THIN SHEET MADE OF A HIGH-DUCTILITY ALUMINUM ALLOY

Description

TECHNICAL FIELD

[0001] The invention relates to the field of thin sheets of high ductility aluminium alloy, in particular for making decorative parts such as, for example, interior parts of motor vehicles.

[0002] The invention relates more particularly to aluminum alloy sheets of the AA5xxx series whose composition and transformation process are particularly suited to this type of application and exhibit excellent ductility. EARLIER ART

[0003] Aluminium alloys are commonly used in the manufacture of decorative parts, particularly for the automotive industry, but also in the household appliance and medical equipment industries, competing with wood, steel and plastics.

[0004] In the automotive industry, this includes the production of interior trim elements, such as those for the center console, including the dashboard, gearshift surround, door handles, interior trim strips, and body moldings, as well as exterior trim elements such as window surrounds, side moldings for the body or doors, tailgate trim strips, grille surrounds, and bumper trim strips. These products may undergo surface treatments such as anodizing, varnishing, and / or lacquering.

[0005] AA5005 aluminum alloy rolled products with various heat treatment states are widely used in drivers, cookware, dashboards, architectural decorations, building materials, vehicle interior and exterior materials, etc.

[0006] International patent application WO2014203077 relates to a method for manufacturing an outer molding ring for a motor vehicle, in particular such as a window frame or body molding, made of aluminum alloy, by shaping and polishing a sheet or strip produced by continuous vertical casting of a high-purity alloy sheet of the AA5xxx series, homogenization-heating of the sheet, hot rolling, cooling, cold rolling with intermediate annealing in a continuous-pass furnace, or holding between the solvus temperature and the combustion temperature of the alloy typically for 3 seconds to 5 minutes, quenching in air or water, and optionally annealing at a temperature of 100°C to 200°C. This application also relates to a molding ring for a motor vehicle manufactured according to such a method.

[0007] US patent 4715901 describes 1XXX and 5XXX type aluminum alloys comprising 0.01 to 0.08% chromium or manganese, preferably both.

[0008] US patent 3793089 describes an alloy comprising 0.05–0.20% silicon, 0.15–0.40% iron, 0.15–0.30% copper, 0.10–0.30% manganese, 0.6–1.0% magnesium, 0.04–0.12% chromium, and the remainder aluminum. When anodized in full color, the product forms an anodic coating ranging in color from gold to black within a commercially acceptable thickness range.

[0009] Patent application CN107805746A describes a rolled product of aluminium alloy 5005H34, with the following composition by mass percentage: Si less than or equal to 0.2%, Fe less than or equal to 0.55%, Cu less than or equal to 0.15%, Mn less than or equal to 0.2%, Mg 0.75 to 1.0%, Cr less than or equal to 0.1%, Zn less than or equal to 0.2% and Ti, 0.01 to 0.05%.

[0010] Patent application CN109266924A describes an aluminum substrate for an anodized aluminum curtain panel. The chemical components of the aluminum substrate include, by weight, 0.10-0.20% Si, 0.16-0.30% Fe, 0.65-0.10% Cu, 0.7-1.3% Mg, 0.01-0.02% Ti and the remainder Al and impurities.

[0011] Patent application CN109825746 A describes a high-quality aluminum base material for certain walls, having a surface roughness Ra 0.3-0.5 [mu] m, Ra 0.3-0.5 [mu] m, Rz 1.4-2.4 [mu] m, a stable after being subjected to anodic oxidation.

[0012] Patent application EP2862952 describes an aluminum alloy plate comprising peritectic elements and Mg.

[0013] US patent 3164494 describes an aluminum alloy suitable for chemical and electrolytic brightening, composed essentially of magnesium up to about 1.20%, copper, 0.01 to 0.08%, manganese up to 0.03%, iron from 0.01 to 0.12% and silicon from 0.01-0.08%; by weight percentage, the remainder being aluminum.

[0014] Alloy 5005 is also used in the field of plated products, which is not the subject of the present invention. Patent application EP2924136 relates to an architectural facade product, with a core layer of AlMg-based aluminum alloy, in particular the AA5xxx series, and with at least one coating layer plated on one side of the core layer containing 0.03 to 0.06% by weight of silicon (Si), 0.15 to 0.20% by weight of iron (Fe), 0.08 to 0.12% by weight of copper (Cu), 0.08 to 0.12% by weight of manganese (Mn), 0.85 to 0.95% by weight of magnesium (Mg) and the remainder aluminum as well as the unavoidable impurities due to production.Similarly, international application WO2010144997A1 describes an architectural product made of aluminium in which a plated layer is applied to at least one side of a core layer, preferably the core layer being made of an alloy selected from the AA5XXX series alloys with a magnesium content greater than 3% by weight, and the plated layer (or each plated layer) being made of an alloy selected from the AA5005, AA5205, AA5052, AA5252 and AA5005A alloys.

[0015] Alloys 5457, 5557 and 5657 are known for applications requiring a bright finish, for example from ASM Handbook, Volume 2B, Properties and Selection of Aluminum Alloys, © 2019

[0016] To produce increasingly complex parts, a high degree of product formability, particularly ductility, is essential. However, other constraints complicate this objective: the product must be easily recyclable to ensure its sustainability, and its decorative and mechanical strength properties must be at least as good as those of previous products.

[0017] Recycled aluminum does indeed emit low levels of greenhouse gases compared to aluminum produced by electrolysis. To improve the carbon footprint of aluminum products, it is particularly beneficial to limit the use of aluminum produced by electrolysis and maximize the use of recycled aluminum.

[0018] The problem that the present invention seeks to solve is thus to produce 5XXX aluminum alloy sheets having improved ductility while being recyclable and having sufficient surface quality and mechanical strength properties. DESCRIPTION OF THE INVENTION

[0019] The invention is described in the attached set of claims.

[0020] A first object of the invention is a thin sheet of aluminium alloy with the composition, in % by weight, Mg: 0.65 - 0.85, Fe: 0.14 - 0.20, Si: 0.05 - 0.09, Mn: ≤ 0.03, Cu: ≤ 0.05, Cr: ≤ 0.02, Zn: ≤ 0.10, Ti: ≤ 0.03, other elements or impurities < 0.05 each and < 0.15 total, remainder aluminium, of which more than 85% of the microstructure is recrystallised.

[0021] A second object of the invention is a method for manufacturing a thin sheet according to the invention in which, successively, (a) An aluminum alloy with the following composition (in wt. %): Mg: 0.65–0.85, Fe: 0.14–0.20, Si: 0.05–0.09, Mn: ≤ 0.03, Cu: ≤ 0.05, Cr: ≤ 0.02, Zn: ≤ 0.10, Ti: ≤ 0.03, other elements or impurities < 0.05 each and < 0.15 total, remaining aluminum, is cast as a rolling slab. (b) The slab thus obtained is scalped. (c) The scalped slab is heated, preferably to a temperature between 480 °C and 500 °C. (d) The heated slab is hot-rolled to obtain a sheet with a thickness between 3 and 10 mm. (e) The sheet thus obtained is cooled. (f) The sheet is cold-rolled. the sheet thus cooled obtain a thin sheet of final thickness (g) optionally the thin sheet thus obtained is degreased and / or pickled and / or polished, (f) the thin sheet is annealed at a temperature of 330 °C to 420 °C.

[0022] Another object of the invention is the use of a thin sheet according to the invention to produce a part of complex shape formed in three dimensions of space in particular by stamping. FIGURES

[0023] [ Fig. 1 ] There Figure 1 represents the elongation A 50 as a function of the tensile strength R m . DETAILED DESCRIPTION OF THE INVENTION

[0024] Unless otherwise stated, all indications concerning the chemical composition of alloys are expressed as a percentage by weight based on the total weight of the alloy. The expression 1.4 Cu means that the copper content expressed as a percentage by weight is multiplied by 1.4. The designation of alloys is in accordance with the regulations of The Aluminium Association, which are familiar to those skilled in the art.

[0025] The static mechanical tensile characteristics, in other words the tensile strength Rm, the conventional yield strength at 0.2% elongation Rp 0.2, and the elongation at break A%, are determined by a tensile test according to standard NF EN ISO 6892-1. The elongation (A%) at break was measured using a 50 mm base extensometer and is noted A 50.

[0026] Unless otherwise stated, the definitions in EN 12258 (2012) apply. A thin sheet is a rolled product with a rectangular cross-section and a uniform thickness between 0.20 mm and 6 mm. For the purposes of this invention, a thin sheet is not a plated sheet.

[0027] The applicant has found that, surprisingly, it is possible to obtain thin sheets of 5XXX aluminum alloy with improved formability while being recyclable and having sufficient surface quality and mechanical strength properties, thanks to a narrow selection of composition and an appropriate manufacturing process.

[0028] The thin sheets according to the invention have the following composition, in % by weight: Mg: 0.65 - 0.85, Fe: 0.14 - 0.20, Si: 0.05 - 0.09, Mn: ≤ 0.03, Cu: ≤ 0.05, Cr: ≤ 0.02, Zn: ≤ 0.10, Ti: ≤ 0.03, other elements or impurities < 0.05 each and < 0.15 total, remainder aluminum.

[0029] It is generally accepted that reducing the iron content of this type of product improves its ductility, which in turn enhances its formability. Thus, in alloys such as AA5395, AA5405, and AA5605, the maximum iron content is 0.08%, 0.04%, and even 0.008% by weight, respectively. Similarly, in AA5457, AA5557, and AA5657, the maximum iron content is 0.10%, 0.12%, and 0.10% by weight, respectively. However, the inventors did not wish to use this type of solution because it would have reduced the recyclability of the alloys. Iron is one of the most common impurities in aluminum alloy scrap and waste, and increasing the iron content of a product limits its recycling potential. The minimum iron content is therefore 0.14% by weight.The maximum iron content required to achieve the desired mechanical properties is 0.20% by weight, and preferably 0.18% by weight. Similarly, and to a lesser extent, the minimum silicon content of 0.05% by weight, and preferably 0.06% by weight, ensures that recycling possibilities are not limited. The inventors have found that, surprisingly, it is possible to improve the formability of products with an iron content of at least 0.14% by weight and a silicon content of at least 0.05% by weight by selecting the composition of the elements Si, Cr, Mn, and Ti. Preferably, the Fe / Si ratio is at least 1.9, preferably at least 1.95, most preferably at least 2.0, and most preferably at least 2.2.The inventors believe that the Fe / Si ratio influences, in particular, the size of the intermetallic phases formed during casting, a high ratio allowing for finer intermetallic phases that are more suitable for shaping. Thus, the maximum silicon content of the products according to the invention is 0.09% by weight and preferably 0.08% by weight; the maximum chromium content is 0.02% by weight and preferably 0.01% by weight; the maximum manganese content is 0.03% by weight and preferably 0.02% by weight; and the maximum titanium content is 0.03% by weight and preferably 0.02% by weight. In an advantageous embodiment, the sum of the Cr + Mn + Ti contents is at most 0.06% by weight and preferably at most 0.04% by weight. In another advantageous embodiment the sum of the Fe + Si + Mn contents is at least 0.22% by weight or even at least 0.24% by weight.In yet another advantageous embodiment, the sum of the Fe + Si contents is at least 0.20% by weight, preferably at least 0.21% by weight, or even at least 0.23% by weight. The inventors believe that the advantageous properties obtained could be linked, in particular, to the low volume fraction of iron-containing intermetallic compounds formed with the composition according to the invention.

[0030] The magnesium (Mg) content of the products according to the invention is from 0.65% to 0.85% by weight, which notably allows for sufficient mechanical properties, such as tensile strength (Rm), while avoiding surface defects such as those known as Lüders bands or Portevin-Le Chatelier instabilities. Advantageously, the magnesium (Mg) content of the products according to the invention is at least 0.69% by weight. Advantageously, the magnesium (Mg) content of the products according to the invention is at most 0.83% by weight. In an embodiment of the invention in which ductility is favored, the magnesium (Mg) content of the products according to the invention is from 0.65% to 0.78% by weight, and preferably from 0.68% to 0.75% by weight. In an embodiment of the invention in which mechanical resistance is favoured, the Mg content of the products according to the invention is 0.72% by weight to 0.82% by weight and preferably 0.76% by weight to 0.83% by weight.

[0031] The copper content of the products according to the invention must also be controlled to obtain the desired mechanical properties and to avoid an undesirable surface appearance after shaping and surface treatment. Therefore, the maximum copper content is 0.05% by weight, and preferably 0.03% by weight. When the copper content exceeds 0.05% by weight, a yellowish appearance may occur on the finished, shaped, and ready-to-use parts, which detracts from their decorative appearance.

[0032] The other elements or impurities have a content of less than 0.05% by weight each and less than 0.15% by weight in total. Preferably, they have a content of less than 0.03% by weight each and < 0.10% by weight in total. These are elements present in the electrolysis or recycling metal used to prepare the alloy and not added individually on a voluntary basis.

[0033] The products according to the invention have an essentially recrystallized microstructure. By essentially recrystallized it is understood that more than 85%, preferably more than 90% and more preferably more than 95% of the microstructure is recrystallized.

[0034] The essentially recrystallized structure is obtained by combining the composition, including the control of Mn, Cr and Ti content, and the manufacturing process.

[0035] The manufacturing process for the products according to the invention includes casting an alloy of composition according to the invention in the form of a rolling plate, heating the plate, hot rolling, cold rolling and annealing.

[0036] After casting an alloy of composition according to the invention in the form of a rolling slab, the slab is scalped and then reheated, preferably to a temperature between 480 °C and 500 °C. The slab is then hot-rolled to obtain a sheet with a thickness between 3 and 10 mm, cooled, and then cold-rolled to the final thickness of the thin sheet. The thin sheet thus obtained can then optionally be degreased and / or pickled and / or brightened, and then annealed, typically in a batch furnace, at a temperature of 330 to 420 °C and preferably 350 to 400 °C. The annealing temperature according to the invention makes it possible, in particular, to obtain the recrystallized microstructure according to the invention, while achieving satisfactory homogeneity in the coil and avoiding oxidation and loss of brightness.

[0037] The brightening can be achieved in particular by rolling with low roughness cylinders and / or by any other suitable surface treatment process such as chemical or electrochemical processes.

[0038] Preferably, the thin sheet according to the invention has a thickness between 0.35 and 1.5 mm and more preferably between 0.4 and 1 mm.

[0039] The mechanical properties of the sheets according to the invention are advantageous.

[0040] The thin sheets according to the invention advantageously exhibit, in the transverse-longitudinal direction TL, a tensile strength Rm of at least 100 MPa and preferably at least 110 MPa, and an elongation A50 of at least 28% and preferably at least 30%. The thin sheets according to the invention also exhibit, in the transverse-longitudinal direction TL, a yield strength RP0.2 of at least 45 MPa and preferably at least 50 MPa, and an elongation A50 of at least 28% and preferably at least 30%.

[0041] The thin sheets according to the invention are used in particular to produce complex shaped parts formed in three dimensions, notably by stamping. The thin sheets according to the invention are suitable for undergoing any decorative surface treatment before or after forming, such as anodizing, varnishing, or lacquering.

[0042] The thin sheets according to the invention, thus shaped, are advantageously used as interior or exterior decorative parts for a motor vehicle, a household appliance, or medical equipment. Preferably, the thin sheets according to the invention are used to produce decorative parts for motor vehicles, such as interior trim elements selected from the center console, such as the dashboard, gearshift housing, door handles, interior decorative strips, body beltlines, and / or exterior trim elements selected from window surrounds, side body or door moldings, tailgate trim strips, grille trims, and bumper trim strips. EXAMPLE

[0043] In this example, rolling plates of thickness 428 mm were cast, made of aluminum alloy whose composition in % by weight is given in Table 1. Alloys B and C have a composition according to the invention. [Table 1] Alloy If Fe Cu Mn Mg Cr Zn Ti Fe / Si A 0,21 0,24 0,01 0,06 0,88 <0,01 <0,01 0,02 1,1 B 0,07 0,17 0,01 0,02 0,70 <0,01 <0,01 0,01 2,4 C 0,07 0,14 <0,01 0,01 0,82 <0,01 <0,01 0,02 2,0 D 0,10 0,13 0,04 0,01 0,67 <0,01 <0,01 0,02 1,3 E 0,11 0,13 0,04 <0,01 0,84 <0,01 <0,01 0,03 1,2 F 0,10 0,18 0,04 0,03 0,75 <0,01 0,01 0,03 1,8

[0044] The plates were scalped, reheated to approximately 490 °C, then hot-rolled to a thickness of 6.5 mm and subsequently cold-rolled to a thickness of 0.76 mm. The resulting thin sheets were annealed at 380 °C. The microstructure of the thin sheets after annealing was completely recrystallized. The mechanical properties were determined in the LT direction. The mechanical properties and surface appearance after forming and surface treatment of the resulting products are presented in Table 2. [Table 2] Alloy R p0.2 [MPa] TL Rm [MPa] TL A50 [%] Surface appearance A 54 120 27,4 OK B 51 111 32,0 OK C 53 118 31,1 OK D 63 110 27,1 Yellowish E 69 121 23,4 Yellowish F 59 117 25,0 Yellowish

[0045] There Figure 1 represents the elongation A 50 as a function of the tensile strength R m. The thin sheets B and C according to the invention present a particularly advantageous compromise of properties.

Claims

1. A thin sheet metal made of aluminium alloy, in % by weight, Mg: 0.65 - 0.85, Fe: 0.14 - 0.20, Si: 0.05 - 0.09, Mn: ≤ 0.03, Cu: ≤ 0.05, Cr: ≤ 0.02, Zn: ≤ 0.10, Ti: ≤ 0.03, other elements or impurities < 0.05 each and < 0.15 total, aluminium remains, of which more than 85% of the microstructure is recrystallized.

2. The thin sheet metal according to claim 1, wherein the sum of the contents of Cr + Mn + Ti is at most 0.06% by weight and preferably at most 0.04% by weight.

3. The thin sheet metal according to claim 1 or claim 2, wherein, in % by weight, Fe: 0.14 -0.18 and / or Si: 0,06-0,08.

4. The thin sheet metal according to any one of claims 1 to 3, wherein the Fe / Si ratio is at least equal to 1.9, preferably at least equal to 1.95, preferably at least equal to 2.0, and preferably at least equal to 2.2.

5. The thin sheet metal according to any one of claims 1 to 4, wherein the sum of the Fe + Si + Mn contents is at least 0.22% by weight or even at least 0.24% by weight.

6. The thin sheet metal according to any one of claims 1 to 5, wherein the sum of the Fe + Si contents is at least 0.20% by weight, preferably at least 0.21% by weight or even at least 0.23% by weight.

7. The thin sheet metal according to any one of claims 1 to 6, wherein, in % by weight, Mg: 0.69-0.83.

8. The thin sheet metal according to any one of claims 1 to 7, wherein, in % by weight, Mn: ≤ 0.02 and / or Cr: ≤ 0.01 and / or Ti: ≤ 0.02 and / or Cu: ≤ 0.03.

9. The thin sheet metal according to any one of claims 1 to 8, having in the long transverse direction TL a breaking strength Rm of at least 100 MPa and preferably at least 110 Mpa and an elongation A50 of at least 28% and preferably at least 30%.

10. The thin sheet metal according to any one of claims 1 to 9, having in the long transverse direction TL a yield strength RP0.2 of at least 45 MPa and preferably at least 50 Mpa and an elongation A50 of at least 28% and preferably at least 30%.

11. A method for manufacturing a thin sheet metal according to any one of claims 1 to 10, wherein, successively, (a) casting in the form of a rolling plate, an aluminium alloy of composition, in % by weight, Mg: 0.65 - 0.85, Fe: 0.14 - 0.20, Si: 0.05 - 0.09, Mn: ≤ 0.03, Cu: ≤ 0.05, Cr: ≤ 0.02, Zn: ≤ 0.10, Ti: ≤ 0.03, other elements or impurities < 0.05 each and < 0.15 total, aluminium remains (b) scalping the plate thus obtained, (c) reheating the plate thus scalped preferably to a temperature between 480°C and 500°C, (d) hot-rolling the plate thus reheated to obtain a sheet metal having a thickness comprised between 3 and 10 mm (e) cooling the sheet metal thus obtained (f) cold-rolling the sheet metal thus cooled to obtain a thin sheet metal of final thickness (g) optionally degreasing and / or stripping and / or polishing the thin sheet metal thus obtained, (h) annealing the thin sheet metal at a temperature of 330°C to 420°C.

12. The method according to claim 11, wherein step (g) is not optional.

13. The method according to claim 11 or claim 12, wherein during step (h) the thin sheet metal is annealed at a temperature of 350°C to 400°C.

14. A use of a thin sheet according to any one of claims 1 to 10 to produce a part of complex shape shaped in the three dimensions of space, in particular by stamping.

15. The use according to claim 14, as an interior or exterior decorative part of a motor vehicle or a household appliance or medical device.