Patent Application
20240392417
The present invention is related to aluminum-zinc-magnesium-copper alloys, which are commonly known as the 7xxx-series of aluminum alloys as defined by The Aluminum Association, and more particularly, Al—Zn—Mg—Cu compositions and processing methods providing extruded products with an improved combination of properties.
The 7xxx-series of aluminum alloys have been extensively utilized for structural components in aerospace applications due to their high specific strengths. However, it is difficult to improve the strength of aluminum alloys without adversely affecting other properties such as corrosion resistance and fracture toughness. For example, peak aged 7xxx-series T6x products often exhibit poor stress corrosion cracking resistance. Accordingly, modern aircraft design dictates these alloys be used in more corrosion resistant T7x tempers at the concession of strength. A 7xxx-series aluminum alloy which displays an improved combination of fracture toughness, corrosion resistance, and high strength would be highly desirable to the aerospace industry.
Aluminum alloy AA7050 was registered in 1971. The alloy exhibited reduced quench sensitivity compared to other 7xxx-series alloys available at the time thus allowing the production of thick 7xxx-series products. Improvements in casting technology and the introduction of high-speed machining allowed thick 7050 plate to be adopted in the aerospace industry.
More recently, the need for high toughness products, especially in plane stress conditions, lead to the introduction of more advanced thick 7050 plate products commonly referred to as “7050 Type II.” These developments lead to the creation of dilute 7xxx-series alloys like AA7040, AA7085, AA7037, AA7160, AA7065 and AA7140 with improved combinations of strength and fracture toughness. These dilute alloys were mostly manufactured as plate or forging products rather than high damage tolerance extrusion products. An aluminum alloy displaying an improved combination of strength and fracture toughness in an extruded product would be highly desirable.
The European Aviation Safety Agency (EASA) released safety information bulletins identifying reports of brittle cracking of aluminum alloy components. EASA Safety Information Bulletin No. 2018-04, “Environmentally Assisted Cracking in certain Aluminium Alloys” dated Feb. 2, 2018; and EASA Safety Information Bulletin No. 2018-04R1, “Environmentally Assisted Cracking in certain Aluminium Alloys” dated Sep. 13, 2018, which are incorporated herein by reference. Investigations by EASA of new generation 7xxx-series alloys showed they were sensitive to a phenomenon known as Environmental Assisted Cracking (EAC). The bulletins indicate that EAC susceptibility was confirmed for AA7037, AA7040-T7651, AA7055, AA7085, AA7099, AA7140 and AA7449. An aluminum alloy product exhibiting high strength, high fracture toughness and improved corrosion resistance would be highly desirable.
The present invention provides improved aluminum-zinc-magnesium-copper alloys and methods of making extruded products therefrom. The alloys may be provided as wrought Al—Zn—Mg—Cu extrusions having improved combinations of strength, fracture toughness, fatigue resistance and corrosion resistance.
An aspect of the present invention is to provide an extruded aluminum alloy product comprising from 5.90 to 6.50 weight percent Zn, from 1.50 to 1.90 weight percent Mg, from 1.60 to 2.30 weight percent Cu, from 0.08 to 0.12 weight percent Zr, from 0.01 to 0.05 weight percent Ti, and the balance Al and incidental impurities.
Another aspect of the present invention is to provide a method of making an extruded aluminum alloy product. The method comprises homogenizing a cast billet or shape of the aluminum alloy described above, hot working the billet or shape into an extruded product, subjecting the extruded product to a solution heat treatment at a temperature of from 880 to 910° F., quenching the solution heat treated product, stretching the extruded product, and artificially aging the extruded product to at least one temperature of from 315 to 345° F. for 5 to 20 hours.
These and other aspects of the present invention will be more apparent from the following description.
Unless otherwise specified, all indications relating to the chemical composition of the alloys herein are expressed as percentage by weight based on the total weight of the alloy. Herein, this may be denoted as wt. % or weight % or weight percent. References to commercially known alloys, where applicable, are named in accordance with the regulations of The Aluminum Association, known to those skilled in the art. The density of an alloy depends upon its composition and can be calculated, when not physically measured, in accordance with The Aluminum Association procedure, which is described on pages 2-13 through 2-15 of “Aluminum Standards and Data 2017.” Definitions of common alloy tempers can also be found in “Aluminum Standards and Data 2017” on pages 1-6 through 1-10.
The present invention provides aluminum-based alloys suitable for forming into extruded products having surprisingly improved combinations of strength, fracture toughness, corrosion resistance, and fatigue resistance. The main alloying elements are Zn, Mg and Cu. The alloys may have a density between 0.101 and 0.103 lbs/in3, for example 0.102 lbs/in3.
A minimum zinc level is needed for strength. However, Zn should be limited, in combination with the Cu and Mg contents, to avoid potential EAC concerns, as more fully described below. Zn may be present in amounts greater than 5.90 weight percent, for example, greater than 6.00 weight percent, or greater than 6.10 weight percent. Zn may be present in amounts less than 6.50 weight percent, for example, less than 6.40 weight percent, or less than 6.35 weight percent, or less than 6.30 weight percent, or less than 6.25 weight percent, or less than 6.20 weight percent. Zn may be present in amounts from 5.90 to 6.50 weight percent, for example, from 6.00 to 6.40 weight percent, or from 6.10 to 6.35 weight percent, or from 6.10 to 6.30 weight percent, or from 6.10 to 6.25 weight percent, or from 6.10 to 6.20 weight percent.
Magnesium may be added to increase strength, any may slightly decrease the alloy's density. Mg may be present in amounts greater than 1.50 weight percent, for example, greater than 1.55 weight percent, or greater than 1.56 weight percent, or greater than 1.60 weight percent, or greater than 1.64 weight percent. Mg may be present in amounts less than 1.90 weight percent, for example, less than 1.85 weight percent, or less than 1.80 weight percent, or less than 1.75 weight percent. Mg may be present in amounts from 1.50 to 1.90 weight percent, for example, from 1.55 to 1.85 weight percent, or from 1.56 to 1.80 weight percent, or from 1.60 to 1.75 weight percent, or from 2.64 to 1.75 weight percent. The Zn:Mg ratio may be less than 3.85, or less than 3.80.
Copper may be provided in sufficient amounts to increase stress corrosion cracking resistance and increase strength. However, care should be taken in selecting Cu content to avoid increases in quench sensitivity. Cu may be present in amounts greater than 1.60 weight percent, for example, greater than 1.70 weight percent, or greater than 1.75 weight percent, or greater than 1.80 weight percent. Cu may be present in amounts less than 2.30 weight percent, for example, less than 2.20 weight percent, or less than 2.10 weight percent, or less than 2.00 weight percent, or less than 1.90 weight percent. Cu may be present in amounts from 1.60 to 2.30 weight percent, for example, from 1.70 to 2.20 weight percent, or from 1.75 to 2.10 weight percent, or from 1.80 to 2.00 weight percent, or from 1.80 to 1.90 weight percent. The Cu content may be greater than Mg content.
Zn, Mg and Cu help form n-type precipitates in the aluminum alloys. While the inventors do not wish to be held to any theory of invention, it is believed that the improved combination of strength, toughness, and corrosion resistance demonstrated herein is due to the balance of these main alloying elements according to help form these precipitates by optimizing the (Zn+Cu)/Mg ratio. In weight percent, the (Zn+Cu):Mg ratio may be from 4.7 to 4.9.
Zirconium may be added as a dispersoid forming element. Dispersoids may control recrystallization and affect quench sensitivity in thick products. The Zr content may be greater 0.08 wt. %, but less than 0.15 or 0.12 wt % to avoid forming primary intermetallics during casting. Zr may be present in amounts greater than 0.05 weight percent, for example, greater than 0.08 weight percent, or greater than 0.09 weight percent. Zr may be present in amounts less than 0.15 weight percent, for example, less than 0.12 weight percent. Zr may be present in amounts from 0.05 to 0.15 weight percent, for example, from 0.08 to 0.12 weight percent, or from 0.09 to 0.12 weight percent.
Titanium additions may be made during the casting process of billets for extrusion. The Ti may limit the as-cast grain size. However, care must be taken in choosing the proper Ti content in order to not negatively affect electrical conductivity. Ti may be present in amounts greater than 0.01 weight percent or greater than 0.02 weight percent. Ti may be present in amounts less than 0.05 weight percent, for example, less than 0.04 weight percent, or less than 0.03 weight percent. Ti may be present in amounts from 0.01 to 0.05 weight percent, for example, from 0.01 to 0.04 weight percent, or from 0.02 to 0.03 weight percent.
Mn may be present in amounts less than 0.05 weight percent, or less than 0.02 weight percent. Mn may be present in amounts of from 0 to 0.05 weight percent, for example, from 0 to 0.02 weight percent. The alloys may also be substantially free of Mn.
Sr may be present in amounts of at least 0.01 weight percent, or at least 0.02 weight percent, or at least 0.03 weight percent. Sr may be present in amounts less than 0.10 weight percent, or less than 0.08 weight percent. Sr may be present in amounts of from 0.02 to 0.10 weight percent, or from 0.03 to 0.08 weight percent. While not intending to be bound by any particular theory, it is believed Sr additions improve EAC resistance by not allowing hydrogen to diffuse to potential initiation sites or crack tips. The alloys may also be substantially free of Sr.
As used herein, the term “substantially free”, when referring to alloying additions, means that a particular element or material is not purposefully added to the alloy, and is only present, if at all, in minor amounts as an impurity.
Si, Fe and Mn may be considered impurities in the present invention. Modern 7xxx-series alloys typically contain Si and Fe content less than or equal to 0.05 wt. % to obtain high mechanical properties. Some conventional alloys only demonstrate high mechanical properties with Si and Fe contents less than 0.04 wt. %, which requires aluminum producers to use higher more expensive grades of prime aluminum during casting and limits the use of recycled scrap materials. Surprisingly, the alloys of the present invention maintain high levels of strength, fracture toughness, and fatigue resistance with moderate Si and Fe levels. For example, Si and Fe contents of 0.04 and 0.07, respectively.
For example, the alloys may comprise in weight percent, 5.9-6.5 wt. % Zn, 1.55-1.80 wt. % Mg, 1.60-2.00 wt. % Cu, 0.05 max wt. % Mn, 0.09-0.12 wt. % Zr, 0.07 wt. % Si, 0.09 wt. % Fe, 0.01-0.05 wt. % Ti, and up to 0.10 wt. % Sr These compositional ranges are listed as Composition I in Table 1. The compositions listed in Table 1 comprise a balance of aluminum and minor incidental impurities.
As another example, the alloys may contain, in weight percent, 1.60-2.00 Cu, 1.56-1.76 Mg, 6.0-6.4 Zn, 0.01-0.05 Ti, 0.09-0.012, 0.07 max Si, and 0.09 max Fe. The balance being aluminum and minor incidental impurities. The calculated density of the alloy composition should round to 0.102 lbs/in3. The alloy of the present invention could also contain Sr up to 0.10 wt. %. These compositional ranges are listed as Composition II in Table 1.
As a further example, an alloy composition in accordance with the present invention may contain, in weight percent, 1.80-1.90 Cu, 1.64-1.72 Mg, 6.10-6.30 Zn, 0.01-0.04 Ti, 0.09-0.12 Zr, 0.07 max Si, 0.08 max Fe, and max 0.02 Mn. This alloy compositional range is listed as Composition III in Table 1.
Another example may contain, in weight percent, 1.80-1.90 Cu, 1.64-1.72 Mg, 6.10-6.30 Zn, 0.01-0.04 Ti, 0.09-0.12 Zr, 0.01-0.07 Sr, 0.07 max Si, 0.08 max Fe, and max 0.02 Mn. This alloy compositional range is listed as Composition IV in Table 1.
Another example may contain, in weight percent, 1.64-1.72 Cu, 1.60-1.68 Mg, 6.10-6.30 Zn, 0.01-0.04 Ti, 0.09-0.12 Zr, 0.07 max Si, 0.08 max Fe, and max 0.02 Mn. This alloy compositional range is listed as Composition V in Table 1.
Extruded products made from Al—Zn—Mg—Cu alloys of the present invention and the methods described herein have been found to possess favorable properties including improved combinations of strength, fracture toughness, fatigue resistance, and corrosion resistance.
Unless otherwise specified, static mechanical characteristics, in other words the ultimate tensile strength (UTS), tensile yield strength (TYS), and the elongation at fracture (e), are determined by a tensile test according to standard ASTM B557-Standard Test Methods for Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products, included herein as reference. Mechanical testing may be performed in selected orientations including longitudinal (L), longitudinal-transverse (LT or L-T), transverse-longitudinal (TL or T-L), short-longitudinal (SL or S-L) and short-transverse (ST or S-T) directions.
It is known that the mechanical properties of extrusions can be affected by the aspect ratio of the extruded section being tested. Herein, the aspect of an extruded product is defined as the ratio of the width (W) to the height (H) of an uninterrupted section. For example, a one-inch by three-inch bar would have an aspect ratio of 3:1 or 3. As used herein, the term low aspect ratio relates to an extruded section with an aspect ratio less than or equal to 4:1. As used herein, the term high aspect ratio relates to an extruded section having an aspect ratio greater than or equal to 7:1. As used herein, the term medium aspect ratio section relates to an extruded section having an aspect ratio between 4:1 and 7:1. It will be recognized that in general for non-recrystallized products that low aspect ratio sections generally display high longitudinal (L) tensile strengths coupled with lower longitudinal-transverse (LT) tensile strengths whereas high aspect ratio sections generally display more isotropic L and LT strengths. As known by those skilled in the art, complex extrusion can have multiple sections or legs with various aspect ratios or textures. Test orientations in extruded sections are defined by the localized grain flow in the extruded section. These regions may be defined as transition zones. The transition zones may be formed at joints of different legs of the same extrusion.
Unless otherwise specified, electrical conductivity testing was performed according to ASTM E1004-Standard Test Method for Determining Electrical Conductivity Using the Electromagnetic (Eddy Current) Method. Conductivity measurements were taken sub-surface near the area of test coupon extraction unless otherwise specified.
Unless otherwise specified, fracture toughness is evaluated according to ASTM E399-Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIC of Metallic Materials and ASTM B645-Standard Practice for Linear-Elastic Plane-Strain Fracture Toughness Testing of Aluminum Alloys. As set forth in ASTM B645, fracture toughness may be given a KIC or Kq.
Unless otherwise specified, Kapp fracture toughness is tested in accordance with ASTM E561-Standard Test Method for KR Curve Determination.
Unless otherwise specified exfoliation corrosion (EXCO) resistance was determined in accordance with ASTM G34-Standard Test Method for Exfoliation Corrosion Susceptibility in 2xxx and 7xxx Series Aluminum Alloys (EXCO Test).
Unless otherwise specified, stress corrosion cracking (SCC) resistance was determined according to either ASTM G47-Standard Test Method for Determining Susceptibility to Stress-Corrosion Cracking of 2xxx and 7xxx Aluminum Alloy Products, ASTM G44-Standard Practice for Exposure of Metals and Alloys by Alternate Immersion in Neutral 3.5% Sodium Chloride Solution, and/or ASTM G38-Standard Practice for Making and Using C-Ring Stress Corrosion Test Specimens as applicable as known by one skilled in the art.
Unless otherwise specified, environmental assisted cracking (EAC) resistance was determined by a constant load tensile sample taken from the mid-thickness of an extrusion and tested in accordance with the procedure detailed in the European Aviation Safety Agency (EASA) safety information bulletin number 2018-04R1, Sep. 13, 2018. Samples subjected to the EAC test at specified ST TYS levels that survive at least 100 days may be deemed to have passed the EAC test.
Unless otherwise specified, Jominey end quenches were performed using rectangular bar 12 in ×1.5 in ×0.40 in where machined from the mid-section of the bar (W/2 and T/2). The bars are then solution heat treated and quenched by being suspended in agitated water such that 1.5 inches of the bar is below the water line. The bars are allowed to quench in this manner for 10 minutes before being fully submerged in the water quenchant.
Unless otherwise specified, Rockwell hardness testing was performed according to ASTM E18-Standard Test Methods for Rockwell Hardness of Metallic Materials using the Rockwell Hardness B-scale.
Unless otherwise specified, fatigue testing was performed according to ASTM E466-Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials using T-type specimens with an open hole Kt of 2.3 with a minimum/maximum load ratio R of 0.1 and a test frequency of 25-30 hz in lab air at room temperature.
Unless otherwise specified, chemical composition was determined according to ASTM E1251-Standard Test Method for Analysis of Aluminum and Aluminum Alloys by Atomic Emission Spectrometry.
Unless otherwise specified, solution heat treatment and artificial aging was performed in accordance with AMS 2772-Heat Treatment of Aluminum Alloy Raw Materials and AMS 2750-Pyrometry.
In accordance with certain embodiments of the present invention, the following method may be followed using the alloy compositions of the present invention to obtain an extruded alloy with the desired combination of strength, fracture toughness, fatigue resistance, and ductility. In certain embodiments, equivalent homogenization times and aging times may be calculated when multi-step homogenization and aging practices are utilized. An equivalent time at temperature during homogenization or aging is given by the following equation:
Where t1 and t2 are times in hours, Tref is the reference temperature in degrees Kelvin, T2 is temperature in degrees kelvin, Q is the activation energy, and R is the universal gas constant.
In accordance with an embodiment of the present invention, the method relates to the manufacturing process for an extruded aluminum product. First, a liquid metal bath is prepared to obtain an aluminum alloy having a composition in accordance with an embodiment of the present invention. The alloy is manufactured by casting a billet, ingot, or shape from a liquid metal bath, for example, by using direct-chill casting.
The unwrought billet, ingot, or shape is homogenized such that at least one step is above 880° F. such that the equivalent time at 890° F. (Tref) of the step using a Q of 125.6 KJ/Mol and R=8.314462 JK−1 mol−1 given by the following equation:
is between 20 and 48 hours. For example, the unwrought shape may be homogenized using a two-step homogenization process. The first step of the homogenization process may be performed at a temperature of at least 820° F., or from 820° F. to 880° F., or from 860° F. to 880° F. A second step of the homogenization process may be performed at least 880° F., or from 890° F. to 910° F. In certain embodiments, a two-step homogenization process is used, but a homogenization process with any other suitable number of steps may be used, e.g., one, three, four, or more steps insofar as the equivalent time-at-temperature conditions are met.
In accordance with an embodiment of the present invention, the unwrought product is then hot worked into an extruded product. As known to those skilled in the art, the extrusion can be done either via direct or indirect extrusion. The extrusion ratio of the extrusion, which herein is defined as:
Where ER is the extrusion ratio, AC is the area of the container, AE is the area of the extrusion, and n is the number of holes may be between 7 and 90. In certain embodiments, the ER may be between 8 and 30 or 10 and 20. In an embodiment of the present invention, the F-temper extrusion may optionally be cold worked. As used herein, the term “F-temper extrusion” means an extrusion that has been fabricated using a shaping process like extrusion without further solution heat treatment.
In accordance with an embodiment of the present invention, the extruded product is then solution heat treated at a temperature between 880° F. and 910° F. and then quenched. In certain embodiments the quenched product may be kept at an ambient temperature for a short period of time before stretching. For example, less than 24 hours, or less than 12 hours, or less than 4 hours.
The extruded product may then be stretched with a permanent set of 0.5-5% on a straight stretch. For example, an embodiment of the present invention may be stretched 1-3%. A conventional forming process can also be applied to the extrusion at this time, which could result in slightly larger or lower stretch percentages locally depending on the final form.
After stretching, the extruded product may be subject to a natural aging period, which occurs at ambient temperatures, as known to those skilled in the art. During this time period, the extrusion may be corrected for any geometrical deviations from straightness commonly referred to as longitudinal bow, lateral bow, twist, and flatness as known to those skilled in art.
As known by those skilled in the art, it is often advantageous to use equivalent aging times (teq) to define and control the artificial aging of aluminum alloys. Herein, the equivalent aging time, in hours, is defined as:
Where Tref is the reference temperature, herein 439° K; Ta is the artificial aging temperature; and ta is the artificial aging time in hours.
In accordance with the present invention, the wrought extruded product may be artificially aged to an overaged or T7x condition to optimize the balance between strength, corrosion resistance, and fracture toughness. A multi-step age practice consisting of two or more steps may be used with at least one step less than 275° F. for 5 to 36 hours and at least one step greater than 275° F., preferably at 315° F. to 345° F. such that the equivalent time at 439° K is 5 to 20 hours, preferably 10 to 16 hours such that the electrical conductivity is at least 39.5% IACS, preferably greater than 40% IACS.
Alloys according to the present invention, when processed, have an improved combination of strength, fracture toughness, corrosion resistance, and fatigue resistance without the need for high purity prime aluminum and have a density of 0.102 lbs/in3.
The following examples are intended to illustrate various aspects of the present invention, and are not intended to limit the scope of the invention.
Several 7-inch billets of 7xxx-series aluminum alloys having compositions listed in Table 2 were cast using direct chill casting. Compositions have balances of aluminum and incidental impurities. Alloys Inv. A and Inv. B are example alloys of the present invention. Alloys 7050 and 7055 represent alloys falling within the registered aluminum association limits of AA7050 and AA7055, respectively. The densities given in Table 2 are calculated in units of lbs/in3.
The billets were then homogenized according to the practices given in Table 3. Billets of Inv. A, Inv. B, and 7050 were homogenized according to practice H1 (865° F. for 8 hours followed by 890° F. for 36 hours). Billets of alloy 7055 were homogenized according to practice H2 (835° F. for 12 hours followed by 860° F. for 12 hours followed by 880° F. for 12 hours followed by 890° F. for 24 hours). After homogenization the billets were allowed to cool to room temperature.
The homogenized billets were then subject to hot extrusion to obtain F-temper bar sections, either a 1.125 inch×4.0 inch or a 1 inch×5 inch bar, as detailed in Table 4. The bar sections were chosen specifically to give extrusion ratios (ER), known to those skilled in the art, of less than 10:1 to simulate the grain size of larger extrusions. The F-Temper sections were then solution heat treated (SHT), quenched in a 15% glycol and water solution, stretched, and aged according to one of the processing procedures detailed in Table 4. Herein, test samples are identified as Alloy-Homogenization-processing procedure. For example, alloy Inv. A homogenized according to practice H1 and thereafter processed according to practice P1 would be identified as “Inv. A-H1-P1.” Equivalent age time (teq) is calculated in this table using a Tref of 330° F.
Samples taken near the rear of each extruded section were then tested to determine the static mechanical properties (ultimate tensile strength UTS, tensile yield strength TYS, and elongation a fracture e), fracture toughness (Kq), and electrical conductivity (% IACS). The results obtained are presented in Table 5,
1Values denoted with a superscript 1 are Klc.
In this example, several billets of Al—Zn—Mg—Cu alloys having compositions listed in Table 6 were cast using direct chill casting techniques. Compositions have balances of aluminum and incidental impurities. Densities are in units of lbs/in3. Alloy Inv. C is an example of an alloy of the present invention. Alloys 7050B, 7050C, and 7050D represent alloys falling within the registered Aluminum Association limits of AA7050.
The billets were homogenized according to the practices in Table 7. Billets of Inv. C were homogenized according to practice H3 (880° F.-4 hours followed by 900° F.-24 hours). Billets of 7050B and 7050C were homogenized according to H4 (865° F.-8 hours followed by 890° F.-30 hours). Billets of 7050D were homogenized according to H5 (865° F.-8 hours followed by 890° F.-15 hours followed by 895° F.-15 hours).
The homogenized billets were then subject to hot extrusion to obtain a wrought F-temper section according to
The wrought F-temper sections were then solution heat treated, quenched, stretched, and aged according to one the processing procedures detailed in Table 8. Equivalent age time (teq) is calculated using a Tref of 330° F. It should be noted that for each of the processing procedures detailed in Table 8 that there was a natural aging period of at least 24 hours between stretching and artificial aging. The microstructure of the resulting T-temper extrusions were largely not recrystallized with at least 75% of the grains being unrecrystallized, generally greater than 90%. Recrystallized grains were limited to the outer most periphery of the profile as would be expected by one skilled in the art of extrusion. Herein, test samples are identified as Alloy-Homogenization-Processing Procedure. For example, alloy 7050D homogenized according to practice H5 and processed according to P2 would be identified as 7050D-H5-P2.
Samples taken from the end of the extruded sections were tested to determine the static mechanical properties (Ultimate Tensile Strength UTS, Tensile Yield Strength TYS, and elongation at fracture e) and fracture toughness (Kq and Kapp). Samples were taken from locations 1, 2 and 3 of
In this example, fracture toughness (Kq) coupons from location 1 had a nominal geometry of W=2.5 inches and B=1.25 inches. Fracture coupons (Kq) taken from location 3 had a nominal geometry of W=2.0 inches and B=1.0 inch. Kapp fracture coupons taken from location 1 and location 3 both had a nominal geometry of W=5.0 inches and B=0.3 inches.
The average results obtained for tensile strength and fracture toughness (ASTM E399/ASTM B645) can be found in Table 9 and
1Values denoted with a superscript 1 are Klc.
In this example, billets of Inv. C per Table 6 homogenized according to H3 per Table 7 were hot extruded into a 3 inch by 21-inch bar section. The ER of the F-temper section was approximately 10:1. Modified Jominey end quench bars, known to those skilled in art, measuring 12 in ×1.5 in ×0.40 in where machined from the mid-section of the bar (W/2 and T/2).
The quench bars were then solution heat treated at 890° F. for 1 hour before being quenched in agitated water such that 1.5 inches of the bar was below the water line. The quench rate was measured at various locations relative to the end of the quench bar in the water as can be seen in Table 11. The average quench rate per TC located in Table 11 is the result of three separate quench trials and constitutes the average quench rate between 750° F. and 500° F.
The end quench bar was then aged at 250° F. for 24 hours before being Rockwell hardness (B-scale) tested (HRB) at the various TC locations to determine a strength factor. The results can be seen in
In this example, several billets of Al—Zn—Mg—Cu alloy having compositions listed in Table 12 were cast into billets. Alloys Inv. C and Inv. D are examples of the present invention.
The as-cast billets were then homogenized according to one of the homogenization practices given in Table 13.
The homogenized billets were then subject to hot extrusion to obtain the wrought F-temper sections in
Samples taken at the rear of the extruded section were tested to determine the static mechanical properties (Ultimate Tensile Strength “UTS,” Tensile Yield Strength “TYS,” and elongation at fracture “e”), fracture toughness (KQ), and electrical conductivity. The results can be seen in Table 15 and Table 16. Tensile tests and fracture toughness tests were taken from location 1 in each test shape in
1Average result of 10 tests.
Fatigue test specimens were machined from samples randomly taken down the length of each extruded section at location 2 for shape 61416, location 2 for shape 63941, location 1 for shape 76145, and location 2 for shape 76145. The T-type kt 2.3 coupons were machined and tested in the L-T orientation.
Additionally, a commercially available 7050-T7451 plate (Th-8 inches) was fatigue tested for comparison. The composition of the comparison plate as reported by the manufacture can be found in Table 17. Herein, this plate product is referred to as 7050E. The remainder of the alloy is aluminum and incidental impurities. Density is given in lbs/in3.
The fatigue test results can be found in Table 18 and
In this example, several billets of Al—Zn—Mg—Cu alloy having compositions listed in Table 19 were cast into billets. Compositions have balances of aluminum and incidental impurities. Densities are in units of lbs/in3. Alloys Inv. C, Inv. E, and Inv. F are examples of the present invention. Alloy 7050F represents an alloy falling within the registered Aluminum Association limits for AA7050. Alloys U1 and U2 are alloys falling within the AA7140 range.
The billets were homogenized according to the practices in Table 7. Alloys Inv. C, Inv. E, and Inv. F were homogenized according to practice H3. Alloy 7050F was homogenized according to practice H4. Alloys U1 and U2 were homogenized according to H7 and H8, respectively.
The homogenized billets were then extruded into wrought F-temper bar sections as detailed in Table 21. The bar sections were then solution heat treated (SHT), quenching using a horizontal spray quench known to those skilled in the art of extrusion, stretched, and artificially aged according to one of the processing procedures detailed in Table 21. Herein, test samples are identified as Alloy-Homogenization-Processing Procedure. For example, Alloy Inv. E homogenized according to practice H3 and then processed according to P14 would be identified as Inv. E-H3-P14.
Samples were taken from the rear of the extruded sections to determine the static mechanical properties (Ultimate Tensile Strength UTS, Tensile Yield Strength TYS, and elongation at fracture e) and fracture toughness. The results can be found in Table 22, Table 23,
Additionally, short-transverse tensile stress corrosion cracking test samples were taken from the back half of several bars. The samples were tested for 20 days in accordance with ASTM G47. The results can be seen in Table 24.
In this example, several Al—Zn—Mg—Cu alloys having compositions listed in Table 25 were cast using direct chill casting techniques. Compositions have balances of aluminum and incidental impurities. Densities are in units of lbs/in3. Alloys Inv. C and alloy Inv. D represent examples of the present invention. Alloy 7040A represents an aluminum alloy falling within the Aluminum Association limits of AA7040. The densities in Table 25 are calculated.
The billets were then homogenized according one of the practices listed in Table 26. Alloy Inv. C homogenized according to practice H3 (880° F. for 8 hours followed by 900° F. for 24 hours). Alloys Inv. D and 7040A were homogenized according to practice H6 (880° F. for 4 hours followed by 895° F. for 26 hours). After homogenization the billets were allowed to slowly cool to room temperature as known to those skilled in the art.
The homogenized billets were then subjected to hot extrusion to obtain wrought F-temper profiles of shape 63941 according to
Samples were taken from the rear of the extruded sections to determine the static mechanical properties (Ultimate Tensile Strength UTS, Tensile Yield Strength TYS, and elongation at fracture e) and fracture toughness. The results can be seen in Table 28, Table 29, and
1Denotes a Kq value.
In this example, billets of Inv. D were cast and homogenized according to practice H6 before being hot extruded into the profile shown in
Samples taken from the rear of the extrusion were then subjected to ST tensile and SCC testing. The results can be seen in Table 30, with DNF designating did not fail. Additionally, a modified EAC test was performed on the extrusion at two different stress levels 45 ksi and 50 ksi. It will be recognized the only modification to the EAC test were the applied stress levels which were approximately 72% (45 ksi) and 80% (50 ksi) of the ST TYS. Surprisingly, all of the Inv. SCC and EAC results are days to failure. SCC tests were discontinued after 20 days and EAC tests were discontinued after 150 days. A result of DNF indicates the sample did not fail. D EAC test specimens passed the EAC test by surviving at least 100 days at specified ST TYS levels as denoted in Table 30.
The following Aspects are provided.
Aspect 1. An extruded aluminum alloy product comprising from 5.90 to 6.50 weight percent Zn, from 1.50 to 1.90 weight percent Mg, from 1.60 to 2.30 weight percent Cu, from 0.08 to 0.12 weight percent Zr, from 0.01 to 0.05 weight percent Ti, and the balance Al and incidental impurities.
Aspect 2. The extruded aluminum alloy product of the preceding aspect, wherein the Cu is less than 2.00 weight percent.
Aspect 3. The extruded aluminum alloy product of any of the preceding aspects, wherein the Cu is less than 1.90 weight percent.
Aspect 4. The extruded aluminum alloy product of any of the preceding aspects, wherein the Cu is greater than 1.70 weight percent.
Aspect 5. The extruded aluminum alloy product of any of the preceding aspects, wherein the Cu is greater than 1.80 weight percent.
Aspect 6. The extruded aluminum alloy product of any of the preceding aspects, wherein the Cu is from 1.70 to 2.00 weight percent.
Aspect 7. The extruded aluminum alloy product of any of the preceding aspects, wherein the Cu is from 1.80 to 1.90 weight percent.
Aspect 8. The extruded aluminum alloy product of any of the preceding aspects, wherein the Mg is less than 1.90 weight percent.
Aspect 9. The extruded aluminum alloy product of any of the preceding aspects, wherein the Mg is less than 1.80 weight percent.
Aspect 10. The extruded aluminum alloy product of any of the preceding aspects, wherein the Mg is greater than 1.55 weight percent.
Aspect 11. The extruded aluminum alloy product of any of the preceding aspects, wherein the Mg is greater than 1.60 weight percent.
Aspect 12. The extruded aluminum alloy product of any of the preceding aspects, wherein the Mg is from 1.55 to 1.90 weight percent.
Aspect 13. The extruded aluminum alloy product of any of the preceding aspects, wherein the Mg is from 1.60 to 1.80 weight percent.
Aspect 14. The extruded aluminum alloy product of any of the preceding aspects, wherein the Zn is less than 6.30 weight percent, or less than 6.25 weight percent.
Aspect 15. The extruded aluminum alloy product of any of the preceding aspects, wherein the Zn is greater than 6.00 weight percent.
Aspect 16. The extruded aluminum alloy product of any of the preceding aspects, wherein the Zn is from 6.00 to 6.30 weight percent.
Aspect 17. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product comprises less than 0.05 weight percent Mn.
Aspect 18. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product is substantially free of Mn.
Aspect 19. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product further comprises from 0.01 to 0.10 weight percent Sr.
Aspect 20. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy has a Zn:Mg weight ratio of less than 3.85.
Aspect 21. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a (Zn+Cu):Mg weight ratio of from 4.7 to 4.9.
Aspect 22. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a density of 0.103 lbs/in3 or less.
Aspect 23. The extruded aluminum alloy product of any of the preceding aspects, wherein the extruded aluminum alloy has a resistance to EAC, when tested at either 72 percent of ST TYS or 80 percent of ST TYS, of greater than 100 days.
Aspect 24. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an L elongation of greater than 14.0 percent.
Aspect 25. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has L TYS of greater than 70 ksi.
Aspect 26. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an L elongation of greater than 15.0 percent, or greater than 15.4 percent, or greater than 15.5 percent.
Aspect 27. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a T-L Kq of greater than 25.0 ksi √inch.
Aspect 28. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a T-L Kq of greater than 25.5 ksi √inch.
Aspect 29. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a T-L Kq of greater than 26.0 ksi √inch.
Aspect 30. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 43.0 ksi √inch.
Aspect 31. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 44.0 ksi √inch.
Aspect 32. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 45.0 ksi √inch.
Aspect 33. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a T-L Kq of greater than 30.0 ksi √inch.
Aspect 34. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a T-L Kq of greater than 34.0 ksi √inch.
Aspect 35. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a T-L Kq of greater than 40.0 ksi √inch.
Aspect 36. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a T-L Kq of greater than 45.0 ksi √inch.
Aspect 37. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 38.0 ksi √inch.
Aspect 38. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 40.0 ksi √inch.
Aspect 39. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 50.0 ksi √inch.
Aspect 40. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 50.0 ksi √inch, or greater than 55.0 ksi √inch.
Aspect 41. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 80.0 ksi √inch.
Aspect 42. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 90.0 ksi √inch.
Aspect 43. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Kq of greater than 95.0 ksi √inch.
Aspect 44. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an ST TYS of greater than 62 ksi.
Aspect 45. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an ST TYS of greater than 65 ksi.
Aspect 46. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an S-L Klc of greater than 26 ksi √inch.
Aspect 47. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an S-L Klc of greater than 27 ksi √inch.
Aspect 48. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an S-L Klc of greater than 30 ksi √inch.
Aspect 49. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an S-L Klc of greater than 26 ksi √inch.
Aspect 50. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L-T Klc of greater than 44 ksi √inch or a L TYS of greater than 68 ksi.
Aspect 51. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has a L TYS of greater than 70 ksi.
Aspect 52. The extruded aluminum alloy product of any of the preceding aspects, wherein the L-T Klc is greater than 44 ksi √inch and the L TYS is greater than 68 ksi.
Aspect 53. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an electrical conductivity greater than 40.6% 1ACS.
Aspect 54. The extruded aluminum alloy product of any of the preceding aspects, wherein the alloy product has an electrical conductivity greater than 41.0% 1ACS.
Aspect 55. A method of making an extruded aluminum alloy product of any of the preceding aspects, the method comprising:
As used herein, “including,” “containing” and like terms are understood in the context of this application to be synonymous with “comprising” and are therefore open-ended and do not exclude the presence of additional undescribed or unrecited elements, materials, phases or method steps. As used herein, “consisting of” is understood in the context of this application to exclude the presence of any unspecified element, material, phase or method step. As used herein, “consisting essentially of” is understood in the context of this application to include the specified elements, materials, phases, or method steps, where applicable, and to also include any unspecified elements, materials, phases, or method steps that do not materially affect the basic or novel characteristics of the invention.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances. In this application and the appended claims, the articles “a,” “an,” and “the” include plural referents unless expressly and unequivocally limited to one referent.
Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention.
This application claims the benefit of U.S. Provisional Patent Application No. 63/468,201 filed May 22, 2023, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63468201 | May 2023 | US |
