IMPROVED THICK WROUGHT 7XXX ALUMINUM ALLOYS, AND METHODS FOR MAKING THE SAME

Abstract

Disclosed are improved thick wrought 7xxx aluminum alloy products, and methods for producing the same. The new 7xxx aluminum alloy products may realize an improved combination of properties, such as an improved combination of two or more of environmentally assisted crack resistance, strength, elongation, and fracture toughness, among other properties. The new 7xxx aluminum alloy products may include 5.5-6.5 wt. % Zn, 1.3-1.7 wt. % Mg, and 1.7-2.3 wt. % Cu.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Patent Application No. PCT/US2020/039196, filed Jun. 23, 2020, which claims the benefit of priority to U.S. Patent Application No. 62/865,716, filed Jun. 24, 2019, entitled “IMPROVED THICK WROUGHT 7XXX ALUMINUM ALLOYS, AND METHODS FOR MAKING THE SAME”, each of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present patent application relates to improved thick wrought 7xxx aluminum alloy products and methods for producing the same.

BACKGROUND

Aluminum alloys are useful in a variety of applications. However, improving one property of an aluminum alloy without degrading another property is elusive. For example, it is difficult to increase the strength of a wrought aluminum alloy without affecting other properties such as fracture toughness or corrosion resistance. 7xxx (Al—Zn—Mg based) are prone to corrosion. See, e.g., Bonn, W. Grubl, “The stress corrosion behavior of high strength AlZnMg alloys,” Paper held at the International Meeting of Associazione Italiana di Metallurgie, “Aluminum Alloys in Aircraft Industries,” Turin, October 1976.

Patent Owner has described some 7xxx aluminum alloy products in, inter alia, U.S. Pat. Nos. 6,972,110, and 8,673,209, and International Patent Application Publication Nos. WO2016/183030 and WO2018/237196.

SUMMARY OF THE DISCLOSURE

Broadly, the present patent application relates to improved thick wrought 7xxx aluminum alloy products, and methods for producing the same. The new thick wrought 7xxx aluminum alloy products (“the new 7xxx aluminum alloy products”) may realize an improved combination of environmentally assisted crack (EAC) resistance and at least one of strength, elongation, and fracture toughness, among other properties.

The new 7xxx aluminum alloy products generally include (and in some instances consist of, or consist essentially of) 5.5-6.5 wt. % Zn, 1.7-2.3 wt. % Cu, and 1.3-1.7 wt. % Mg. The new wrought 7xxx aluminum alloy products are generally at least 2.5 inches thick, and may be up to 12 inches thick, and realize resistance to environmentally assisted cracking in the short transverse (ST) direction, which resistance is important for aerospace and other applications, especially those with structural loading in the short transverse (ST) direction. Such thick, wrought 7xxx aluminum alloy product generally also realize good strength, elongation, fracture toughness and/or crack-deviation resistance properties. Thus, the new wrought 7xxx aluminum alloy products may realize 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 new 7xxx aluminum alloy products may include normal grain structure control materials, grain refiners, and impurities. For instance, the new 7xxx aluminum alloy products may include one or more of Zr, Cr, Sc, and Hf as grain structure control materials (e.g., from 0.05-0.25 wt. % each of one or more of Zr, Cr, Sc, and Hf), limiting the total amounts of these elements such that large primary particles do not form in the alloy. As another example, new 7xxx aluminum alloy products may include less than 0.15 wt. % Mn. As yet another example, the new 7xxx aluminum alloy products may include up to 0.15 wt. % Ti as a grain refiner, optionally with some of the titanium in the form of TiB₂ and/or TiC. The new 7xxx aluminum alloy products may include up to 0.20 wt. % Fe and up to 0.15 wt. % Si as impurities. Lower amounts of iron and silicon may be used. The balance of the new 7xxx aluminum alloy products is generally aluminum and other unavoidable impurities (other than iron and silicon).

As noted above, the new 7xxx aluminum alloy products generally include tailored amounts of zinc, magnesium and copper to facilitate realization of EAC resistance in combination with good strength and/or fracture toughness properties, among others. In this regard, the new 7xxx aluminum alloy products generally include from 5.5 to 6.5 wt. % Zn. In one embodiment, a new alloy includes not greater than 6.4 wt. % Zn. In another embodiment, a new alloy includes not greater than 6.3 wt. % Zn. In yet another embodiment, a new alloy includes not greater than 6.2 wt. % Zn. In one embodiment, a new alloy includes at least 5.6 wt. % Zn. In another embodiment, a new alloy includes at least 5.7 wt. % Zn. In yet another embodiment, a new alloy includes at least 5.8 wt. % Zn. In another embodiment, a new alloy includes at least 5.9 wt. % Zn.

As noted above, the new 7xxx aluminum alloy products generally include from 1.7 to 2.3 wt. % Cu. In one embodiment, a new alloy includes not greater than 2.25 wt. % Cu. In another embodiment, a new alloy includes not greater than 2.20 wt. % Cu. In one embodiment, a new alloy includes at least 1.75 wt. % Cu. In another embodiment, a new alloy includes at least 1.80 wt. % Cu. In yet another embodiment, a new alloy includes at least 1.85 wt. % Cu. In another embodiment, a new alloy includes at least 1.90 wt. % Cu. In yet another embodiment, a new alloy includes at least 1.95 wt. % Cu. In another embodiment, a new alloy includes at least 2.00 wt. % Cu.

As noted above, the new 7xxx aluminum alloy products generally include from 1.3 to 1.7 wt. % Mg. In one embodiment, a new alloy includes at least 1.35 wt. % Mg. In another embodiment, a new alloy includes at least 1.40 wt. % Mg. In one embodiment, a new alloy includes not greater than 1.65 wt. % Mg. In another embodiment, a new alloy includes not greater than 1.60 wt. % Mg. In yet another embodiment, a new alloy includes not greater than 1.55 wt. % Mg. In another embodiment, a new alloy includes not greater than 1.50 wt. % Mg. In another embodiment, a new alloy includes not greater than 1.45 wt. % Mg.

In one embodiment, the amounts of zinc, magnesium and copper within the 7xxx aluminum alloy product satisfy the relationship: 2.569≤Mg+0.500*Cu+0.067*Zn≤3.269. In another embodiment, the amounts of zinc, magnesium and copper within the 7xxx aluminum alloy product satisfy the relationship: 2.709≤Mg+0.500*Cu+0.067*Zn≤3.119. In yet another embodiment, the amounts of zinc, magnesium and copper within the 7xxx aluminum alloy product satisfy the relationship: 2.869≤Mg+0.500*Cu+0.067*Zn≤3.269. In another embodiment, the amounts of zinc, magnesium and copper within the 7xxx aluminum alloy product satisfy the relationship: 2.869≤Mg+0.500*Cu+0.067*Zn≤3.119. Any of the zinc, magnesium, and copper amounts described in the preceding paragraphs may be used in combination with the above-shown empirical relationships.

In one approach, the amounts of zinc and magnesium within the 7xxx aluminum alloy product are such that the weight ratio of zinc-to-magnesium is not greater than 4.75:1 (i.e., (wt. % Zn/wt. % Mg)≤4.75:1). In one embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.60:1 (i.e., (wt. % Zn/wt. % Mg)≤4.60:1). In another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.50:1 (i.e., (wt. % Zn/wt. % Mg)≤4.50:1). In yet another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.40:1 (i.e., (wt. % Zn/wt. % Mg)≤4.40:1). In another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.35:1 (i.e., (wt. % Zn/wt. % Mg)≤4.35:1). In yet another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.30:1 (i.e., (wt. % Zn/wt % Mg)≤4.30:1). In another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.25:1 (i.e., (wt. % Zn/wt. % Mg)≤4.25:1). In yet another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.20:1 (i.e., (wt. % Zn/wt. % Mg)≤4.20:1). In another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.15:1 (i.e., (wt. % Zn/wt. % Mg)≤4.15:1). In yet another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.10:1 (i.e., (wt. % Zn/wt. % Mg)≤4.10:1). In another embodiment, a weight ratio of zinc-to-magnesium is not greater than 4.00:1 (i.e., (wt. % Zn/wt. % Mg)≤4.00:1). In yet another embodiment, a weight ratio of zinc-to-magnesium is not greater than 3.95:1 (i.e., (wt. % Zn/wt. % Mg)≤3.95:1). In another embodiment, a weight ratio of zinc-to-magnesium is not greater than 3.90:1 (i.e., (wt. % Zn/wt. % Mg)≤3.90:1).

In one approach, the amounts of zinc and magnesium within 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 within 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 within 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 within 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 within 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).

As noted above, the new 7xxx aluminum alloy product may include one or more of Zr, Cr, Sc, and Hf as grain structure control materials (e.g., from 0.05-0.25 wt. % each of one or more of Zr, Cr, Sc, and Hf), limiting the total amounts of these elements such that large primary particles do not form in the alloy. Grain structure control materials may, for instance, facilitate an appropriate grain structure (e.g., an unrecrystallized grain structure). When employed, a new 7xxx aluminum alloy product generally includes at least 0.05 wt. % of the grain structure control materials. In one embodiment, a new 7xxx aluminum alloy product includes at least 0.07 wt. % of the grain structure control materials. In another embodiment, a new 7xxx aluminum alloy product includes at least 0.09 wt. % of the grain structure control materials. When employed, a new 7xxx aluminum alloy product generally includes not greater than 1.0 wt. % of the grain structure control materials. In one embodiment, a new 7xxx aluminum alloy product includes not greater than 0.75 wt. % of the grain structure control materials. In yet another embodiment, a new 7xxx aluminum alloy product includes not greater 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.

In one embodiment, the grain structure control materials comprise both Zr and Cr, and a new 7xxx aluminum alloy product includes at least 0.07 wt. % Zr and at least 0.07 wt. % Cr, wherein the wt. % Zr plus the wt. % Cr is not greater than 0.40 wt. % (i.e., wt. % Zr+wt. % Cr≤0.40 wt. %). In another embodiment, the grain structure control materials comprise both Zr and Cr, and a new 7xxx aluminum alloy product includes at least 0.07 wt. % Zr and at least 0.07 wt. % Cr, wherein the wt. % Zr plus the wt. % Cr is not greater than 0.35 wt. % (i.e., wt. % Zr+wt. % Cr ≤0.35 wt. %). In another embodiment, the grain structure control materials comprise both Zr and Cr, and a new 7xxx aluminum alloy product includes at least 0.07 wt. % Zr and at least 0.07 wt. % Cr, wherein the wt. % Zr plus the wt. % Cr is not greater than 0.30 wt. % (i.e., wt. % Zr+wt. % Cr≤0.30 wt. %). In another embodiment, the grain structure control materials comprise both Zr and Cr, and a new 7xxx aluminum alloy product includes at least 0.07 wt. % Zr and at least 0.07 wt. % Cr, wherein the wt. % Zr plus the wt. % Cr is not greater than 0.25 wt. % (i.e., wt. % Zr+wt. % Cr≤0.25 wt. %). In another embodiment, the grain structure control materials comprise both Zr and Cr, and a new 7xxx aluminum alloy product includes at least 0.07 wt. % Zr and at least 0.07 wt. % Cr, wherein the wt. % Zr plus the wt. % Cr is not greater than 0.20 wt. % (i.e., wt. % Zr+wt. % Cr≤0.20 wt. %). In any of these embodiment, a new 7xxx aluminum alloy product may include at least 0.09 wt. % of at least one of Zr and Cr. In any of these embodiments, a new 7xxx aluminum alloy product may include at least 0.09 wt. % of both Zr and Cr.

In one embodiment, the grain structure control material is Zr, and a new 7xxx aluminum alloy product includes from 0.07 to 0.18 wt. % Zr. In another embodiment, the grain structure control material is Zr, and a new 7xxx aluminum alloy product includes from 0.07 to 0.16 wt. % Zr. In yet another embodiment, the grain structure control material is Zr, and a new 7xxx aluminum alloy product includes from 0.08 to 0.15 wt. % Zr. In another embodiment, the grain structure control material is Zr, and a new 7xxx aluminum alloy product includes from 0.09 to 0.14 wt. % Zr. In embodiments where the grain structure control material is Zr, a new 7xxx aluminum alloy product generally contains low amounts of the Cr, Sc, and Hf (e.g., ≤0.04 wt. % each of Cr, Sc, and Hf). In one embodiment, a new 7xxx aluminum alloy product contains not greater than 0.03 wt. % each of Cr, Sc, and Hf In another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.02 wt. % each of Cr, Sc, and Hf. In another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.01 wt. % each of Cr, Sc, and Hf In another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.005 wt. % each of Cr, Sc, and Hf.

In one embodiment, the grain structure control material is Cr, and a new 7xxx aluminum alloy product includes from 0.07 to 0.25 wt. % Cr. In another embodiment, the grain structure control material is Cr, and a new 7xxx aluminum alloy product includes from 0.07 to 0.20 wt. % Cr. In yet another embodiment, the grain structure control material is Cr, and a new 7xxx aluminum alloy product includes from 0.08 to 0.15 wt. % Cr. In another embodiment, the grain structure control material is Cr, and a new 7xxx aluminum alloy product includes from 0.10 to 0.15 wt. % Cr. In other embodiments, a new 7xxx aluminum alloy product contains low amounts of Cr (e.g., ≤0.04 wt. % Cr.) In one embodiment, a new 7xxx aluminum alloy product contains not greater than 0.03 wt. % Cr. In another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.02 wt. % Cr. In yet another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.01 wt. % Cr. In another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.005 wt. % Cr.

In some embodiments, a new 7xxx aluminum alloy includes low amounts of zirconium (e.g., ≤0.04 wt. % Zr). In one embodiment, a new 7xxx aluminum alloy product contains not greater than 0.03 wt. % Zr. In another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.02 wt. % Zr. In yet another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.01 wt. % Zr. In another embodiment, a new 7xxx aluminum alloy product contains not greater than 0.005 wt. % Zr.

As noted above, the new 7xxx aluminum alloy product generally includes less than 0.15 wt. % Mn. In one embodiment, a new 7xxx aluminum alloy product includes not greater than 0.12 wt. % Mn. In another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.10 wt. % Mn. In yet another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.08 wt. % Mn. In another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.05 wt. % Mn. In yet another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.04 wt. % Mn. In another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.03 wt. % Mn. In yet another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.02 wt. % Mn. In another embodiment, a new 7xxx aluminum alloy product includes not greater than 0.01 wt. % Mn.

As noted above, the new 7xxx aluminum alloy product may include up to 0.15 wt. % Ti. Titanium may be used to facilitate grain refining during casting, such as by using TiB₂ or TiC. Elemental titanium may also or alternatively be used. In one embodiment, the new 7xxx aluminum alloy product includes from 0.005 to 0.025 wt. % Ti.

As noted above, the new 7xxx aluminum alloy product may include up to 0.15 wt. % Si and up to 0.20 wt. % Fe as impurities. The amount of silicon and iron may be limited so as to avoid detrimentally impacting the combination of strength, fracture toughness and crack deviation resistance. In one embodiment, the new 7xxx aluminum alloy product may include up to 0.12 wt. % Si and up to 0.15 wt. % Fe as impurities. In another embodiment, the new 7xxx aluminum alloy product may include up to 0.10 wt. % Si and up to 0.12 wt. % Fe as impurities. In another embodiment, the new 7xxx aluminum alloy product may include up to 0.08 wt. % Si and up to 0.10 wt. % Fe as impurities. In yet another embodiment, the new 7xxx aluminum alloy product may include up to 0.06 wt. % Si and up to 0.08 wt. % Fe as impurities. In yet another embodiment, the new 7xxx aluminum alloy product may include up to 0.04 wt. % Si and up to 0.06 wt. % Fe as impurities. In another embodiment, the new 7xxx aluminum alloy product may include up to 0.03 wt. % Si and up to 0.05 wt. % Fe as impurities.

As noted above, the new 7xxx aluminum alloy product has a thickness of from 2.5 to 12.0 inches. Thickness refers to the cross sectional thickness of the product at its thickest point. In one embodiment, a new 7xxx aluminum alloy product has a thickness of at least 3.0 inches. In another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 3.5 inches. In yet another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 4.0 inches. In another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 4.5 inches. In yet another embodiment, a new 7xxx aluminum alloy product has a thickness of at least 5.0 inches. In one embodiment, a new 7xxx aluminum alloy product has a thickness of not greater than 10.0 inches. In another embodiment, a new 7xxx aluminum alloy product has a thickness of not greater than 9.0 inches. In yet another embodiment, a new 7xxx aluminum alloy product has a thickness of not greater than 8.0 inches.

In one embodiment, a new 7xxx aluminum alloy product is a rolled product (e.g., a plate product). In another embodiment, a new 7xxx aluminum alloy product is an extruded product. In yet another embodiment, a new 7xxx aluminum alloy product is a forged product (e.g., a hand forged product, a die forged product).

As mentioned above, the new 7xxx aluminum alloy products may realize an improved combination of properties. In one embodiment, a new 7xxx aluminum alloy product realizes a typical tensile yield strength (L) of at least 63 ksi as per ASTM E8 and B557. In another embodiment, a new 7xxx aluminum alloy product realizes a typical tensile yield strength (L) of at least 64 ksi. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical tensile yield strength (L) of at least 65 ksi. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (L) of at least 66 ksi. In yet another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (L) of at least 67 ksi. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (L) of at least 68 ksi. In yet another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (L) of at least 69 ksi. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (L) of at least 70 ksi. In yet another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (L) of at least 71 ksi. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (L) of at least 72 ksi. In yet another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (L) of at least 73 ksi.

In one embodiment, a new 7xxx aluminum alloy product realizes a typical tensile yield strength (ST) of at least 57 ksi as per ASTM E8 and B557. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 58 ksi. In yet another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 59 ksi. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 60 ksi. In yet another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 61 ksi. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 62 ksi. In yet another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 63 ksi. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 64 ksi. In yet another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 65 ksi. In another embodiment, a 7xxx aluminum alloy product may realize a typical tensile yield strength (ST) of at least 66 ksi.

In one embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (L-T) of at least 25 ksi-sqrt-inch as per ASTM E8 and E399-12. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 27 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 28 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 29 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 30 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 31 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 32 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 33 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 34 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 35 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 36 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 37 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 38 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 39 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 40 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 41 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 42 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 43 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 44 ksi-sqrt-inch. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-stain fracture toughness (L-T) of at least 45 ksi-sqrt-inch.

In one embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 20 ksi-sqrt-inch as per ASTM E8 and E399-12. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 22 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 24 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 26 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 28 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 30 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 32 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 34 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 36 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 38 ksi-sqrt-inch. In another embodiment, a new 7xxx aluminum alloy product realizes a typical K_IC plane-strain fracture toughness (S-L) of at least 40 ksi-sqrt-inch.

In one embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 6% as per ASTM E8 and B557. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 7%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 8%. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 9%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 10%. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 11%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 12%. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 13%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 14%. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 15%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (L) of at least 16%.

In one embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (ST) of at least 3% as per ASTM E8 and B557. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (ST) of at least 4%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (ST) of at least 5%. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (ST) of at least 6%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (ST) of at least 7%. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (ST) of at least 8%. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (ST) of at least 9%. In another embodiment, a new 7xxx aluminum alloy product realizes a typical elongation (ST) of at least 10%.

In one embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 25 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 27 ksi-sqrt-in. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 29 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 31 ksi-sqrt-in. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 33 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 35 ksi-sqrt-in. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 37 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 39 ksi-sqrt-in. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 41 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 43 ksi-sqrt-in. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 45 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 47 ksi-sqrt-in. In yet another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 49 ksi-sqrt-in. In another embodiment, a new 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (K_max-dev) of at least 50 ksi-sqrt-in.

As noted above, the new 7xxx aluminum alloys may be EAC resistant, which EAC resistance may be determined by Hot and Humid SCC testing. In one embodiment, a new 7xxx aluminum alloy product has a thickness of at least 63.5 mm and passes Hot and Humid SCC (stress corrosion cracking) testing using standard stress-corrosion tension test specimens conforming to ASTM G49, as defined below (“HHSCC-G49”). To create the HHSCC-G49 test specimens, at least three short transverse (ST) samples are taken from mid-thickness of the final product and between W/4 and 3W/4 of the final product. The extracted specimens are then machined into tensile specimens with a diameter as defined in ASTM G47-20 and dimensions proportional to the standard specimen as defined in ASTM E8/8M-16ael. If the final product thickness is at least 2.25 inches (57.15 mm), then the length of the tensile specimen is 2.00 inches (50.8 mm), as shown in FIG. 2. 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 to 2.00 inches (50.8 mm) as possible. Prior to testing the tensile specimens are to be cleaned/degreased by washing in acetone. The tensile specimens are then strained in the short-transverse direction at 85% of their ST tensile yield strength at T/2. The alloy's ST tensile yield strength is measured at room temperature and in accordance with ASTM E8 and B557 prior to the HHSCC-G49 testing. The stressing frame used is a constant strain type per ASTM G49, section 7.2.2 (see, e.g., FIG. 4a of ASTM G49). The strained specimens are then placed into a controlled cabinet having air at 85% relative humidity (without additions to the air, such as chlorides) and a temperature of 70° C. or 90° C. At least three specimens must be tested. For purposes of this patent application, an alloy passes HHSCC-G49 testing at 70° C. when all specimens survive at least 100 days. For purposes of this patent application, an alloy passes HHSCC-G49 testing at 90° C. when all specimens survive at least 10 days. A failure is when the specimen breaks into two halves, either along the gauge length or at one of the specimen shoulders adjoining the gauge length. Shoulder failures are statistically equivalent to gauge length failures. Thread failures are only included when they are statistically equivalent to the gauge length failures when determining whether an alloy passes HHSCC-G49. A thread failure is when a crack occurs in a threaded end of a specimen as opposed to in the gauge length. In some instance, thread failures may not be detectable until the specimen is removed from the stressing frame.

In one approach, the HHSCC-G49 testing is conducted at 70° C. and a new 7xxx aluminum alloy product passes 120 days of HHSCC-G49 testing at 70° C., wherein all samples survive 120 days of the HHSCC-G49 test defined above. In one embodiment, a new 7xxx aluminum alloy product passes 140 days of HHSCC-G49 testing at 70° C., wherein all samples survive 140 days of the HHSCC-G49 test defined above. In yet another embodiment, a new 7xxx aluminum alloy product passes 150 days of HHSCC-G49 testing at 70° C., wherein all samples survive 150 days of the HHSCC-G49 test defined above. In another embodiment, a new 7xxx aluminum alloy product passes 160 days of HHSCC-G49 testing at 70° C., wherein all samples survive 160 days of the HHSCC-G49 test defined above. In yet another embodiment, a new 7xxx aluminum alloy product passes 180 days of HHSCC-G49 testing at 70° C., wherein all samples survive 180 days of the HHSCC-G49 test defined above. In another embodiment, a new 7xxx aluminum alloy product passes 200 days of HHSCC-G49 testing at 70° C., wherein all samples survive 200 days of the HHSCC-G49 test defined above. In yet another embodiment, a new 7xxx aluminum alloy product passes 220 days of HHSCC-G49 testing at 70° C., wherein all samples survive 220 days of the HHSCC-G49 test defined above. In another embodiment, a new 7xxx aluminum alloy product passes 240 days of HHSCC-G49 testing at 70° C., wherein all samples survive 240 days of the HHSCC-G49 test defined above. In yet another embodiment, a new 7xxx aluminum alloy product passes 260 days of HHSCC-G49 testing at 70° C., wherein all samples survive 260 days of the HHSCC-G49 test defined above. In another embodiment, a new 7xxx aluminum alloy product passes 280 days of HHSCC-G49 testing at 70° C., wherein all samples survive 280 days of the HHSCC-G49 test defined above. In yet another embodiment, a new 7xxx aluminum alloy product passes 300 days of HHSCC-G49 testing at 70° C., wherein all samples survive 300 days of the HHSCC-G49 test defined above. The above stress corrosion cracking resistance properties may be realized in products having a thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least 140 mm, or higher.

In another approach, the HHSCC-G49 testing is conducted at 90° C. and a new 7xxx aluminum alloy product passes 15 days of HHSCC-G49 testing at 90° C., wherein all samples survive 15 days of the HHSCC-G49 test defined above. In one embodiment, a new 7xxx aluminum alloy product passes 20 days of HHSCC-G49 testing at 90° C., wherein all samples survive 20 days of the HHSCC-G49 test defined above. In another embodiment, a new 7xxx aluminum alloy product passes 25 days of HHSCC-G49 testing at 90° C., wherein all samples survive 25 days of the HHSCC-G49 test defined above. The above stress corrosion cracking resistance properties may be realized in products having a thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least 140 mm, or higher.

In one embodiment, a new 7xxx aluminum alloy product has a thickness of at least 63.5 mm and passes stress corrosion cracking, per ASTM G47 using standard stress-corrosion tension test specimens conforming to ASTM G49 under alternate immersion exposure conditions per ASTM G44 (“SCC alternate immersion testing”). For purposes of this patent application, a new 7xxx aluminum alloy passes SCC alternate immersion testing when all samples survive 20 days of the SCC alternate immersion testing at a net stress of 172 MPa in the ST direction, where the test environment is 3.5% NaCl, and with a minimum of five (5) samples required to be tested. In one embodiment, a new 7xxx aluminum alloy passes 30 days of SCC alternate immersion testing, as defined above. In another embodiment, a new 7xxx aluminum alloy passes 20 days of SCC alternate immersion testing, as defined above, but at a net stress of 241 MPa. In yet another embodiment, a new 7xxx aluminum alloy passes 30 days of SCC alternate immersion testing, as defined above, but at a net stress of 241 MPa. The above stress corrosion cracking resistance properties may be realized in products having a thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least 140 mm, or higher.

In one embodiment, a new 7xxx aluminum alloy product has a thickness of at least 63.5 mm and passes Hot and Humid SCC (stress corrosion cracking) testing under ASTM G168, as defined below (“HHSCC-G168”). For purpose of this patent application, a new 7xxx aluminum alloy passes HHSCC-G168 testing when (a) the stress intensity factor gives a crack growth rate of not greater than 10⁻⁷ mm/s, and (b) the realized K value is at least 13 MPa-sqrt-m (MPa√m). The HHSCC-G168 testing is to be conducted at 70° C. and 85% relative humidity, at T/2 and with S-L specimens. In one embodiment, the realized K value is at least 14 MPa-sqrt-m at a crack growth rate of not greater than 10⁻⁷ mm/s. In another embodiment, the realized K value is at least 15 MPa-sqrt-m at a crack growth rate of not greater than 10⁻⁷ mm/s. In yet another embodiment, the realized K value is at least 16 MPa-sqrt-m at a crack growth rate of not greater than 10⁻⁷ mm/s. In another embodiment, the realized K value is at least 17 MPa-sqrt-m at a crack growth rate of not greater than 10⁻⁷ mm/s. In yet another embodiment, the realized K value is at least 18 MPa-sqrt-m, or higher, at a crack growth rate of not greater than 10⁻⁷ mm/s. The above stress corrosion cracking resistance properties may be realized in products having a thickness of at least 80 mm, or at least 100 mm, at least 120 mm, or at least 140 mm, or higher.

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

While the above L and ST properties generally relate to thick plate products, similar properties may also be realized in thick forged product and thick extruded products. Further, many of the above properties may be realized in combination, as shown by the below examples.

As noted above, the new thick 7xxx aluminum alloy products may be suitable for parts in various aerospace applications. In one embodiment, the alloy product is an aerospace structural component. The aircraft structural component may be any of an upper wing panel (skin), an upper wing stringer, an upper wing cover with integral stringers, a spar, a spar cap, a spar web, a rib, rib feet or a rib web, stiffening elements, frames, a landing gear component (e.g., a cylinders, beams), drag braces, bulkheads, flap track assemblies, fuselage and windshield frames, gear ribs, side stays, fittings, a fuselage component (e.g., a fuselage skin), and space components (e.g., for rockets and other vehicles that may exit the earth). In one embodiment, the alloy product is an armor component (e.g., of a motorized 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 mold block/mold plate product (e.g., for injection molding). In one embodiment, the alloy product is an automotive product.

The new thick 7xxx aluminum alloy products may be made into wrought products by casting an aluminum alloy having any of the aforementioned compositions into an ingot or billet, followed by homogenizing of the ingot or billet. The homogenized ingot or billet may be worked by rolling, extruding, or forging to final gauge, generally by hot working, optionally with some cold working. The final gauge product may be solution heat treated, and then quenched, and then stress relieved (e.g., by stretching or compression) and then artificially aged.

Aside from traditional wrought products, the new 7xxx aluminum alloys may be made into shape castings or by additive manufacturing into additively manufactured products. The additively manufactured products may be used as-is, or may be subsequently processed, e.g., processed via mechanical, thermal, or thermomechanical treatment.

Definitions

As used herein, “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 location from at least three different lots of material, and with at least duplicate specimens being tested for each lot, for a total of at least 6 different measured specimen values, with the typical TYS(L) being the average of the at least 6 different measured specimen values. Typical elongation (L) is measured during longitudinal tensile testing.

As used herein, “typical longitudinal (ST) tensile yield strength” or TYS(ST) is determined in accordance with ASTM B557-10 and by measuring the tensile yield strength (TYS) in the short transverse direction (ST) from at least three different lots of material, and with at least duplicate specimens being tested for each lot, for a total of at least 6 different measured specimen values, with the typical TYS(ST) being the average of the at least 6 different measured specimen values. Short transverse tensile specimens are taken so that the midpoint of the gage section coincides with the plate mid-thickness plane. Typical elongation (ST) is measured during short transverse tensile testing.

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 at least three different lots of material using a C(T) specimen, where “W” is 4.0 inches, and where “B” is 2.0 inches for products having a thickness of at least 2.0 inches and where “B” is 1.5 inches for products having a thickness less than 2.0 inches, with at least duplicate specimens being tested for each lot, for a total of at least 6 different measured specimen values, and with the typical plane strain fracture toughness (K_IC) (L-T) being the average of the at least 6 different valid K_IC measured specimen values.

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 at least three different lots of material using a C(T) specimen, where “W” and “B” are per the below table, with at least duplicate specimens being tested for each lot, for a total of at least 6 different measured specimen values, and with the typical plane strain fracture toughness (K_IC) (S-L) being the average of the at least 6 different valid K_IC measured specimen values.

S-L Specimen Parameters

	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

The typical L-S crack deviation resistance properties (K_max-dev) are to be determined per the procedure described in commonly-owned U.S. Patent Application Publication No. 2017/0088920, paragraph 0058, which procedure is incorporated herein by reference, except: (a) the “W” dimension of the specimen shall be 2.0 inches (5.08 cm), (b) the specimen shall be centered at T/2 (as opposed to the notch tip), and (c) the test specimens may be tested in lab air as opposed to high humidity air.

The term “square root” may be abbreviated herein as “sqrt.”

Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in one embodiment” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though they may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although they may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.

In addition, 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 being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of “a,” “an,” and “the” include plural references, unless the context clearly dictates otherwise. The meaning of “in” includes “in” and “on”, unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the strength versus K_IC fracture toughness properties for the Example 1 alloys.

FIG. 2 is a graph illustrating the strength versus EAC resistance for the Example 1 alloys.

DETAILED DESCRIPTION

Example 1

Two aluminum alloys were cast as 6×18-inch (D×W) ingots, the compositions of which are provided in Table 1, below.

TABLE 1
Composition of Example 1 Alloys (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 conventionally prepared for homogenization (e.g. by sawing and scalping). The first ingot was then processed to its final temper as per Japanese Patent No. H03-41540 (1991), Example 1, Alloy 4.¹ The second ingot was processed according to the inventive processes disclosed herein. ¹ Also published as JP01-290737 (1989).

Specifically, Alloy 1 was homogenized at 842° F. (450° C.) as per JPH03-41540. The alloy was then hot rolled to a final gauge of 1.75 inches (44.45 mm). Alloy 1 was then solution heat treated at 842° F. (450° C.) for 1 hour as per JPH03-41540, then quenched in 190° F. water (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, heating to 302° F. and then aging at 302° F. (150° C.) for 24 hours as per JPH034-41540.

Alloy 2 was homogenized at 895° F. (479° C.) and then hot rolled to a final gauge of 1.75 inches (44.45 mm). Alloy 2 was then 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 Alloy 2 was subjected to two different artificially aging practices:

• • Practice 1: First aging at 250° F. (121° C.) for 6 hours, then heating to 320° F. (160° C.) and holding for 5.6 hours, air cooling to ambient, and then reheating to 250° C. (121° C.) and holding for 24 hours.
  • Practice 2: First aging at 250° F. (121° C.) for 6 hours, then heating to 320° F. (160° C.) and holding for 9.75 hours, air cooling to ambient, and then reheating to 250° C. (121° C.) and holding for 24 hours.
    The 190° F. quench temperature simulates the quench rate of the middle of a thick ingot (e.g., an eight-inch (203.2 mm) thick ingot).

Alloys 1-2 were metallographically examined and were found to be unrecrystallized, i.e., contained not greater than 45% recrystallized grains as determined using standard metallographic analysis procedures. In one embodiment, a new wrought 7xxx aluminum alloy product contains not greater than 35% recrystallized grains. In another embodiment, a new wrought 7xxx aluminum alloy product contains not greater than 25% recrystallized grains. In another embodiment, a new wrought 7xxx aluminum alloy product contains not greater than 15% recrystallized grains. In another embodiment, a new wrought 7xxx aluminum alloy product contains not greater than 5% recrystallized grains.

The alloys were then subjected to mechanical testing, the results of which are shown in Table 2, below. Test results relating to similarly produced conventional 7050 alloys are also provided, which results are from commonly-owned International Patent Application Publication No. WO2020/102441. Measurements are relative to the T/2 location for all alloys. Fracture toughness is relative to the S-L orientation.

TABLE 2
Mechanical Properties of Example 1 Alloys*
	Strength				KIC
	Testing	UTS	TYS	Elong.	(ksi-
Alloy	Orientation	(ksi)	(ksi)	(%)	sqrt-in.)
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 practice 1;
AP2 = aging practice 2;
sqrt = square root

The alloys were also subjected to EAC (environmentally assisted crack) resistance testing as per the HHSCC-G49 procedure provided above. Plant produced 7050-T7651 (3.9 inches thick) having a strength level similar to that of Alloys 1-2 was also tested. The HHSCC-G49 results are provided in Table 3, below.

TABLE 3
HHSCC-G49 Test Results
	Stress		90° C./85% RH
	(%	Applied	Days	Days to failure
	TYS-	stress	in	rep	rep	rep	rep	rep
Alloy	ST)	(ksi)	test	1	2	3	4	5
1	85	54	18	11	11	14	18	18
2 (API)	85	55.9	21	11	11	11	21	18
2 (AP2)	85	53.1	46	28	32	28	46	35
7050	85	53.0	55	28	55	55	19	41

As shown above and in FIGS. 1-2, Alloy 2 realizes an improved combination of properties over Alloy 1. As shown in FIG. 1, Alloy 2 realizes a much higher combination of strength and toughness over Alloy 1 and the conventional 7050 alloy. As shown in FIG. 2, Alloy 2 also realizes a much better combination of strength and EAC resistance over Alloy 1. Further, as shown in Table 2, the ST ductility of Alloy 2 is significantly higher than that of Alloy 1.

An analysis of the homogenization temperature for this alloy system was completed. It was determined that, for these particular alloys having 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.), wherein T(homog.) is calculated in degrees Fahrenheit from the following formula:

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

For the above formula, the Cu, the Mg, and the Zn are the weight percent amounts of copper, magnesium and zinc, respectively, in the wrought 7xxx aluminum alloy. The below table shows the calculation for Alloys 1 and 2.

TABLE 4
T(homog.) of Alloys 1-2
				T(homog.)
Alloy	Zn	Mg	Cu	(° 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 of Alloy 1 is 856.5° F. and the minimum homogenization temperature of Alloy 2 is 845.3° F.

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

As it relates to solution heat treatment, all of the above teachings regarding homogenization apply equally to the solution heat treatment temperature. That is, the solution heat treatment temperature may be the same as T(homog.) and preferably is from 10-50° F. higher than T(homog.), as per above, but below the incipient melting temperature of the aluminum alloy, and preferably at least 10° F. below the incipient melting temperature of the aluminum alloy. Following solution heat treatment the alloy should be quenched in an appropriate medium, such as water or air. Preferably, the water is room temperature.

Based on the above data, an aging analysis was also completed. It was found that the alloys should be aged to a total equivalent aging time, t(eq.), of from 7 to 20 hours, the total equivalent artificial aging time being:

$t\left(\mathrm{eq}.\right)=\frac{\int \exp \left(-12800/T\right)\mathrm{dt}}{\exp \left(-12800/\mathrm{Tref}\right)}$

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

TABLE 5
t(eq.) of Alloys 1-2
      t(eq.)
Alloy (hours)
1     14.58
2-AP1 10.57
2-AP2 14.57

As shown, both Alloy 1 and Alloy 2-AP2 were aged to generally the same total equivalent aging time. However, the aging practice of Alloy 2 is superior, at least partially contributing to its significantly improved properties. Accordingly, 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.

It is believed that both a two-step and a three-step aging practice may be used with the presently disclosed wrought 7xxx aluminum alloys provided the proper homogenization and solution heat treatment practices are followed. Thus, in one embodiment, the artificial aging comprises first aging at a first aging temperature of from 200-300° F. followed by second aging at a second aging temperature of from 250-350° F., wherein 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.

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 may be used within the first aging temperature range provided t(eq) is achieved.

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 used within the second aging temperature range provided t(eq) is achieved. After the second aging step, the product may be cooled to room temperature.

When a third aging step is used, it follows the second aging step. In one approach, the third aging step is similar or the same as the first aging step, such as by using an aging temperature of from 200-300° F. Multiple aging temperatures may be used within the third aging temperature range provided t(eq) is achieved. In one embodiment, the third aging temperature is at least 10° F. lower than second aging temperature. In another embodiment, the third aging temperature is at least 20° F. lower than second aging temperature. In yet another embodiment, the third aging temperature is at least 30° F. lower than second aging temperature. In another embodiment, the third aging temperature is at least 40° F. lower than second aging temperature. In yet another embodiment, the third aging temperature is at least 50° F. lower than second aging temperature. In another embodiment, the third aging temperature is at least 60° F. lower than second aging temperature. In yet another embodiment, the third aging temperature is at least 70° F. lower than second aging temperature.

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. Multiple aging temperatures may be used within the third aging temperature range provided t(eq) is achieved.

While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.

Claims

1. A wrought 7xxx aluminum alloy product comprising:

5.5-6.5 wt. % Zn;

1.3-1.7 wt. % Mg;

1.7-2.3 wt. % Cu;

less than 0.15 wt. % Mn;

up to 1.0 wt. % of grain structure control materials, wherein the grain structure control materials comprise at least one of Zr, Cr, Sc, and Hf; and

up to 0.15 wt. % Ti;

the balance being aluminum and unavoidable impurities;

wherein the wrought 7xxx aluminum alloy product has a thickness of from 2.5 to 12 inches.

2. The wrought 7xxx aluminum alloy product of claim 1, wherein the wrought 7xxx aluminum alloy product includes not greater than 0.12 wt. % Mn.

3. The wrought 7xxx aluminum alloy product of claim 2, comprising from 0.05 to 0.15 wt. % Zr and not greater than 0.04 wt. % Mn.

4. The wrought 7xxx aluminum alloy product of claim 1, wherein the wrought 7xxx aluminum alloy product includes not greater than 6.4 wt. % Zn.

5. The wrought 7xxx aluminum alloy product of claim 4, wherein the wrought 7xxx aluminum alloy product includes at least 5.6 wt. % Zn.

6. The wrought 7xxx aluminum alloy product of claim 1, wherein the wrought 7xxx aluminum alloy product includes not greater than 2.25 wt. % Cu.

7. The wrought 7xxx aluminum alloy product of claim 6, wherein the wrought 7xxx aluminum alloy product includes at least 1.75 wt. % Cu.

8. The wrought 7xxx aluminum alloy product of claim 1, wherein the wrought 7xxx aluminum alloy product includes at least 1.35 wt. % Mg.

9. The wrought 7xxx aluminum alloy product of claim 8, wherein the wrought 7xxx aluminum alloy product includes not greater than 1.65 wt. % Mg.

10. The wrought 7xxx aluminum alloy product of claim 1, wherein the 7xxx aluminum alloy product realizes a typical L-S crack deviation resistance (Kmax-dev) of at least 25 ksi-sqrt-in.

11. The wrought 7xxx aluminum alloy product of claim 1, wherein the wrought aluminum alloy product passes HHSCC-G49 testing at 90° C. for 10 days.

12. An aerospace structural component made from the wrought 7xxx aluminum alloy product of claim 1.

13. A method for producing a wrought 7xxx aluminum alloy, the method comprising:

(a) casting an alloy having the composition of claim 1 as an ingot or billet;

(b) homogenizing the ingot or billet;

(c) hot working the ingot or billet to an intermediate gauge product or final gauge product;

(d) optionally cold working the intermediate gauge product into the final gauge product;

(e) solution heat treating the final gauge product followed by quenching;

(f) optionally stretching or compressing the solution heat treated and quenched product by 1-5%;

(g) artificially aging the solution heat treated and quenched product.

14. The method of claim 13, wherein the homogenization temperature is at least T(homog.), wherein T(homog.) is calculated in degrees Fahrenheit from the formula 614.4+55.2*Cu+83.1*Mg−1.8*Zn, wherein the Cu, the Mg, and the Zn are the weight percent amounts of copper, magnesium and zinc, respectively, in the wrought 7xxx aluminum alloy.

15. The method of claim 13, wherein the artificial aging comprises first aging at a first aging temperature of from 200-300° F. followed by second aging at a second aging temperature of from 250-350° F., wherein the second aging temperature is at least 10° F. higher than the first aging temperature.

16. The method of claim 13, wherein the total equivalent artificial aging time is t(eq.), wherein t(eq.) is from 7 to 20 hours, wherein t(eq.) is calculated from the formula t ⁡ ( eq. ) = ∫ exp ⁡ ( - 12800 / T ) ⁢ dt exp ⁡ ( - 12800 / Tref ) wherein T is the instantaneous temperature in ° K during the artificial aging, and wherein Tref is a reference temperature selected at 160° C. (433.15° K).

17. The method of claim 16, wherein t(eq) is not greater than 19 hours.

18. A rolled 7xxx aluminum alloy plate product comprising:

5.9-6.2 wt. % Zn;

1.4-1.7 wt. % Mg;

2.0-2.3 wt. % Cu;

0.05-0.15 wt. % Zr;

up to 0.20 wt. % Cr;

up to 0.15 wt. % Ti; and

not greater than 0.04 wt. % Mn;

the balance being aluminum and unavoidable impurities;

wherein the rolled 7xxx aluminum alloy plate product has a thickness of from 3 to 12 inches; and

wherein the rolled 7xxx aluminum alloy plate product realizes at least three of: (a) a typical tensile yield strength (ST) of at least 57 ksi; (b) a typical KIC plane-strain fracture toughness (S-L) of at least 20 ksi-sqrt-inch; (c) a typical elongation (ST) of at least 5%; and (d) passing of the HHSCC-G49 test at 90° C. for 15 days.