RU2813825C2 - Improved wrought aluminum alloys of 7xxx series of large thickness and methods of production thereof - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to products from wrought aluminium alloy of 7xxx series of large thickness and methods of their production. Product from wrought aluminium alloy of 7xxx series contains, wt.%: 5.5–6.5 Zn, 1.3–1.7 Mg, 1.7–2.3 Cu, less than 0.15 Mn, up to 1.0 materials for controlling grain structure, wherein said materials for controlling grain structure contain at least one of Zr, Cr, Sc and Hf, and up to 0.15 Ti, the remainder being aluminium and unavoidable impurities. Product of the wrought aluminium alloy of 7xxx series has thickness of 2.5 to 12 inches, wherein the product passes the HHSCC-G49 test at 70 °C for 100 days or at 90 °C for 10 days.

EFFECT: product from wrought aluminium alloy of 7xxx series has improved combination of two or more of the following properties: resistance to cracking under effect of environment, strength, relative elongation and resistance to destruction.

17 cl, 2 dwg, 5 tbl

Description

TECHNICAL FIELD

[001] This patent application relates to improved 7xxx series heavy gauge wrought aluminum alloy products and methods for producing the same.

BACKGROUND OF THE ART

[002] Aluminum alloys can be used in a wide variety of products. However, improving one property of an aluminum alloy without degrading another property is difficult to achieve. For example, it is difficult to increase the strength of a ductile aluminum-based alloy without negatively affecting other properties such as fracture toughness or corrosion resistance. Alloys of the 7xxx series (Al-Zn-Mg based) are prone to corrosion. See, for example , Bonn, W. Grubl, " The stress corrosion behavior of high strength AIZnMg alloys ", Paper held at the International Meeting of Associazione Italiana di Metallurgie, "Aluminum Alloys in Aircraft Industries", Turin, October 1976.

[003] The patentee has described certain 7xxx series aluminum alloy products in, among other things, U.S. Patent Nos. 6,972,110 and 8,673,209 and International Patent Application Publication Nos. WO2016/183030 and WO2018/237196.

DISCLOSURE OF THE INVENTION

[004] Broadly speaking, the present patent application relates to improved 7xxx series wrought aluminum alloy heavy gauge products and methods for producing the same. New thick 7xxx series wrought aluminum alloy products ("new 7xxx series aluminum alloy products") may have an improved combination of environmental stress cracking (EAC) resistance and at least one of properties selected from strength, elongation and toughness destruction, among other properties.

[005] New 7xxx series aluminum alloy products typically contain (and in some cases consist of or consist essentially of) 5.5 to 6.5 wt%. Zn, from 1.7 to 2.3% wt. Cu and from 1.3 to 1.7% wt. Mg. The new 7xxx Series aluminum ductile alloy products are typically at least 2.5 inches thick and can be as thin as 12 inches and exhibit resistance to environmental stress cracking in the lateral direction height (ST), and this stability is important for aerospace and other applications, especially those with loads on structures in the transverse height (ST) direction. In addition, such a thick 7xxx series wrought aluminum alloy product generally has good properties in terms of strength, elongation, fracture toughness and/or crack deflection resistance. Thus, the new 7xxx series wrought aluminum alloy products may have an improved combination of environmental cracking resistance and at least one of the properties selected from strength, elongation, fracture toughness, and crack deflection resistance. In addition to zinc, magnesium and copper, the new 7xxx series aluminum alloy products may contain conventional grain structure control materials, grain refinement additives and impurities. For example, new 7xxx series aluminum alloy products may contain one or more of Zr, Cr, Sc, and Hf as grain structure control materials (e.g., 0.05-0.25 wt.% each of one or more Zr, Cr, Sc and Hf), limiting the total amounts of these elements so that large primary particles do not form in the alloy. As another example, new 7xxx series aluminum alloy products may contain less than 0.15 wt%. Mn. As another example, the new 7xxx series aluminum alloy products can contain up to 0.15% wt. Ti as a grain refiner, optionally with some titanium in the form of TiB ₂ and/or TiC. New 7xxx series aluminum alloy products can contain up to 0.20% wt. Fe and up to 0.15% wt. Si as impurities. Lower amounts of iron and silicon can be used. The residue in new 7xxx series aluminum alloy products is usually aluminum and other unavoidable impurities (other than iron and silicon).

[006] As stated above, new 7xxx series aluminum alloy products typically contain predetermined amounts of zinc, magnesium and copper to facilitate the implementation of EAC resistance in combination with good strength and/or toughness properties, among other things. Therefore, new 7xxx series aluminum alloy products typically contain 5.5 to 6.5 wt.% Zn. According to one embodiment, the new alloy contains no more than 6.4 wt.% Zn. According to another embodiment, the new alloy contains no more than 6.3 wt.%. Zn. According to another embodiment, the new alloy contains no more than 6.2 wt.%. Zn. According to one embodiment, the new alloy contains at least 5.6 wt.%. Zn. According to another embodiment, the new alloy contains at least 5.7 wt.%. Zn. According to another embodiment, the new alloy contains at least 5.8 wt.%. Zn. According to another embodiment, the new alloy contains at least 5.9 wt.%. Zn.

[007] As stated above, new 7xxx series aluminum alloy products typically contain 1.7 to 2.3 wt.% Cu. According to one embodiment, the new alloy contains no more than 2.25 wt.%. Cu. According to another embodiment, the new alloy contains no more than 2.20 wt.%. Cu. According to one embodiment, the new alloy contains at least 1.75 wt.%. Cu. According to another embodiment, the new alloy contains at least 1.80 wt.%. Cu. According to another embodiment, the new alloy contains at least 1.85 wt.%. Cu. According to another embodiment, the new alloy contains at least 1.90 wt.%. Cu. According to another embodiment, the new alloy contains at least 1.95 wt.%. Cu. According to another embodiment, the new alloy contains at least 2.00 wt.%. Cu.

[008] As stated above, new 7xxx series aluminum alloy products typically contain 1.3 to 1.7 wt.% Mg. According to one embodiment, the new alloy contains at least 1.35 wt.%. Mg. According to another embodiment, the new alloy contains at least 1.40 wt.%. Mg. According to one embodiment, the new alloy contains no more than 1.65 wt.%. Mg. According to another embodiment, the new alloy contains no more than 1.60 wt.%. Mg. According to another embodiment, the new alloy contains no more than 1.55 wt.%. Mg. According to another embodiment, the new alloy contains no more than 1.50 wt.%. Mg. According to another embodiment, the new alloy contains no more than 1.45 wt.%. Mg.

[009] In one embodiment, the amount of zinc, magnesium and copper in a 7xxx series aluminum alloy product is 2.569 ≤ Mg+0.500*Cu+0.067*Zn ≤ 3.269. According to another embodiment, the amount of zinc, magnesium and copper in the 7xxx series aluminum alloy product corresponds to the relationship: 2.709 ≤ Mg+0.500*Cu+0.067*Zn ≤ 3.119. According to another embodiment, the amount of zinc, magnesium and copper in the 7xxx series aluminum alloy product corresponds to the ratio: 2.869 ≤ Mg+0.500*Cu+0.067*Zn ≤ 3.269. According to another embodiment, the amount of zinc, magnesium and copper in the 7xxx series aluminum alloy product corresponds to the relationship: 2.869 ≤ Mg+0.500*Cu+0.067*Zn ≤ 3.119. Any of the amounts of zinc, magnesium and copper described in the previous paragraphs can be used in combination with the above empirical ratios.

[0010] In one approach, the amounts of zinc and magnesium in the 7xxx series aluminum alloy product are such that the weight ratio of zinc to magnesium is no more than 4.75:1 (i.e., (wt.% Zn/wt.% Mg) ≤ 4.75:1). In one embodiment, the weight ratio of zinc to magnesium is no more than 4.60:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.60:1). In another embodiment, the weight ratio of zinc to magnesium is no more than 4.50:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.50:1). In yet another embodiment, the weight ratio of zinc to magnesium is no more than 4.40:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.40:1). In another embodiment, the weight ratio of zinc to magnesium is no more than 4.35:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.35:1). In yet another embodiment, the weight ratio of zinc to magnesium is no more than 4.30:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.30:1). In another embodiment, the weight ratio of zinc to magnesium is no more than 4.25:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.25:1). In yet another embodiment, the weight ratio of zinc to magnesium is no more than 4.20:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.20:1). In another embodiment, the weight ratio of zinc to magnesium is no more than 4.15:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.15:1). In yet another embodiment, the weight ratio of zinc to magnesium is no more than 4.10:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.10:1). In another embodiment, the weight ratio of zinc to magnesium is no more than 4.00:1 (ie (wt.% Zn/wt.% Mg) ≤ 4.00:1). In yet another embodiment, the weight ratio of zinc to magnesium is no more than 3.95:1 (ie (wt.% Zn/wt.% Mg) ≤ 3.95:1). In another embodiment, the weight ratio of zinc to magnesium is no more than 3.90:1 (ie (wt.% Zn/wt.% Mg) ≤ 3.90:1).

[0011] In one approach, the amounts of zinc and magnesium in the 7xxx series aluminum alloy product are such that the weight ratio of zinc to magnesium is at least 3.25:1 (i.e., (wt.% Zn/wt. % Mg) ≥ 3.25:1). In one embodiment, the amounts of zinc and magnesium in the 7xxx series aluminum alloy product are such that the weight ratio of zinc to magnesium is at least 3.33:1 (i.e., (wt.% Zn/wt.% Mg ) ≥ 3.33:1). In another embodiment, the amounts of zinc and magnesium in the 7xxx series aluminum alloy product are such that the weight ratio of zinc to magnesium is at least 3.45:1 (i.e., (wt.% Zn/wt.% Mg ) ≥ 3.45:1). In another embodiment, the amounts of zinc and magnesium in the 7xxx series aluminum alloy product are such that the weight ratio of zinc to magnesium is at least 3.55:1 (i.e., (wt.% Zn/wt.% Mg ) ≥ 3.55:1). In yet another embodiment, the amounts of zinc and magnesium in the 7xxx series aluminum alloy product are such that the weight ratio of zinc to magnesium is at least 3.60:1 (i.e., (wt.% Zn/wt.% Mg) ≥ 3.60:1).

[0012] As stated above, the new 7xxx series aluminum alloy product may contain one or more elements of Zr, Cr, Sc and Hf as grain structure control materials (for example, 0.05 to 0.25 wt.% each one or more of the elements Zr, Cr, Sc and Hf), while limiting the total amount of said elements so that large primary particles are not formed in the alloy. Grain structure control materials may, for example, help provide a suitable grain structure (eg, non-recrystallized grain structure). When used, the new 7xxx series aluminum alloy product typically contains at least 0.05% by weight. materials for grain structure control. According to one embodiment, the new 7xxx series aluminum alloy product contains at least 0.07 wt.%. materials for grain structure control. According to another embodiment, the new 7xxx series aluminum alloy product contains at least 0.09% by weight. materials for grain structure control. When applied, the new 7xxx series aluminum alloy product generally contains no more than 1.0 wt%. materials for grain structure control. In one embodiment, the new 7xxx series aluminum alloy product contains no more than 0.75 wt.% materials for grain structure control. In another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.50 wt.% materials for grain structure control. In one embodiment, the grain structure control materials are selected from the group consisting of Zr, Cr, Sc and Hf. In another embodiment, the grain structure control materials are selected from the group consisting of Zr and Cr. In another embodiment, the grain structure control material is Zr. In another embodiment, the grain structure control material is Cr.

[0013] In one embodiment, the grain structure control materials include both Zr and Cr, and the new 7xxx series aluminum alloy product contains at least 0.07 wt%. Zr and at least 0.07% wt. Cr, with % wt. Zr plus wt.% Cr is no more than 0.40% by weight. (i.e. wt.% Zr + wt.% Cr ≤ 0.40 wt.%). In another embodiment, the grain structure control materials include both Zr and Cr, and the new 7xxx series aluminum alloy product contains at least 0.07 wt%. Zr and at least 0.07% wt. Cr, with % wt. Zr plus wt.% Cr is no more than 0.35% by weight. (i.e. wt.% Zr + wt.% Cr ≤ 0.35 wt.%). In another embodiment, the grain structure control materials include both Zr and Cr, and the new 7xxx series aluminum alloy product contains at least 0.07 wt%. Zr and at least 0.07% wt. Cr, with % wt. Zr plus wt.% Cr is no more than 0.30% by weight. (i.e. wt.% Zr + wt.% Cr ≤ 0.30 wt.%). In another embodiment, the grain structure control materials include both Zr and Cr, and the new 7xxx series aluminum alloy product contains at least 0.07 wt%. Zr and at least 0.07% wt. Cr, with % wt. Zr plus wt.% Cr is no more than 0.25% by weight. (i.e. wt.% Zr + wt.% Cr ≤ 0.25 wt.%). In another embodiment, the grain structure control materials include both Zr and Cr, and the new 7xxx series aluminum alloy product contains at least 0.07 wt%. Zr and at least 0.07% wt. Cr, with % wt. Zr plus wt.% Cr is no more than 0.20% by weight. (i.e. wt.% Zr + wt.% Cr ≤ 0.20 wt.%). According to any of the above embodiments, the new 7xxx series aluminum alloy product may contain at least 0.09 wt%. at least one element from Zr and Cr. According to any of the above embodiments, the new 7xxx series aluminum alloy product may contain at least 0.09 wt%. both Zr and Cr.

[0014] In one embodiment, the grain structure control material is Zr, and the new 7xxx series aluminum alloy product contains from 0.07 to 0.18 wt%. Zr. According to another embodiment, the grain structure control material is Zr, and the new 7xxx series aluminum alloy product contains from 0.07 to 0.16 wt%. Zr. In another embodiment, the grain structure control material is Zr, and the new 7xxx series aluminum alloy product contains from 0.08 to 0.15 wt%. Zr. According to another embodiment, the grain structure control material is Zr, and the new 7xxx series aluminum alloy product contains from 0.09 to 0.14 wt%. Zr. According to embodiments in which the grain structure control material is Zr, the new 7xxx series aluminum alloy product typically contains low amounts of Cr, Sc and Hf (for example, ≤ 0.04 wt% each of Cr, Sc and Hf) . In one embodiment, the new 7xxx series aluminum alloy product contains no more than 0.03 wt.% each element from Cr, Sc and Hf. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.02% by weight. each element from Cr, Sc and Hf. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.01% by weight. each element from Cr, Sc and Hf. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.005% by weight. each element from Cr, Sc and Hf.

[0015] In one embodiment, the grain structure control material is Cr, and the new 7xxx series aluminum alloy product contains from 0.07 to 0.25 wt%. Cr. According to another embodiment, the grain structure control material is Cr, and the new 7xxx series aluminum alloy product contains from 0.07 to 0.20 wt%. Cr. According to another embodiment, the grain structure control material is Cr, and the new 7xxx series aluminum alloy product contains from 0.08 to 0.15 wt%. Cr. According to another embodiment, the grain structure control material is Cr, and the new 7xxx series aluminum alloy product contains from 0.10 to 0.15 wt%. Cr. In other embodiments, the new 7xxx series aluminum alloy product contains low amounts of Cr (e.g., ≤ 0.04 wt.% Cr.) In one embodiment, the new 7xxx series aluminum alloy product contains no more than 0.03 wt.%. Cr. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.02% by weight. Cr. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.01% by weight. Cr. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.005% by weight. Cr.

[0016] In some embodiments, the new 7xxx series aluminum alloy contains low amounts of zirconium (eg, ≤0.04 wt.% Zr). In one embodiment, the new 7xxx series aluminum alloy product contains no more than 0.03 wt.% Zr. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.02% by weight. Zr. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.01% by weight. Zr. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.005% by weight. Zr.

[0017] As stated above, the new 7xxx aluminum alloy product typically contains less than 0.15 wt%. Mn. In one embodiment, the new 7xxx series aluminum alloy product contains no more than 0.12% by weight. Mn. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.10% by weight. Mn. In another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.08 wt.% Mn. In another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.05 wt.% Mn. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.04% by weight. Mn. In another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.03 wt.% Mn. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.02% by weight. Mn. According to another embodiment, the new 7xxx series aluminum alloy product contains no more than 0.01% by weight. Mn.

[0018] As stated above, the new 7xxx series aluminum alloy product may contain up to 0.15 wt%. Ti. Titanium can be used to facilitate grain size reduction during casting, for example by using TiB ₂ or TiC. Elemental titanium can also be used or can be used as an alternative. According to one embodiment, the new 7xxx series aluminum alloy product contains from 0.005 to 0.025 wt%. Ti.

[0019] As stated above, the new 7xxx series aluminum alloy product may contain up to 0.15 wt%. Si and up to 0.20% wt. Fe as impurities. The amount of silicon and iron may be limited to avoid detrimental effects on the combination of strength, fracture toughness and crack deflection resistance. In one embodiment, the new 7xxx series aluminum alloy product may contain up to 0.12 wt.%. Si and up to 0.15% wt. Fe as impurities. According to another embodiment, the new 7xxx series aluminum alloy product may contain up to 0.10% wt. Si and up to 0.12% wt. Fe as impurities. According to another embodiment, the new 7xxx series aluminum alloy product may contain up to 0.08 wt.%. Si and up to 0.10% wt. Fe as impurities. In yet another embodiment, the new 7xxx series aluminum alloy product may contain up to 0.06 wt.%. Si and up to 0.08% wt. Fe as impurities. According to another embodiment, the new 7xxx series aluminum alloy product may contain up to 0.04 wt.%. Si and up to 0.06% wt. Fe as impurities. According to another embodiment, the new 7xxx series aluminum alloy product may contain up to 0.03 wt.%. Si and up to 0.05% wt. Fe as impurities.

[0020] As stated above, the thickness of the new 7xxx series aluminum alloy product ranges from 2.5 to 12.0 inches. Thickness refers to the cross-sectional thickness of the product at its widest point. In one embodiment, the thickness of the new 7xxx series aluminum alloy product is at least 3.0 inches. In another embodiment, the thickness of the new 7xxx series aluminum alloy product is at least 3.5 inches. In another embodiment, the thickness of the new 7xxx series aluminum alloy product is at least 4.0 inches. In another embodiment, the thickness of the new 7xxx series aluminum alloy product is at least 4.5 inches. In another embodiment, the thickness of the new 7xxx series aluminum alloy product is at least 5.0 inches. In one embodiment, the thickness of the new 7xxx series aluminum alloy product is no more than 10.0 inches. In another embodiment, the thickness of the new 7xxx series aluminum alloy product is no more than 9.0 inches. In another embodiment, the thickness of the new 7xxx series aluminum alloy product is no more than 8.0 inches.

[0021] In one embodiment, the new 7xxx series aluminum alloy product is a rolled product (eg, a sheet product). In another embodiment, the new 7xxx series aluminum alloy product is an extruded product. In another embodiment, the new 7xxx series aluminum alloy product is a forged product (eg, hand forged product, die forged product).

[0022] As stated above, new 7xxx series aluminum alloy products may have an improved combination of properties. In one embodiment, the typical tensile yield strength in the (L) direction of the new 7xxx series aluminum alloy product is at least 63 ksi according to ASTM E8 and B557. In another embodiment, the typical tensile yield strength in the (L) direction of the new 7xxx series aluminum alloy product is at least 64 ksi. In another embodiment, the typical tensile yield strength in the (L) direction of the new 7xxx series aluminum alloy product is at least 65 ksi. In another embodiment, the typical tensile yield strength in the (L) direction of a 7xxx series aluminum alloy product may be at least 66 ksi. In yet another embodiment, the typical tensile yield strength in the (L) direction of a 7xxx series aluminum alloy product may be at least 67 ksi. In another embodiment, the typical tensile yield strength in the (L) direction of a 7xxx series aluminum alloy product may be at least 68 ksi. In yet another embodiment, the typical tensile yield strength in the (L) direction of a 7xxx series aluminum alloy product may be at least 69 ksi. In another embodiment, the typical tensile yield strength in the (L) direction of a 7xxx series aluminum alloy product may be at least 70 ksi. In yet another embodiment, the typical tensile yield strength in the (L) direction of a 7xxx series aluminum alloy product may be at least 71 ksi. In another embodiment, the typical tensile yield strength in the (L) direction of a 7xxx series aluminum alloy product may be at least 72 ksi. In another embodiment, the typical tensile yield strength in the (L) direction of a 7xxx series aluminum alloy product may be at least 73 ksi.

[0023] In one embodiment, the typical tensile yield strength in the direction (ST) of the new 7xxx series aluminum alloy product is at least 57 ksi according to ASTM E8 and B557. In another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 58 ksi. In yet another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 59 ksi. In another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 60 ksi. In yet another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 61 ksi. In another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 62 ksi. In yet another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 63 ksi. In another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 64 ksi. In yet another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 65 ksi. In another embodiment, the typical tensile yield strength in the (ST) direction of a 7xxx series aluminum alloy product may be at least 66 ksi.

[0024] In one embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 25 ksi√in according to ASTM E8 and E399-12. In yet another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 27 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 28 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 29 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 30 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 31 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 32 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 33 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 34 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 35 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 36 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 37 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 38 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 39 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 40 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 41 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 42 ksi√in. In yet another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 43 ksi√in. In another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 44 ksi√in. In yet another embodiment, the typical plane strain fracture strength (LT) K _IC of the new 7xxx series aluminum alloy product is at least 45 ksi√in.

[0025] In one embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 20 kpsi. inch * square root inches per ASTM E8 and E399-12. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 22 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 24 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 26 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 28 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 30 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 32 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 34 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain fracture toughness (SL) _KIC of at least 36 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain toughness (SL) _KIC of at least 38 kpsi. inch * square root inches. In another embodiment, the new 7xxx series aluminum alloy product has a typical plane strain toughness (SL) _KIC of at least 40 kpsi. inch * square root inches.

[0026] In one embodiment, the typical L-direction elongation of the new 7xxx series aluminum alloy product is at least 6% according to ASTM E8 and B557. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 7%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 8%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 9%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 10%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 11%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 12%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 13%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 14%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 15%. In another embodiment, the typical elongation in the (L) direction of the new 7xxx series aluminum alloy product is at least 16%.

[0027] In one embodiment, the typical elongation in the direction (ST) of the new 7xxx series aluminum alloy product is at least 3% according to ASTM E8 and B557. In another embodiment, the typical elongation in the (ST) direction of the new 7xxx series aluminum alloy product is at least 4%. In yet another embodiment, the typical elongation in the (ST) direction of the new 7xxx series aluminum alloy product is at least 5%. In another embodiment, the typical elongation in the (ST) direction of the new 7xxx series aluminum alloy product is at least 6%. In another embodiment, the typical elongation in the (ST) direction of the new 7xxx series aluminum alloy product is at least 7%. In another embodiment, the typical elongation in the (ST) direction of the new 7xxx series aluminum alloy product is at least 8%. In another embodiment, the typical elongation in the (ST) direction of the new 7xxx series aluminum alloy product is at least 9%. In another embodiment, the typical elongation in the (ST) direction of the new 7xxx series aluminum alloy product is at least 10%.

[0028] In one embodiment, the typical crack deflection resistance LS ( _{Kmax-deviation} ) of a new 7xxx series aluminum alloy product is at least 25 ksi√in. In another embodiment, the typical crack deflection resistance LS ( _{Kmax-deviation} ) of the new 7xxx series aluminum alloy product is at least 27 ksi√in. In yet another embodiment, the typical crack deflection resistance LS (K _max-div ) of the new 7xxx series aluminum alloy product is at least 29 ksi√in. In another embodiment, the typical crack deflection strength LS ( _{Kmax-deviation} ) of the new 7xxx series aluminum alloy product is at least 31 ksi√in. In yet another embodiment, the typical crack deflection resistance LS (K _max-div ) of the new 7xxx series aluminum alloy product is at least 33 ksi√in. In another embodiment, the typical crack deflection resistance LS ( _{Kmax-deviation} ) of the new 7xxx series aluminum alloy product is at least 35 ksi√in. In yet another embodiment, the typical crack deflection resistance LS (K _max-div ) of the new 7xxx series aluminum alloy product is at least 37 ksi√in. In another embodiment, the typical crack deflection strength LS ( _{Kmax-deviation} ) of the new 7xxx series aluminum alloy product is at least 39 ksi√in. In yet another embodiment, the typical crack deflection strength LS ( _{Kmax-deviation} ) of the new 7xxx series aluminum alloy product is at least 41 ksi√in. In another embodiment, the typical crack deflection resistance LS ( _{Kmax-deviation} ) of the new 7xxx series aluminum alloy product is at least 43 ksi√in. In yet another embodiment, the typical crack deflection resistance LS (K _max-div ) of the new 7xxx series aluminum alloy product is at least 45 ksi√in. In another embodiment, the typical crack deflection resistance LS ( _{Kmax-deviation} ) of the new 7xxx series aluminum alloy product is at least 47 ksi√in. In yet another embodiment, the typical crack deflection strength LS (K _max-div ) of the new 7xxx series aluminum alloy product is at least 49 ksi√in. In another embodiment, the typical crack deflection resistance LS ( _{Kmax-deviation} ) of the new 7xxx series aluminum alloy product is at least 50 ksi√in.

[0029] As stated above, the new 7xxx series aluminum alloys can be resistant to EAC, and EAC resistance can be determined by SCC (stress corrosion cracking) testing when exposed to heat and moisture. In one embodiment, the new 7xxx series aluminum alloy product has a thickness of at least 63.5 mm and is tested for SCC (stress corrosion cracking) under heat and moisture using standard stress corrosion and tensile test specimens corresponding to ASTM G49, as defined below (“HHSCC-G49”). To prepare test specimens for HHSCC-G49, at least three specimens are taken in the transverse height (ST) direction from the middle of the thickness of the final product and from the area between W/4 and 3W/4 of the final product. The samples taken are then machined to produce tensile test specimens with a diameter defined in ASTM G47-20 and dimensions proportional to the standard specimen defined in ASTM E8/8M-16ae1. If the thickness of the final product is at least 2.25 inches (57.15 mm), then the length of the tensile test piece is 2.00 inches (50.8 mm), as shown in FIG. 2. If the final product thickness is between 1.50 inches (38.1 mm) and less than 2.25 inches (<50.8 mm), the sample length must be at least 1.25 inches (31.75 mm) and should be as close to 2.00 inches (50.8 mm) as possible. Before testing, tensile test specimens must be cleaned/degreased by rinsing in acetone. The tensile test specimens are then strained in the transverse vertical direction at 85% of their tensile yield strength in the ST direction at position T/2. The tensile yield strength of the ST alloy is measured at room temperature according to ASTM E8 and B557 before testing HHSCC-G49. The load frame used is of the permanent deformation type according to ASTM G49, section 7.2.2 (see, for example, ASTM G49 Fig. 4a). The deformed specimens are then placed in a controlled atmosphere chamber containing air at 85% relative humidity (no added air, such as chlorides) and a temperature of 70°C or 90°C. At least three samples must be tested. For the purposes of this patent application, the alloy passes the HHSCC-G49 test at 70°C, where all samples fail to fail for at least 100 days. For the purposes of this patent application, the alloy passes the HHSCC-G49 test at 90°C, where all samples fail for at least 10 days. Fracture occurs when a specimen breaks into two halves, either along the working length or along one of the sides of the specimen adjacent to the working length. Failures along the lateral side are statistically equivalent to failures along the working length. Thread failures are included only if they are statistically equivalent to thickness gauge length failures when determining whether an alloy passes HHSCC-G49. Thread failure occurs when a crack occurs at the threaded end of the specimen rather than along the working length. In some cases, thread failure may not be detected until the specimen is removed from the loading frame.

[0030] In one approach, the HHSCC-G49 test is performed at 70°C, and the new 7xxx series aluminum alloy product passes the 120 days HHSCC-G49 test at 70°C, with all samples remaining intact during the 120 days HHSCC-G49 test. G49 defined above. In one embodiment, a new 7xxx series aluminum alloy product passes 140 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 140 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 150 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 150 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 160 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 160 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 180 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 180 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 200 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 200 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 220 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 220 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 240 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 240 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 260 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 260 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 280 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 280 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product passes 300 days of HHSCC-G49 testing at 70°C, with all samples failing to fail within the 300 days of HHSCC-G49 testing defined above. The above properties regarding resistance to stress corrosion cracking can be achieved in products whose thickness is at least 80 mm, at least 100 mm, at least 120 mm or at least 140 mm or higher.

[0031] In another approach, the HHSCC-G49 test is carried out at 90 °C, and the new 7xxx series aluminum alloy product passes 15 days of the HHSCC-G49 test at 90 °C, and all samples do not fail within the 15 days of the HHSCC-G49 test , defined above. In one embodiment, a new 7xxx series aluminum alloy product undergoes 20 days of HHSCC-G49 testing at 90°C, with all samples failing to fail within the 20 days of HHSCC-G49 testing defined above. In another embodiment, a new 7xxx series aluminum alloy product undergoes 25 days of HHSCC-G49 testing at 90°C, with all samples failing to fail within the 25 days of HHSCC-G49 testing defined above. The above properties regarding resistance to stress corrosion cracking can be achieved in products whose thickness is at least 80 mm, at least 100 mm, at least 120 mm or at least 140 mm or higher.

[0032] In one embodiment, the new 7xxx series aluminum alloy product has a thickness of at least 63.5 mm and is subjected to stress corrosion cracking testing in accordance with ASTM G47 using stress corrosion and tensile test specimens conforming to ASTM G49. , under alternative immersion exposure conditions per ASTM G44 (“SCC alternate immersion testing”). For the purposes of this patent application, the new 7xxx series aluminum alloy passes the alternative SCC immersion test if all specimens survive 20 days of the alternative SCC immersion test at a net stress of 172 MPa in the ST direction where the test environment is 3.5% NaCl and requires testing of a minimum of five (5) samples. In one embodiment, the new 7xxx series aluminum alloy is subjected to 30 days of alternating immersion SCC testing as defined above. In another embodiment, the new 7xxx series aluminum alloy is subjected to 20 days of alternating immersion SCC testing as defined above, but at a total stress of 241 MPa. In yet another embodiment, the new 7xxx series aluminum alloy is subjected to 30 days of alternating immersion SCC testing as defined above, but at a total stress of 241 MPa. The above properties regarding resistance to stress corrosion cracking can be achieved in products whose thickness is at least 80 mm, at least 100 mm, at least 120 mm or at least 140 mm or higher.

[0033] In one embodiment, the new 7xxx series aluminum alloy product has a thickness of at least 63.5 mm and is tested for SCC (stress corrosion cracking) heat and moisture in accordance with ASTM G168, as defined below ("HHSCC-G168"). For the purposes of this patent application, the new 7xxx series aluminum alloy passes the HHSCC-G168 test when (a) the stress intensity factor produces a crack growth rate of no more than 10 ^-7 mm/s, and (b) the resulting K value is at least 13 MPa -square root m (MPa√m). HHSCC-G168 testing must be performed at 70°C and 85% RH at T/2 using SL specimens. According to one embodiment, the resulting K value is at least 14 MPa√m with a crack growth rate of no more than 10 ^-7 mm/s. According to another embodiment, the obtained K value is at least 15 MPa√m with a crack growth rate of no more than 10 ^-7 mm/s. According to another embodiment, the obtained K value is at least 16 MPa√m with a crack growth rate of no more than 10 ^-7 mm/s. According to another embodiment, the obtained K value is at least 17 MPa√m with a crack growth rate of no more than 10 ^-7 mm/s. According to another embodiment, the resulting K value is at least 18 MPa√m or higher with a crack growth rate of no more than 10 ^-7 mm/s. The above properties regarding resistance to stress corrosion cracking can be achieved in products whose thickness is at least 80 mm, at least 100 mm, at least 120 mm or at least 140 mm or higher.

[0034] In one embodiment, a new 7xxx series aluminum alloy product passes at least two of the SCC tests mentioned above (i.e., at least two of: (a) the HHSCC-G49 test defined above, (b) the alternating immersion SCC test defined above, and (c) the HHSCC-G168 test defined above). In another embodiment, the new 7xxx series aluminum alloy passes all of the SCC tests mentioned above.

[0035] Although the L and ST direction properties described above generally apply to thick plate products, similar properties can also be achieved in thick forged products and thick extruded products. In addition, many of the properties mentioned above can be provided in combination, as illustrated by the examples below.

[0036] As stated above, the new 7xxx series thick aluminum alloy products can be suitable as parts for various products in the aerospace industry. In one embodiment, the alloy product is an aerospace structural component. An aircraft structural component may be any of an upper wing (skin), an upper wing stringer, an upper wing skin with integral stringers, a spar, a spar flange, a spar web, a rib, a rib shoe or rib web, stiffeners, frames, landing gear components ( e.g., cylinders, bogies), front struts, frames, flap guide assemblies, fuselage and windshield frames, landing gear crossmembers, side struts, attachment assemblies, fuselage component (e.g. fuselage skin) and aerospace components (e.g. rockets and other vehicles that may leave the Earth's atmosphere). In one embodiment, the alloy product is an armored component (eg, in a motorized vehicle). In one embodiment, the alloy product is used in the oil and gas industry (eg, pipes, structural components). In one embodiment, the alloy product is a thick mold block/mold plate product (eg, injection molding). In one embodiment, the alloy product is a product for the automotive industry.

[0037] The new high-thickness 7xxx series aluminum alloy products can be converted into wrought products by casting an aluminum alloy with any of the above compositions into an ingot or billet, followed by homogenizing said ingot or billet. The homogenized ingot or billet can be processed by rolling, extruding or forging to a final thickness, typically by hot working, optionally using some cold working. A finite thickness product can be solution heat treated, then quenched and then stress relieved (e.g. by tension or compression) before being artificially aged.

[0038] In addition to traditional wrought products, the new 7xxx series aluminum alloys can be formed into shape-specific castings or by additive manufacturing into additive manufactured products. Products manufactured through additive manufacturing can be used as is or can be subsequently processed, for example processed using a mechanical, thermal or thermo-mechanical processing method.

Definitions

[0039] Herein, "typical tensile yield strength in the longitudinal direction (L)" or TYS(L) is determined according to ASTM B557-10 and by measuring the tensile yield strength (TYS) in the longitudinal direction (L) at position T/ 4, using at least three different batches of material, and at least two duplicate samples from each batch are tested to obtain a total of at least 6 measured values for the different samples, with the typical TYS(L) being the average value from at least 6 measured values for different samples. A typical elongation in the (L) direction is measured during a tensile test in the longitudinal direction.

[0040] Herein, "typical transverse height tensile strength (ST)" or TYS(ST) is determined according to ASTM B557-10 and by measuring the transverse height (ST) tensile yield strength (TYS) , using at least three different batches of material, and at least two duplicate samples from each batch are tested to obtain a total of at least 6 measured values for the different samples, with the typical TYS(ST) being the average of at least 6 measured values for different samples. Samples for transverse tensile testing in height are selected in such a way that the midpoint of the working area coincides with the plane of the middle of the sheet thickness. Typical elongation in the direction (ST) is measured during a transverse height tensile test.

[0041] Herein, "typical plane strain (LT) fracture toughness (K _IC )" is determined according to ASTM E399-12 by measuring the plane strain fracture toughness in the LT direction at the T/4 position using at least three different batches material, using sample C(T), where "W" is 4.0 inches and where "B" is 2.0 inches for products with a thickness of at least 2.0 inches, and where "B" is 1.5 in. for products less than 2.0 in. thick, with at least two duplicate specimens from each batch tested to obtain a total of at least 6 measured values for the different specimens, and with a typical plane strain (LT) fracture strength of (K _IC ) is the average of at least 6 valid measured K _IC values for different samples.

[0042] Herein, "typical plane strain fracture toughness (SL) (K _IC )" is determined according to ASTM E399-12 by measuring plane strain fracture toughness in the SL direction at position T/2 using at least three different batch of material, using sample C(T), where "W" and "B" are given in the table below, with at least two duplicate samples from each batch being tested to obtain a total of at least 6 measured values for different specimens, wherein the typical plane strain fracture strength (SL) (K _IC ) is the average of at least 6 valid measured K _IC values for different specimens.

Sample parameters in S-L direction

Product thickness "W" "B" ≥ 5.0 inches 4.0 inches 2.0 inches <5.0" to ≥3.8" 3.0 inches 1.5 inches <3.8" to ≥3.2" 2.5 inches 1.25 inches <3.2" to ≥2.6" 2.0 inches 1.0 inch <2.6" to ≥2.0" 1.5 inches 0.75 inch <2.0" to ≥1.5" 1.0 inch 0.5 inches

[0043] Typical crack deflection resistance properties LS (K _max-devit ) should be determined according to the procedure described in US Patent Application Publication No. 2017/0088920, paragraph 0058, which procedure is incorporated herein by reference. except : (a) the "W" dimension of the specimen must be 2.0 inches (5.08 cm), (b) the specimen must be centered at the T/2 position (relative to the apex of the notch), and (c) the specimens being examined can be tested in laboratory air rather than in high humidity air.

[0044] As used herein, the term "square root" may be abbreviated as "√".

[0045] As used herein in the specification and claims, the following terms have clearly related meanings unless the context clearly indicates otherwise. As used herein, the expressions “according to one embodiment” and “according to some embodiments” do not necessarily refer to the same embodiment(s), although it is possible. In addition, as used herein, the expressions “according to another embodiment” and “according to some embodiments” do not necessarily refer to another embodiment, although such a possibility exists. Thus, as described below, various embodiments of the invention can be easily combined without departing from the scope or spirit of the present invention.

[0046] Additionally, as used herein, the term “or” is an inclusive “or” operator and is equivalent to the term “and/or” unless the context clearly indicates otherwise. The term “based on” is not exclusive and may be based on additional factors not described unless the context clearly indicates otherwise. In addition, in the specification, singular nouns include references to plural forms unless the context clearly indicates otherwise. The meaning of "in" includes "in" and "on" unless the context clearly indicates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In FIG. 1 is a graph showing strength versus fracture toughness properties K _IC for the alloys according to Example 1.

[0048] In FIG. Figure 2 is a graph showing strength versus EAC resistance for the alloys of Example 1.

IMPLEMENTATION OF THE INVENTION

[0049] Example 1

[0050] Two aluminum alloys were cast into 6 x 18 inch (D x W) ingots, the compositions of which are shown in Table 1 below.

Table 1. Composition of alloys according to example 1 (wt.%)

Alloy Si Fe Zn Mg Cu Zr Mn Cr Ti 1 0.05 0.05 5.88 1.60 2.17 0.10 0.02 0.02 0.02 2 0.02 0.06 5.98 1.50 2.12 0.10 -- -- 0.02

The ingots were then prepared for homogenization in the traditional manner (eg sawing and scraping). The first ingot was then processed to its final state according to Japanese Patent No. H03-41540 (1991), Example 1, Alloy 4 ¹ (also published as JP01-290737 (1989)). The second ingot was processed in accordance with the methods of the present invention described herein.

[0051] Specifically, Alloy 1 was homogenized at 842 °F (450 °C) according to JPH03-41540. The alloy was then hot rolled to a final thickness of 1.75 inches (44.45 mm). Alloy 1 was then solution heat treated at 842°F (450°C) for 1 hour per JPH03-41540, then water quenched at 190°F (87.8°C) and then stretched 1.5%. After stretching, Alloy 1 was artificially aged by first aging at 248°F (120°C) for 24 hours, heated to 302°F, and then aged at 302°F (150°C) for 24 hours per JPH034- 41540.

[0052] Alloy 2 was homogenized at 895°F (479°C) and then hot rolled to a final thickness of 1.75 inches (44.45 mm). Alloy 2 was then solution heat treated at 895°F (479°C) for 2 hours, water quenched at 190°F (87.8°C), and then stretched 2.25%. After stretching, a quantity of alloy 2 was subjected to two different artificial aging methods:

Method 1: First age at 250°F (121°C) for 6 hours, then heat to 320°F (160°C) and hold for 5.6 hours, air cool to ambient temperature, then repeat heating to 250°C (121°C) and holding for 24 hours.

Method 2: First age at 250°F (121°C) for 6 hours, then heat to 320°F (160°C) and hold for 9.75 hours, air cool to ambient temperature, then repeat heating to 250°F (121°C) and holding for 24 hours.

A quench temperature of 190°F simulates the cooling rate of mid-quenching of a large thickness ingot (for example, an 8-inch (203.2 mm) thick ingot).

[0053] Alloys 1-2 were subjected to metallographic examination and found to be non-recrystallized, i.e. contained no more than 45% recrystallized grains, as determined using standard metallographic analysis procedures. In one embodiment, the new 7xxx series wrought aluminum alloy product contains no more than 35% recrystallized grains. In another embodiment, the new 7xxx series wrought aluminum alloy product contains no more than 25% recrystallized grains. In another embodiment, the new 7xxx series wrought aluminum alloy product contains no more than 15% recrystallized grains. In another embodiment, the new 7xxx series wrought aluminum alloy product contains no more than 5% recrystallized grains.

[0054] The alloys were then subjected to mechanical testing, the results of which are shown below in Table 2. Also presented are test results relating to similarly prepared conventional 7050 alloys, the results of which are taken from Joint International Patent Application Publication No. WO2020/102441. Measurements refer to T/2 position for all alloys. Fracture toughness refers to the S-L orientation.

Table 2. Mechanical properties of alloys according to example 1*

Alloy Strength
Trial
Orientation Tensile strength (ksi) Tensile yield strength (ksi) Relative extension
(%) K _IC (ksi√inch) 1 L 76.8 70.2 12.1 -- 1 ST 73.4 63.5 5.6 18.1 2 (AP1) L 78.0 72.1 12.6 -- 2 (AP1) ST 75.5 65.8 9.4 20.7 2 (AP2) L 76.7 69.9 13.7 -- 2 (AP2) ST 73.2 62.5 9.5 23.3 7050 L 72.3 61.6 11.7 30.7 ( _KQ ) 7050 L 72.2 61.2 12.5 28.2 ( _KQ ) 7050 ST 70.4 56.3 9.4 18.5 7050 ST 70.3 56.2 10.2 18.4

*AP1=aging method 1; AP2=aging mode 2; √=square root

[0055] In addition, the alloys were subjected to EAC (environmental stress cracking) resistance testing according to the HHSCC-G49 procedure described above. A fabricated 7050-T7651 plate (3.9 in. thick) with a strength level similar to that of Alloys 1-2 was also examined. The results of HHSCC-G49 are shown below in Table 3.

Table 3. HHSCC-G49 test results

Alloy Voltage
(%TYS-ST) Applied voltage (ksi) 90°C/85% RH Number of days on test Number of days until destruction Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 1 85 54 18 eleven eleven 14 18 18 2 (AP1) 85 55.9 21 eleven eleven eleven 21 18 2 (AP2) 85 53.1 46 28 32 28 46 35 7050 85 53.0 55 28 55 55 19 41

[0056] As shown above and in FIG. 1-2, Alloy 2 has an improved combination of properties compared to Alloy 1. As shown in FIG. 1, Alloy 2 has a combination of much higher strength and toughness values compared to Alloy 1 and conventional 7050 alloy. As shown in FIG. 2, Alloy 2 also has a much better combination of strength and EAC resistance compared to Alloy 1. In addition, as shown in Table 2, the ST ductility of Alloy 2 is significantly higher than that of Alloy 1.

[0057] An analysis of the homogenization temperature for this alloy system was performed. It was determined that for these specific alloys containing from 5.5 to 6.5 wt.%. Zn, from 1.3 to 1.7% wt. Mg and from 1.7 to 2.3% wt. Cu, the homogenization temperature must be at least as high as T(homog.), where T(homog.) is calculated in degrees Fahrenheit using the following formula:

T(homog.)=614.4+55.2*Cu+83.1*Mg-1.8*Zn.

In the above formula, Cu, Mg and Zn represent the mass percentage amounts of copper, magnesium and zinc, respectively, in the 7xxx series wrought aluminum alloy. The table below shows the calculations for alloys 1 and 2.

Table 4 - T(homogeneous) alloys 1-2

Alloy Zn Mg Cu T(homog.) (°F) 1 5.88 1.60 2.17 856.5 2 5.98 1.50 2.12 845.3

As shown, the minimum homogenization temperature for alloy 1 is 856.5 °F and the minimum homogenization temperature for alloy 2 is 845.3 °F.

[0058] The homogenization temperature is preferably higher than T(homogeneous). In one embodiment, the homogenization temperature is at least 5°F higher than T(homogeneity), i.e. is ≥ 5 °F+T(homogeneous). In another embodiment, the homogenization temperature is at least 10°F higher than T(homogeneous), i.e. is ≥ 10 °F+T(homogeneous). In another embodiment, the homogenization temperature is at least 15°F higher than T(homogeneous), i.e. is ≥ 15 °F+T(homogeneous). In another embodiment, the homogenization temperature is at least 20°F higher than T(homogeneous), i.e. is ≥ 20 °F+T(homogeneous). In another embodiment, the homogenization temperature is at least 25°F higher than T(homogeneous), i.e. is ≥ 25 °F+T(homogeneous). In another embodiment, the homogenization temperature is at least 30°F higher than T(homogeneous), i.e. is ≥ 30 °F+T(homogeneous). In yet another embodiment, the homogenization temperature is at least 35°F higher than T(homogeneous), i.e. is ≥ 35 °F+T(homogeneous). In another embodiment, the homogenization temperature is at least 40°F higher than T(homogeneous), i.e. is ≥ 40 °F+T(homogeneous). In another embodiment, the homogenization temperature is at least 45°F higher than T(homogeneous), i.e. is ≥ 45 °F+T(homogeneous). In another embodiment, the homogenization temperature is at least 50°F higher than T(homogeneous), i.e. is ≥ 50 °F+T(homogeneous). However, the homogenization temperature must be lower than the initial melting temperature of the aluminum alloy. The homogenization temperature is preferably at least 10°F below the initial melting temperature of the aluminum alloy.

[0059] With regard to solution heat treatment, all of the above ideas regarding homogenization apply equally to the solution heat treatment temperature. That is, the solution heat treatment temperature may be the same as T(homogeneous) and preferably 10 to 50°F higher than T(homogeneous) as described above, but lower than the initial melting temperature of the aluminum alloy and preferably at least 10°F below the initial melting temperature of the aluminum alloy. After solution heat treatment, the alloy should be quenched in a suitable environment such as water or air. The water is preferably at room temperature.

[0060] Based on the above data, aging analysis was also performed. It has been found that alloys should be aged until a total equivalent aging time, t(eq), of 7 to 20 hours is achieved, with a total artificial aging equivalent time of:

In the above formula, T represents the instantaneous temperature in Kelvin (K) during artificial aging, and Tref represents the reference temperature selected at 160 °C (433.15K). The t(eq.) values for alloys 1-2 are given in the table below.

Table 5 - t(equivalent) of alloys 1-2

Alloy t(eq.)
(watch) 1 14.58 2-AP1 10.57 2-AP2 14.57

[0061] As shown, both Alloy 1 and Alloy 2-AP2 were aged for essentially the same total equivalent aging time. However, the aging method of Alloy 2 is excellent and at least partially contributes to its significantly improved properties. Accordingly, in one embodiment, t(eq.) is from 7 to 19 hours. According to another embodiment, t(eq.) is from 7 to 18 hours. According to another embodiment, t(eq.) is from 7 to 17 hours. According to another embodiment, t(eq.) is from 7 to 16 hours. According to another embodiment, t(eq.) is from 7 to 15 hours. According to another embodiment, t(eq.) is from 7 to 14 hours. In yet another embodiment, t(eq) is between 7 and 13.5 hours. According to another embodiment, t(eq.) is from 7 to 13 hours. In yet another embodiment, t(eq.) is between 7 and 12.5 hours. According to another embodiment, t(eq.) is from 7 to 12 hours. In yet another embodiment, t(eq) is between 7 and 11.5 hours. In another embodiment, t(eq.) is from 7 to 11 hours.

[0062] It is believed that both the two-stage and three-stage aging methods can be used with the 7xxx series wrought aluminum alloys described herein, provided that appropriate homogenization and solution heat treatment procedures are followed. Thus, in one embodiment, artificial aging includes a first aging at a first aging temperature of 200 to 300°F followed by a second aging at a second aging temperature of 250 to 350°F, the second aging temperature being at least 10°F higher first aging temperature. In one embodiment, the second aging temperature is at least 20°F higher than the first aging temperature. In another embodiment, the second aging temperature is at least 30°F higher than the first aging temperature. In yet another embodiment, the second aging temperature is at least 40°F higher than the first aging temperature. In another embodiment, the second aging temperature is at least 50°F higher than the first aging temperature. In yet another embodiment, the second aging temperature is at least 60°F higher than the first aging temperature. In another embodiment, the second aging temperature is at least 70°F higher than the first aging temperature.

[0063] In one embodiment, the first aging temperature is no more than 280°F. In another embodiment, the first aging temperature is no more than 270°F. In yet another embodiment, the first aging temperature is no more than 260°F. In another embodiment, the first aging temperature is no more than 250°F. Several aging temperatures may be applied within the first aging temperature range, provided that t(eq) is achieved.

[0064] In one embodiment, the second aging temperature is at least 305°F. In another embodiment, the second aging temperature is at least 310°F. In yet another embodiment, the second aging temperature is at least 315°F. In another embodiment, the second aging temperature is at least 320°F. Multiple aging temperatures may be applied within the second aging temperature range, provided that t(eq) is achieved. After the second aging stage, the product can be cooled to room temperature.

[0065] When the third aging stage is used, it follows the second aging stage. In one approach, the third aging stage is similar to or the same as the first aging stage, for example, using an aging temperature of 200-300°F. Several aging temperatures within the third aging temperature range may be used, provided that t(eq) is achieved. In one embodiment, the third aging temperature is at least 10°F lower than the second aging temperature. In another embodiment, the third aging temperature is at least 20°F lower than the second aging temperature. In yet another embodiment, the third aging temperature is at least 30°F lower than the second aging temperature. In another embodiment, the third aging temperature is at least 40°F lower than the second aging temperature. In yet another embodiment, the third aging temperature is at least 50°F lower than the second aging temperature. In another embodiment, the third aging temperature is at least 60°F lower than the second aging temperature. In yet another embodiment, the third aging temperature is at least 70°F lower than the second aging temperature.

[0066] In one embodiment, the third aging temperature is no more than 280°F. In another embodiment, the third aging temperature is no more than 270°F. In yet another embodiment, the third aging temperature is no more than 260°F. In another embodiment, the third aging temperature is no more than 250°F. Several aging temperatures within the third aging temperature range may be used, provided that t(eq) is achieved.

[0067] Although various embodiments of the present invention have been described in detail, it will be appreciated that modifications and adaptations to such embodiments will be apparent to those skilled in the art. However, it should be clearly understood that such modifications and adaptations are within the spirit and scope of the present invention.

Claims (49)

1. 7xxx series wrought aluminum alloy product containing, by weight. %: 5.5-6.5 Zn; 1.3-1.7 Mg; 1.7-2.3 Cu; less than 0.15 Mn; up to 1.0 grain structure control materials, wherein said grain structure control materials contain at least one of Zr, Cr, Sc and Hf; And up to 0.15 Ti; the remainder consists of aluminum and inevitable impurities; wherein the 7xxx series wrought aluminum alloy product has a thickness of 2.5 to 12 inches; wherein the wrought aluminum alloy product passes the HHSCC-G49 test at 70°C for 100 days or at 90°C for 10 days. 2. The 7xxx series wrought aluminum alloy product according to claim 1, wherein the 7xxx series wrought aluminum alloy product contains no more than 0.12 wt. % Mn. 3. A 7xxx series wrought aluminum alloy product according to claim 2, containing from 0.05 to 0.15 wt. % Zr and not more than 0.04 wt. % Mn. 4. The 7xxx series wrought aluminum alloy product according to claim 1, wherein the 7xxx series wrought aluminum alloy product contains no more than 6.4 wt. %Zn. 5. The 7xxx series wrought aluminum alloy product according to claim 4, wherein the 7xxx series wrought aluminum alloy product contains at least 5.6 wt. %Zn. 6. The 7xxx series wrought aluminum alloy product according to claim 1, wherein the 7xxx series wrought aluminum alloy product contains no more than 2.25 wt. % Cu. 7. The 7xxx series wrought aluminum alloy product according to claim 6, wherein the 7xxx series wrought aluminum alloy product contains at least 1.75 wt. % Cu. 8. The 7xxx series wrought aluminum alloy product according to claim 1, wherein the 7xxx series wrought aluminum alloy product contains at least 1.35 wt. % Mg. 9. The 7xxx series wrought aluminum alloy product according to claim 8, wherein the 7xxx series wrought aluminum alloy product contains no more than 1.65 wt. % Mg. 10. The 7xxx series wrought aluminum alloy product according to claim 1, wherein the 7xxx series aluminum alloy product exhibits a typical crack deflection resistance LS (K _{max.-deviation} ) of at least 25 ksi√in. 11. An aerospace structural component made from any of the 7xxx series wrought aluminum alloy products of claim. 1-10. 12. A method for producing a product from a wrought aluminum alloy of the 7xxx series, including: (a) casting an alloy having a composition according to any one of claims. 1-9, in the form of an ingot or billet; (b) homogenizing said ingot or billet; (c) hot working the ingot or billet to produce an intermediate thickness product or a finite thickness product; (d) optionally cold processing the intermediate thickness product to produce a final thickness product; (e) solution heat treatment of the product to a final thickness followed by quenching; (f) optionally stretching or compressing the solution heat treated and hardened product by 1-5%; (g) artificial aging of the solution heat treated and quenched product. 13. The method of claim 12, wherein the homogenization temperature is at least T(homogeneous), wherein T(homogeneity) is calculated in degrees Fahrenheit using the formula 614.4+55.2⋅Cu+83.1⋅ Mg-1.8⋅Zn, where Cu, Mg and Zn represent the amounts in mass percent of copper, magnesium and zinc, respectively, in the 7xxx series wrought aluminum alloy. 14. The method of claim 12, wherein the artificial aging includes a first aging at a first aging temperature of 200-300°F followed by a second aging at a second aging temperature of 250-350°F, wherein the second aging temperature is at least 10 °F above the first aging temperature. 15. The method according to claim 12, in which the total equivalent artificial aging time is t(eq.), where t(eq.) is from 7 to 20 hours, and t(eq.) is calculated by the formula , where T is the instantaneous temperature in K during artificial aging, and where Tref is the reference temperature selected at 160°C (433.15 K). 16. The method according to claim 15, in which t(eq.) is no more than 19 hours. 17. Product in the form of rolled sheets of aluminum alloy of the 7xxx series, containing, by weight. %: 5.9-6.2 Zn; 1.4-1.7 Mg; 2.0-2.3 Cu; 0.05-0.15 Zr; up to 0.20 Cr; up to 0.15 Ti; And no more than 0.04 Mn; the remainder consists of aluminum and inevitable impurities; wherein the product in the form of rolled 7xxx series aluminum alloy sheets has a thickness of 3 to 12 inches; And while the 7xxx series aluminum alloy sheet product passes the HHSCC-G49 test at 90°C for 15 days; wherein the 7xxx series aluminum alloy sheet product exhibits at least two of the following: (a) a typical tensile yield strength in the (ST) direction of at least 57 ksi; (b) a typical plane strain fracture toughness K _IC (SL) of at least 20 ksi√in; And (c) a typical elongation in the (ST) direction of at least 5%.

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