     
     
         44 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises ≤0.15 wt. % Fe. 
     
     
         45 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises ≤0.08 wt. % Fe. 
     
     
         46 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises Zr in the range from 0.05 to 0.15 wt %. 
     
     
         47 . The 7xxx aluminum alloy product of  claim 28  wherein said 7xxx aluminum alloy product comprises ≤0.04 wt. % Cr. 
     
     
         48 . The 7xxx aluminum alloy product of  claim 28  wherein said aluminum alloy product is a 3-10 inches thick plate, extrusion, or forging product. 
     
     
         49 . The 7xxx aluminum alloy product of  claim 28  wherein said aluminum alloy product is a 4-8 inches thick plate, extrusion, or forging product. 
     
     
         50 . The 7xxx aluminum alloy product of  claim 28  wherein said aluminum alloy product is a thick plate product. 
     
     
         51 . The 7xxx aluminum alloy product of  claim 28  wherein said K max-dev  at crack deviation is higher than 34 ksi*in 1/2 . 
     
     
         52 . The 7xxx aluminum alloy product of  claim 28  wherein said K max-dev  at crack deviation is lower than 64 ksi*in 1/2 . 
     
     
         53 . The 7xxx aluminum alloy product of  claim 28  wherein said minimum elongation is lower than 6% for all tensile orientations. 
     
     
         54 . The 7xxx aluminum alloy product of  claim 28  wherein said tensile yield strength (TYS) along the rolling (LT) direction is lower than 83 ksi.