Ultra-Thick High Strength 7xxx Series Aluminum Alloy Products and Methods of Making Such Products

Abstract

The present invention is directed to an ultra-thick high strength aluminum alloy, comprising 7.5 to 8.4 wt. % Zn, 1.6 to 2.3 wt. % Mg, 1.4 to 2.1 wt. % Cu, and 0.05 to 0.15 wt. % Zr. This alloy can be fabricated to produce 2-10 inch thick plate, extrusion or forging products, and is especially suitable for aerospace structural components, especially large commercial airplane wing structure applications. The aluminum product has a minimum yield strength of [75 ksi−0.8×(thickness in inch−3.94 inch)] in LT direction and [76 ksi−0.8×(thickness in inch−3.94 inch)] in L direction for more than 2 inch thick product in T7651 temper. Besides strength, product provides necessary damage tolerance performance as well as corrosion resistance performance suitable for aerospace application.

We claim: 
     
         1 . An ultra-thick high strength aluminum alloy product comprising
 7.5 to 8.4 wt. % Zn,   1.6 to 2.3 wt. % Mg,   1.4 to 2.1 wt. % Cu, and   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, incidental elements and impurities,   wherein said aluminum alloy product is a 2-10 inches thick plate, extrusion, or forging product and has a minimum yield strength of [75 ksi−0.8×(thickness in inch−3.94 inch)] in LT direction and [76 ksi−0.8×(thickness in inch−3.94 inch)] in L direction.   
     
     
         2 . The ultra-thick high strength aluminum alloy product of  claim 1  comprising ≦0.12 wt. % Si. 
     
     
         3 . The ultra-thick high strength aluminum alloy product of  claim 2  comprising ≦0.05 wt. % Si. 
     
     
         4 . The ultra-thick high strength aluminum alloy product of  claim 1  comprising ≦0.15 wt. % Fe. 
     
     
         5 . The ultra-thick high strength aluminum alloy product of  claim 4  comprising ≦0.08 wt. % Fe. 
     
     
         6 . The ultra-thick high strength aluminum alloy product of  claim 1  comprising ≦0.04 wt. % Mn. 
     
     
         7 . The ultra-thick high strength aluminum alloy product of  claim 1  comprising ≦0.04 wt. % Cr. 
     
     
         8 . The ultra-thick high strength aluminum alloy product of  claim 1  comprising ≦0.06 wt. % Ti. 
     
     
         9 . The ultra-thick high strength aluminum alloy product of  claim 1  consisting essential of
 7.5 to 8.4 wt. % Zn, 
 1.6 to 2.3 wt. % Mg, 
 1.4 to 2.1 wt. % Cu, and 
 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, 
 ≦0.04 wt. % Mn, 
 ≦0.04 wt. % Cr, 
 and ≦0.06 wt. % Ti 
 with the balance Al, incidental elements and impurities. 
 
     
     
         10 . The ultra-thick high strength aluminum alloy product of  claim 1  consisting essentially of 
       
         
           
                 
                 
                 
                 
                 
                 
               
                     
                 
                   7.65-7.95 
                   wt. % Zn 
                   2.00-2.20 
                   wt. % Mg 
                   1.55-1.75 
                   wt. % Cu 
                 
                   0.08-0.11 
                   wt. % Zr 
                   ≦0.05 
                   wt. % Si 
                   ≦0.08 
                   wt. % Fe 
                 
                     
                 
             
                
               
               
                
                
                
               
            
           
         
         with the balance Al, incidental elements and impurities. 
       
     
     
         11 . The ultra-thick high strength aluminum alloy product of  claim 1  consisting essentially of 
       
         
           
                 
                 
                 
                 
               
                     
                 
                   7.78-7.94 
                   wt. % Zn 
                   2.06-2.10 wt. % Mg 
                   1.65-1.70 wt. % Cu 
                 
                   0.08-0.09 
                   wt. % Zr 
                   0.03-0.04 wt. % Si 
                   0.06-0.07 wt/% Fe 
                 
                   about 0.03 
                   wt. % Ti 
                 
                     
                 
             
                
               
               
                
                
                
                
               
            
           
         
         with the balance Al, incidental elements and impurities. 
       
     
     
         12 . The ultra-thick high strength aluminum alloy product of  claim 1  wherein said aluminum alloy product is a 4-10 inches thick plate, extrusion, or forging product. 
     
     
         13 . The ultra-thick high strength aluminum alloy product of  claim 12  wherein said aluminum alloy product is a 4-8 inches thick plate, extrusion, or forging product. 
     
     
         14 . The ultra-thick high strength aluminum alloy product of  claim 1  wherein said aluminum alloy product is a 2-6 inches thick plate, extrusion, or forging product. 
     
     
         15 . The ultra-thick high strength aluminum alloy product of  claim 1  having a minimum short transverse (ST) stress corrosion cracking (SCC) of 25 ksi. 
     
     
         16 . The ultra-thick high strength aluminum alloy product of  claim 1  having a minimum short transverse (ST) stress corrosion cracking (SCC) of 30 ksi. 
     
     
         17 . The ultra-thick high strength aluminum alloy product of  claim 1  having a minimum short transverse elongation of 2%. 
     
     
         18 . The ultra-thick high strength aluminum alloy product of  claim 1  having a minimum short transverse elongation of 3%. 
     
     
         19 . A method of manufacturing an ultra-thick high strength aluminum alloy product of an AA7xxx-series alloy, the method comprising the steps of:
 a. casting stock of an ingot of an AA7xxx-series aluminum alloy comprising the aluminum alloy product of  claim 1     b. homogenizing the cast stock;   c. hot working the 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.   
     
     
         20 . The method of  claim 19 , wherein said step of homogenizing includes homogenizing at temperatures from 454 to 491° C. (850 to 915° F.). 
     
     
         21 . The method of  claim 19 , wherein said step of hot working includes hot rolling at a temperature of 399 to 443° C. (750 to 830° F.). 
     
     
         22 . The method of  claim 19 , wherein said step of solution heat treating includes solution heat treated at temperature range from 454 to 491° C. (850 to 915° F.). 
     
     
         23 . The method of  claim 19 , wherein said step of optionally stretching includes stretching at about 1.5 to 3%. 
     
     
         24 . The method of  claim 19 , 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 150 to 200° C. (212 to 392° F.) for 5 to 20 hours. 
     
     
         25 . The method of  claim 19 , wherein
 b. said step of homogenizing includes homogenizing at temperatures from 454 to 491° C. (850 to 915° F.);   c. said step of hot working includes hot rolling at a temperature of 399 to 443° C. (750 to 830° F.);   d. said step of solution heat treating includes solution heat treated at temperature range from 454 to 491° C. (850 to 915° F.);   e. said step of cold water quenching includes cold water quenching to room temperature;   f. said step of optionally stretching includes stretching at about 1.5 to 3%;   g. 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 150 to 200° C. (212 to 392° F.) for 5 to 20 hours.