Patent Application
20240102141
The invention relates to a method of manufacturing 2XXX-series aluminum alloy wrought products, and in particular, to an improved aging process. Products made from this alloy are very suitable for aerospace applications, but not limited to that. The aluminum alloy can be processed to various product forms, e.g., sheet, thin plate, thick plate, extruded, or forged products.
Aerospace applications generally require a very specific set of properties. High strength alloys are generally desired, but according to the desired intended use, other properties such as high fracture toughness or ductility, as well as good corrosion resistance are also required.
An important property is the stress corrosion cracking (“SCC”) resistance of a product, particularly when loaded in the short-transverse (ST) orientation. Historically, in higher-strength alloys (e.g., aircraft structures) most service failures involving SCC of aluminum alloys have resulted from assembly or residual stresses acting in a short-transverse direction relative to the grain flow of the product. This is generally more troublesome for parts machined from relatively thick sections of rolled plate, extrusions, or forgings of complex shape where short-transverse grain orientation might be exposed. Within the high strength alloy classes, including the 2XXX-series aluminum alloys, broad generalizations that relate susceptibility to SCC and strength or fracture toughness do not appear possible. Controls on alloy processing and heat treatment are key to ensuring high resistance to SCC without appreciable loss in mechanical properties. Thick-section products of 2XXX-series aluminum alloys in the naturally aged T3 and T4 tempers have low ratings of resistance to SCC in the short-transverse direction. Ratings of such products in other directions are higher, as are ratings of thin-section products in all directions. These differences are related to the effects of quenching rate (largely determined by section thickness) on the amount of precipitation that occurs during quenching.
Artificial aging of 2XXX-series aluminum alloys to precipitation hardened T8 tempers provides relatively high resistance to exfoliation and SCC and very good elevated temperature characteristics with modest strength increase over their naturally aged counterparts. This temper requires stretching, or cold working by other means, after quenching from the solution heat treatment temperature and before artificial aging (e.g., the 2XXX alloy is solution-heat-treated, quenched and subsequently cold worked or cold formed. Optionally, the cold working is applied in one or more cold working steps which are applied after solution heat treatment and quenching, optionally after further natural aging, and either before final artificial aging or in between the two artificial aging steps.
The response to the age-hardening is enhanced by the strain hardening due to the stretching, or cold working by other means, prior to artificial aging (T8 temper) and the yield strength may be increased very significantly as compared to the T6 temper. The T6 tempers, on the other hand, relate to wrought products that are solution heat treated, quenched and artificially aged with little or no cold work such that the cold work is not thought to affect mechanical property limits. What is needed is a high strength 2XXX-series aluminum alloy having very high resistance to stress corrosion cracking.
Covered embodiments of the invention are defined by the claims, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification, any or all drawings, and each claim.
Described herein is an aging process of a solution-heat-treated and quenched 2XXX-series aluminum alloy wrought product, comprising the steps of: (1) aging the product in a first aging step at one or more temperatures within a range of 90° C. to 120° C. for a cumulative period time of at least 10 hours; and (2) subsequently aging the product in a second aging step at one or more temperatures within a range of 150° C. to 205° C. for a cumulative period of time of at least 4 hours, and preferably within a range of 150° C. to 195° C. for a cumulative period of time of at least 8 hours.
Also described herein is a method of manufacturing a 2XXX-series aluminum alloy wrought product, the method comprising the following steps: (i) casting of an ingot of an 2XXX-series aluminum alloy as described herein; (ii) preheating and/or homogenizing the ingot; (iii) hot working the ingot by one or more methods selected from the group consisting of rolling, extrusion, and forging, into a hot worked wrought product; (iv) optionally cold working the hot worked wrought product; (v) solution heat treating (“SHT”) the wrought product; (vi) rapid cooling or quenching the SHT product; (vii) optionally cold working or cold forming the SHT and quenched product; and (viii) artificial aging in accordance with the methods described herein of the SHT, quenched product and optionally cold working or cold forming.
Further described herein are wrought 2XXX-series aluminum alloy products. In some examples, the wrought 2XXX-series aluminum alloy product, optionally having a clad layer on one or two sides, has a cross-sectional thickness from 1.6 mm to 12 mm, and preferably from 1.6 mm to 8 mm, and is aged to achieve (1) a conventional tensile yield strength (in MPa) measured in L-direction of more than 400 MPa; or (2) an improved IGC resistance measured without cladding showing predominantly pitting attack and negligent IGC.
In some examples, the wrought 2XXX-series aluminum alloy product having a cross-sectional thickness from 12 mm to 250 mm, and preferably from 12 mm to 130 mm is aged to achieve (1) a conventional tensile yield strength (in MPa) measured in L-direction at quarter thickness of more than 380 MPa+0.57 (120−t) MPa, wherein t is the thickness of the product in mm; or (2) a minimum service life without failure due to stress corrosion cracking in accordance with ASTM G47 of at least 20 days, preferably of at least 25 days at a short transverse stress level of 250 MPa.
Optionally, the wrought 2XXX-series aluminum alloy product having a cross-sectional thickness from 12 mm to 250 mm, and preferably from 12 mm to 130 mm, is aged to achieve (1) a conventional tensile yield strength (in MPa) measured in L-direction at quarter thickness of more than 380 MPa+0.57 (120−t) MPa, wherein t is the thickness of the product in mm; or (2) an improved IGC resistance measured without cladding showing predominantly pitting attack and negligent IGC.
Other objects and advantages of the invention will be apparent from the following detailed description of non-limiting examples and drawings.
As will be appreciated herein, except as otherwise indicated, aluminum alloy designations and temper designations refer to the Aluminum Association designations in Aluminum Standards and Data and the Registration Records, as published by the Aluminum Association in 2019 and are well known to the person skilled in the art for example as the “Teal Sheets.” The temper designations are laid down in European standard EN515.
For any description of alloy compositions or preferred alloy compositions, all references to percentages are by weight percent unless otherwise indicated.
As used herein, the term “about” when used to describe a compositional range or amount of an alloying addition means that the actual amount of the alloying addition may vary from the nominal intended amount due to factors such as standard processing variations as understood by those skilled in the art.
The terms “up to” and “up to about,” as employed herein, explicitly include, but are not limited to, the possibility of zero weight-percent of the particular alloying component to which it refers. For example, up to 0.25% Cr may include an aluminum alloy having no Cr.
As used herein, the meaning of “a,” “an,” or “the” includes singular and plural references unless the context clearly dictates otherwise.
All ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, e.g., 1 to 6.1, and ending with a maximum value of 10 or less, e.g., 5.5 to 10.
For purposes herein, a sheet product or a sheet material (also referred to herein as “sheet”) is to be understood as a rolled product having a thickness of not less than 1.3 mm (0.05 inches) and not more than 6.3 mm (0.25 inches). For example, a sheet may have a thickness of 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8 mm, 3.9 mm, 4.0 mm, 4.1 mm, 4.2 mm, 4.3 mm, 4.4 mm, 4.5 mm, 4.6 mm, 4.7 mm, 4.8 mm, 4.9 mm, 5.0 mm, 5. 1 mm, 5.2 mm, 5.3 mm, 5.4 mm, 5.5 mm, 5.6 mm, 5.7 mm, 5.8 mm, 5.9 mm, 6.0 mm, 6.1 mm, 6.2 mm, or 6.3 mm. See Aluminium Standard and Data, the Aluminium Association, Chapter 5 Terminology, 1997.
For purposes herein, a plate material or a plate product (also referred to herein as “plate”) is to be understood as a rolled product having a thickness of more than 6.3 mm (0.25 inches). For example, a plate material or a plate product may have a thickness of more than 6.3 mm, more than 6.4 mm, more than 6.5 mm, more than 6.6 mm, more than 6.7 mm, more than 6.8 mm, more than 6.9 mm, more than 7.0 mm, more than 7.1 mm, more than 7.2 mm, more than 7.3 mm, more than 7.4 mm, more than 7.5 mm, more than 7.8 mm, more than 7.9 mm, more than 8.0 mm, more than 10.0 mm, more than 15.0 mm, more than 20.0 mm, more than 25.0 mm, more than 30.0 mm, more than 35.0 mm, more than 40.0 mm, more than 45.0 mm, more than 50.0 mm, or more than 100.0 mm. See Aluminium Standard and Data, the Aluminium Association, Chapter 5 Terminology, 1997.
As used herein, the meaning of “ambient temperature” can include a temperature of from about 15° C. to a temperature of a first aging step as described herein (e.g., about 15° C. to about 90° C., about 15° C. to about 120° C., about 20° C. to about 90° C., about 20° C. to about 120° C., about 22° C. to about 90° C., about 22° C. to about 120° C., about 20° C. to about 100° C., about 20° C. to about 110° C., about 15° C. to about 100° C., or about 15° C. to about 110° C.). For example, “ambient temperature” can be about 15° C., about 16° C., about 17° C., about 18° C., about 19° C., about 20° C., about 21° C., about 22° C., about 23° C., about 24° C., about 25° C., about 26° C., about 27° C., about 28° C., about 29° C., about 30° C., about 31° C., about 32° C., about 33° C., about 34° C., about 35° C., about 36° C., about 37° C., about 38° C., about 39° C., about 40° C., about 41° C., about 42° C., about 43° C., about 44° C., about 45° C., about 46° C., about 47° C., about 48° C., about 49° C., about 50° C., about 51° C., about 52° C., about 53° C., about 54° C., about 55° C., about 56° C., about 57° C., about 58° C., about 59° C., about 60° C., about 61° C., about 62° C., about 63° C., about 64° C., about 65° C., about 66° C., about 67° C., about 68° C., about 69° C., about 70° C., about 71° C., about 72° C., about 73° C., about 74° C., about 75° C., about 76° C., about 77° C., about 78° C., about 79° C., about 80° C., about 81° C., about 82° C., about 83° C., about 84° C., about 85° C., about 86° C., about 87° C., about 88° C., about 89° C., about 90° C., about 91° C., about 92° C., about 93° C., about 94° C., about 95° C., about 96° C., about 97° C., about 98° C., about 99° C., about 100° C., about 101° C., about 102° C., about 103° C., about 104° C., about 105° C., about 106° C., about 107° C., about 108° C., about 109° C., about 110° C., about 111° C., about 112° C., about 113° C., about 114° C., about 115° C., about 116° C., about 117° C., about 118° C., about 119° C., or about 120° C.
It is an object of the disclosure to provide a method of manufacturing 2XXX-series aluminum alloy wrought products having improved properties at least in the short-transverse direction (ST-direction). As used herein, a wrought product is a cast aluminum alloy that is solution-heat-treated, quenched, and subsequently cold worked or cold formed.
It is another object of the disclosure to provide a method of manufacturing 2XXX-series aluminum alloy wrought products having at least improved SCC resistance in the ST-direction.
These and other objects and further advantages are met or exceeded by the present disclosure providing an aging process of a solution-heat-treated and quenched 2XXX-series aluminum alloy wrought product, comprising the steps of, in the following order:
In addition to the above multiple step aging process, the aging process described herein can include any desired number of aging steps. For example, the aging process can include two steps, three steps, four steps, five steps, six steps, seven steps, eight steps, nine steps, ten steps, or greater. An aging step can include heating the aluminum alloy wrought product to any desired temperature and holding the aluminum alloy wrought product at the desired temperature for any desired period of time. As described herein, all ranges describing processes, properties, compositions, characteristics, or the like encompass any and all endpoints and any and all subranges subsumed therein.
Where in the prior art 2XXX-series aluminum alloy wrought products after solution heat-treatment and quenching are artificially aged in a one-step aging process at relatively high temperature to bring it to a T6 or T8 condition, it has been found in accordance with the disclosure herein that improvements in properties, in particular in the ST-direction, can be achieved after applying an aging process comprising of a first step, phase or treatment at relatively low temperature for a cumulative period of time of at least 10 hours, and preferably for at least 24 hours followed by a second step, phase or treatment at higher temperature exceeding the temperature of said first step and for a cumulative period of time of at least 8 hours.
In some cases, the cooling from solution heat treatment (i.e., quenching) for a 2XXX-series aluminum alloy plate in the thickness range of 1.6 mm to 12 mm is performed with a cooling rate between 100° C./min and 1000° C./min (e.g., 110° C./min to 900° C./min, 100° C./min to 800° C./min, 110° C./min to 700° C./min, or 120° C./min to 600° C./min), more preferably between 200° C./min and 600° C./min (e.g., 210° C./min to 600° C./min, 200° C./min to 550° C./min, or 250° C./min to 500° C./min) when measured during cooling when the temperature of the 2XXX-series aluminum alloy is in a range from 150° C. to 400° C. For example, the cooling rate is similar to a cooling rate using a water quench on a 120 mm thick 2XXX-series aluminum alloy plate.
The aging process achieves improved metallurgical properties in the ST-direction. In particular, the 2XXX-series aluminum alloy wrought product is more ST stress corrosion cracking resistant. The improvement in SCC resistance in ST-direction is particularly noticeable in thicker gauge wrought products. “ST stress corrosion cracking resistant” means that at least two-of-three specimens of a 2XXX-series aluminum alloy product do not fail after 20 days of alternate immersion testing at a net stress of 250 megaPascals (MPa) in the ST direction and in accordance with ASTM G47 and with at least 3 specimens being required for testing. In one embodiment, all three specimens do not fail after 20 days of alternate immersion testing at a net stress of 250 MPa in the ST direction and in accordance with ASTM G47. In another embodiment, all three specimens do not fail after 25 days of alternate immersion testing at a net stress of 250 MPa in the ST direction and in accordance with ASTM G47.
The aging process as described herein achieves an improved balance in engineering properties in the 2XXX-series aluminum alloy wrought product, as SCC corrosion resistance is improved and the mechanical strength levels are maintained at least to the level of a counterpart aged in a one-step aging process for 12 hours at 190° C. A counterpart is a wrought product of the same thickness and having a similar alloy composition and the same thermo-mechanical history except for the final aging treatment.
In an embodiment of the aging process, the wrought product in the first aging step is aged at one or more temperatures within a range of 90° C. to 120° C. for a cumulative period of time of at least 10 hours, and more preferably for at least 24 hours. In a preferred embodiment of the first aging step, the wrought product is aged for a cumulative period of time not longer than 144 hours, and preferably for not longer than 96 hours, and more preferably for not more than 64 hours.
In an embodiment of the aging process, the wrought product in the second aging step is aged at one or more temperatures within a range of 150° C. to 195° C. for a cumulative period of time of at least 8 hours, and preferably for at least 12 hours. In a preferred embodiment of the second aging step, the wrought product is aged for a cumulative period of time of no longer than 144 hours and preferably not longer than 96 hours. In a preferred embodiment of the second aging step, the wrought product is aged at one or more temperatures within a range of about 160° C. to 190° C.
In an embodiment of the aging process, the aging of the wrought product may be effected in a single, programmable furnace for convenience purposes as is known in the art for other aging treatment for other heat-treatable aluminum alloys.
In another embodiment of the aging process, the wrought product is cooled at the end of the first aging step, e.g., to ambient temperature, and reheated to the second aging step for completing the aging cycle as described herein to realize the improved metallurgical properties. This intermediate cooling to ambient temperature can be done for reasons of logistics; however, also an intermediate cold working operation can be done, in particular a stretching operation by stretching in the range of about 0.5% to 11% of its original length to enhance subsequent aging kinetics and to increase strength levels, if so desired. Preferably, the stretching is in the range of about 0.5% to 6%, more preferably of about 1% to 3%, of its original length.
The aging process in accordance with the invention can be used for a wide range of 2XXX-series aluminum alloy wrought products.
In an embodiment, the 2XXX-series aluminum alloy wrought product comprising at least the following main constituents, in wt. %: about 3.0 to 5.5% Cu, about 0.15 to 1.0% Mn, about 0.2 to 1.8% Mg, and up to about 0.7% Ag, impurities up to 0.15%, and aluminum, and with preferred compositional ranges as herein described and/or claimed. The term “comprising” in the context of the aluminum alloy is to be understood in the sense that the alloy may contain further alloying elements, as exemplified below.
In another embodiment the 2XXX-series aluminum alloy wrought product has a composition, in wt. %:
and optionally one or more dispersoid forming elements selected from the group consisting of about 0.05% to 0.25% Cr, about 0.05% to 0.25% Zr, about 0.05% to 0.25% V, about 0.05% to 0.4% Hf, and about 0.05% to 0.4% Sc, preferably 0.05% to 0.2% Cr, 0.05% to 0.15% Zr, 0.05% to 0.15% V, 0.05% to 0.25% Hf, 0.05% to 0.25% Sc; impurities up to 0.15%, and aluminum; and with preferred narrower compositional ranges as herein described and/or claimed. Typically, impurities can be present each up to 0.05% and in total up to 0.15%.
The Cu is the main alloying element in 2XXX-series alloys and for the method or process described herein it should be in a range of about 3.0% to 5.5%. A preferred lower limit for the Cu content is about 3.5%. A preferred upper limit for the Cu content is about 5.1%. In one embodiment, the Cu content is in a range of about 3.0% to 4.4%, and preferably in a range of about 3.5% to 4.4% (e.g., 3.6% to 4.4%, 3.5% to 4.3%, 3.75% to 4.25%, or 3.6% to 4.3%). In another embodiment, the Cu content is in a range of about 4.4% to 5.5%, and preferably in a range of about 4.4% to 5.1% (e.g., 4.4% to 5.4%, 4.5% to 5.5%, 4.5% to 5.4%, 4.7% to 5.2%, or 4.75% to 5.25%).
Mn is another important alloying element in the 2XXX-series aluminum alloy and should be present in a range of about 0.15% to 1.0%. In an embodiment, the Mn content is in a range of about 0.15% to 0.8%, and preferably about 0.2% to about 0.8% (e.g., 0.25% to 0.75%, 0.3% to 0.8%, 0.2% to 0.5%, 0.2% to 0.6%, or 0.21% to 0.79%).
Mg is another important alloying element and should be present in a range of about 0.2% to 1.8% (e.g., 0.25% to 1.75%, 0.3% to 1.8%, 0.2% to 1.5%, 0.2% to 1.6%, or 0.21% to 1.79%). A preferred lower limit for the Mg content is about 0.4%. A preferred upper limit for the Mg content is about 1.4%.
Ag in a range of up to about 0.7% can be added to further enhance the strength following artificial aging. A preferred lower limit for the purposive Ag addition would be about 0.05%, and more preferably about 0.2%. A preferred upper limit is about 0.7%. For example, Ag can be added in an amount of 0.05% to 0.7%, 0.1% to 0.7%, 0.2% to 0.7%, 0.15% to 0.69%, 0.05% to 0.65%, or from 0.2% to 0.66%.
In an embodiment, the Ag is an impurity element and it can be present up to about 0.05%, and preferably up to about 0.03%.
Zn in a range of up to about 1% (e.g., 0.05% to 1%, 0.05% to 0.99%, 0.1% to 1%, 0.1% to 0.9%, or 0.09% to 0.99%) can be purposively added to further enhance the strength during aging and may replace some of the purposive Ag, if added. A preferred lower limit for the purposive Zn addition would be 0.2% and more preferably about 0.3%. A preferred upper limit would be about 0.5%.
In an embodiment, the Zn is an impurity element and it can be present up to about 0.25%, and preferably up to about 0.15%.
Optionally, dispersoid forming elements can be added to the aluminum alloy to control the evolution of grain structure or grain size during hot working operations such as hot rolling, extrusion, or forging. If added, the one or more dispersoid forming elements can be selected from the group consisting of: about 0.05% to 0.25% Cr (e.g., 0.05% to 0.2%, 0.05% to 0.15%, or 0.09% to 0.24%), up to about 0.15% Zr or about 0.05% to 0.25% Zr (e.g., 0.05% to 0.2%, 0.05% to 0.15%, or 0.09% to 0.24%), about 0.05% to 0.25% V (e.g., 0.05% to 0.2%, 0.05% to 0.15%, or 0.09% to 0.24%), about 0.05% to 0.4% Hf (e.g., 0.05% to 0.35%, 0.05% to 0.25%, or 0.09% to 0.39%), and/or about 0.05% to 0.4% Sc (e.g., 0.05% to 0.35%, 0.05% to 0.25%, or 0.09% to 0.39%).
Ti can be added to the alloy product amongst others for grain refiner purposes during casting of the 2XXX-series aluminum alloy. The addition of Ti should not exceed about 0.2%, and preferably it does not exceed 0.15% (e.g., 0.05% to 0.2%, 0.05% to 0.15%, 0.1% to 0.15%, or 0.09% to 0.15%). A preferred lower limit for the Ti addition is about 0.01%. Ti can be added as a sole element or with either B (e.g., TiB2) or C (TiC) serving as a casting aid, for grain size control. The addition of Ti at the higher end of this range, i.e., above about 0.08%, may also further improve the SCC resistance and the strength of the product.
Fe is a regular impurity in aluminum alloys and can be tolerated up to about 0.3% (e.g., 0.05% to 0.3%, 0.05% to 0.2%, 0.05% to 0.1%, 0.1% to 0.3%, 0.1% to 0.2%, or 0.09% to 0.29%). Preferably it is kept to a level of up to about 0.2%, and more preferably up to about 0.1%.
Si is also a regular impurity in aluminum alloys and can be tolerated up to about 0.2% (e.g., 0.05% to 0.2%, 0.1% to 0.2%, 0.05% to 0.15%, or 0.05% to 0.1%). Preferably it is kept to a level of up to 0.15%, and more preferably up to 0.1%.
The balance being aluminum and normal and/or inevitable impurities. Typically, impurities can be present each up to 0.05% and in total up to 0.15%. In an embodiment, the impurities can be present each up to 0.03% and in total up to 0.1%. For the purpose of this invention, inevitable impurities include other elements that can be added during casting operations, e.g., Be or Ca. These elements are generally referred to as deoxidizers and are used to control or limit oxidation of the molten aluminum. These elements are regarded as trace elements or impurities with additions typically less than 0.01%, with preferred additions less than about 100 ppm, e.g., 10 to 80 ppm of Ca and/or up to about 20 ppm of Be.
The 2XXX-series aluminum alloy wrought products processed in accordance with the methods described herein are products being hot worked after casting, and includes rolled products (i.e. sheet or plate), extruded products, and forged products. Forged products are either die forged or hand forged.
In an embodiment the 2XXX-series aluminum alloy wrought product processed or manufactured in accordance with the method described herein is in the form of thin gauge plate product having a cross-sectional thickness in the range of 1.6 mm to 12 mm (e.g., 1.7 mm to 12 mm, 1.6 mm to 11.9 mm, 1.7 mm to 11 mm, 1.6 mm to 8 mm, 2 mm to 12 mm, 2 mm to 10 mm, or 2.5 mm to 9.5 mm).
In an embodiment the 2XXX-series aluminum alloy wrought product processed or manufactured in accordance with the invention is a thick product with a cross-sectional thickness of at least 12 mm. The wrought product may be rolled product, forged product or extruded product. In an embodiment the thick wrought product is a plate product having a cross-sectional thickness of at least 12 mm, and preferably of at least 25 mm. In another embodiment, the thick wrought product is a plate product having a cross-sectional thickness of at least 38 mm. The improved properties described herein may be achieved with thick wrought products having a cross-sectional thickness of up to 250 mm. In one embodiment, the thick wrought product is a plate product having a cross-sectional thickness of up to 250 mm. In another embodiment, the thick wrought product is a plate product having a cross-sectional thickness of up to 180 mm. In yet another embodiment, the thick wrought product is a plate product having a cross-sectional thickness of up to 130 mm. As used in this paragraph, thickness refers to the minimum thickness of the product, realizing that some portions of the product may legalize slightly larger thicknesses than the minimum stated.
In one embodiment, the 2XXX-series aluminum alloy product has a thickness in the range of 1.6 mm to 12 mm and realises a conventional yield strength (in MPa) measured in the longitudinal direction relative to the rolling direction (i.e., L-direction) of more than 400 MPa.
In one embodiment, the 2XXX-series aluminum alloy product has a thickness in the range of 1.6 mm to 12 mm and achieves an improved intergranular corrosion (IGC) resistance measured without cladding showing predominantly pitting attack and negligent IGC (e.g., pitting attack accounts for greater than 50% of the total corrosion attack, preferably greater than 70%, and more preferably greater than 90%). In some cases, described herein is a wrought 2XXX-series aluminum alloy product, optionally having a clad layer on at least one side, or on two sides, of the wrought aluminum alloy product. As noted, the wrought aluminum alloy product can have a cross-sectional thickness from 1.6 mm to 12 mm (and preferably from 1.6 mm to 8 mm) and can be aged according to the methods described herein to achieve a conventional tensile yield strength (in MPa) measured in the L-direction of more than 400 MPa and/or an improved IGC resistance measured without cladding showing predominantly pitting attack and negligent IGC.
In one embodiment, the 2XXX-series aluminum alloy product has a thickness of at least 12 mm and achieves a minimum life without failure due to stress corrosion cracking (SCC) measured in accordance with ASTM G47-98 of at least 20 days preferably at least 25 days) at a short transverse (ST) stress level of 250 MPa. In certain aspects, described herein is a wrought 2XXX-series aluminum alloy product having a cross-sectional thickness from 12 mm to 250 mm (and preferably from 12 mm to 130 mm). The wrought aluminum alloy product having a thickness of 12 mm to 250 mm can be aged according to the methods described herein to achieve a conventional tensile yield strength measured in the L-direction at quarter thickness of more than 380 MPa+0.57 (120−t) MPa (where t is the quarter thickness of the wrought aluminum alloy product in mm). Additionally, the wrought aluminum alloy product can exhibit a minimum service life without failure due to stress corrosion cracking in accordance with ASTM G47 of at least 20 days (preferably of at least 25 days) at a short transverse stress level of 250 MPa.
In one embodiment, the 2XXX-series aluminum alloy product has a thickness of at least 12 mm and achieves a conventional tensile yield strength (in MPa) measured in the L-direction at quarter thickness of more than 380 MPa+0.57 (120−t) MPa (t being the thickness of the product in mm). In some non-limiting examples, the wrought aluminum alloy product can be a wrought 2XXX-series aluminum alloy product having a cross-sectional thickness from 12 mm to 250 mm (preferably from 12 mm to 130 mm) and can be aged according to the methods described herein to achieve a conventional tensile yield strength measured in the L-direction at a quarter thickness of more than 380 MPa+0.57 (120−t) MPa. The wrought aluminum alloy product can further exhibit an improved IGC resistance measured without cladding showing a predominantly pitting-type corrosion attack and negligent IGC.
Depending on the final application of the 2XXX-series aluminum alloy wrought product processed in accordance with the methods described herein, the disclosure also includes embodiments in which the 2XXX-series wrought product may be provided with a cladding, in particular for the thinner gauge rolled product. Such clad products utilize a core of the 2XXX-series aluminum base alloy and a cladding of usually higher purity which in particular further corrosion protects the 2XXX-series aluminum alloy core. The cladding includes, but is not limited to, essentially unalloyed aluminum or aluminum containing not more than 0.1% or 1% of all other elements. Aluminum alloys herein designated as 1xxx-type series include all Aluminum Association (AA) alloys, including the sub-classes of the 1000-type, 1100-type, 1200-type, and 1300-type. Thus, the cladding on the core may be selected from alloys such as 1060, 1045, 1100, 1200, 1230, 1135, 1235, 1435, 1145, 1345, 1250, 1350, 1170, 1175, 1180, 1185, 1285, 1188, or 1199. In addition, alloys of the AA7000-series alloys, such as 7072 containing zinc (0.8 to 1.3%), can serve as the cladding and alloys of the AA6000-series alloys, such as 6003 or 6253, which contain typically more than 1% of alloying additions, can serve as cladding. Other alloys could also be useful as cladding as long as they provide in particular sufficient overall corrosion protection to the core alloy. The clad layer or layers are usually much thinner than the core, each constituting 1% to 15% of the total composite thickness. A cladding layer more typically constitutes around 1% to 10% of the total composite thickness.
In a further aspect, described herein is a method of producing a 2XXX-series aluminum alloy wrought product, the method comprising the steps, in the following order, of:
In accordance with the invention, the artificial aging comprises the steps of, in the following order: (1) aging the product in a first aging step at one or more temperatures within a range of 90° C. to 120° C. for a cumulative period of time of at least 10 hours; and (2) subsequently aging the product in a second aging step at one or more temperatures within a range of 150° C. to 205° C. for a cumulative period of time of at least 4 hours, and preferably within a range of 150° C. to 195° C. for a cumulative period of time of at least 8 hours.
The 2XXX-series aluminum alloy can be provided as an ingot or slab or billet for fabrication into a suitable wrought product by casting techniques regular in the art for cast products, e.g., direct-chill (DC)-casting, electro-magnetic-casting (EMC)-casting, or electro-magnetic-stirring (EMS)-casting. Slabs resulting from continuous casting, e.g., belt casters or roll casters, also may be used, which in particular may be advantageous when producing thinner gauge (e.g., up to 12 mm thick) rolled end products. Grain refiners such as those containing Ti and B, or Ti and C, may also be used as is well known in the art. The Ti content in the aluminum alloy is up to about 0.2%, and preferably up to about 0.15%, and more preferably in a range of about 0.01% to 0.12%. Ti can be added as a sole element or with either boron or carbon serving as a casting aid, for grain size control. After casting the aluminum alloy ingot it is commonly scalped to remove segregation zones near the as-cast surface of the ingot.
The purpose of a homogenization heat treatment has at least the following objectives: (i) to dissolve as many as possible coarse soluble phases formed during solidification, and (ii) to reduce concentration gradients to facilitate the dissolution step. A preheat treatment achieves also some of these objectives. A typical preheat treatment for 2xxx-series alloys would be a temperature of about 420° C. to 505° C. with a soaking time in the range of about 3 to 50 hours, more typically for about 3 to 20 hours. A common homogenization and/or preheating process can also be done in one or more steps if desired, and which are typically carried out in a temperature range of about 400° C. to 505° C. For example, in a two-step process, there is a first step between about 480° C. and 500° C., and a second step between about 450° C. and 490° C., to optimize the dissolving process of the various phases depending on the exact alloy composition. In either case, the segregation of alloying elements in the as-cast ingot is reduced and soluble elements are dissolved. If the treatment is carried out below 400° C., the resultant homogenization effect is inadequate. If the temperature is above 505° C., eutectic melting might occur resulting in undesirable pore formation. The soaking time at the homogenization temperature is in the range of about 1 to 50 hours, and more typically for about 2 to 20 hours. The heat-up rates that can be applied are those which are regular in the art.
Following the preheat and/or homogenization practice, the stock is hot worked by one or more methods selected from the group consisting of rolling, extrusion, and forging. The method of hot rolling is preferred for the present invention.
In an embodiment, the plate material is hot rolled to final hot rolled thickness.
In an embodiment, the hot working step can be performed to provide stock at intermediate thickness. Thereafter, this stock at intermediate thickness can be cold worked, e.g., by means of rolling, to a thinner thickness. Depending on the amount of cold work an intermediate anneal may be used before or during the cold working operation.
A next process step is solution heat treating (“SHT”) of the hot worked product and optionally cold worked product. The product should be heated to bring as much as possible all or substantially all portions of the soluble Cu, Mg, and the optional Ag into solution. The SHT is preferably carried out in the temperature range of about 450° C. to 505° C. for a time sufficient for solution effects to approach equilibrium, with typical soaking times in the range of about 5 minutes to 300 minutes, more preferably in a range of about 5 minutes to 120 minutes. The solution heat treatment is typically carried out in a batch furnace. After SHT, it is important that the aluminum alloy product be cooled with a high cooling rate to a temperature of about 100° C. or lower, preferably to ambient temperature, to prevent or minimize the uncontrolled precipitation of secondary phases, e.g., Al2CuMg and Al2Cu.
Cooling rates should preferably not be too high to allow for a sufficient flatness and acceptable level of residual stresses in the product. Suitable cooling rates can be achieved with the use of water, e.g., water immersion or water jets.
The SHT and quenched product may be further cold worked. “Cold working” means working or forming the aluminum alloy product at temperatures that are not considered hot working temperatures, generally below about 120° C. (e.g., at ambient temperature).
Cold working and/or stretching can be done to develop adequate strength, relieve internal stresses, and/or straighten the product. For example, stretching in the range of about 0.5% to 11% of its original length can be performed to relieve residual stresses therein and to improve the flatness of the product. Preferably, the stretching is in the range of about 0.5% to 6%, more preferably of about 1% to 3%.
In an embodiment, the SHT and quenched product is naturally aged, for example to a T3X temper, e.g., T39 or T351, and is subsequently subjected to a cold deformation or cold forming process by for example an aircraft manufacturer or supplier to produce a structural component. After such a cold working operation, the product is artificially aged in accordance with the method described herein. Such a cold working operation includes, but is not limited to, a bending operation, a roll forming operation, or an electrohydraulic forming operation. The cold deformation step can be performed by stretching, cold compression, bending, rolling, roll forming, or whatever quasi-static or higher speed cold deformation (quasi static speed below 0.008 s−1 typically, higher speed for example typically up to 100 to 150 s−1 max or higher) with a total range of deformation typically up to 10% max but not limited to that.
In a next step, the wrought product is artificially aged in accordance with the methods as herein described and/or claimed to increase strength and to achieve improved metallurgical properties, e.g., SCC resistance.
Next a desired final structural shape or near-net structural shape can be machined from the wrought products aged in accordance with this invention.
The SHT, quench, cold working, and the artificial aging in accordance with the methods described herein are also used in the manufacture of sections made by extrusion or forged processing steps.
Another aspect of the disclosure relates to an aircraft structural member made from the 2XXX-series aluminum alloy wrought product manufactured and aged in accordance with the methods described herein.
The 2XXX-series aluminum alloy product manufactured according to these methods can be used, amongst other uses, in the thickness range of up to about 12 mm to have properties that will be excellent for fuselage sheet. In the thin plate thickness range of about 12 mm to 76 mm, the properties will be excellent for wing plate, e.g., lower wing plate. The thin plate thickness range can be used also for stringers or to form an integral wing panel and stringer for use in an aircraft wing structure. When processed to thicker gauges of more than about 60 mm to 250 mm excellent properties have been obtained for integral part machined from plates, or to form an integral spar for use in an aircraft wing structure, or in the form of a rib for use in an aircraft wing structure. The thicker gauge products can be used also as tooling plate, e.g., moulds for manufacturing formed plastic products, for example via die-casting or injection moulding. The alloy products as described herein can also be provided in the form of a stepped extrusion or extruded spar for use in an aircraft structure, or in the form of a forged spar for use in an aircraft wing structure.
The invention will now be illustrated with reference to the following non-limiting examples according to the invention.
On an industrial processing scale a 33 mm thick plate material was manufactured by DC-casting of an ingot having a chemical composition as set out in Table 1. The ingot was homogenised for 21 hours at 495° C. and subsequently hot rolled from a thickness of about 400 mm to 33 mm. The plate material was solution heat treated for 2 hours at 495° C. on laboratory scale; cooled down by a water quench; and subsequently artificially aged to a T8 temper using various aging practices, both according to standard industrial practice and according to the methods described herein see Table 2. In Table 2, aging practice 1 is a standard aging practice for arriving at a T8 condition; aging practice 2 is a second industrial practice, and aging practice 3 is according to the methods described herein.
Following the aging treatment, mechanical properties (tensile yield strength (YS), ultimate tensile strength (UTS) and elongation A50mm) in the L- and ST-direction were determined at mid-thickness in accordance with ASTM B 557. The average over three samples are listed in Table 3.
The minimum life (in days) without failure due to stress corrosion cracking (SCC) measured in accordance with ASTM G47-98 at a short transverse (ST) stress level of 250 MPa under constant load was tested. The results are also listed in Table 3. The average over three samples are listed in Table 3.
From the results of Table 3, it can be seen that an aging treatment according to the methods described herein significantly improves SCC resistance while maintaining comparably high mechanical properties.
On an industrial processing scale, a 120 mm thick plate material was manufactured by DC-casting of an ingot having a chemical composition as set out in Table 4. The ingot was homogenized for 36 hours at 495° C. and subsequently hot rolled from a thickness of about 430 mm to 120 mm. The plate material was solution heat treated for 6 hours at 495° C. on production scale; cooled down by a water quench; stretched by 1.4% cold deformation in the L-direction, and was subsequently artificially aged to a T8 temper using an aging practice as described herein and outlined in Table 5.
Following the aging treatment, mechanical properties (tensile yield strength (YS), ultimate tensile strength (UTS) and elongation A50mm) in the L- and ST-direction were determined at mid-thickness (ST-direction) or quarter thickness (L-direction) in accordance with ASTM B 557. The average over three samples are listed in Table 6.
The minimum life (in days) without failure due to stress corrosion cracking (SCC) measured in accordance with ASTM G47-98 at a short transverse (ST) stress level of 250 MPa under constant load has been tested. The results are also listed in Table 6. The average over three samples are listed in Table 6.
From the results of Table 6, it can be seen that also for thicker plates the aging treatment as described herein results in a combination of excellent SCC resistance and high mechanical properties.
Illustration 1 is an aging process of a solution-heat-treated and quenched 2XXX-series aluminum alloy wrought product, comprising the steps of: (1) aging the product in a first aging step at one or more temperatures within a range of 90° C. to 120° C. for a cumulative period time of at least 10 hours; and (2) subsequently aging the product in a second aging step at one or more temperatures within a range of 150° C. to 205° C. for a cumulative period of time of at least 4 hours, and preferably within a range of 150° C. to 195° C. for a cumulative period of time of at least 8 hours.
Illustration 2 is the aging process according to any preceding or subsequent illustration, wherein the aging process is of a solution-heat-treated, quenched, and subsequently cold worked or cold formed 2XXX-series aluminum alloy product.
Illustration 3 is the aging process according to any preceding or subsequent illustration, wherein cold working is applied in one or more cold working steps which are applied after solution heat treatment and quenching, optionally after further natural aging, and either before final artificial aging or in between the two artificial aging steps.
Illustration 4 is the aging process according to any preceding or subsequent illustration, wherein the quenching from solution heat treatment for a plate in a thickness range of 1.6 to 12 mm is performed with a cooling rate similar to the cooling rate with water quench of a 120 mm thick plate at mid thickness, preferably between 100° C./min and 1000° C./min, more preferably between 200° C./min and 600° C./min (when measured during cooling within a temperature range from 400° C. to 150° C.).
Illustration 5 is the aging process according to any preceding or subsequent illustration, wherein the aging process is of a worked product to provide a wrought product, solution-heat-treated, quenched, and subsequently cold worked or cold formed 2XXX-series aluminum alloy product.
Illustration 6 is the aging process according to any preceding or subsequent illustration, wherein the second aging step is for a cumulative period of time of at least 12 hours, and preferably for 12 to 144 hours.
Illustration 7 is the aging process according to any preceding or subsequent illustration, wherein the 2XXX-series aluminum alloy comprises, in wt. %: Cu 3.0% to 5.5%; Mn 0.15% to 1.0%; Mg 0.2% to 1.8%; Ag up to 0.7%; Zr up to 0.25%, Zn up to 0.25%, impurities up to 0.15%, and aluminum.
Illustration 8 is the aging process according to any preceding or subsequent illustration, wherein the 2XXX-series aluminum alloy comprises, in wt. %: Cu 3.0% to 5.5%; Mn 0.15% to 1.0%; Mg 0.2% to 1.8%; Ag up to 0.7%; Zn up to 1.0%; Fe up to 0.3%; Si up to 0.2%; Ti 0.01% to 0.2%; optionally one or more dispersoid forming elements selected from the group consisting of (0.05% to 0.25% Cr, 0.05% to 0.25% Zr, 0.05% to 0.25% V, 0.05% to 0.4% Hf, 0.05% to 0.4% Sc) preferably 0.05% to 0.2% Cr, 0.05% to 0.15% Zr, 0.05% to 0.15% V, 0.05% to 0.25% Hf, 0.05% to 0.25% Sc; impurities up to 0.15%; and aluminum.
Illustration 9 is the aging process according to any preceding or subsequent illustration, wherein the 2XXX-series aluminum alloy comprises Ag in a range of 0.1% to 0.7%, and preferably in a range of 0.2% to 0.7%.
Illustration 10 is the aging process according to any preceding or subsequent illustration, wherein the 2XXX-series aluminum alloy comprises a Cu content in a range of 3.5% to 4.4%.
Illustration 11 is the aging process according to any preceding or subsequent illustration, wherein the 2XXX-series aluminum alloy comprises a Cu content in a range of 4.4% to 5.5%, and preferably in a range of 4.4% to 5.1%.
Illustration 12 is the aging process according to any preceding or subsequent illustration, wherein the 2XXX-series aluminum alloy is provided as a rolled product.
Illustration 13 is the aging process according to any preceding or subsequent illustration, wherein the 2XXX-series aluminum alloy product is an aircraft structural member.
Illustration 14 is a method of manufacturing a 2XXX-series aluminum alloy wrought product, the method comprising the following steps: (i) casting of an ingot of an 2XXX-series aluminum alloy having a composition according to any preceding or subsequent illustration; (ii) preheating and/or homogenizing the ingot; (iii) hot working the ingot by one or more methods selected from the group consisting of rolling, extrusion, and forging, into a hot worked wrought product; (iv) optionally cold working the hot worked wrought product; (v) solution heat treating (“SHT”) of the wrought product; (vi) rapid cooling or quenching of the SHT product; (vii) optionally cold working or cold forming of the SHT and quenched product; and (viii) artificial aging in according to any preceding or subsequent illustration of the SHT, quenched product and optionally cold worked or cold formed to achieve improved metallurgical properties in the wrought product.
Illustration 15 is a wrought 2XXX-series aluminum alloy product, optionally having a clad layer on one or two sides, according to any preceding or subsequent illustration, wherein said product having a cross-sectional thickness from 1.6 mm to 12 mm, and preferably from 1.6 mm to 8 mm is aged to achieve (1) a conventional tensile yield strength (in MPa) measured in L-direction of more than 400 MPa and/or (2) an improved IGC resistance measured without cladding showing predominantly pitting attack and negligent IGC.
Illustration 16 is a wrought 2XXX-series aluminum alloy product according to any preceding or subsequent illustration, wherein said product having a cross-sectional thickness from 12 mm to 250 mm, and preferably from 12 mm to 130 mm is aged to achieve: (1) a conventional tensile yield strength (in MPa) measured in L-direction at quarter thickness of more than 380 MPa+0.57 (120−t) MPa (t being the thickness of the product in mm); and/or (2) a minimum service life without failure due to stress corrosion cracking in accordance with ASTM G47 of at least 20 days, preferably of at least 25 days at a short transverse stress level of 250 MPa.
Illustration 17 is a wrought 2XXX-series aluminum alloy product according to any preceding illustration, wherein said product having a cross-sectional thickness from 12 mm to 250 mm, and preferably from 12 mm to 130 mm is aged to achieve: (1) a conventional tensile yield strength (in MPa) measured in L-direction at quarter thickness of more than 380 MPa+0.57 (120−t) MPa (t being the thickness of the product in mm); and (2) an improved IGC resistance measured without cladding showing predominantly pitting attack and negligent IGC.
All patents, publications and abstracts cited above are incorporated herein by reference in their entireties. Various embodiments of the invention have been described in fulfillment of the various objectives of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptions thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the present invention as defined in the following claims.
This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63/198,906, filed Nov. 20, 2020, the contents of which are herein incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/060749 | 11/19/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63198906 | Nov 2020 | US |
