Improved thick forged 7XXX aluminum alloys and methods of making same

Abstract

The invention discloses an improved thick forged 7xxx aluminum alloy product and a method for producing the same. The novel 7xxx aluminum alloy products can achieve an improved combination of properties, such as two or more of environmental fracture resistance, strength, elongation, and fracture toughness. The novel 7xxx aluminum alloy product may include 5.5 to 6.5 wt% of Zn, 1.3 to 1.7 wt% of Mg, and 1.7 to 2.3 wt% of Cu.

Description

[0001] Divisional case information

[0002] This application is a divisional application of the invention patent application with the application number 202080044888.2 and the invention title "Improved thick-forged 7XXX aluminum alloy and its manufacturing method", which was filed on June 23, 2020. Technical field

[0003] This patent application relates to improved thick-forged 7xxx aluminum alloy products and their production methods. Background art

[0004] Aluminum alloys can be used in a variety of applications. However, it is difficult to improve one property of an aluminum alloy without degrading another. For example, it is difficult to increase the strength of wrought aluminum alloys without affecting other properties such as fracture toughness or corrosion resistance. 7xxx (based on Al-Zn-Mg) is prone to corrosion. See, for example, Bonn, W. Grubl, "The stress-corrosion behaviour of high strength AIZnMg alloys", paper presented at the International Meeting of Associazione Italiana di Metallurgie, "Aluminum Alloys in Aircraft Industries", Turin, October 1976.

[0005] The patent owners have described some 7xxx aluminum alloy products in particular in US Patent Nos. 6,972,110 and 8,673,209 and International Patent Application Publication Nos. WO2016 / 183030 and WO2018 / 237196. Summary of the invention

[0006] Broadly speaking, this patent application relates to improved thick-forged 7xxx aluminum alloy products and their production methods. The novel thick-forged 7xxx aluminum alloy products ("novel 7xxx aluminum alloy products") can achieve an improved combination of environmentally assisted cracking (EAC) resistance and at least one of properties such as strength, elongation, and fracture toughness.

[0007] The novel 7xxx aluminum alloy product typically comprises (and in some cases consists of or consists essentially of) 5.5 - 6.5 wt% Zn, 1.7 - 2.3 wt% Cu, and 1.3 - 1.7 wt% Mg. The novel wrought 7xxx aluminum alloy product typically has a thickness of at least 2.5 inches and can be as thick as 12 inches, and achieves resistance to environmentally assisted cracking in the short transverse (ST) direction, which is important for aerospace and other applications, especially those with structural loads in the short transverse (ST) direction. Such thick wrought 7xxx aluminum alloy products typically also achieve good strength, elongation, fracture toughness, and / or crack-deviation resistance properties. Thus, the novel wrought 7xxx aluminum alloy product can achieve an improved combination of environmentally assisted cracking resistance and at least one of strength, elongation, fracture toughness, and crack-deviation resistance. In addition to zinc, magnesium, and copper, the novel 7xxx aluminum alloy product can also include conventional grain structure control materials, grain refiners, and impurities. For example, the novel 7xxx aluminum alloy product can include one or more of Zr, Cr, Sc, and Hf as grain structure control materials (e.g., each of Zr, Cr, Sc, and Hf is 0.05 - 0.25 wt%), which limits the total amount of these elements so that no large primary particles form in the alloy. As another example, the novel 7xxx aluminum alloy product can include less than 0.15 wt% Mn. As yet another example, the novel 7xxx aluminum alloy product can include up to 0.15 wt% Ti as a grain refiner, optionally some of the titanium in the form of TiB2 and / or TiC. The novel 7xxx aluminum alloy product can include up to 0.20 wt% Fe and up to 0.15 wt% Si as impurities. Less amounts of iron and silicon can be used. The balance of the novel 7xxx aluminum alloy product is typically aluminum and other unavoidable impurities (other than iron and silicon).

[0008] As described above, the novel 7xxx aluminum alloy product typically comprises a customized amount of zinc, magnesium, and copper, thus facilitating the achievement of a combination of EAC resistance and good strength and / or fracture toughness properties, etc. In this regard, the novel 7xxx aluminum alloy product typically comprises 5.5 to 6.5 wt% Zn. In one embodiment, the novel alloy comprises no more than 6.4 wt% Zn. In another embodiment, the novel alloy comprises no more than 6.3 wt% Zn. In yet another embodiment, the novel alloy comprises no more than 6.2 wt% Zn. In one embodiment, the novel alloy comprises at least 5.6 wt% Zn. In another embodiment, the novel alloy comprises at least 5.7 wt% Zn. In yet another embodiment, the novel alloy comprises at least 5.8 wt% Zn. In another embodiment, the novel alloy comprises at least 5.9 wt% Zn.

[0009] As described above, the novel 7xxx aluminum alloy products typically contain 1.7 to 2.3 wt% Cu. In one embodiment, the novel alloy contains no more than 2.25 wt% Cu. In another embodiment, the novel alloy contains no more than 2.20 wt% Cu. In one embodiment, the novel alloy contains at least 1.75 wt% Cu. In another embodiment, the novel alloy contains at least 1.80 wt% Cu. In yet another embodiment, the novel alloy contains at least 1.85 wt% Cu. In another embodiment, the novel alloy contains at least 1.90 wt% Cu. In yet another embodiment, the novel alloy contains at least 1.95 wt% Cu. In another embodiment, the novel alloy contains at least 2.00 wt% Cu.

[0010] As described above, the novel 7xxx aluminum alloy products typically contain 1.3 to 1.7 wt% Mg. In one embodiment, the novel alloy contains at least 1.35 wt% Mg. In another embodiment, the novel alloy contains at least 1.40 wt% Mg. In one embodiment, the novel alloy contains no more than 1.65 wt% Mg. In another embodiment, the novel alloy contains no more than 1.60 wt% Mg. In yet another embodiment, the novel alloy contains no more than 1.55 wt% Mg. In another embodiment, the novel alloy contains no more than 1.50 wt% Mg. In another embodiment, the novel alloy contains no more than 1.45 wt% Mg.

[0011] In one embodiment, the amounts of zinc, magnesium, and copper in the 7xxx aluminum alloy product satisfy the following relationship: 2.569 ≤ Mg + 0.500*Cu + 0.067*Zn ≤ 3.269. In another embodiment, the amounts of zinc, magnesium, and copper in the 7xxx aluminum alloy product satisfy the following relationship: 2.709 ≤ Mg + 0.500*Cu + 0.067*Zn ≤ 3.119. In yet another embodiment, the amounts of zinc, magnesium, and copper in the 7xxx aluminum alloy product satisfy the following relationship: 2.869 ≤ Mg + 0.500*Cu + 0.067*Zn ≤ 3.269. In another embodiment, the amounts of zinc, magnesium, and copper in the 7xxx aluminum alloy product satisfy the following 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 empirical relationships shown above.

[0012] In one method, the amounts of zinc and magnesium in the 7xxx aluminum alloy product are such that the weight ratio of zinc to magnesium does not exceed 4.75:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.75:1). In one embodiment, the weight ratio of zinc to magnesium does not exceed 4.60:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.60:1). In another embodiment, the weight ratio of zinc to magnesium does not exceed 4.50:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.50:1). In yet another embodiment, the weight ratio of zinc to magnesium does not exceed 4.40:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.40:1). In another embodiment, the weight ratio of zinc to magnesium does not exceed 4.35:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.35:1). In yet another embodiment, the weight ratio of zinc to magnesium does not exceed 4.30:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.30:1). In another embodiment, the weight ratio of zinc to magnesium does not exceed 4.25:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.25:1). In yet another embodiment, the weight ratio of zinc to magnesium does not exceed 4.20:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.20:1). In another embodiment, the weight ratio of zinc to magnesium does not exceed 4.15:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.15:1). In yet another embodiment, the weight ratio of zinc to magnesium does not exceed 4.10:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.10:1). In another embodiment, the weight ratio of zinc to magnesium does not exceed 4.00:1 (i.e., (wt% Zn / wt% Mg) ≤ 4.00:1). In yet another embodiment, the weight ratio of zinc to magnesium does not exceed 3.95:1 (i.e., (wt% Zn / wt% Mg) ≤ 3.95:1). In another embodiment, the weight ratio of zinc to magnesium does not exceed 3.90:1 (i.e., (wt% Zn / wt% Mg) ≤ 3.90:1).

[0013] In one method, the amounts of zinc and magnesium in the 7xxx 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 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 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 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 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).

[0014] As described above, the novel 7xxx aluminum alloy product may include one or more of Zr, Cr, Sc, and Hf as grain structure control materials (e.g., each of one or more of Zr, Cr, Sc, and Hf accounts for 0.05 - 0.25 wt%), which limits the total amount of these elements so that large primary particles do not form in the alloy. The grain structure control materials can, for example, promote an appropriate grain structure (e.g., a non-recrystallized grain structure). When employed, the novel 7xxx aluminum alloy product generally includes at least 0.05 wt% of the grain structure control materials. In one embodiment, the novel 7xxx aluminum alloy product includes at least 0.07 wt% of the grain structure control materials. In another embodiment, the novel 7xxx aluminum alloy product includes at least 0.09 wt% of the grain structure control materials. When employed, the novel 7xxx aluminum alloy product generally includes no more than 1.0 wt% of the grain structure control materials. In one embodiment, the novel 7xxx aluminum alloy product includes no more than 0.75 wt% of the grain structure control materials. In yet another embodiment, the novel 7xxx aluminum alloy product includes no more than 0.50 wt% of the grain structure control materials. 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.

[0015] In one embodiment, the grain structure control material contains both Zr and Cr, and the novel 7xxx aluminum alloy product contains at least 0.07 wt% of Zr and at least 0.07 wt% of Cr, where wt% Zr plus wt% Cr does not exceed 0.40 wt% (i.e., wt% Zr + wt% Cr ≤ 0.40 wt%). In another embodiment, the grain structure control material contains both Zr and Cr, and the novel 7xxx aluminum alloy product contains at least 0.07 wt% of Zr and at least 0.07 wt% of Cr, where wt% Zr plus wt% Cr does not exceed 0.35 wt% (i.e., wt% Zr + wt% Cr ≤ 0.35 wt%). In another embodiment, the grain structure control material contains both Zr and Cr, and the novel 7xxx aluminum alloy product contains at least 0.07 wt% of Zr and at least 0.07 wt% of Cr, where wt% Zr plus wt% Cr does not exceed 0.30 wt% (i.e., wt% Zr + wt% Cr ≤ 0.30 wt%). In another embodiment, the grain structure control material contains both Zr and Cr, and the novel 7xxx aluminum alloy product contains at least 0.07 wt% of Zr and at least 0.07 wt% of Cr, where wt% Zr plus wt% Cr does not exceed 0.25 wt% (i.e., wt% Zr + wt% Cr ≤ 0.25 wt%). In another embodiment, the grain structure control material contains both Zr and Cr, and the novel 7xxx aluminum alloy product contains at least 0.07 wt% of Zr and at least 0.07 wt% of Cr, where wt% Zr plus wt% Cr does not exceed 0.20 wt% (i.e., wt% Zr + wt% Cr ≤ 0.20 wt%). In any of these embodiments, the novel 7xxx aluminum alloy product may contain at least 0.09 wt% of at least one of Zr and Cr. In any of these embodiments, the novel 7xxx aluminum alloy product may contain at least 0.09 wt% of both Zr and Cr.

[0016] In one embodiment, the grain structure control material is Zr, and the novel 7xxx aluminum alloy product contains 0.07 to 0.18 wt% of Zr. In another embodiment, the grain structure control material is Zr, and the novel 7xxx aluminum alloy product contains 0.07 to 0.16 wt% of Zr. In yet another embodiment, the grain structure control material is Zr, and the novel 7xxx aluminum alloy product contains 0.08 to 0.15 wt% of Zr. In another embodiment, the grain structure control material is Zr, and the novel 7xxx aluminum alloy product contains 0.09 to 0.14 wt% of Zr. In embodiments where the grain structure control material is Zr, the novel 7xxx aluminum alloy product typically contains small amounts of Cr, Sc, and Hf (e.g., ≤ 0.04 wt% of each of Cr, Sc, and Hf). In one embodiment, the novel 7xxx aluminum alloy product contains no more than 0.03 wt% of each of Cr, Sc, and Hf. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.02 wt% of each of Cr, Sc, and Hf. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.01 wt% of each of Cr, Sc, and Hf. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.005 wt% of each of Cr, Sc, and Hf.

[0017] In one embodiment, the grain structure control material is Cr, and the novel 7xxx aluminum alloy product contains 0.07 to 0.25 wt% of Cr. In another embodiment, the grain structure control material is Cr, and the novel 7xxx aluminum alloy product contains 0.07 to 0.20 wt% of Cr. In yet another embodiment, the grain structure control material is Cr, and the novel 7xxx aluminum alloy product contains 0.08 to 0.15 wt% of Cr. In another embodiment, the grain structure control material is Cr, and the novel 7xxx aluminum alloy product contains 0.10 to 0.15 wt% of Cr. In other embodiments, the novel 7xxx aluminum alloy contains a small amount of Cr (e.g., ≤ 0.04 wt% of Cr). In one embodiment, the novel 7xxx aluminum alloy product contains no more than 0.03 wt% of Cr. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.02 wt% of Cr. In yet another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.01 wt% of Cr. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.005 wt% of Cr.

[0018] In some embodiments, the novel 7xxx aluminum alloy contains a small amount of zirconium (e.g., ≤ 0.04 wt% Zr). In one embodiment, the novel 7xxx aluminum alloy product contains no more than 0.03 wt% Zr. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.02 wt% Zr. In yet another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.01 wt% Zr. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.005 wt% Zr.

[0019] As noted above, the novel 7xxx aluminum alloy product typically contains less than 0.15 wt% Mn. In one embodiment, the novel 7xxx aluminum alloy product contains no more than 0.12 wt% Mn. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.10 wt% Mn. In yet another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.08 wt% Mn. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.05 wt% Mn. In yet another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.04 wt% Mn. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.03 wt% Mn. In yet another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.02 wt% Mn. In another embodiment, the novel 7xxx aluminum alloy product contains no more than 0.01 wt% Mn.

[0020] As noted above, the novel 7xxx aluminum alloy product may contain, for example, up to 0.15 wt% Ti. Titanium can be used to promote grain refinement during casting, such as by using TiB2 or TiC. Elemental titanium can be used additionally or alternatively. In one embodiment, the novel 7xxx aluminum alloy product contains 0.005 to 0.025 wt% Ti.

[0021] As noted above, the novel 7xxx aluminum alloy product can contain, for example, up to 0.15 wt% Si and up to 0.20 wt% Fe as impurities. The amounts of Si and Fe can be limited to avoid detrimentally affecting the combination of strength, fracture toughness, and crack growth resistance. In one embodiment, the novel 7xxx aluminum alloy product can contain up to 0.12 wt% Si and up to 0.15 wt% Fe as impurities. In another embodiment, the novel 7xxx aluminum alloy product can contain up to 0.10 wt% Si and up to 0.12 wt% Fe as impurities. In another embodiment, the novel 7xxx aluminum alloy product can contain up to 0.08 wt% Si and up to 0.10 wt% Fe as impurities. In yet another embodiment, the novel 7xxx aluminum alloy product can contain up to 0.06 wt% Si and up to 0.08 wt% Fe as impurities. In yet another embodiment, the novel 7xxx aluminum alloy product can contain up to 0.04 wt% Si and up to 0.06 wt% Fe as impurities. In another embodiment, the novel 7xxx aluminum alloy product can contain up to 0.03 wt% Si and up to 0.05 wt% Fe as impurities.

[0022] As described above, the novel 7xxx aluminum alloy product has a thickness of 2.5 to 12.0 inches. The thickness refers to the cross-sectional thickness of the product at its thickest point. In one embodiment, the novel 7xxx aluminum alloy product has a thickness of at least 3.0 inches. In another embodiment, the novel 7xxx aluminum alloy product has a thickness of at least 3.5 inches. In yet another embodiment, the novel 7xxx aluminum alloy product has a thickness of at least 4.0 inches. In another embodiment, the novel 7xxx aluminum alloy product has a thickness of at least 4.5 inches. In yet another embodiment, the novel 7xxx aluminum alloy product has a thickness of at least 5.0 inches. In one embodiment, the novel 7xxx aluminum alloy product has a thickness of no more than 10.0 inches. In another embodiment, the novel 7xxx aluminum alloy product has a thickness of no more than 9.0 inches. In yet another embodiment, the novel 7xxx aluminum alloy product has a thickness of no more than 8.0 inches.

[0023] In one embodiment, the novel 7xxx aluminum alloy product is a rolled product (e.g., a sheet product). In another embodiment, the novel 7xxx aluminum alloy product is an extruded product. In yet another embodiment, the novel 7xxx aluminum alloy product is a forged product (e.g., a hand-forged product, a die-forged product).

[0024] As described above, the novel 7xxx aluminum alloy products can achieve an improved combination of properties. In one embodiment, in accordance with ASTM E8 and B557, the novel 7xxx aluminum alloy products achieve a typical tensile yield strength (L) of at least 63 ksi. In another embodiment, the novel 7xxx aluminum alloy products achieve a typical tensile yield strength (L) of at least 64 ksi. In yet another embodiment, the novel 7xxx aluminum alloy products achieve a typical tensile yield strength (L) of at least 65 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (L) of at least 66 ksi. In yet another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (L) of at least 67 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (L) of at least 68 ksi. In yet another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (L) of at least 69 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (L) of at least 70 ksi. In yet another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (L) of at least 71 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (L) of at least 72 ksi. In yet another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (L) of at least 73 ksi.

[0025] In one embodiment, in accordance with ASTM E8 and B557, the novel 7xxx aluminum alloy products achieve a typical tensile yield strength (ST) of at least 57 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 58 ksi. In yet another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 59 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 60 ksi. In yet another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 61 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 62 ksi. In yet another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 63 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 64 ksi. In yet another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 65 ksi. In another embodiment, the 7xxx aluminum alloy products can achieve a typical tensile yield strength (ST) of at least 66 ksi.

[0026] In one embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 25 ksi-sqrt-inch according to ASTM E8 and E399-12. IC In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 27 ksi-sqrt-inch. IC In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 28 ksi-sqrt-inch. IC In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 29 ksi-sqrt-inch. IC In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 30 ksi-sqrt-inch. IC In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 31 ksi-sqrt-inch. IC In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 32 ksi-sqrt-inch. IC In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 33 ksi-sqrt-inch. IC In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 34 ksi-sqrt-inch. IC In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 35 ksi-sqrt-inch. IC In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 36 ksi-sqrt-inch. IC In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 37 ksi-sqrt-inch. IC In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K-plane strain fracture toughness (L-T) of at least 38 ksi-sqrt-inch. ICPlane strain fracture toughness (L-T). In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 39 ksi-sqrt-inch IC Plane strain fracture toughness (L-T). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 40 ksi-sqrt-inch IC Plane strain fracture toughness (L-T). In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 41 ksi-sqrt-inch IC Plane strain fracture toughness (L-T). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 42 ksi-sqrt-inch IC Plane strain fracture toughness (L-T). In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 43 ksi-sqrt-inch IC Plane strain fracture toughness (L-T). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 44 ksi-sqrt-inch IC Plane strain fracture toughness (L-T). In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 45 ksi-sqrt-inch IC Plane strain fracture toughness (L-T).

[0027] In one embodiment, according to ASTM E8 and E399-12, the novel 7xxx aluminum alloy product achieves a typical K of at least 20 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 22 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 24 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 26 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 28 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 30 ksi-sqrt-inch ICPlane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 32 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 34 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 36 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 38 ksi-sqrt-inch IC Plane strain fracture toughness (S-L). In another embodiment, the novel 7xxx aluminum alloy product achieves a typical K of at least 40 ksi-sqrt-inch IC Plane strain fracture toughness (S-L).

[0028] In one embodiment, in accordance with ASTM E8 and B557, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 6%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 7%. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 8%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 9%. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 10%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 11%. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 12%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 13%. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 14%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 15%. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (L) of at least 16%.

[0029] In one embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (ST) of at least 3%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (ST) of at least 4%. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (ST) of at least 5%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (ST) of at least 6%. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (ST) of at least 7%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (ST) of at least 8%. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (ST) of at least 9%. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical elongation (ST) of at least 10%.

[0030] In one embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev ) of at least 25 ksi-sqrt-in. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev ) of at least 27 ksi-sqrt-in. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev ) of at least 29 ksi-sqrt-in. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev ) of at least 31 ksi-sqrt-in. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev ) of at least 33 ksi-sqrt-in. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev ) of at least 35 ksi-sqrt-in. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev ) of at least 37 ksi-sqrt-in. In another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev ) of at least 39 ksi-sqrt-in. In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K max-dev)。In another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K) of at least 43 ksi-sqrt-in. max-dev )。In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K) of at least 45 ksi-sqrt-in. max-dev )。In another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K) of at least 47 ksi-sqrt-in. max-dev )。In yet another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K) of at least 49 ksi-sqrt-in. max-dev )。In another embodiment, the novel 7xxx aluminum alloy product achieves a typical L-S crack opening resistance (K) of at least 50 ksi-sqrt-in. max-dev )。

[0031] As described above, the novel 7xxx aluminum alloy can be EAC resistant, and this EAC resistance can be determined by a thermohydrogen SCC test. In one embodiment, the novel 7xxx aluminum alloy product has a thickness of at least 63.5 mm and is subjected to a thermohydrogen SCC (stress corrosion cracking) test using standard stress-corrosion tension specimens ("HHSCC-G49") that comply with ASTM G49 as defined below. To fabricate the HHSCC-G49 specimens, at least three short transverse (ST) samples are taken from the mid-thickness of the final product and between W / 4 and 3W / 4 of the final product. The extracted samples are then machined into tensile samples having a diameter as defined in ASTM G47-20 and dimensions proportional to a standard sample as defined in ASTM E8 / 8M-16ae1. If the final product thickness is at least 2.25 inches (57.15 mm), the length of the tensile specimen is 2.00 inches (50.8 mm), as Figure 2As shown. If the final product thickness is from 1.50 inches (38.1 mm) to less than 2.25 inches (<50.8 mm), the length of the specimen must be at least 1.25 inches (31.75 mm) and should be as close as possible to 2.00 inches (50.8 mm). Prior to testing, the stretchable specimen is cleaned / degreased by washing in acetone. The stretchable specimen is then tensioned in the short transverse direction at T / 2 to 85% of its ST tensile yield strength. Prior to the HHSCC-G49 test, the ST tensile yield strength of the alloy is measured at room temperature and in accordance with ASTM E8 and B557. In accordance with Section 7.2.2 of ASTM G49, the stress frame used is of the constant strain type (see, for example, Figure 4a of ASTM G49). The tensioned specimen is then placed in a controlled chamber with a relative air humidity of 85% (no additives such as chlorides are added to the air) and a temperature of 70 °C or 90 °C. At least three specimens must be tested. For the purposes of this patent application, the alloy passes the HHSCC-G49 test at 70 °C when all specimens remain intact for at least 100 days. For the purposes of this patent application, the alloy passes the HHSCC-G49 test at 90 °C when all specimens remain intact for at least 10 days. If a specimen breaks in half along the gauge length or at one of the specimen shoulders adjacent to the gauge length, it is a failure. Shoulder failure is statistically equivalent to gauge failure. When determining whether the alloy passes the HHSCC-G49, thread failure is included only when the thread failure is statistically equivalent to gauge failure. If a crack appears at the threaded end of the specimen rather than in the gauge length, it is a thread failure. In some cases, thread failure may not be detected until the specimen is removed from the stress frame.

[0032] In a method, the HHSCC-G49 test is carried out at 70 °C and the new 7xxx aluminum alloy passes the 120-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 120-day HHSCC-G49 test defined above. In one embodiment, the new 7xxx aluminum alloy passes the 140-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 140-day HHSCC-G49 test defined above. In yet another embodiment, the new 7xxx aluminum alloy passes the 150-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 150-day HHSCC-G49 test defined above. In another embodiment, the new 7xxx aluminum alloy passes the 160-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 160-day HHSCC-G49 test defined above. In yet another embodiment, the new 7xxx aluminum alloy passes the 180-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 180-day HHSCC-G49 test defined above. In another embodiment, the new 7xxx aluminum alloy passes the 200-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 200-day HHSCC-G49 test defined above. In yet another embodiment, the new 7xxx aluminum alloy passes the 220-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 220-day HHSCC-G49 test defined above. In another embodiment, the new 7xxx aluminum alloy passes the 240-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 240-day HHSCC-G49 test defined above. In yet another embodiment, the new 7xxx aluminum alloy passes the 260-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 260-day HHSCC-G49 test defined above. In another embodiment, the new 7xxx aluminum alloy passes the 280-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 280-day HHSCC-G49 test defined above. In yet another embodiment, the new 7xxx aluminum alloy passes the 300-day HHSCC-G49 test at 70 °C, where all samples remain intact in the 300-day HHSCC-G49 test defined above. The above stress corrosion cracking resistance properties can be achieved in products with a thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least 140 mm, or higher.

[0033] In another embodiment, the HHSCC-G49 test is conducted at 90 °C and the novel 7xxx aluminum alloy passes the 15-day HHSCC-G49 test at 90 °C, where all samples remain intact during the 15-day HHSCC-G49 test as defined above. In one embodiment, the novel 7xxx aluminum alloy passes the 20-day HHSCC-G49 test at 90 °C, where all samples remain intact during the 20-day HHSCC-G49 test as defined above. In another embodiment, the novel 7xxx aluminum alloy passes the 25-day HHSCC-G49 test at 90 °C, where all samples remain intact during the 25-day HHSCC-G49 test as defined above. The above stress corrosion cracking resistance properties can be achieved in products with a thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least 140 mm, or higher.

[0034] In one embodiment, the novel 7xxx aluminum alloy product has a thickness of at least 63.5 mm and passes a stress corrosion cracking test ("SCC alternate immersion test") conducted in accordance with ASTM G47 under alternate immersion exposure conditions in accordance with ASTM G44 using standard stress-corrosion tension specimens conforming to ASTM G49. For the purposes of this patent application, the novel 7xxx aluminum alloy passes the SCC alternate immersion test when all samples remain intact during a 20-day SCC alternate immersion test conducted at a net stress of 172 MPa in the ST direction, where the test environment is 3.5% NaCl and at least five (5) samples are required to be tested. In one embodiment, the novel 7xxx aluminum alloy passes the 30-day SCC alternate immersion test as defined above. In another embodiment, the novel 7xxx aluminum alloy passes the 20-day SCC alternate immersion test as defined above but at a net stress of 241 MPa. In yet another embodiment, the novel 7xxx aluminum alloy passes the 30-day SCC alternate immersion test as defined above but at a net stress of 241 MPa. The above stress corrosion cracking resistance properties can be achieved in products with a thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least 140 mm, or higher.

[0035] In one embodiment, the novel 7xxx aluminum alloy product has a thickness of at least 63.5 mm and passes a damp heat SCC (stress corrosion cracking) test ("HHSCC-G168") conducted in accordance with ASTM G168 as defined below. For the purposes of this patent application, when (a) the stress intensity factor gives a value not exceeding 10 -7A crack growth rate of mm / s, and (b) when the achieved K value is at least 13 MPa-sqrt-m (MPa√m), the new 7xxx aluminum alloy passes the HHSCC-G168 test. The HHSCC-G168 test is carried out at 70 °C and 85% relative humidity at T / 2 using S-L specimens. In one embodiment, the K value achieved at a crack growth rate not exceeding 10 -7 mm / s is at least 14 MPa-sqrt-m. In another embodiment, the K value achieved at a crack growth rate not exceeding 10 -7 mm / s is at least 15 MPa-sqrt-m. In yet another embodiment, the K value achieved at a crack growth rate not exceeding 10 -7 mm / s is at least 16 MPa-sqrt-m. In another embodiment, the K value achieved at a crack growth rate not exceeding 10 -7 mm / s is at least 17 MPa-sqrt-m. In yet another embodiment, the K value achieved at a crack growth rate not exceeding 10 -7 mm / s is at least 18 MPa-sqrt-m or higher. The above stress corrosion cracking resistance properties can be achieved in products with a thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least 140 mm, or higher.

[0036] In one embodiment, the new 7xxx aluminum alloy passes at least two of the SCC tests defined above (i.e., at least two of the following: (a) the HHSCC-G49 test as defined above, (b) the SCC alternative immersion test as defined above, and (c) the HHSCC-G168 test as defined above). In another embodiment, the new 7xxx aluminum alloy passes all of the SCC tests defined above.

[0037] Although the above L and ST properties generally relate to thick plate products, similar properties can also be achieved in thick forged products and thick extruded products. In addition, many of the above properties can also be achieved in combination, as shown in the examples below.

[0038] As described above, the novel thick 7xxx aluminum alloy products can be applied to components in various aerospace applications. In one embodiment, the alloy product is an aerospace structural component. The aircraft structural component can be any of the following: upper wing panel (skin), upper wing spar, upper wing cover with an integral spar, spar, spar cover, spar web, rib, rib bracket or rib web, reinforcement element, frame, landing gear assembly (e.g., cylinder, beam), load-bearing tie rod, bulkhead, flap track assembly, fuselage and windshield frame, wheel rib, side brace, fitting, fuselage component (e.g., fuselage skin) and space component (e.g., for rockets and other carriers that can leave the earth). In one embodiment, the alloy product is an armor component (e.g., an armor component of a motor vehicle). In one embodiment, the alloy product is used in the oil and gas industry (e.g., as pipes, structural components). In one embodiment, the alloy product is a thick casting block / casting plate product (e.g., for injection molding). In one embodiment, the alloy product is an automotive product.

[0039] The novel thick 7xxx aluminum alloy products can be made into forged products by casting an aluminum alloy having any of the foregoing compositions into an ingot or billet, and then subjecting the ingot or billet to homogenization treatment. The homogenized ingot or billet can be processed by rolling, extrusion or forging into a final specification, typically by hot working, optionally with some cold working. The final specification product can be solution heat treated, then quenched, then stress relieved (e.g., by tension or compression) and then artificially aged.

[0040] In addition to traditional forged products, the novel 7xxx aluminum alloy can also be made into shaped castings or additive manufacturing products by additive manufacturing. The additive manufacturing products can be used as they are, or can be subsequently processed, for example, by mechanical, thermal or thermo-mechanical processing methods.

[0041] Definition

[0042] As used herein, the "typical longitudinal (L) tensile yield strength" or TYS(L) is determined in accordance with ASTM B557-10 and by measuring the tensile yield strength (TYS) in the longitudinal direction (L) at the T / 4 position from materials of at least three different batches, with at least two parallel specimens tested for each batch, resulting in a total of at least 6 different measured specimen values, and the typical TYS(L) is the average of at least 6 different measured specimen values. The typical elongation (L) is measured during the longitudinal tensile test.

[0043] As used herein, "Typical Transverse (ST) Tensile Yield Strength" or TYS(ST) is determined in accordance with ASTM B557-10 by measuring the tensile yield strength (TYS) in the short transverse direction (ST) from materials of at least three different lots, testing at least two parallel specimens per lot, resulting in a total of at least 6 different measured specimen values, and the typical TYS(ST) is the average of at least 6 different measured specimen values. Collect short transverse tensile specimens such that the midpoint of the gage section coincides with the mid-thickness plane of the sheet. Measure the typical elongation (ST) during short transverse tensile testing.

[0044] As used herein, "Typical Plane Strain Fracture Toughness (K IC )(L-T)" is determined in accordance with ASTM E399-12 by measuring the plane strain fracture toughness in the L-T direction at the T / 4 location from materials of at least three different lots using C(T) specimens, where "W" is 4.0 inches, and where for products with a thickness of at least 2.0 inches, "B" is 2.0 inches, and where for products with a thickness less than 2.0 inches, "B" is 1.5 inches, testing at least one specimen in duplicate per lot, resulting in a total of at least 6 different measured specimen values, and the typical plane strain fracture toughness (K IC )(L-T) is the average of at least 6 different valid K IC measured specimen values.

[0045] As used herein, "Typical Plane Strain Fracture Toughness (K IC )(S-L)" is determined in accordance with ASTM E399-12 by measuring the plane strain fracture toughness in the S-L direction at the T / 2 location from materials of at least three different lots using C(T) specimens, where "W" and "B" are as per the following table, testing at least two parallel specimens per lot, resulting in a total of at least 6 different measured specimen values, and the typical plane strain fracture toughness (K IC )(S-L) is the average of at least 6 different valid K IC measured specimen values.

[0046] S-L specimen parameters

[0047] Product thickness "W” "B” ≥5.0 inches 4.0 inches 2.0 inches <5.0 inches to ≥3.8 inches 3.0 inches 1.5 inches <3.8 inches to ≥ 3.2 inches 2.5 inches 1.25 inches <3.2 inches to ≥ 2.6 inches 2.0 inches 1.0 inches <2.6 inches to ≥ 2.0 inches 1.5 inches 0.75 inches <2.0 inches to ≥ 1.5 inches 1.0 inches 0.5 inches

[0048] The typical L-S crack opening resistance property (K max-dev ) is determined in accordance with the procedure described in paragraph 0058 of commonly owned U.S. Patent Application Publication No. 2017 / 0088920, which is incorporated herein by reference. Except the following points:(a) The "W" dimension of the sample shall be 2.0 inches (5.08 cm), (b) the sample shall be centered at T / 2 (opposite the notch tip), and (c) the specimen can be tested in laboratory air rather than in high humidity air.

[0049] The term "square root" may be abbreviated as "sqrt" herein.

[0050] Throughout the specification and claims, unless the context clearly dictates otherwise, the following terms take the meanings explicitly associated herein. As used herein, the phrases "in one embodiment" and "in some embodiments" do not necessarily refer to the same embodiment (although they may). Additionally, as used herein, the phrases "in another embodiment" and "in some other embodiments" do not necessarily refer to different embodiments (although they may). Thus, as described below, the various embodiments of the present invention can be readily combined without departing from the scope or spirit of the invention.

[0051] Furthermore, unless the context clearly dictates otherwise, as used herein, the term "or" is an inclusive "or" operator and is equivalent to the term "and / or". Unless the context clearly dictates otherwise, the term "based on" is not exclusive and allows for additional factors not described. Additionally, throughout this specification, unless the context clearly dictates otherwise, the meanings of "a", "an", and "the" include plural referents. Unless the context clearly dictates otherwise, the meaning of "in" includes "in" and "on". BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a graph showing the strength (ST-TYS) of the alloy of Example 1 relative to K IC fracture toughness property (S-L K IC ).

[0053] Figure 2 is a graph showing the EAC resistance of the alloy of Example 1 at 90 °C / 85% RH / 85% ST-TYS. DETAILED DESCRIPTION

[0054] Example 1

[0055] Two aluminum alloys were cast into 6 x 18-inch (D x W) ingots, and their compositions are provided in Table 1 below.

[0056] Table 1 - Compositions of the alloys of Example 1 (wt%)

[0057] 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

[0058] Then, ingots for homogenization are conventionally prepared (e.g., by sawing and scraping). Then, according to Japanese Patent No. H03-41540 (1991) (also published as JP01-290737 (1989)), the first ingot is processed to its final temper, Example 1, Alloy 4. The second ingot is processed according to the inventive method disclosed herein.

[0059] Specifically, Alloy 1 is homogenized at 842°F (450°C) according to JPH03-41540. Then the alloy is hot rolled to a final gauge of 1.75 inches (44.45 mm). Then, according to JPH03-41540, Alloy 1 is solution heat treated at 842°F (450°C) for 1 hour, then quenched in 190°F water (87.8°C), and then stretched 1.5%. After stretching, Alloy 1 is artificially aged according to JPH034-41540 by first aging at 248°F (120°C) for 24 hours, heating to 302°F, and then aging at 302°F (150°C) for 24 hours.

[0060] Alloy 2 is homogenized at 895°F (479°C), then hot rolled to a final gauge of 1.75 inches (44.45 mm). Then Alloy 2 is solution heat treated at 895°F (479°C) for 2 hours, quenched in 190°F water (87.8°C), and then stretched 2.25%. After stretching, some of Alloy 2 is subjected to two different artificial aging practices:

[0061] · Practice 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, then reheat to 250°C (121°C) and hold for 24 hours.

[0062] · Practice 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, then reheat to 250°C (121°C) and hold for 24 hours.

[0063] The 190°F quench temperature simulates the quench rate in the middle of a thick ingot cast (e.g., an eight-inch (203.2 mm) thick ingot).

[0064] Alloy 1-2 was examined metallographically and found to be non-recrystallized, i.e., containing no more than 45% recrystallized grains as determined using standard metallographic analysis procedures. In one embodiment, the novel forged 7xxx aluminum alloy product contains no more than 35% recrystallized grains. In another embodiment, the novel forged 7xxx aluminum alloy product contains no more than 25% recrystallized grains. In another embodiment, the novel forged 7xxx aluminum alloy product contains no more than 15% recrystallized grains. In another embodiment, the novel forged 7xxx aluminum alloy product contains no more than 5% recrystallized grains.

[0065] The alloy was then mechanically tested and the results are shown in Table 2 below. Test results for a similarly produced conventional 7050 alloy are also provided, which results are from co-owned International Patent Application Publication No. WO2020 / 102441. The measurements were made relative to the T / 2 position of all alloys. The fracture toughness was relative to the S-L direction.

[0066] Table 2 - Mechanical properties of the alloy of Example 1*

[0067]

[0068] *AP1 = Aging Practice 1; AP2 = Aging Practice 2; sqrt = square root

[0069] The alloy was also tested for EAC (environmentally assisted cracking) resistance in accordance with the HHSCC-G49 procedure provided above. A mill-produced 7050-T7651 (3.9 inches thick) with a strength level similar to that of Alloy 1-2 was also tested. The HHSCC-G49 results are provided in Table 3 below.

[0070] Table 3 - HHSCC-G49 test results

[0071]

[0072] As shown above and Figure 1 to Figure 2 as shown in, Alloy 2 achieves an improved combination of properties compared to Alloy 1. As Figure 1 shown in, Alloy 2 achieves a higher combination of strength and toughness than Alloy 1 and the conventional 7050 alloy. As Figure 2 shown in, Alloy 2 also achieves a much higher combination of strength and EAC resistance than Alloy 1. In addition, as shown in Table 2, the ST ductility of Alloy 2 is significantly higher than that of Alloy 1.

[0073] Complete the homogenization temperature analysis of this alloy system. It is determined that for these specific alloys with 5.5 - 6.5 wt% Zn, 1.3 - 1.7 wt% Mg, and 1.7 - 2.3 wt% Cu, the homogenization temperature should be at least as high as T(homog.), where T(homog.) is calculated in degrees Fahrenheit according to the following formula:

[0074] ·T(homog.) = 614.4 + 55.2*Cu + 83.1*Mg - 1.8*Zn

[0075] For the above formula, Cu, Mg, and Zn are the weight percentages of copper, magnesium, and zinc, respectively, in the forged 7xxx aluminum alloy. The following table shows the calculations for Alloys 1 and 2.

[0076] Table 4 - T(homog.) for Alloys 1 - 2

[0077]

[0078] 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.

[0079] Preferably, the homogenization temperature is higher than T(homog.). In one embodiment, the homogenization temperature is at least 5°F higher than T(homog.), i.e., ≥ 5°F + T(homog.). In another embodiment, the homogenization temperature is at least 10°F higher than T(homog.), i.e., ≥ 10°F + T(homog.). In yet another embodiment, the homogenization temperature is at least 15°F higher than T(homog.), i.e., ≥ 15°F + T(homog.). In another embodiment, the homogenization temperature is at least 20°F higher than T(homog.), i.e., ≥ 20°F + T(homog.). In yet another embodiment, the homogenization temperature is at least 25°F higher than T(homog.), i.e., ≥ 25°F + T(homog.). In another embodiment, the homogenization temperature is at least 30°F higher than T(homog.), i.e., ≥ 30°F + T(homog.). In yet another embodiment, the homogenization temperature is at least 35°F higher than T(homog.), i.e., ≥ 35°F + T(homog.). In another embodiment, the homogenization temperature is at least 40°F higher than T(homog.), i.e., ≥ 40°F + T(homog.). In yet another embodiment, the homogenization temperature is at least 45°F higher than T(homog.), i.e., ≥ 45°F + T(homog.). In another embodiment, the homogenization temperature is at least 50°F higher than T(homog.), i.e., ≥ 50°F + T(homog.). However, the homogenization temperature should be lower than the primary melting temperature of the aluminum alloy. Preferably, the homogenization temperature is at least 10°F lower than the stable primary melting temperature of the aluminum alloy.

[0080] Since it involves solution heat treatment, all of the above teachings regarding homogenization equally apply to the solution heat treatment temperature. That is, the solution heat treatment temperature can be the same as T(homog.) and is preferably 10 - 50°F higher than T(homog.), as described above, but lower than the primary melting temperature of the aluminum alloy, and preferably at least 10°F lower than the primary melting temperature of the aluminum alloy. After solution heat treatment, the alloy should be quenched in a suitable medium such as water or air. Preferably, the water is at room temperature.

[0081] Based on the above data, aging analysis was also completed. It was found that the alloy should be aged to a total equivalent aging time t(eq.) of 7 to 20 hours, and the total equivalent artificial aging time is:

[0082]

[0083] In the above formula, T is the instantaneous temperature in Kelvin (K) during artificial aging, and Tref is the reference temperature selected as 160°C (433.15K). The t(eq.) of Alloys 1 - 2 is shown in the following table.

[0084] Table 5 - t(eq.) of Alloy 1 - 2

[0085]

[0086] As shown, both Alloy 1 and Alloy 2 - AP2 are aged to substantially the same total equivalent aging time. However, the aging practice of Alloy 2 is excellent and at least partially contributes to its significantly improved properties. Thus, in one embodiment, t(eq.) is from 7 to 19 hours. In another embodiment, t(eq.) is from 7 to 18 hours. In yet another embodiment, t(eq.) is from 7 to 17 hours. In another embodiment, t(eq.) is from 7 to 16 hours. In yet another embodiment, t(eq.) is from 7 to 15 hours. In another embodiment, t(eq.) is from 7 to 14 hours. In yet another embodiment, t(eq.) is from 7 to 13.5 hours. In another embodiment, t(eq.) is from 7 to 13 hours. In yet another embodiment, t(eq.) is from 7 to 12.5 hours. In another embodiment, t(eq.) is from 7 to 12 hours. In yet another embodiment, t(eq.) is from 7 to 11.5 hours. In another embodiment, t(eq.) is from 7 to 11 hours.

[0087] It is believed that both two - step aging practice and three - step aging practice can be used with the presently disclosed wrought 7xxx aluminum alloys, provided that appropriate homogenization and solution heat treatment practices are followed. Thus, in one embodiment, 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, where the second aging temperature is at least 10°F higher than the 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.

[0088] In one embodiment, the first aging temperature is not greater than 280°F. In another embodiment, the first aging temperature is not greater than 270°F. In yet another embodiment, the first aging temperature is not greater than 260°F. In another embodiment, the first aging temperature is not greater than 250°F. Multiple aging temperatures can be used within the first aging temperature range, provided that t(eq) is achieved.

[0089] 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. A plurality of aging temperatures may be used within the second aging temperature range provided that t(eq) is achieved. After the second aging step, the product may be cooled to room temperature.

[0090] When a third aging step is used, it follows the second aging step. In one method, the third aging step is similar or identical to the first aging step, such as by using an aging temperature of 200 - 300°F. A plurality of aging temperatures may be used within the third aging temperature range 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.

[0091] In one embodiment, the third aging temperature is not greater than 280°F. In another embodiment, the third aging temperature is not greater than 270°F. In yet another embodiment, the third aging temperature is not greater than 260°F. In another embodiment, the third aging temperature is not greater than 250°F. A plurality of aging temperatures may be used within the third aging temperature range provided that t(eq) is achieved.

[0092] Although the various embodiments of the present disclosure have been described in detail, it will be apparent to those skilled in the art that modifications and adaptations of those embodiments will occur to them. However, it should be clearly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.

Claims

1. A forged 7xxx aluminum alloy product, comprising: 5.5 - 6.5 wt% of Zn; 1.3 - 1.7 wt% of Mg; 1.7 - 2.3 wt% of Cu; Less than 0.15 wt% of Mn; Up to 1.0 wt% of a grain structure control material, wherein the grain structure control material comprises at least one of Zr, Cr, Sc, and Hf; And Up to 0.15 wt% of Ti; The balance being aluminum and unavoidable impurities; Wherein the forged 7xxx aluminum alloy product has a thickness of 2.5 to 12 inches; Wherein the forged 7xxx aluminum alloy product passes the HHSCC - G49 test at 70 °C for 100 days or at 90 °C for 10 days; and Wherein the forged 7xxx aluminum alloy product achieves a typical short transverse elongation (ST) of at least 5% and a typical longitudinal elongation (L) of at least 10%.

2. The forged 7xxx aluminum alloy product according to claim 1, wherein the forged 7xxx aluminum alloy product comprises no more than 0.12 wt% of Mn.

3. The forged 7xxx aluminum alloy product according to claim 2, wherein the forged 7xxx aluminum alloy product comprises 0.05 to 0.15 wt% of Zr and no more than 0.04 wt% of Mn.

4. The forged 7xxx aluminum alloy product according to claim 1, wherein the forged 7xxx aluminum alloy product comprises at least 5.6 wt% of Zn, or at least 5.7 wt% of Zn, or at least 5.8 wt% of Zn, or at least 5.9 wt% of Zn.

5. The forged 7xxx aluminum alloy product according to claim 1, wherein the forged 7xxx aluminum alloy product achieves a tensile yield strength (L) of at least 63 ksi, or at least 64 ksi, or at least 65 ksi, or at least 66 ksi, or at least 67 ksi, or at least 68 ksi, or at least 69 ksi, or at least 70 ksi, or at least 71 ksi, or at least 72 ksi, or at least 73 ksi.

6. The forged 7xxx aluminum alloy product according to claim 1, wherein the forged 7xxx aluminum alloy product contains no more than 2.25 wt% of Cu, or no more than 2.20 wt% of Cu.

7. The forged 7xxx aluminum alloy product according to claim 6, wherein the forged 7xxx aluminum alloy product contains at least 1.75 wt% of Cu, or at least 1.80 wt% of Cu, or at least 1.85 wt% of Cu, or at least 1.90 wt% of Cu, or at least 1.95 wt% of Cu, or at least 2.00 wt% of Cu.

8. The forged 7xxx aluminum alloy product as claimed in claim 1, wherein the forged 7xxx aluminum alloy product contains at least 1.35 wt% of Mg, or at least 1.40 wt% of Mg.

9. The forged 7xxx aluminum alloy product as claimed in claim 8, wherein the forged 7xxx aluminum alloy product contains no more than 1.65 wt% of Mg, or no more than 1.60 wt% of Mg, or no more than 1.55 wt% of Mg, or no more than 1.50 wt% of Mg, or no more than 1.45 wt% of Mg.

10. The forged 7xxx aluminum alloy product as claimed in any one of the preceding claims, wherein the forged 7xxx aluminum alloy product contains no more than 6.4 wt% of Zn, or no more than 6.3 wt% of Zn, or no more than 6.2 wt% of Zn.

11. The forged 7xxx aluminum alloy product as claimed in claim 1, wherein the forged 7xxx aluminum alloy product has a thickness of at least 3 inches, or at least 3.5 inches, or at least 4.0 inches, or at least 4.5 inches, or at least 5.0 inches.

12. The forged 7xxx aluminum alloy product as claimed in claim 1, wherein the forged 7xxx aluminum alloy product achieves a typical L-S crack resistance (K max-dev ) of at least 25 ksi-sqrt-in, or at least 27 ksi-sqrt-in, or at least 29 ksi-sqrt-in, or at least 31 ksi-sqrt-in, or at least 33 ksi-sqrt-in, or at least 35 ksi-sqrt-in, or at least 37 ksi-sqrt-in, or at least 39 ksi-sqrt-in, or at least 41 ksi-sqrt-in, or at least 43 ksi-sqrt-in, or at least 45 ksi-sqrt-in, or at least 47 ksi-sqrt-in, or at least 49 ksi-sqrt-in, or at least 50 ksi-sqrt-in.

13. The forged 7xxx aluminum alloy product as claimed in claim 1, wherein the forged 7xxx aluminum alloy product passes the HHSCC-G49 test at 70 °C for 120 days, or 140 days, or 160 days, or 180 days, or 200 days, or 220 days, or 240 days, or 260 days, or 280 days, or 300 days.

14. The forged 7xxx aluminum alloy product as claimed in claim 1, wherein the forged 7xxx aluminum alloy product passes the HHSCC-G49 test at 90 °C for 15 days, or 20 days, or 25 days.

15. The forged 7xxx aluminum alloy product according to claim 1, wherein the forged 7xxx aluminum alloy product achieves a typical short transverse elongation (ST) of at least 6%, or at least 7%, or at least 8%, or at least 9%, or at least 10%.

16. The forged 7xxx aluminum alloy product according to claim 1, wherein the forged 7xxx aluminum alloy product achieves a typical longitudinal elongation (L) of at least 6%, or at least 7%, or at least 8%, or at least 9%, or at least 10%, or at least 11%, or at least 12%, or at least 13%, or at least 14%, or at least 15%, or at least 16%.

17. The forged 7xxx aluminum alloy product according to any one of claims 1-9 or 11-16, wherein the forged 7xxx aluminum alloy product has an equivalent artificial aging time t(eq.); wherein t(eq.) is from 7 to 20 hours, wherein t(eq.) is calculated by the following formula: where T is the instantaneous temperature in degrees K during the artificial aging, and where Tref is a reference temperature selected as 160 °C (433.15 °K).

18. The forged 7xxx aluminum alloy product according to claim 17, wherein the 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, wherein the second aging temperature is at least 10 °F higher than the first aging temperature.

19. The forged 7xxx aluminum alloy product according to claim 18, wherein the artificial aging includes a third aging at a third aging temperature of 200 °F to 300 °F.

20. The forged 7xxx aluminum alloy product according to claim 17, wherein t(eq.) does not exceed 19 hours, or does not exceed 18 hours, or does not exceed 17 hours, or does not exceed 16 hours, or does not exceed 15 hours, or does not exceed 14 hours, or does not exceed 13.5 hours, or does not exceed 13 hours, or does not exceed 12.5 hours, or does not exceed 12 hours, or does not exceed 11.5 hours, does not exceed 11 hours.

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