Patent Application
20250215532
The invention relates methods for producing aluminum-zinc-magnesium-copper alloy products, and more particularly methods for producing Al—Zn—Mg—Cu extrusions with an improved combination of properties.
High strength Al—Zn—Mg—Cu alloys, which include the 7xxx-series of aluminum alloys, are conventionally used for structural components in aerospace applications due to their high specific strengths. However, it is difficult to obtain high strength in 7xxx-series aluminum alloys without adversely affecting other properties such as toughness and corrosion resistance. This is particularly difficult in high solute 7xxx-series alloys, which may have Zn concentrations greater than 8.4 weight percent, Mg concentrations greater than 1.8 weight percent, and Cu concentrations greater than 1.9 weight percent. Methods for producing high-solute 7xxx-series alloys with improved combinations of strength, toughness, and corrosion resistance would be highly desirable.
Several registered aluminum alloys have compositional ranges that can be considered in whole or in part high solute alloys. For example, AA7136, AA70755 and AA7449, which are listed in Table 1 and are commonly used for aerospace applications, have registered ranges the fall within or partially within the high solute compositional ranges.
Methods of manufacturing extruded aluminum alloy products are provided. Aluminum alloy billets including Zn, Mg and Cu are subjected to a multiple-step homogenization process, followed by hot working into an extruded product, solution heat treating, quenching, stretching, and artificial aging with multiple aging steps. The resultant extruded products possess desirable mechanical properties in combination with desirable electrical conductivity and corrosion resistance properties.
An aspect of the present invention is to provide a method of manufacturing an extruded aluminum alloy product comprising homogenizing a cast unwrought billet having a composition comprising from 8.40 to 9.10 weight percent Zn, from 1.80 to 2.10 weight percent Mg, from 1.90 to 2.33 weight percent Cu, from 0.01 to 0.05 weight percent Ti, and from 0.10 to 0.14 weight percent Zr, with the balance comprising aluminum and incidental impurities in multiple steps comprising a first homogenization step at a temperature of from 820° F. to 850° F. for from 6 to 30 hours followed by another homogenization step at a temperature of from 870° F. to 890° F. for 30 to 58 hours, wherein a total equivalent time of the multiple steps at 880° F. is from 28 to 77 hours; hot working the billet into an extruded product; subjecting the product to a solution heat treatment at a temperature of from 870 to 890° F.; quenching the solution heat treated product; stretching the product with a permanent set of from 1 to 3 percent; and artificially aging the product in multiple aging steps comprising a first aging step at a temperature of from 212° F. to 275° F. for 4 to 36 hours followed by a second aging step at a temperature of from 292° F. to 335° F. for 4 to 18 hours. The artificially aged product has a density of from 0.1036 to 0.1041 lbs/in3 and: (a) a combined tensile yield strength and elongation (TYS+e) greater than or equal to −3.25*X+221.75 where X is an electrical conductivity of from 35% IACS to 39% IACS; or (b) a combined tensile yield strength and residual strength (TYS+RS) greater than or equal to 5.57148*X′−64.343 where X′ is an electrical conductivity of from 36% IACS to 37.5% IACS.
Another aspect of the present invention is to provide an extruded aluminum alloy product manufactured by the method described above.
A further aspect of the present invention is to provide an extruded aluminum alloy product comprising from 8.40 to 9.10 weight percent Zn, from 1.80 to 2.10 weight percent Mg, from 1.90 to 2.33 weight percent Cu, from 0.01 to 0.05 weight percent Ti, and from 0.10 to 0.14 weight percent Zr, with the balance comprising aluminum and incidental impurities. The product has a density of from 0.1036 to 0.1041 lbs/in3 and has: (a) a combined tensile yield strength and elongation (TYS+e) greater than or equal to −3.25*X+221.75 where X is an electrical conductivity of from 35% IACS to 39% IACS; or (b) a combined tensile yield strength and residual strength (TYS+RS) greater than or equal to 5.57148*X′−64.343 where X′ is an electrical conductivity of from 36% IACS to 37.5% IACS.
These and other aspects of the present invention will be more apparent from the following description.
The present invention provides methods of manufacturing extruded aluminum-based alloy products having improved combinations of strength, residual strength, conductivity, and corrosion resistance.
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. References to commercially known alloys, when applicable, are named in accordance with the regulations of The Aluminum Association, known to those skilled in the art.
The alloy may comprise at least 8.40 weight percent Zn, for example, at least 8.50 weight percent Zn, or at least 8.55 weight percent Zn, or at least 8.60 weight percent Zn, or at least 8.65 weight percent Zn. The alloy may comprise no greater than 9.10 Zn, for example, no greater than 9.08 weight percent Zn, or no greater than 9.05 weight percent Zn, or no greater than 9.00 weight percent Zn, or no greater than 8.95 weight percent Zn.
The alloy may comprise at least 1.80 weight percent Mg, for example, at least 1.90 weight percent Mg, or at least 1.95 weight percent Mg. The alloy may comprise no greater than 2.10 weight percent Mg, for example, no greater than 2.05 weight percent Mg.
The alloy may comprise at least 1.90 weight percent Cu, for example, at least 1.90 weight percent Cu, or at least 1.95 weight percent Cu, or at least 2.00 weight percent Cu, or at least 2.10 weight percent Cu, or at least 2.13 weight percent Cu. The alloy may comprise no greater than 2.33 weight percent Cu, for example, no greater than 2.20 weight percent Cu, or no greater than 2.15 weight percent Cu.
The alloy may comprise at least 0.01 weight percent Ti, for example, at least 0.015 weight percent Ti, or at least 0.02 weight percent Ti. The alloy may comprise no greater than 0.05 weight percent Ti, for example, no greater than 0.04 weight percent Ti, or no greater than 0.03 weight percent Ti.
The alloy may comprise at least 0.10 weight percent Zr, for example, at least 0.11 weight percent Zr, or at least 0.12 weight percent Zr. The alloy may comprise no greater than 0.14 weight percent Zr, for example, no greater than 0.13 weight percent Zr.
The alloys may comprise from 8.40 to 9.10 weight percent Zn, from 1.80 to 2.10 weight percent Mg, from 1.90 to 2.33 weight percent Cu, from 0.01 to 0.05 weight percent Ti, from 0.10 to 0.14 weight percent Zr, 0.04 max weight percent Mn, 0.11 max weight percent Si, 0.11 weight percent Fe, and 0.04 weight percent Cr, with the remainder being aluminum and incidental impurities. The (Zn+Cu):Mg ratio in weight percent may be greater than 5.3. These compositional ranges are listed as Composition I in Table 2.
The alloy products may have a density of from 0.1036 to 0.1041 lbs/in3. 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 in “Aluminum Standards and Data 2017”, pages 2-13 through 2-15. Definitions of common alloy tempers can also be found in “Aluminum Standards and Data 2017”, pages 1-6 through 1-10.
An alloy composition of the present invention may comprise from 8.60 to 9.08 weight percent Zn, from 1.90 to 2.10 weight percent Mg, from 2.10 to 2.33 weight percent Cu, from 0.10 to 0.13 weight percent Zr, from 0.01 to 0.04 weight percent Ti, 0.08 max weight percent Si, 0.10 max weight percent Fe, 0.03 max weight percent Mn, and 0.03 max weight percent Cr, with the remainder being aluminum and incidental impurities. These compositional ranges are listed in Table 2 as Composition II.
An alloy composition of the present invention may comprise from 8.65 to 9.05 weight percent Zn, from 1.95 to 2.10 weight percent Mg, from 2.13 to 2.33 weight percent Cu, from 0.01 to 0.03 weight percent Ti, from 0.10 to 0.12 weight percent Zr, 0.07 max weight percent Si, 0.08 weight percent Fe, 0.03 max weight percent Mn, and 0.03 max weight percent Cr, with the remainder being aluminum and incidental impurities. These compositional ranges are listed in Table 2 as Composition III.
A specific example of an alloy composition within the ranges of Compositions II and III may comprise 8.81 weight percent Zn, 2.01 weight percent Mg, 2.16 weight percent Cu, 0.02 weight percent Ti, and 0.11 weight percent Zr, with the remainder being aluminum and incidental impurities such as Si and Fe. This exemplary alloy is listed as Composition IV in Table 2.
An alloy composition of the present invention may comprise from 8.50 to 9.00 weight percent Zn, from 1.90 to 2.10 weight percent Mg, from 1.95 to 2.20 weight percent Cu, from 0.010 to 0.03 weight percent Ti, from 0.10 to 0.12 weight percent Zr, 0.06 max weight percent Si, 0.08 max weight percent Fe, 0.03 max weight percent Mn, and 0.03 max weight percent Cr with the remainder being aluminum and incidental impurities. These compositional ranges are listed as Composition V in Table 2.
An alloy composition of the present invention may comprise from 8.55 to 8.95 weight percent Zn, from 1.95 to 2.05 weight percent Mg, from 2.00 to 2.15 weight percent Cu, from 0.01 to 0.03 weight percent Ti, from 0.10 to 0.12 weight percent Zr, 0.06 max weight percent Si, 0.08 max weight percent Fe, 0.03 max weight percent Mn, and 0.03 max weight percent Cr with the remainder being aluminum and incidental impurities. These compositional ranges are listed as Composition VI in Table 2.
A specific example of an alloy composition within the ranges of Compositions V and VI may comprise 8.76 weight percent Zn, 2.00 weight percent Mg, 2.07 weight percent Cu, 0.02 weight percent Ti, and 0.11 weight percent Zr, with the remainder being aluminum and incidental impurities such as Si and Fe. These compositional ranges are listed as Composition VII in Table 2.
Extrusions comprising Compositions I-VII may be provided in selected thicknesses or gauges. For example, Composition I may be provided in thicknesses of from 0.04 to 0.5 inch or greater. A Composition I extrusion may have a relatively thin gauge or thickness, for example, less than 0.5 inch, or less than 0.4 inch, or less than 0.3 inch, or less than 0.25 inch. A Composition I extrusion may have a thickness of greater than 0.25 inch, such as a thickness of from 0.25 inch to 0.5 inch.
Extrusions of Compositions I-IV may have relatively thin gauges or thicknesses of, for example, from 0.04 to 0.25 inch for some uses. Extrusions of Compositions I and V-IV may have relatively thick gauges or thicknesses of, for example, from 0.25 to 0.5 inch for some uses.
The additions of Zn, Mg, and Cu, particularly in the ranges set forth herein in accordance with the present invention, may provide the capability of yielding high strength. While the inventors do not wish to be held to any theory of invention, it believed the ranges set forth herein provide an optimum compositional balance for producing f-phase, known to those skilled in the art, and typically given as MgZn2 or Mg (Zn,Cu,Al)2, while importantly being able to properly homogenize the product.
The (Zn+Cu):Mg ratio in weight percent may be greater than 5.25:1, or greater than 5.3:1, or greater than 5.35:1. The (Zn+Cu):Mg ratio may be less than 5.6:1, or less than 5.59:1, or less than 5.55:1. The (Zn+Cu):Mg ratio may be from 5.25:1 to 5.6:1, or from 5.3:1 to 5.59:1, or from 5.35 to 5.55:1. The Zn:Cu ratio in weight percent may be greater than 3.6:1, or greater than 3.8:1, or greater than 4.0:1. The Zn:Cu ratio may be less than 4.79:1, or less than 4.7:1, or less than 4.5:1. The Zn:Cu ratio may range from 3.6:1 to 4.79:1, or from 3.8:1 to 4.7:1, or from 4.0:1 to 4.5:1.
Zirconium may be added a grain controlling element, although other grain controlling elements such as Sc, Ti, Hf, Cr, or combination therefore maybe utilized. The amount of Zr alloyed into the product in accordance with the present invention may provide recrystallization resistance following the extrusion process. Additions of Zr may be kept at or below 0.14 weight percent to avoid the formation of primary intermetallics, especially when combined with Mn, Cr, and Ti additions. Additions of Zr in accordance with the present invention, especially when homogenized in accordance with the method of manufacture detailed herein, may provide enhanced recrystallization resistance over the prior art.
Titanium may be added as a grain refining element, typically via TiB or TiC, during the casting process. In accordance with the present invention, Ti additions may be controlled in order to not adversely affect electrical conductivity.
Extruded products made using the methods of the present invention have been found to exhibit favorable properties including high strength, good damage tolerance, and good corrosion resistance.
It is known that the mechanical properties of extrusions can be affected by the aspect ratio of the extruded texture being tested. As used herein, the aspect ratio of an extruded section 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 or 3:1. As used herein, the term high aspect ratio relates to a section of an extrusion have an aspect ratio greater than or equal to 7:1. As used herein, the term low aspect ratio section relates to a section of an extrusion having an aspect ratio less than or equal to 4:1. As used herein, the term medium aspect ratio relates to a section of an extrusion with an aspect ratio between 4:1 and 7:1. It is known that complex extrusions can have multiple sections with various aspect ratios. It will be recognized that, in general, low aspect ratio sections display high L tensile strengths coupled with lower LT tensile strengths, whereas high aspect ratio sections display more isotropic L and LT strengths.
It is known that the orientations of extruded sections are based on the localized grain flow in the extruded section, and therefore in complex extrusions there is no global orientation system governing the entire extruded body. It is also known that regions in complex extrusions can have complex grain flows which are not easily defined by a simple planar orientation system. The regions are defined herein as transition zones, and when tested can potentially exhibit mechanical properties akin to those tested in off-axis orientation depending on several factors including sample location, sample size, grain flow, test, and testing direction. The transition zones may be formed at joints of different legs of the same extrusion.
Herein, a “lot” of material, or a heat treatment lot, is defined as a quantity of products of the same grade or alloy, form, thickness or cross-section and produced in the same way, heat-treated in furnace load, or such productions solution treated and subsequently precipitation treated in one furnace load as defined in “Aluminum Standards and Data 2017”.
Unless otherwise specified, static mechanical characteristics including ultimate tensile strength (UTS), tensile yield strength (TYS), and 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.
Unless otherwise specified, electrical conductivity (% IACS) is determined in accordance with ASMT E1004—Standard Test Method for Determining Electrical Conductivity Using Electromagnetic (Eddy Current) Method.
Unless otherwise specified, residual strength (RS) testing is carried out according to AMS4337. Residual strength tests can be used to measure the damage and durability characteristics of an aluminum alloy.
Unless otherwise specified, exfoliation corrosion (EXCO) resistance is 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 is 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.
In certain embodiments, equivalent homogenization or 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, T1 and T2 are temperatures 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 alloy 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 then manufactured by casting a billet, ingot, or shape from a liquid metal bath, for example, by using direct-chill (DC) casting techniques. It should be noted that “billet” is typically the term used for a unwrought cast product intended for extrusion.
Following casting, the unwrought billet, ingot, or shape may optionally be stress-relieved to avoid cracking prior to homogenization due to residual stress as known by those skilled in the art. Herein, a stress relief operation is considered any high temperature step given to an unhomogenized billet below 800° F.
The unwrought billet, ingot, or shape is then homogenized using a multi-step homogenization practice such that at least one step is at a temperature between 820° F. and 850° F., such that the equivalent time at 880° F. of that step or steps using a Q of 125.6 kJ/mol and a R=8.314462 JK−1 mol−1 is between 6 and 30 hours. While the inventors do not wish to be held to any theory of invention, it is believed homogenization steps or slow ramps through this temperature range are critical for promoting a fine dispersion of Zr-dispersoids.
Following the homogenization step between 820° F. and 850° F., a subsequent homogenization step or steps between 870° F. and 900° F. may be used. The equivalent time of these subsequent homogenization step or steps at 880° F. should be at least 26 hours, and preferably between 30 and 70 hours. In certain embodiments, a two-step homogenization process is used. In other embodiments, a three or more-step homogenization process is used. Care should be taken to avoid melting the billet, ingot, or shape during the homogenization process, especially when the homogenization oven set-point is raised above 880° F. It will be recognized that typical oven uniformities ranges can vary, but generally range from ±5° F. to ±15° F. Therefore, care must be taken when homogenizing at high temperature, for example 888° F., to avoid melting.
While not wishing to be held to any theory of invention, the inventors believe that the homogenization steps between 870° F. and 890° F. are critical for cleaning the grain boundaries of eutectics that form during solidification. Due to the different diffusion rates between elements like Zn, Mg, and Cu, the homogenization set point temperatures can in some instances be slowly raised as the overall melting temperature rises. The inventors believe these critical step or steps not only reduces the risk of eutectic melting in subsequent processing steps, but the step or steps also increase residual strength and the inherent corrosion resistance of the final product.
In accordance with an embodiment of the present invention, the unwrought product is then hot worked into an extrude product using either direct or indirect extrusion processes as known by those skilled in the art. In an embodiment of the presentation invention, the F-temper extrusion may optionally be cold worked. As used herein, the term “F-Temper extrusion” refers to extrusions that has been fabricated using a shape process, but has undergone no further thermal treatments like annealing or solution heating as known to those moderately skilled in the art.
In an embodiment, the wrought F-temper product can then annealed to produce an O-temper extrusion. As known to those skilled in the art, O-temper extrusions typically undergo further user solution heat treatments to produce a T6 or T7 product. As defined herein, a user is an individual or organization that is not the producer of the present invention. As known by those skilled the art, the extrusions may require stretching before or after annealing; therefore, stretching before or after the annealing operation is allowed per the method detailed herein.
The wrought F-temper extrusion may then be solution heat treated (SHT) at a temperature above 870° F. for a minimum of 30 minutes and up to 6 hours using a load thermocouple as known by those skilled in the art. Care must also be taken to avoid incipient melting of the extruded product. The alloy may be heat treated below 890° F. Examples of appropriate target solution heat treat temperatures in accordance with the method of manufacture detailed herein are 880° F. and 882° F. After the solution heat treatment is completed, the parts may be quenched in either water-glycol mixture or using a spray quench system. If a water-glycol mixture is used, the glycol concentrations may be below 20%.
After the alloy has been quenched from SHT, the resulting W-temper extrusion may be stretched or stretch formed to relieve residual stress. The W-temper extrusion may be stretched 1 to 3% to produce a W511 temper. Further cold working may be required to ensure the extrusions meet customer or industry standard geometrical requirements such as twist, bow, and flatness.
The resulting extrusion microstructure may be largely not recrystallized (REX), e.g., the grain fraction of REX grains is less than 15 volume percent, or less than 14 volume percent, or less than 12 volume percent, or less than 10 volume percent, or less than 9 volume percent. Such REX grain fractions of the solution heat treated and quenched product may be maintained during subsequent artificial aging, as described below, such that the final artificially aged product possesses substantially the same REX grain fractions. REX grain volume percent may be determined in accordance with ASTM E340 procedures.
After the extruded product has been worked, the product may be artificially aged, or capable of being artificially aged, using a multi-step aging cycle. The aging practice may be adjusted using an equivalent time at temperature calculation based on the desired mechanical properties and production time constraints. Herein, for calculating equivalent aging times a Q=125.6 kJ/mol and a T1 (or Tref) of 315° F. is used. The alloy may be aged in at least temperature between 212° F. and 275° F. for 4 to 36 hours. Afterwards, the alloy may be overaged at temperature between 292° F. and 335° F. for 4 to 18 hours to create a T7 product. Optionally, the T7 product can be given a subsequent age between 212° F. and 275° F. for 4 to 36 hours.
Extruded alloy products according to the present invention, when properly processed, may have improved combinations of strength, residual strength, and corrosion resistance. The alloy density may be between 0.1036 and 0.1041 lbs/in3 when calculated in accordance with the procedures detailed within Aluminum Standards and Data.
The following examples are intended to illustrate various aspects of the present invention and are not intended to limit the scope of the invention.
In this example, 7-inch billets of an Al—Zn—Mg—Cu alloy having the composition listed in Table 3 were cast using a standard direct-chill casting technique. The cast billets constitute alloys falling within the registered compositional limits of AA7136. The composition corresponds to the examples of U.S. Pat. No. 7,214,281 containing 8.9 weight percent Zn, 2.1 weight percent Mg, 2.1 weight percent Cu, and 0.11 weight percent Zr.
The cast billet logs were then cut into approximately 1-inch-thick slices. A series of small blocks, whose dimensions can be seen in
Once homogenized the blocks were then pre-heated to 650° F. and held for 3 hours before being rolled using a one stand unheated rolling mill to a 60% reduction over the course of three passes with each individual pass reducing the thickness by 20%. Between passes, the blocks were allowed to soak in the furnace for an additional hour at 650° F. Following the final pass, the resulting plates were allowed to air cool to room temperature.
The resulting F-temper plates were then solution heat treated according to the post-plastic deformation process (PPDP) listed in Table 5. Test results are labeled as Alloy-Homogenization-PPDP. For example, alloy Inv 6A homogenized per practice 19 and then processed according to PPDP I would be denoted as “Inv 6A-194I” It should be noted that following the solution heat treatment operation the parts were quenched in water. The parts were not stretched or aged following the quenching operation.
Following solution heat treatment and quench, full thickness metallographic samples were then taken in the L-S plane at mid-width and mid-length. The metallographic samples were then etched and analyzed to determine the volume fracture of recrystallized grains in the microstructure. The results are shown in Table 6.
U.S. Pat. No. 7,214,281 uses a first temperature homogenization step of 870° F. for 8 hours in the examples. The first homogenization step in U.S. Pat. No. 7,214,281 has an equivalent time at 880° F. of 6.9 hours. Herein, sample Inv 6A-9-1 also uses a first homogenization step of 870° F. Microstructural analysis indicates the sample contained 16.67% REX grains.
The improved methods of manufacture detailed herein utilize multi-step homogenization practices resulting in final products having microstructures with largely unrecrystallized grains, for example, with less than 15 volume percent REX grains, or less than 14 volume percent REX grains, or less than 12 volume percent REX grains, or less than 10 volume percent REX grains, or less than 9 volume percent REX grains.
While the inventors do not wish to be held to any theory, it is believed that, by using an optimized low temperature homogenization step, a relatively uniform dispersion of small Al3Zr dispersoids can be precipitated. These resulting dispersoids are believed to be more stable at high homogenization temperatures than those precipitated at hotter or lower temperatures. These stable dispersoids in high solute 7xxx-series alloys like AA7136 can be homogenized at longer, hotter homogenization steps, which aids in cleaning up grain boundaries and improving corrosion, without the disadvantage of the Zr-dispersoids coarsening and resulting in deleterious REX grains.
In this example, several billets of Al—Zn—Mg—Cu alloy having the compositions given in Table 7 were cast into 23-inch diameter billets using direct-chill casting techniques.
The as-cast billets were then homogenized according to homogenization practice 19 found in Table 8. After the homogenization cycle was completed, the billets were allowed to slowly cool to room temperature as known by those moderately skilled in the art.
The homogenized billets were then hot extruded into a 3.800-inch by 5.450-inch bar using a one-hole die. The resulting F-temper extrusion was then processed according to one of the PPDP listed in Table 9. It should be noted that each extrusion was spray quenched from the solution heat treatment temperature using the same quench practice.
The rear of the resulting T7 extrusions were then tested for tensile strength, electrical conductivity, and residual strength. The results are shown in Table 10. It will be recognized that Inv 5A-20-II gives a surprisingly improved combination of strength and residual strength compared.
In this example, several billets of Al—Zn—Mg—Cu alloy wherein the compositions are given in Table 11 were cast using direct-chill casting techniques.
The as-cast billets were homogenized according to one of the homogenization practices given in Table 12. After the homogenization cycle was completed, the billets were allowed to slowly cool to room temperature as known by those moderately skilled in the art.
The homogenized billets were then hot extruded into a series of bar profiles with a thickness greater than or equal to 4.5 inches per Table 13. The resulting F-temper extrusion were then solution heat treated, stretched, and artificially aged per one of the PPDP detailed in Table 13. The extrusion were solution heat treated at the temperature listed in Table 13 for at least 1.75 hours.
The resulting T7 extrusions were then mechanically tested for tensile strength and electrical conductivity. The results are shown in Table 14. It will be recognized that, for some alloy-homogenization-PPDP combinations, multiple lots are denoted in Table 14.
A section of the resulting aged products were also tested for EXCO and SCC resistance. SCC specimens were taken in the ST direction and exposed for 20 days at 45 ksi. The results are shown in Table 15.
In this example, several billets of different Al—Zn—Mg—Cu alloys wherein the compositions are given in Table 16 were cast into 10-inch billets using direct-chill casting techniques.
The as-cast billets were then homogenized according to the practices given in Table 17.
The homogenized billets were then hot extruded into T-sections using a standard direct extrusion process. The resulting F-temper extrusions were then solution heat treated, immersion quenched (15% glycol solution), stretched, and artificially aged according to the PPDP listed in Table 18. The extrusions were solution heat treated for at least 0.92 hrs before being quenched. The extrusions were aged using a two-step aging process where the time at 315° F. (i.e. —the second aging step) was varied to create an aging curve as known by those moderately skilled in the art.
The resulting aged T7 extrusions were then tested at Location 1 shown in
In this example, several billets of Al—Zn—Mg—Cu alloy were cast using a standard direct-chill casting technique. The composition of these billets are listed in Table 20.
The as-cast billets were then homogenized according to one of the practices in Table 21. Then, the homogenized billets were hot extruded into the profile shown in
The resulting F-temper extrusions were then solution heated, stretched, and artificially aged according to one the PPDP given in Table 22 resulting in a series of T7 temper extrusions.
Then, the extrusions were tested for tensile strength and electrical conductivity. The extrusions in this example were tested using full-thickness flat tension bars to ensure the REX grain layer was tested. The results are shown in Table 23.
As known by those skilled in the art, thicker REX grain layers typically result in lower mechanical properties like tensile yield strength. While not wishing to be held to any theory of invention, the inventors believe the finer dispersion of Zr dispersoids created by the homogenization combined with the optimized compositional balance results in an increase in mechanical performance.
In this example, several billets of Al—Zn—Mg—Cu alloys were cast into 8-inch billets using a standard direct-chill casting technique. The compositions of the as-cast billets are listed in Table 24.
The as-cast billets were then homogenized according to one of the practices in Table 25. The homogenized billets were then extruded into the Type II (Seamed Hollow) profile shown in
The resulting F-Temper extrusions were then solution heat treated, quenched, stretch, and artificially aged according to one of the PPDF processes listed in Table 26, resulting in a T7 product.
The extrusions were then tested down the length for tensile strength and electrical conductivity. The average results are shown in Table 27. It will be appreciated that this example highlights the importance of one critical aspect of the present invention, which is the effect of the low temperature homogenization step, as all other variables were essentially held constant.
In this example, a series of 27-inch billets were cast using direct-chill casting techniques. The chemical composition of the various billets are listed in Table 28. The as-cast billets were then homogenized using homogenization practice 20, which is shown in Table 8.
The homogenized billets were then hot extruded into the profile shown in
The resulting T7 extrusions were then tested for electrical conductivity, tensile strength, and residual stress. The results are shown in Table 30. All electrical conductivity measurements are sub-surface.
In this example, lot release data from several lots were compared. The average chemical composition of each data set can be found in Table 31. Prior to extrusion, the billets were homogenized according to one of the practices listed in Table 32.
The billets were hot extruded into various profile sections ranging from 0.040 inches to 0.500 inches thick. The lots were then solution heat treated at 880° F. before being quench in a water-glycol solution. The various lots were aged to a T76511 temper per AMS 4415 using a two-step aging process such that the electrical conductivity of every lot tested was between 36.0 and 38.5% IACS. The various lots were then tested for tensile strength.
The tensile strength results were then analyzed using statistical techniques described in Metallic Materials Properties Development and Standardization (MMPDS)—2024 volume I to determine T90 values for UTS and TYS for each data set as known to those skilled in the art. Herein, a T90 value indicates that at least 90% of the population of values are expected to meet or exceed the T90 value with a 95% confidence. Elongation results were analyzed to determine a T99 values; herein, a T99 values indicates at least 99% of the population of values are expected to meet or exceed the T99 values with a 95% confidence. The T90 values for strength and the T99 values for elongation for each dataset can be found in Table 33. The histograms for each dataset can be seen in
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/of” unless specifically stated otherwise, even though “and/of” 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. For example, while the methods detailed herein are designed to improve the combination of properties in high solute 7xxx-series alloys, the methods may also result in an improvement in alloys within other compositional ranges.
This application claims the benefit of U.S. Provisional Patent Application No. 63/617,176 filed Jan. 3, 2024, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63617176 | Jan 2024 | US |
