Aluminum-zinc-copper-magnesium-silver alloy wrought product

Abstract

An aluminum wrought alloy product having improved strength, fracture toughness, and excellent exfoliation corrosion resistance, the aluminum base alloy comprised of 1.6 to 2.5 wt. % Mg, 0.01 to 0.9 wt. % Cu, 7.5 to 9.5 wt. % Zn, 0.1 to 1 wt. % Ag, 0.05 to 0.25 wt. % Zr, 0.05 to 0.8 wt. % Mn, max. 0.15 wt. % Si, max. 0.15 wt. % Fe, the remainder aluminum and incidental elements and impurities.

1 . a method of producing a wrought aluminum alloy product having: improved strength, fracture toughness, excellent exfoliation corrosion resistance, and a minimum electrical conductivity in peak strength of 34% IACS, the method comprising the steps of:
 (a) providing a molten body of an aluminum base alloy comprised of 0.01 to 0.9 wt. % Cu, 1.6 to 2.5 wt. % Mg, 6.5 to 9.5 wt. % Zn, 0.01 to 1 wt. % Ag, 0.05 to 0.25 wt. % Zr, 0.01 to 0.8 wt. % Mn, max. 0.15 wt. % Si, max. 0.15 wt. % Fe, the remainder aluminum and incidental elements and impurities;   (b) casting said molten body of said aluminum base alloy to provide a solid body, said molten aluminum base alloy being cast at a rate in the range of 1 to 6 inches per minute;   (c) homogenizing said solid body by heating in a first temperature range of 840 to 860° F. followed by heating in a second temperature range of 860° to 910° F., the second homogenization temperature being greater than the first temperature to provide a homogenized body having a uniformi distribution of Zn, Cu, Mg, Ag, and dispersoids;   (d) working said homogenized body to provide a wrought product, said working being carried out in a temperature range of 550° to 850° F.;   (e) solution heat treating said wrought product; and   (f) artificial aging said product to provide a product having improved strength, fracture toughness, and an exfoliation corrosion rating of EA or better.   
   
   
       2 . The method in accordance with  claim 1  wherein the wrought product is an extrusion or flat rolled product stretched between 0.5 and 5% permanent stretch. 
   
   
       3 . The method in accordance with  claim 1  wherein wrought product is a forging. 
   
   
       4 . The method in accordance with  claim 1  wherein the alloy contains 0.1 to 0.5 wt. % Ag. 
   
   
       5 . The method in accordance with  claim 1  wherein the alloy contains 0.05 to 0.6 wt. % Cu. 
   
   
       6 . The method in accordance with  claim 1  wherein the alloy contains 1.6 to 2.3 wt. % Mg. 
   
   
       7 . The method in accordance with  claim 1  wherein the alloy contains 0.2 to 0.4 wt. % Ag. 
   
   
       8 . The method in accordance with  claim 1  wherein the alloy contains 7.5 to 8.6 wt. % Zn. 
   
   
       9 . The method in accordance with  claim 1  wherein the alloy contains 0.01 to 0.25 wt. % Sc. 
   
   
       10 . The method in accordance with  claim 1  wherein the alloy contains 0.05 to 0.2 wt. % Cr. 
   
   
       11 . The method in accordance with  claim 1  wherein the alloy contains 0.2 to 0.4 wt. % Mn. 
   
   
       12 . The method in accordance with  claim 1  wherein the alloy contains 0.01 to 0.2 wt. % Ti. 
   
   
       13 . The method in accordance with  claim 1  where the second homogenization step is carried out for a period of 4 to 36 hours. 
   
   
       14 . The method in accordance with  claim 1  including rapidly quenching said wrought product from its solution heat treat temperature. 
   
   
       15 . The method in accordance with  claim 1  wherein said solution heat treating is carried out in a temperature range of 875° to 885° F. for 5 to 120 minutes. 
   
   
       16 . The method in accordance with  claim 1  wherein said artificial aging is carried out by aging in a temperature range of 175° to 300° F. for 3 to 30 hours. 
   
   
       17 . The method in accordance with  claim 1  wherein said artificial aging is carried out by aging in a temperature range of 175° to 300° F. for 3 to 30 hours followed by aging at 280° to 360° F. for 3 to 24 hours. 
   
   
       18 . The method in accordance with  claim 1  wherein said artificial aging is carried out by aging in a temperature range of 210° to 280° F. for 4 to 24 hours followed by aging at 340° to 400° F. for 30 minutes to 120 minutes. 
   
   
       19 . The method in accordance with  claim 1  wherein said artificial aging is carried out by aging in a temperature range of 150° to 325° F. for 2 to 30 hours followed by aging at 300° to 500° F. for 5 minutes to 3 hours followed by aging at 175° to 325° F. for 2 to 30 hours. 
   
   
       20 . The method in accordance with  claim 1  wherein said artificial aging is a three-step process wherein the first and third steps improve strength and the second step improves stress corrosion resistance. 
   
   
       21 . The method in accordance with  claim 1  wherein said artificial aging includes aging:
 (i) at a low temperature above room temperature to precipitation harden said extrusion;   (ii) at temperatures to improve corrosion resistance properties of said extrusion; and   (iii) at lower temperatures above room temperature to precipitation harden said extrusion.   
   
   
       22 . The method in accordance with  claim 1  wherein the product has a fracture toughness at least 10% greater than a similarly tempered product fabricated from 7075 alloy. 
   
   
       23 . The method in accordance with  claim 1  wherein the product has a significantly improved exfoliation corrosion and stress corrosion cracking resistance than a similarly tempered product fabricated from 7075 alloy. 
   
   
       24 . The method in accordance with  claim 1  wherein the product has a significantly higher electrical conductivity than a similarly tempered product fabricated from 7075 alloy. 
   
   
       25 . The method in accordance with  claim 1  wherein the product has a fracture toughness at least 25% greater than a similar product fabricated from 7075 alloy. 
   
   
       26 . The method in accordance with  claim 1  wherein the extruded product is an extrusion having a thickness in the range of 0.04 to 10 inches. 
   
   
       27 . The method in accordance with  claim 1  wherein the flat rolled product is a sheet product having a thickness in the range of 0.035 to 0.25 inches. 
   
   
       28 . The method in accordance with  claim 1  wherein the flat rolled product is a plate product having a thickness in the range of 0.25 to 12 inches. 
   
   
       29 . A method of producing a wrought aluminum alloy product having improved strength, fracture toughness and an EA or better exfoliation corrosion resistance rating, the method comprising the steps of:
 (a) providing a molten body of an aluminum base alloy comprised of 1.6 to 2.3 wt. % Mg, 0.01 to 0.9 wt. % Cu, 7.5 to 9.5 wt. % Zn, 0.1 to 0.5 wt. % Ag, 0.05 to 0.4 wt. % Mn, 0.05 to 0.15 wt. % Zr, max. 0.15 wt. % Si, max. 0.15 wt. % Fe, the remainder aluminum and incidental elements and impurities;   (b) casting said molten body of said aluminum base alloy to provide an ingot, said molten aluminum base alloy being cast at a rate in the range of 1 to 6 inches per minute;   (c) homogenizing said ingot by heating in a temperature range of 840° to 910° F. for 6 to 36 hours to provide a homogenized body having a uniform distribution of Zn, Cu, Mg, Ag and zirconium and chromium containing dispersoids;   (d) extruding said homogenized ingot to provide an extrusion product, said extruding being carried out in a temperature range of 550° to 850° F.;   (f) solution heat treating said extrusion product;   (g) stretching said extruded product 0.5 to 5% permanent stretch of said product to reduce internal residual stresses; and   (h) artificial aging said product to provide a product having improved strength, fracture toughness, and an exfoliation corrosion resistance of EA or better.   
   
   
       30 . The method in accordance with  claim 29  wherein the alloy contains 0.01 to 0.1 wt. % Sc. 
   
   
       31 . The method in accordance with  claim 29  wherein the alloy contains 0.01 to 0.2 wt. % Ti. 
   
   
       32 . The method in accordance with  claim 29  wherein the alloy contains 0.05 to 0.2 wt. % Cr. 
   
   
       33 . The method in accordance with  claim 29  wherein said solution heat treating is carried out in a temperature range of 875° to 890° F. for 5 to 120 minutes. 
   
   
       34 . The method in accordance with  claim 29  wherein said artificial aging is carried out by aging. in a temperature range of 175° to 300° F. for 3 to 30 hours followed by aging at 280° to 360° F. for 3 to 24 hours. 
   
   
       35 . The method in accordance with  claim 29  wherein said artificial aging is carried out by aging in a temperature range of 175° to 300° F. for 3 to 30 hours. 
   
   
       36 . The method in accordance with  claim 29  wherein said artificial aging is carried out by aging in a temperature range of 245° to 255° F. for 6 to 24 hours followed by aging at 310° to 340° F. for 5 to 120 minutes. 
   
   
       37 . The method in accordance with  claim 29  wherein said artificial aging is carried out by aging in a temperature range of 245° to 255° F. for 6 to 24 hours followed by aging at 340° to 400° F. for 5 to 120 minutes. 
   
   
       38 . The method in accordance with  claim 29  wherein said artificial aging is a three-step process wherein said first and third steps improve strength and the second step improves corrosion resistance. 
   
   
       39 . The method in accordance with  claim 29  wherein said artificial aging includes aging:
 (i) at a low temperature above room temperature to precipitation harden said extrusion;   (ii) at temperatures to improve corrosion resistance properties of said extrusion; and   (iii) at lower temperatures above room temperature to precipitation harden said extrusion.   
   
   
       40 . The method in accordance with  claim 29  wherein the product has a fracture toughness at least 10% greater than a similar plate product fabricated from 7075 alloy. 
   
   
       41 . The method in accordance with  claim 29  wherein the product has an electrical conductivity of 34% IACS or greater when aged to peak strength. 
   
   
       42 . The method in accordance with  claim 29  wherein said artificial aging is carried out by aging in a temperature range of 150° to 325° F. for 2 to 30 hours followed by aging at 300° to 500° F. for 5 minutes to 3 hours followed by aging at 175° to 325° F. for 2 to 30 hours. 
   
   
       43 . The method in accordance with  claim 29  wherein the wrought product is an extrusion having thickness in the range of 0.04 to 10 inches. 
   
   
       44 . A method of producing a wrought aluminum alloy flat rolled product having improved strength, fracture toughness, and an exfoliation corrosion resistance rating of EA or better, the method comprising the steps of:
 (a) providing a molten body of an aluminum base alloy comprised of 1.8 to 2.2 wt. % Mg, 0.01 to 0.9 wt. % Cu, 7.5 to 9.5 wt. % Zn, 0.1 to 0.4 wt. % Ag, 0.07 to 0.15 wt. % Zr, 0.05 to 0.8 wt. % Mn, max. 0.10 wt. % Si, max. 0.10 wt. % Fe, the remainder aluminum and incidental elements and impurities;   (b) casting said molten body of said aluminum base alloy to provide an ingot, said molten aluminum base alloy being cast at a rate in the range of 1 to 4 inches per minute;   (c) homogenizing said ingot by heating in a 840° to 910° F. to provide a homogenized ingot having a uniform distribution of Zn, Cu, Mg, Ag;   (d) rolling said homogenized ingot to provide a flat rolled product, said rolling being carried out in a temperature range of 600° to 850° F. to provide said flat rolled product in a substantially non-recrystallized condition;   (e) solution heat treating said flat rolled product; and   (f) stretching said flat rolled product 0.5 to 5% permanent stretch or compressing said product in order to relief the internal stresses impaired during the quenching of the product;   (g) artificial aging said flat rolled product to improve strength and fracture toughness and an exfoliation rating of EA or better.   
   
   
       45 . The method in accordance with  claim 44  wherein the alloy contains 0.05 to 0.2 wt. % Cr. 
   
   
       46 . The method in accordance with  claim 44  wherein the alloy contains 0.01 to 0.2 wt. % Ti. 
   
   
       47 . The method in accordance with  claim 44  wherein the alloy contains 0.01 to 0.2 wt. % Sc. 
   
   
       48 . The method in accordance with  claim 44  wherein said solution heat treating is carried out in a temperature range of 875° to 885° F. for 5 to 120 minutes. 
   
   
       49 . The method in accordance with  claim 44  wherein said artificial aging is carried out by aging in a temperature range of 175° to 300° F. for 3 to 30 hours followed by aging at 280° to 360° F. for 3 to 24 hours. 
   
   
       50 . The method in accordance with  claim 44  wherein said artificial aging is carried out by aging in a temperature range of 175° to 300° F. for 3 to 30 hours. 
   
   
       51 . The method in accordance with  claim 44  wherein said artificial aging is carried out by aging in a temperature range of 210° to 280° F. for 4 to 24 hours followed by aging at 300° to 400° F. for 1 to 14 hours. 
   
   
       52 . The method in accordance with  claim 44  wherein said artificial aging includes aging:
 (i) at a low temperature above room temperature to precipitation harden said extrusion;   (ii) at temperatures to improve corrosion resistance properties of said extrusion; and   (iii) at lower temperatures above room temperature to precipitation harden said extrusion.   
   
   
       53 . The method in accordance with  claim 44  wherein said artificial aging is carried out by aging in a temperature range of 150° to 325° F. for 2 to 30 hours followed by aging at 300° to 500° F. for 5 minutes to 3 hours followed by aging at 175° to 325° F. for 2 to 30 hours. 
   
   
       54 . The method in accordance with  claim 44  wherein the flat rolled product is a sheet product having thickness in the range of 0.035 to 0.25 inches. 
   
   
       55 . The method in accordance with  claim 44  wherein the flat rolled product is a plate product having thickness in the range of 0.5 to 12 inches. 
   
   
       56 . An improved aluminum base alloy extrusion product consisting essentially of 1.6 to 2.5 wt. % Mg, 0.01 to 0.9 wt. % Cu, 7.5 to 9.5 wt. % Zn, 0.1 to 0.8 wt. % Mn, 0.05 to 0.15 wt. % Zr, 0.05 to 0.5 wt. % Ag, max. 0.15 wt. % Si, max. 0.15 wt. % Fe, max. 0.1 wt. % Mn, the remainder aluminum and incidental elements and impurities, said extrusion product having a fracture toughness of 10% or more and an exfoliation corrosion resistance significantly greater than a similarly sized 7075 product. 
   
   
       57 . The extrusion product in accordance with  claim 56  wherein the alloy contains 0.2 to 0.45 wt. % Ag. 
   
   
       58 . The extrusion product in accordance with  claim 56  wherein the alloy contains 1.8 to 2.2 wt. % Mg. 
   
   
       59 . The extrusion product in accordance with  claim 56  wherein the alloy contains 0.05 to 0.6 wt. % Cu. 
   
   
       60 . The extrusion product in accordance with  claim 56  wherein the alloy contains 0.05 to 0.5 wt. % Mn. 
   
   
       61 . The extrusion product in accordance with  claim 56  wherein the alloy contains 7.5 to 8.8 wt. % Zn. 
   
   
       62 . The extrusion product in accordance with  claim 56  wherein the alloy contains 0.01 to 0.2 wt. % Sc. 
   
   
       63 . The extrusion product in accordance with  claim 56  wherein the alloy contains 0.01 to 0.2 wt. % Ti. 
   
   
       64 . The extrusion product in accordance with  claim 56  wherein said product is a wing spar. 
   
   
       65 . The extrusion product in accordance with  claim 56  wherein said product is a wing rib. 
   
   
       66 . The extrusion product in accordance with  claim 56  wherein said product is an aircraft stringer. 
   
   
       67 . The extrusion product in accordance with  claim 56  wherein said product is an aircraft floor beam. 
   
   
       68 . The extrusion product in accordance with  claim 56  wherein said product is an aircraft fuselage beam. 
   
   
       69 . An aluminum base alloy comprised of 1.6 to 2.5 wt. % Mg, 0.01 to 0.9 wt. % Cu, 7.5 to 9.5 wt. % Zn, 0.1 to 1 wt. % Ag, and at least one of the elements selected from the group Mn, Si, Fe, the remainder aluminum and incidental elements and impurities. 
   
   
       70 . An aluminum base alloy product comprised of 1.2 to 2.5 wt. % Mg, 0.01 to 1.0 wt. % Cu, 6.5 to 10.5 wt. % Zn, 00.1 to 1 wt. % Ag, 0.01 to 0.25 wt. % Zr, 0.01 to 0.8 wt. % Mn, 0.01 to 0.2 wt. % Ti, 0.01 to 0.4 wt. % Sc, max. 0.1 wt. % Si, max. 0.1 wt. % Fe, the remainder aluminum and incidental elements and impurities.