High Strength and High Fracture Toughness 7xxx Aerospace Alloy Products

Abstract

High strength and high fracture toughness 7xxx aluminum alloy products comprise 6.5 to 7.2 wt. % Zn, 1.55 to 1.95 wt. % Cu, 1.75 to 2.15 wt. % Mg, 0.095 to 0.15 wt. % Zr, incidental elements, and the balance Al. In one embodiment, the aluminum alloy product includes Mg/Cu and Zn/Mg ratios in the range of 1.05 to 1.35, and 3.2 to 4.0, respectively. This aluminum alloy product can be fabricated to produce plate, extrusion or forging products, and is especially suitable for aerospace structural components. The products have an excellent combination of strength, fracture toughness, Kmax at the fatigue crack deviation point, ductility in different orientations, and corrosion resistance suitable for aerospace application.

We claim: 
     
         1 . A high strength and high fracture toughness 7xxx aluminum alloy product comprising,
 6.5 to 7.2 wt. % Zn, 1.55 to 1.95 wt. % Cu,   1.75 to 2.15 wt. % Mg, 0.095 to 0.15 wt. % Zr,   up to 0.15 wt. % incidental elements, with the total of these incidental elements not exceeding 0.35 wt. %, and the balance Al.   
     
     
         2 . The aluminum alloy product of  claim 1  comprising a Mg/Cu ratio of 1.05 to 1.35. 
     
     
         3 . The aluminum alloy product of  claim 1  comprising a Zn/Mg ratio of 3.2 to 4.0. 
     
     
         4 . The aluminum alloy product of  claim 1  further comprising ≤0.12 wt. % Si. 
     
     
         5 . The aluminum alloy product of  claim 4  comprising ≤0.05 wt. % Si. 
     
     
         6 . The aluminum alloy product of  claim 1  further comprising ≤0.15 wt. % Fe. 
     
     
         7 . The aluminum alloy product of  claim 6  comprising ≤0.10 wt. % Fe. 
     
     
         8 . The aluminum alloy product of  claim 1  further comprising ≤0.04 wt. % Cr. 
     
     
         9 . The aluminum alloy product of  claim 1  further comprising 0.005-0.10 wt. % Ti. 
     
     
         10 . The aluminum alloy product of  claim 1  wherein said aluminum alloy product is a 1-10 inches thick plate, extrusion, or forging product. 
     
     
         11 . The aluminum alloy product of  claim 10  having a yield tensile strength (YTS) in the LT direction ≥67 ksi. 
     
     
         12 . The aluminum alloy product of  claim 10  having a K1c value in the T-L direction of ≥28 ksi-in 1/2 . 
     
     
         13 . The aluminum alloy product of  claim 10  having a K1c value in the T-L direction of ≥28 ksi-in 1/2  and a yield tensile strength (YTS) in the LT direction ≥67 ksi. 
     
     
         14 . The aluminum alloy product of  claim 13  having K max-dev  values ≥33 MP-m 1/2 . 
     
     
         15 . The aluminum alloy product of  claim 13  having EAC values ≥100 days. 
     
     
         16 . A high strength and high fracture toughness 7xxx aluminum alloy product consisting of,
 6.5 to 7.2 wt. % Zn, 1.55 to 1.95 wt. % Cu,   1.75 to 2.15 wt. % Mg, 0.095 to 0.15 wt. % Zr,   a Mg/Cu ratio of 1.05 to 1.35, a Zn/Mg ratio of 3.2 to 4.0,   ≤0.12 wt. % Si, ≤0.15 wt. % Fe,   ≤0.04 wt. % Cr, 0.005-0.10 wt. % Ti,   up to 0.15 wt. % incidental elements, with the total of these incidental elements not exceeding 0.35 wt. %, and the balance Al.   
     
     
         17 . The aluminum alloy product of  claim 16  comprising ≤0.05 wt. % Si. 
     
     
         18 . The aluminum alloy product of  claim 16  comprising ≤0.10 wt. % Fe. 
     
     
         19 . The aluminum alloy product of  claim 16  wherein said aluminum alloy product is a 1-10 inches thick plate, extrusion, or forging product. 
     
     
         20 . The aluminum alloy product of  claim 19  having a yield tensile strength (YTS) in the LT direction ≥67 ksi. 
     
     
         21 . The aluminum alloy product of  claim 19  having a K1c value in the T-L direction of ≥28 ksi-in 1/2 . 
     
     
         22 . The aluminum alloy product of  claim 19  having a K1c value in the T-L direction of ≥28 ksi-in 1/2  and a yield tensile strength (YTS) in the LT direction ≥67 ksi. 
     
     
         23 . The aluminum alloy product of  claim 22  having K max-dev  values ≥33 MPa-m 1/2 . 
     
     
         24 . The aluminum alloy product of  claim 22  having EAC values ≥100 days. 
     
     
         25 . A method of manufacturing a thick plate, high strength 7xxx aluminum alloy product 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 at temperatures from 454 to 491° C. (849 to 916° F.);   c. hot working the stock by one or more methods selected from the group consisting of rolling, extrusion, and forging at a temperature of 385 to 450° C. (725 to 842° F.);   d. solution heat treating (SHT) of the hot worked stock at temperature range from 454 to 491° C. (849 to 916° F.);   e. cold water quenching said SHT stock;   f. optionally stretching the SHT stock at about 1.5 to 3%; and   h. ageing of the SHT, cold water quenched and optionally stretched stock to a desired temper.   
     
     
         26 . The method of  claim 25 , wherein said step of ageing includes a two-step 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.