RU2779736C1 - Method for manufacturing products from almgsc series alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to a method for manufacturing products from an aluminum alloy of the AlMgSc series. A method for manufacturing a product from an aluminum alloy of the AlMgSc series includes cooling a product from an aluminum alloy of the AlMgSc series from the final annealing temperature to a temperature below 150°C, wherein cooling in the first temperature range from 250°C to 200°C is carried out for an equivalent time equal to more than 4 hours, and cooling in the second temperature range from 200°C to 150°C is carried out for an equivalent time equal to more than 0.2 hours, and the equivalent time, t(eq), is determined from the following relationship:

, where T, in degrees Kelvin, is the heat treatment temperature that changes over time t, in hours, and Tref, in degrees Kelvin, is the reference temperature chosen at 473°K.

EFFECT: invention is aimed at improving the resistance of aluminum alloy products of the AlMgSc system to corrosion delamination and intergranular corrosion.

13 cl, 1 ex, 1 tbl

Description

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing an AlMgSc series aluminum alloy product. The resulting product provides improved corrosion resistance. The aluminum alloy product may be in the form of a rolled product (sheet or plate), an extruded product, a forged product, or a powder metallurgy product.

BACKGROUND OF THE INVENTION

Aluminum alloys of the AlMg series, which may optionally or necessarily contain Sc as an alloying element, are well known in the art, for example, from the following documents.

US-6695935-B1 (Corus/Aleris) discloses an alloy in the form of a rolled or extruded product having the following composition: 3.5-6.0% Mg, 0.4-1.2% Mn, 0.4-1 .5% Zn, up to and including 0.25% Zr, up to and including 0.3% Cr, up to and including 0.2% Ti, up to and including 0.5% Fe, up to and including 0.5% Si, up to and including 0.4 % Cu, one or more elements selected from the group (0.005-0.1% Bi, 0.005-0.1% Pb, 0.01-0.1% Sn, 0.01-0.5% Ag, 0, 01-0.5% Sc, 0.01-0.5% Li, 0.01-0.3% V, 0.01-0.3% Ce, 0.01-0.3% Y, 0, 01-0.3% Ni), other elements each containing 0.05%, total 0.15%, the balance is aluminum. The alloy provides improved long-term corrosion resistance in both softening heat treatments (annealing) and work hardening or hardening heat treatments (hardening) compared to the standard AA5454 alloy.

EP-1917373-B1 (Aleris) describes an aluminum alloy body containing 3.5-6.0% Mg, 0.4-1.2% Mn, up to and including 0.5% Fe, up to and including 0.5 % Si, up to and including 0.15% Cu, 0.05-0.25% Zr, 0.03-0.15% Cr, 0.03-0.2% Ti, 0.1-0.3% Sc , up to and including 1.7% Zn, up to and including 0.4% Ag, up to and including 0.4% Li, optionally one or more dispersing elements selected from the group consisting of (Er, Y, Hf, V) with a content of each element up to and including 0.5%, by-elements and impurities with a content of each <0.05%, total <0.15%, and the remainder is aluminum.

Document RU-2280705-C1 describes an alloy containing 4.2-6.5% Mg, 0.5-1.2% Mn, up to and including 0.2% Zn, up to and including 0.2% Cr, up to and including 0 15% Ti, up to and including 0.25% Si, up to and including 0.30% Fe, up to and including 0.1% Cu, 0.05-0.3% Zr, at least one element selected from the group consisting of from (0.05-0.3% Sc, 0.0001-0.01% Be, 0.001-0.1% Y, 0.001-0.1% Nd, 0.001-0.1% Ce), the remainder is aluminum . Aluminum alloy has improved ballistic properties. The content of Zn and Si is reduced to improve the weldability and increase the corrosion resistance of the aluminum alloy.

Document RU-2268319-C1 describes an alloy containing 5.5-6.5% Mg, 0.10-0.20% Sc, 0.5-1.0% Mn, 0.10-0.25% Cr , 0.05-0.20% Zr, 0.02-0.15% Ti, 0.1-1.0% Zn, 0.003-0.015% B, 0.0002-0.005% Be, the remainder is aluminum, and the sum of Sc+Mn+Cr is at least 0.85%.

WO-01/12869-A (Kaiser Aluminum) describes an alloy containing 4.0-8.0% Mg, 0.05-0.6% Sc, 0.1-0.8% Mn, 0.5 -2.0% Cu or Zn, 0.05-0.20% Hf or Zr, the rest is aluminum and impurities.

WO-98/35068 (Alcoa) describes an aluminum alloy body containing 3-7% Mg, 0.03-0.2% Zr, 0.2-1.2% Mn, up to and including 0.15% Si , as well as 0.05-0.5% of a dispersion-forming element selected from the group consisting of (Sc, Er, Y, Ga, Ho, Hf), the balance is aluminum and by-products and impurities, and the aluminum alloy product is preferably not contains Zn and Li.

WO-2018/073533-A1 (Constellium) describes a method for manufacturing a hot-worked product, in particular a sheet product with a thickness of less than 12 mm, from an aluminum alloy consisting of Mg: 3.8-4.2%, Mn: 0.3-0 .8%, Sc: 0.1-0.3%, Zn: 0.1-0.4%, Ti: 0.01-0.05%, Zr: 0.07-0.15%, Cr: <0.01%, Fe: <0.15%, Si <0.1%, while homogenization is performed at a temperature of 370°C to 450°C for 2-50 hours so that the equivalent time at 400°C was 5-100 hours, and hot deformation is carried out at an initial temperature of 350°C to 450°C. Such products provide advantages as they have improved mechanical strength, stiffness and thermoformability.

DESCRIPTION OF THE INVENTION

As will be described below, unless otherwise noted, aluminum alloy designations and hardness grades refer to the Aluminum Association designations in aluminum standards and data and registry entries published by the Aluminum Association in 2018 and are well known to those skilled in the art.

For any description of alloy compositions or preferred alloy compositions, all references to percentages are by weight unless otherwise indicated.

As used herein, the terms "up to and including about" expressly include, among other things, the possibility of zero weight percent of the particular alloying component to which they refer. For example, up to and including 0.10% Zn may include an alloy without Zn.

An object of the present invention is to provide a method for manufacturing an AlMgSc series aluminum alloy body with improved corrosion resistance.

An object of the present invention is to provide a method for manufacturing an AlMgSc series aluminum alloy body with improved resistance to corrosion exfoliation in combination with improved resistance to intergranular corrosion.

The present invention accomplishes these and other objects and provides additional benefits by providing a method for manufacturing an AlMgSc series aluminum alloy body, the method comprising the step of cooling said AlMgSc series aluminum alloy body from a final annealing temperature or a target annealing temperature to a temperature below 150 °C, and the cooling performed in the first temperature range from about 250°C to about 200°C, is carried out for an equivalent time equal to more than 4 hours, preferably more than 6.5 hours and more preferably more than 26 hours, and the cooling performed in the second temperature range from about 200°C to about 150°C, carried out for an equivalent time equal to more than 0.2 hours, preferably more than 0.4 hours and more preferably more than 0.8 hours, and the equivalent time (t( _eq )) is defined as

where T (in degrees Kelvin) indicates the heat treatment temperature that changes over time t (in hours) and T _ref (in degrees Kelvin) is the reference temperature selected at 473°K (200°C).

The method according to the present invention provides aluminum alloy products of the AlMgSc series with high strength, preferably Rp > 200 MPa, combined with high corrosion resistance, in particular high resistance to corrosion exfoliation combined with high resistance to intergranular corrosion. The applied cooling rate values are economically feasible from the point of view of the industrial production of AlMgSc series aluminum alloy products.

Aluminum alloy products of the AlMgS series made according to the present invention are resistant to corrosion exfoliation. The term "resistance to corrosion exfoliation" should be understood that the aluminum alloy product complies with the requirements of ASTM G66-99 (2013), entitled "Standard Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET test)" . The designations N, PA, PB, PC and PD indicate the results of the ASSET test, and N indicates the best result. Aluminum alloy products made according to the present invention show a PB result or better both before and after sensitization.

Aluminum alloy products of the AlMgS series made according to the present invention are also resistant to intergranular corrosion. The term "resistance to intergranular corrosion" should be understood that both before and after sensitization of the aluminum alloy of the AlMgSc series, the aluminum alloy product complies with the requirements of ASTM G67-13, entitled "Standard Test Method for Determining the Susceptibility to Intergranular Corrosion of 5XXX Series Aluminum Alloys by Mass Loss After Exposure to Nitric Acid (NAMLT test)". If the measured weight loss in accordance with ASTM G67-13 does not exceed 15 mg/cm ² , the sample is considered insensitive to intergranular corrosion. If the measured mass loss is greater than 25 mg/cm ² , the sample is considered to be susceptible to intergranular corrosion. If the measured weight loss is in the range of 15 mg/cm ² to 25 mg/cm ² , additional microscopic examinations are carried out to determine the type and depth of impact, and a person skilled in the art can determine the presence of intergranular corrosion from the results of microscopic examination. AlMgSc series aluminum alloy articles made according to the present invention achieve a measured weight loss according to ASTM G67-13 of not more than 15 mg/cm ² both before and after sensitization. Preferably the measured weight loss does not exceed 12 mg/cm ² , more preferably does not exceed 9 mg/cm ² . The term "sensitization" is understood to mean that the aluminum alloy body of the AlMgSc series is annealed to a state that provides a service life of at least 20 years. For example, an aluminum alloy body may be continuously exposed to high temperatures for several days (eg, temperatures ranging from 100°C to 120°C for about 7 days/168 hours).

The AlMgSc series aluminum alloy body can exhibit resistance to stress corrosion cracking and intergranular corrosion as a result of, at least in part, the absence of a continuous film of β-phase particles at the grain boundaries. Aluminum alloy products are polycrystalline. "Grain" is a polycrystalline aluminum alloy crystal, and "grain boundaries" are boundaries connecting polycrystalline aluminum alloy grains, "phase" is Al ₃ Mg ₂ , and "continuous film of phase" means a continuous volume of phase particles present on most grain boundaries. Phase continuity can be determined, for example, during microscopic examinations at appropriate resolution (eg, at least 200x magnification).

In accordance with the present invention, it has been found that a very high rate of cooling, for example, as a result of hardening, from the final annealing temperature to a temperature below 150°C, adversely affects the corrosion resistance of the AlMgSc series aluminum alloy product, in particular the corrosion resistance tested with using the NAMLT test after sensitization. The lower cooling rate results in improved intergranular corrosion resistance.

When cooled from the final annealing temperature to about 150°C, more specifically in the first temperature range from about 250°C to about 200°C, the equivalent time should be greater than 4 hours, preferably greater than 6.5 hours, more preferably greater than 26 hours, during the second temperature range from about 200°C to about 150°C equivalent time should be more than 0.2 hours, preferably more than 0.4 hours, more preferably more than 0.8 hours. Relatively slow cooling plays an important role in the deposition of discontinuous phase particles at the grain boundaries and in preventing the deposition of a continuous film of phase particles both after cooling to ambient temperature and after sensitization of the Al-Mg-Sc alloy. The cooling is preferably carried out continuously so that the temperature of the metal decreases continuously over time.

Cooling from the final annealing temperature to the temperatures of the first range, starting from about 250°C, is not critical. When applying the method according to the present invention on an industrial scale, it may be useful or convenient to use the same cooling rate as for the first temperature range.

Further cooling from about 150° C. to a temperature below about 85° C. is less critical and can be carried out at a higher cooling rate, which will minimize coarsening of the precipitate particles. The cooling rate for cooling from about 85° C. to ambient temperature is not critical.

In one embodiment, the AlMgSc series aluminum alloy product is in a form selected from the group consisting of a rolled product (sheet or plate), an extruded product, a forged product, and a powder metallurgy product. In a further embodiment, any of these articles are welded or formed.

In a specific embodiment, the AlMgSc series aluminum alloy product is in the form of a rolled product. In a further embodiment, the rolled product is welded or formed.

In one embodiment, the thickness of the AlMgSc series aluminum alloy rolled product does not exceed 25.4 mm (1 inch), preferably does not exceed 12 mm (0.47 inch), more preferably 6 mm (0.24 inch), and preferably 4.5 mm (0.18 in.). In one embodiment, the thickness of the AlMgSc series aluminum rolled product is at least 0.047 inches (1.2 mm).

In a particular embodiment, the AlMgSc series aluminum alloy product is in the form of an extruded product.

In one embodiment, the AlMgSc series aluminum alloy rolled product is a casting rolled to final gauge and annealed. The alloy may be provided in the form of an ingot or slab for conversion into a billet for rolling using casting techniques common in the manufacture of cast products, such as continuous casting into a mold, preferably with a thickness of the ingot in the range of about 220 mm or more, such as 400 mm, 500 mm or 600 mm. In another embodiment, thin sized continuous cast slabs, such as strip-cast or roll-cast products, up to and including about 40 mm thick can be used. After casting a billet for rolling from a thick ingot immediately after casting, it is common to remove the surface layer to remove segregation zones near the cast surface of the ingot.

Preferably, the rolling process employed includes hot rolling, and optionally also includes hot rolling followed by cold rolling to a final gauge, and if necessary, an intermediate annealing is applied either before the cold rolling operation or during the cold rolling operation to an intermediate cold rolling gauge.

Prior to hot rolling, the AlMgSc series aluminum alloy body is homogenized or preheated for up to and including about 50 hours, preferably up to and including about 24 hours, at a temperature in the range of about 320°C to 470°C, preferably about 320°C. up to 450°C.

In one embodiment, after the hot rolling operation, the hot rolled product is subjected to very moderate cold rolling (smoothing or skin pass) with a thickness reduction of less than about 1%, preferably less than about 0.5%, to improve the flatness of the rolled product. In an alternative embodiment, the hot rolled product may be stretched. The stretching step can be performed with a reduction of up to and including 3%, preferably from about 0.5% to 1%, to improve the flatness of the hot rolled product.

Final annealing or annealing heat treatment to final gauge is necessary to restore the microstructure and is typically carried out at a predetermined annealing temperature in the range of 250°C to 400°C, preferably in the range of 260°C to 375°C, most preferably in the range of about 280°C. C to 350°C, for about 0.5 hour to 20 hours, preferably from about 0.5 hour to 10 hours.

In one embodiment, an AlMgSc series aluminum alloy extruded body is manufactured by a method comprising the following steps: (a) providing an ingot for extrusion, for example, by continuous casting into an aluminum alloy mold as described and claimed herein; (b) preheating and/or homogenizing the ingot for extrusion, preferably at a temperature and for a time similar to the billet for rolling; (c) hot extruding the ingot to form an extruded profile with a section or wall thickness ranging from 1 mm to about 20 mm, preferably from 1 mm to about 15 mm; while the temperature of the workpiece at the beginning of the extrusion process is usually in the range from about 400°C to about 500°C; optionally stretching the extruded profile to increase the straightness of the article; and (d) annealing the extruded profile at a final annealing temperature followed by a cooling procedure according to the present invention.

In one embodiment of the present invention, a method for cooling an aluminum alloy body is carried out immediately after a hot forming operation to shape an AlMgSc series aluminum alloy body into a single or double curved body. The hot forming operation is performed at a final annealing temperature in the range of 180°C to 500°C, preferably in the range of 250°C to 400°C, more preferably in the range of 260°C to 375°C, most preferably in the range of 280 °C to 350°C, for example at approximately 300°C or 325°C. In a particular preferred embodiment, the hot forming operation at the final annealing temperature is carried out by a creep forming operation or a stress relieving forming operation. Creep molding is the process or operation of restricting a component to a particular shape during heat treatment, which causes the component to relieve stress and creep to a contour, such as a double-curve aircraft skin. The creep forming process, for example, is explained in a paper by S. Jambu et al. "Creep forming of AlMgSc alloys for aeronautic and space applications" published at ICAS-2002.

In a preferred embodiment of the hot forming operation at the final annealing temperature to produce a single or double curved product, an AlMgSc series aluminum alloy rolled product is used. The AlMgSc series aluminum alloy body can be provided in an annealed state, also obtained by the method of the present invention.

Optionally, aluminum alloy extruded products of the AlMgSc series are also used, for example, as extruded stringers as part of the fuselage panel.

In one embodiment of the present invention, a method of cooling an aluminum alloy body is applied to a welded body or panel containing an AlMgSc series aluminum alloy body immediately after post-weld heat treatment to restore some strength, in particular by redepositing AlScZr dispersoids. The post-weld heat treatment is performed at a temperature similar to the final annealing heat treatment and in the range of 250°C to 400°C, preferably in the range of 260°C to 375°C, and more preferably in the range of about 260°C to 350°C , for about 0.5 hour to 20 hours, preferably from about 0.5 hour to 10 hours.

In one embodiment of the present invention, a method of cooling an aluminum alloy body is applied to a cold-formed and shaped aluminum alloy body of the AlMgSc series, wherein the annealing heat treatment is performed to reduce residual stress in the cold-formed and shaped body or to restore certain technical properties, such as elongation or fracture resistance. Such annealing heat treatment is performed at a temperature similar to the final annealing heat treatment and in the range of 250°C to 400°C, preferably in the range of 260°C to 375°C, and more preferably in the range of about 280°C to 350°C. C, for about 0.5 hour to 20 hours, preferably from about 0.5 hour to 10 hours.

In one embodiment, the AlMgSc series aluminum alloy has a composition containing, in wt %:

mg 3.0% to 6.0%, preferably 3.2%-4.8%, more preferably 3.5% to 4.5%, sc from 0.02% to 0.5%, preferably 0.02%-0.40%, more preferably 0.05%-0.3%, Mn up to and including 1%, preferably 0.3%-1.0%, more preferably 0.3%-0.8%, Zr up to and including 0.3%, preferably 0.05%-0.3%, more preferably 0.07%-0.15%, Cr up to and including 0.3%, preferably 0.02%-0.2%, Ti up to and including 0.2%, preferably 0.01%-0.2%, Cu up to and including 0.2%, preferably up to and including 0.1%, more preferably up to and including 0.05%, Zn up to and including 1.5%, preferably up to and including 0.8%, more preferably 0.1%-0.8%, Fe up to and including 0.4%, preferably up to and including 0.3%, more preferably up to and including 0.20%, Si up to and including 0.3%, preferably up to and including 0.2%, more preferably up to and including 0.1%,

impurities and the remainder are aluminum.

Typically, such impurities are present in amounts of <0.05% each and <0.15% in total.

Mg is the main alloying element in the AlMgSc series alloys and should be in the range of 3.0% to 6.0% in the process of the present invention. The preferred lower limit for the Mg content is about 3.2%, more preferably about 3.8%. The preferred upper limit for the Mg content is about 4.8%. In one embodiment, the upper limit for the Mg content is about 4.5%.

Sc is another important alloying element which should be in the range of 0.02% to 0.5%. The preferred lower limit for the Sc content is about 0.05%, and more preferably about 0.1%. In one embodiment, the Sc content is up to and including about 0.4%, and preferably up to and including about 0.3%.

Mn may be added to the AlMgSc series aluminum alloys and may be present in the range up to and including about 1%. In one embodiment, the Mn content is in the range from about 0.3% to 1%, and preferably from about 0.3% to 0.8%.

It is also preferable to add Zr in the range up to and including about 0.3% to increase Sc efficiency. In one embodiment, Zr is present in the range from 0.05% to 0.30%, preferably in the range from about 0.05% to 0.25%, and more preferably is present in the range from about 0.07% to 0.15 %.

Cr may be present up to and including about 0.3%. If intentionally added, it is preferably in the range of about 0.02% to 0.3%, and more preferably in the range of about 0.05% to 0.15%. In one embodiment, Cr is not intentionally added and may be present in amounts up to and including 0.05%, and is preferably kept below 0.02%.

Ti can be added in amounts up to and including about 0.2% to the AlMgSc alloy as a hardening element either to increase corrosion resistance or to refine grain. Ti is preferably added in the range from about 0.01% to 0.2%, and preferably in the range from about 0.01% to 0.10%.

In one embodiment, the intentional combined addition of Zr+Cr+Ti is provided. In this embodiment, the combined addition is at least 0.15% to achieve sufficient strength, and preferably not more than 0.30% to prevent the formation of too large sediment particles.

In another embodiment, there is intentional combined addition of Zr and Ti, but no intentional addition of Cr. In this embodiment, the combined addition of Zr+Ti is carried out in an amount of at least 0.08%, and preferably not more than 0.25%, and wherein Cr is present in an amount up to and including 0.02%, and preferably only up to and including 0.01 %.

Zinc (Zn) up to and including 1.5% may be intentionally added to further increase the strength of the aluminum alloy product. The preferred lower limit for intentional addition of Zn is 0.1%. The preferred upper limit should be approximately 0.8%, and more preferably 0.5%, to provide a balance of strength and corrosion resistance.

In one embodiment, Zn is an acceptable impurity element and can be up to and including 0.15% and preferably up to and including 0.10%.

Cu may be present in the AlMgSc alloy as a strengthening element in the range up to and including about 2%. However, in product applications in which corrosion resistance is a critical technical property, it is preferable to keep Cu at a low level of about 0.2% or less, and preferably at a level of about 0.1% or less, and more preferably at a level of 0 .05% or less. In one embodiment, the Cu content is 0.01% or less.

Fe is a common impurity in aluminum alloys and can be tolerated up to and including about 0.4%. Preferably it is maintained at up to and including about 0.3%, and more preferably up to and including about 0.20%.

Si is also a common impurity in aluminum alloys and can be tolerated up to and including about 0.3%. Preferably it is maintained at up to and including 0.2%, and more preferably up to and including 0.10%.

In one embodiment, the AlMgSc series aluminum alloy has a composition consisting of, in wt %: Mg from 3.0% to 6.0%, Sc from 0.02% to 0.5%, Mn up to and including 1%, Zr up to and including 0.3%, Cr up to and including 0.3%, Ti up to and including 0.2%, Cu up to and including 0.2%, Zn up to and including 1.5%, Fe up to and including 0.4%, Si up to and including 0.3%, balance: aluminum and impurities each <0.05% and <0.15% total, with preferred narrower composition ranges being described and claimed herein.

In accordance with the present invention, it has been found that the method can be applied to a wide range of aluminum alloys of the AlMgSc series. It has been found that as the Cu content of the aluminum alloy is increased, it is preferable to decrease the cooling rate and, accordingly, a longer equivalent time in certain first and second temperature ranges from the final annealing temperature. Such a very low cooling rate does not adversely affect the corrosion resistance of AlMgSc series aluminum alloys having a very low Cu content, such as less than 0.05%, or even less than 0.01%.

In one embodiment, the aluminum alloy body is a single or double curved panel, in particular a single or double curved aircraft fuselage panel.

Hereinafter, the present invention will be illustrated with reference to a non-limiting example corresponding to the present invention and comparative.

EXAMPLE

Sheet products of 4.5 mm in size were produced on an industrial scale in the steps of continuous casting into the ingot catalyst for rolling, removing the surface layer, milling, preheating to a hot rolling temperature of 400°C to 450°C, hot rolling, cold rolling to 4, 5 mm and with intermediate annealing during the cold rolling operation, and with final annealing at a set temperature of 325°C (598 K) for 2 hours, followed by different controlled cooling rates according to table 1, with samples A, B and C made according to this of the invention, and sample D is comparative.

The AlMgSc aluminum alloy casting has the following composition in wt%: 4.0% Mg, 0.55% Mn, 0.2% Sc, 0.3% Zn, 0.1% Zr, 0.07% Cr, 0 0.07% Ti, 0.02% Si, 0.02% Fe, 0.006% Cu, the rest is aluminum and unavoidable impurities.

Table 1 lists the measured weight loss according to ASTM G67-13 for each sample with different cooling conditions from the final annealing temperature after sensitization at 120°C for 168 hours.

The AlMgSc series aluminum alloy rolled products produced according to the present invention are resistant to intergranular corrosion. "Resistant to intergranular corrosion" means that before and after sensitization of the aluminum alloy of the AlMgSc series, the aluminum alloy product meets the requirements of ASTM G67-13, (NAMLT test). All sensitized samples had a PA score and all non-sensitized samples also had a PA score.

From the results of Table 1, it can be seen that the AlMgSc series aluminum alloy rolled products manufactured according to the present invention achieve a measured weight loss according to ASTM G67-13 of not more than 15 mg/cm ² after sensitization. In the best examples, the mass loss does not exceed 9 mg/cm². With a lower cooling rate or a longer equivalent time within a certain temperature range, the weight loss is further reduced. Sample D at 473 K to 423 K had too high a cooling rate and was not made according to the present invention, resulting in a significant increase in weight loss according to ASTM G67-13.

Thus, the method of the present invention results in an aluminum alloy body having good intergranular corrosion resistance combined with high resistance to corrosion exfoliation.

A similar corrosion resistance of an aluminum alloy body will be achieved when cooled from a hot forming operation performed at the final annealing temperature, such as a creep forming operation performed at 310°C or 325°C.

The present invention is not limited to the previously described embodiments, which may vary widely within the scope of the present invention as defined by the appended claims.

Claims (19)

1. A method for manufacturing an AlMgSc series aluminum alloy body, the method comprising the step of cooling said AlMgSc series aluminum alloy body from a final annealing temperature to a temperature below 150°C, the cooling being performed in a first temperature range of 250°C to 200°C , is carried out for an equivalent time of more than 4 hours, and the cooling performed in the second temperature range from 200°C to 150°C, is carried out for an equivalent time of more than 0.2 hours, and moreover, the equivalent time (t(eq )) is defined as

where T, in degrees Kelvin, indicates the heat treatment temperature that changes over time t, in hours, and T _ref , in degrees Kelvin, is the reference temperature selected at 473°K (200°C). 2. Method according to claim 1, characterized in that the equivalent time in the first temperature range is greater than 6.5 hours, and preferably greater than 26 hours. 3. Method according to claim 1 or 2, characterized in that the equivalent time in the second temperature range is greater than 0.4 hours, and preferably greater than 0.8 hours. 4. The method according to any one of paragraphs. 1-3, characterized in that the final annealing temperature is in the range from 250°C to 400°C, preferably in the range from 260°C to 375°C, and more preferably in the range from 280°C to 350°C. 5. The method according to any one of paragraphs. 1-4, characterized in that said aluminum alloy product of the AlMgSc series is presented in a form selected from the group consisting of a rolled product, an extruded product, a forged product, and a powder metallurgy product. 6. The method according to any one of paragraphs. 1-5, characterized in that said aluminum alloy product of the AlMgSc series is a rolled product. 7. The method according to claim 6, characterized in that the rolled product has a thickness of up to and including 25.4 mm, and preferably up to and including 12 mm, more preferably up to and including 6 mm. 8. The method according to claim 1 or 7, characterized in that the method includes the steps of casting an aluminum alloy ingot of the AlMgSc series, rolling the ingot to a final caliber to obtain a rolled product, and heat treatment by annealing the rolled product at the final annealing temperature, followed by cooling over any of paragraphs. 1-3 . 9. The method according to any one of paragraphs. 1-8, characterized in that the method includes the steps of hot forming an aluminum alloy product of the AlMgSc series to obtain a product with one or two curved contours at a final annealing temperature, followed by cooling according to any one of paragraphs. 1-3 . 10. Method according to claim 9, characterized in that the hot forming operation at the final annealing temperature is carried out by creep forming or stress relieving forming. 11. The method according to any one of paragraphs. 1-10, characterized in that the aluminum alloy product of the AlMgSc series has a composition containing in wt.%: mg 3.0 to 6.0, preferably 3.2 to 4.8, sc from 0.02 to 0.5, preferably from 0.02 to 0.40, Mn up to and including 1, Zr up to and including 0.3, preferably from 0.05 to 0.3, impurities and the remainder are aluminum. 12. The method according to any one of paragraphs. 1-10, characterized in that the aluminum alloy product of the AlMgSc series has a composition containing in wt.%: mg 3.0 to 6.0, preferably 3.2 to 4.8, sc from 0.02 to 0.5, preferably from 0.02 to 0.40, Mn up to and including 1, preferably from 0.3 to 1.0, Zr up to and including 0.3, preferably from 0.05 to 0.3, Cr up to and including 0.3, Ti up to and including 0.2, preferably 0.01-0.2, Cu up to and including 0.2, Zn up to and including 1.5, Fe up to and including 0.4, Si up to and including 0.3, impurities and the remainder are aluminum. 13. The method according to any one of paragraphs. 1-12, characterized in that the AlMgSc series aluminum alloy body manufactured according to the present invention achieves a measured weight loss according to ASTM G67-13 of not more than 15 mg/cm ² both before and after sensitization, and preferably the weight loss does not exceed 12 mg/cm², and more preferably does not exceed 9 mg/cm².