Specific aluminium alloy and associated method for producing a part comprising such an aluminium alloy

Abstract

The invention relates to an aluminium alloy consisting of the following, in wt%: Si: between 6.50 and 8.50; Zn: between 0.20 and 0.80; Mn: between 0.20 and 0.50; Mg: between 0.10 and 0.50; Fe: 0.15<Fe≤0.35; Cu: between 0.05 and 0.35; Ti: less than or equal to 0.20; Zr: less than or equal to 0.30; Mo: less than or equal to 0.20; Ni: less than or equal to 0.10; Pb: less than or equal to 0.10; Cr: less than or equal to 0.03; V: less than or equal to 0.03; Sr: between 0.010 and 0.025; the balance being aluminum and unavoidable impurities.

Description

[0001] DESCRIPTION

[0002] Title of the invention: A special aluminum alloy and a method for manufacturing a part comprising such an associated aluminum alloy

[0003] TECHNICAL FIELD

[0004] The present invention relates, in general, to an aluminum alloy, in particular a secondary aluminum alloy.

[0005] Furthermore, the invention relates to a method of producing a part from such an aluminum alloy, in particular a secondary melting alloy.

[0006] STATE OF THE ART

[0007] In a motor vehicle, some parts are made from aluminum alloy known as "primary smelting", that is to say, directly derived from an ore, Bauxite.

[0008] Traditionally, the parts are manufactured by casting process from this alloy.

[0009] In particular, certain structural parts of a motor vehicle's body are made from a primary aluminum alloy, conforming to standard EN 1706-2021, consisting of, as a percentage by weight:

[0010] If: between 6.5 and 8.5;

[0011] Mn: between 0.35 and 0.75;

[0012] Mg: between 0.10 and 0.45;

[0013] Fe: less than 0.25;

[0014] Cu: less than or equal to 0.05;

[0015] Zn: less than or equal to 0.03;

[0016] Ti: less than or equal to 0.2; the remainder being aluminum and unavoidable impurities.

[0017] This primary aluminum alloy exhibits sufficient deformation capacity, i.e., a good elongation at break (A%) of 7% or greater, suitable for use in such structural components. It has a yield strength at 0.2% plastic deformation (Rp0.2) of 100 MPa or greater, a tensile strength (Rm) of 200 MPa or greater, and a hardness (HB) of 60 or greater.

[0018] These performance levels are achieved in the as-founded state thanks to the limited presence of residual metallic elements, such as iron, copper, nickel and zinc, which degrade the performance properties of the aluminum alloy.

[0019] However, the energy consumption required to produce this primary aluminum alloy results in the emission of a particularly high amount of CO2.

[0020] On the contrary, obtaining an aluminum alloy called "second melting", that is to say a recycled aluminum alloy, obtained at least 90% by weight by a new melting of aluminum alloy parts and / or scraps, generates a much lower quantity of CO2.

[0021] Scrap refers to debris, waste or other aluminum alloy waste, particularly from all industrial sectors.

[0022] However, the residual element content of secondary aluminum alloys is higher than in primary aluminum alloys. This results in a negative impact on the material's mechanical properties.

[0023] BRIEF DESCRIPTION OF THE INVENTION

[0024] The invention therefore aims to remedy these drawbacks and to offer an aluminum alloy that can be derived from the recovery of secondary aluminum alloy while guaranteeing mechanical performance equivalent to a primary aluminum alloy.

[0025] Therefore, an aluminum alloy is proposed, consisting of, as a percentage by weight:

[0026] If: between 6.50 and 8.50;

[0027] Zn: between 0.20 and 0.80;

[0028] Mn: between 0.20 and 0.50;

[0029] Mg: between 0.10 and 0.50;

[0030] Fe: 0.15 < Fe < 0.35; Cu: between 0.05 and 0.35;

[0031] Ti: less than or equal to 0.20;

[0032] Zr: less than or equal to 0.30;

[0033] Mo: less than or equal to 0.20;

[0034] Ni: less than or equal to 0.10;

[0035] Pb: less than or equal to 0.10;

[0036] Cr: less than or equal to 0.03;

[0037] V: less than or equal to 0.03;

[0038] Sr: between 0.010 and 0.025, preferably between 0.015 and 0.025; the remainder being aluminium and unavoidable impurities, each unavoidable impurity being present in a content of less than 0.05% by weight relative to the total weight of the aluminium alloy, and the total content of unavoidable impurities representing less than 0.15% by weight.

[0039] The aluminum alloy according to the invention allows for a greater number of residual elements compared to a primary alloy. Such iron, copper, and zinc contents in the aluminum alloy make it possible to consider the use of secondary aluminum alloys while guaranteeing equivalent mechanical properties, and in particular sufficient deformation capacity for automotive applications, with suitable material behavior in case of impact and suitability for mechanical assemblies.

[0040] In particular, the mechanical properties of the aluminum alloy according to the invention in as-cast form are at least equivalent to the mechanical properties of a primary aluminum alloy according to standard EN 1706-2021, without the need to carry out heat treatment of the aluminum alloy according to the invention.

[0041] Depending on other characteristics of the alloy, taken alone or in combination where technically possible:

[0042] - the manganese content is between 0.25% and 0.50% by weight,

[0043] - The manganese content is between 0.30% and 0.50% by weight,

[0044] - The manganese content is between 0.35% and 0.50% by weight, - The copper content is between 0.05% and 0.30% by weight.

[0045] - the copper content is between 0.15% and 0.30% by weight,

[0046] - the magnesium content is between 0.20% and 0.50% by weight,

[0047] - the titanium content is between 0.05% and 0.20% by weight, preferably between 0.10% and 0.20% by weight,

[0048] - the alloy has a dendritic microstructure with an interdendritic spacing (DAS) of less than 22 pm.

[0049] Another object of the invention relates to a method for making a part comprising the following steps: a) supplying an aluminum alloy as previously described; b) making the part from the aluminum alloy supplied in step a) according to one of the casting processes among high pressure die casting (HPDC), low pressure die casting (LPDC) and counter pressure casting (CPC).

[0050] Such a manufacturing process allows the development of a secondary aluminum alloy with particularly advantageous mechanical properties for the formation of structural parts for automotive bodywork, via CO2 emissions up to three times lower than for the development of a primary aluminum alloy.

[0051] Depending on other optional but nonetheless advantageous characteristics of the part manufacturing process, taken alone or in combination where technically possible:

[0052] - the process further includes the following step: c) performing a cataphoresis step on the part, including baking at a temperature between 160°C and 195°C, for a time between 15 and 25 minutes,

[0053] - the aluminium alloy supplied in step a) is a secondary melt alloy obtained at least partially by remelting previous parts and / or scraps,

[0054] - the process further includes, prior to step a), a step of adjusting the quantity of the chemical elements of the secondary aluminum alloy to obtain an aluminum alloy as previously described.

[0055] Another object of the invention is a part for a motor vehicle comprising at least one aluminium alloy as previously described.

[0056] Another object of the invention is a motor vehicle comprising at least one aluminium alloy, in particular secondary smelting, as previously described and / or at least one part as previously described, and / or at least one part produced by a process as previously described.

[0057] Other characteristics, aspects, objects and advantages will emerge from the description that follows and the following examples, given for purely illustrative purposes.

[0058] DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0059] In what follows, the expression "at least one" used is equivalent to the expression "one or more".

[0060] Furthermore, the boundaries of a domain of values ​​are included in that domain, notably in the expression "between".

[0061] Furthermore, for the purposes of the invention, the expression "less than" is equivalent to the expression "strictly less than".

[0062] The aluminum alloy according to the invention consists of, in % by weight: Si: between 6.50 and 8.50;

[0063] Zn: between 0.20 and 0.80;

[0064] Mn: between 0.20 and 0.50;

[0065] Mg: between 0.10 and 0.50;

[0066] Fe: 0.15 < Fe < 0.35;

[0067] Cu: between 0.05 and 0.35;

[0068] Ti: less than or equal to 0.20;

[0069] Zr: less than or equal to 0.30;

[0070] Mo: less than or equal to 0.20; Ni: less than or equal to 0.10;

[0071] Pb: less than or equal to 0.10;

[0072] Cr: less than or equal to 0.03;

[0073] V: less than or equal to 0.03;

[0074] Sr: between 0.010 and 0.025, preferably between 0.015 and 0.025; the remainder being aluminum and unavoidable impurities.

[0075] For the purposes of this invention, "unavoidable impurity" means an atom, or group of atoms, other than Si, Zn, Mn, Mg, Fe, Cu, Ti, Zr, Mo, Ni, Pb, Cr, V and Sr which is present in a content of less than 0.05% by weight relative to the total weight of the aluminum alloy and whose presence does not affect the properties, in particular mechanical properties, of the aluminum alloy.

[0076] In other words, each unavoidable impurity is present in a content of less than 0.05% by weight relative to the total weight of the aluminum alloy, and the total of the unavoidable impurities represents less than 0.15% by weight.

[0077] The aluminum alloy is therefore made up of aluminum in the majority quantity, as well as addition elements, residual elements and possible unavoidable impurities.

[0078] The aluminum alloy according to the invention is a secondary aluminum alloy.

[0079] The term "secondary aluminum alloy" refers to a recycled aluminum alloy, of which at least 90% by weight comes from the remelting of aluminum alloy parts and / or scrap. The remaining material (10% by weight or less) may have been added to adjust the content of the various constituent elements of the aluminum alloy and thus obtain the desired final composition.

[0080] The term "scraps" refers to waste from metallurgical industries, or materials recycled after their manufacturing process, otherwise known as pre-industrial scraps or PIR (acronym for Post-industrial Recycling), or parts discarded after consumption, otherwise known as post-industrial scraps or PCR (acronym for Post-consumer Recycling).

[0081] Remelting aluminum alloy parts and / or scraps generates a much lower amount of CO2 than the initial melting of the aluminum alloy.

[0082] For the purposes of the invention, silicon, zinc, manganese, magnesium, iron, copper, titanium, and strontium are added alloying elements whose content is adjusted to improve the performance of the aluminum alloy, and zirconium, molybdenum, nickel, lead, chromium, and vanadium are residual elements resulting from the recycling of the primary aluminum alloy.

[0083] Such a secondary aluminum alloy can be used for manufacturing a part for an automotive vehicle, such as a structural part of a painted assembled body, a door or a chassis part.

[0084] The aluminum alloy according to the invention is not limited to application in the automotive field and can be used in any type of industrial field requiring such a material.

[0085] The copper content of the alloy is chosen to be greater than 0.05% by weight, which allows for sufficient mechanical properties, notably through the precipitation of AhCu-type compounds, and the S (AhCuMg) and Q (AhCu-Q) phases. Preferably, the copper content is even greater than 0.15% by weight.

[0086] On the other hand, the copper content must not exceed 0.50% by weight to obtain sufficient resistance of the alloy to corrosion, particularly in the case where the alloy, in the final part, would not be protected by a protective coating, typically a paint.

[0087] Preferably, the copper content does not exceed 0.35% by weight, or even 0.30% by weight, which advantageously avoids the material's high reactivity when a cataphoresis step is performed on the aluminum alloy, thus limiting a decrease in the material's deformation capacity. As an example only, in one embodiment, the copper content may be between 0.05 and 0.30.

[0088] In another embodiment, the copper content can be: 0.05 < Cu < 0.30.

[0089] In another embodiment, the copper content can be: 0.05 < Cu < 0.30.

[0090] In another embodiment, the copper content can be: 0.05 < Cu < 0.30.

[0091] As another example, in another embodiment, the copper content can be between 0.15 and 0.30.

[0092] In another embodiment, the copper content can be: 0.15 < Cu < 0.30.

[0093] In another embodiment, the copper content can be: 0.15 < Cu < 0.30.

[0094] In another embodiment, the copper content can be: 0.15 < Cu < 0.30.

[0095] A zinc content of between 0.20 and 0.80% by weight also slightly increases the mechanical characteristics of the material.

[0096] Limiting the zinc content to a maximum value of 0.80% by weight helps to avoid the risk of hot cracking, and to ensure that the resistance to atmospheric corrosion is not degraded.

[0097] The presence of zinc in such a range of values ​​allows in particular the use of 7000 series aluminum alloy scraps (Al-Zn) which makes it possible to increase the mechanical characteristics of the aluminum alloy part according to the invention to be manufactured.

[0098] A silicon content between 6.50 and 8.50% by weight maximizes the deformation capacity of the aluminum alloy. This level of content prevents an excessive proportion of the eutectic phase.

[0099] Furthermore, the flowability obtained through such a silicon content is advantageous for casting the aluminum alloy in the liquid state into a mold, particularly for pressure die casting, commonly known as the HPDC process for the abbreviation of the English terms "High Pressure Die Casting".

[0100] The strontium content should be between 0.010 and 0.025 wt%. A strontium content below 0.025 wt% advantageously prevents the formation of gas porosity during the injection of the molten alloy into a mold. Conversely, a strontium content above 0.010 wt% modifies the morphology of the eutectic phase, making it sufficiently fine so as not to impair the elongation capacity of the aluminum alloy. The modification of the eutectic phase by strontium is particularly effective when the strontium wt% is between 0.015 wt% and 0.025 wt%.

[0101] Strontium is therefore an addition element intended to modify the structure of the eutectic phase by obtaining a granular morphology, improving the deformation capacity of the aluminum alloy in the solid state.

[0102] The aluminum alloy contains a magnesium content ranging from 0.10 to 0.50 wt%. This range is particularly advantageous for further improving the material's mechanical properties, notably through the precipitation of hardening compounds such as MgSi and S-phases. The improvement of the material's mechanical properties by magnesium is more effective if the magnesium content exceeds 0.20 wt%. Thus, in a preferred embodiment, the magnesium content of the aluminum alloy can range from 0.20 wt% to 0.50 wt%.

[0103] An iron content of 0.15 < Fe < 0.35 helps to limit the sticking of the recycled, second-melt aluminum alloy in the metal mold, in particular.

[0104] In one embodiment, the iron content may be: 0.15 < Fe < 0.35.

[0105] The iron, chromium, and manganese contents are thus adjusted to minimize the formation of harmful intermetallic compounds and their growth in size and percentage. To this end, in one embodiment, the chromium content of the aluminum alloy, as a percentage by weight, can be: 0 < Cr < 0.03.

[0106] In one embodiment, the chromium content of the aluminum alloy, in % by weight, can be: 0 < Cr < 0.03.

[0107] Preferably, the titanium content is between 0.05 and 0.20 wt%, and even more preferably between 0.10 and 0.20 wt%. This allows for refining the material's microstructure by enabling the formation of nuclei before the aluminum alpha phase solidifies. The greater the number of nuclei, the smaller the grain size. Thus, a minimum titanium content of 0.10 wt% is preferable.

[0108] Titanium is an alloying element used to refine the structure of aluminum alloys in the solid state. This refinement can be determined by measuring the dendritic arm spacing, known by the acronym DAS (Dendrite Arm Spacing).

[0109] In one embodiment, the manganese content may advantageously be between 0.25% and 0.50% by weight, preferably between 0.30% and 0.50% by weight, most preferably between 0.35% and 0.50% by weight, and even more preferably between 0.40% and 0.50% by weight. This provides an advantageous compromise between a minimum manganese content to prevent sticking during the molding process and a maximum manganese content to prevent the formation of harmful intermetallics in the finished aluminum alloy part. A manganese content strictly below 0.20% by weight does not allow for proper demolding of the part. To effectively prevent sticking during the molding process, it is preferable to choose a manganese content greater than 0.35% by weight.

[0110] In one embodiment, the manganese content may be: 0.40 < Mn < 0.50% by weight.

[0111] Preferably, the proposed aluminum alloy exhibits a dendritic microstructure with an interdendritic arm spacing (DAS), less than 22 pm. Such a fine microstructure advantageously provides mechanical properties equivalent to, or even superior to, those of a primary aluminum alloy commonly used in the automotive industry, notably good deformation capacity and high mechanical strength (a conventional yield strength Rc). P O,2 greater than 120 MPa and A% greater than 6%). The SAR can be measured using an optical microscope by averaging the width of 10 dendrites on a micrograph.

[0112] Thanks to the proposed aluminum alloy's chemical composition, such fine microstructure and associated mechanical properties can typically be achieved directly after high-pressure die casting (HPDC) or vacuum die casting (i.e., directly after casting), without the need for further heat treatment to improve the conventional yield strength and, to a lesser extent, the tensile strength (Rm), and without cataphoresis curing, as described below, significantly altering these mechanical properties. In particular, the proposed aluminum alloy's chemical composition ensures that cataphoresis curing does not significantly affect the deformation capacity of the material cast by HPDC or vacuum HPDC. Heat treatment is defined as the application of a minimum temperature of 160 °C for a minimum duration of 60 minutes.

[0113] In addition, the copper content is limited in order to maintain very good corrosion behavior, in the event that the aluminum alloy is not protected by an anti-corrosion paint.

[0114] Another object of the invention relates to a method for manufacturing a part comprising the following steps: a) supplying an aluminum alloy as previously described; b) manufacturing the part from the aluminum alloy supplied in step a) using one of the following casting processes: high-pressure die casting (HPDC), low-pressure die casting (LPDC), and counter-pressure casting (CPC). High-pressure die casting (HPDC) can be performed under vacuum.

[0115] Preferably, however, the part is produced from the aluminum alloy supplied in step a) by HPDC or vacuum HPDC, which is a highly advantageous process because it is faster than other molding methods. In particular, it allows for increased production rates. As previously mentioned, the proposed aluminum alloy has been optimized to achieve the desired mechanical properties for automotive applications directly from the foundry. Therefore, the subsequent heat treatment step can be advantageously avoided, simplifying the process.

[0116] Preferably, the aluminum alloy supplied in step a) is a secondary smelting alloy obtained at least partially by remelting aluminum alloy parts and / or scraps, which allows for the recycling of these alloys and the production of the metallic alloy in a less energy-intensive way and therefore with limited CO2 emissions.

[0117] Preferably, the manufacturing process includes, prior to step a), a step for adjusting the quantity of chemical elements in the secondary aluminum alloy, obtained from the recycling of primary aluminum alloy, to obtain the aluminum alloy supplied in step a). For example, the manufacturing process includes, prior to the step for adjusting the quantity of chemical elements in the secondary aluminum alloy, a step for melting parts and / or scrap to be recycled, for example carried out in a melting furnace, and then the step for adjusting the quantity of chemical elements in the secondary aluminum alloy can be carried out in a holding furnace using the molten parts and / or scrap to be recycled.

[0118] Advantageously, in step a), the manufacturing process may include a substep of casting the supplied aluminum alloy in order to give it a shape characteristic of its subsequent use.

[0119] Preferably, the manufacturing process further includes the following step: c) carrying out a cataphoresis step on the part, including a firing carried out at a temperature between 160°C and 195°C, for a time between 15 and 25 minutes.

[0120] Step c) is carried out on the part obtained at the end of step b).

[0121] Certain mechanical properties, such as the yield strength at 0.2% plastic deformation (Rp0.2) and the elongation at break (A%), can depend on the thickness of the manufactured part. The local cooling rate depends not only on the thickness of the part but also on the cooling capacity of the metal mold in which the part is cast. A difference in thickness between several portions of the part manufactured from the aluminum alloy according to the invention can lead to a slight disparity in the mechanical properties of the part.

[0122] The advantage of step c) of cataphoresis is to homogenize the mechanical characteristics of the part.

[0123] In particular, on a part comprising a first portion having a thickness El and a second portion of thickness having a thickness E2, El and E2 being different, El being for example double E2, step c) of cataphoresis makes it possible to bring the mechanical properties of the first portion to properties equivalent to the mechanical properties of the second portion, the mechanical properties of the second portion remaining unchanged.

[0124] In addition, cataphoresis provides the material with anti-corrosion properties.

[0125] Another object of the invention is a part for a motor vehicle comprising at least one aluminium alloy, in particular secondary smelting, as previously described.

[0126] Another object of the invention is a motor vehicle comprising at least one aluminium alloy, in particular secondary smelting, as previously described and / or at least one part as previously described, and / or at least one part produced by a process as previously described.

Claims

DEMANDS 1. Aluminum alloy composed of, in % by weight: If: between 6.50 and 8.50; Zn: between 0.20 and 0.80; Mn: between 0.20 and 0.50; Mg: between 0.10 and 0.50; Fe: 0.15 < Fe < 0.35; Cu: between 0.05 and 0.35; Ti: less than or equal to 0.20; Zr: less than or equal to 0.30; Mo: less than or equal to 0.20; Ni: less than or equal to 0.10; Pb: less than or equal to 0.10; Cr: less than or equal to 0.03; V: less than or equal to 0.03; Sr: between 0.010 and 0.025, preferably between 0.015 and 0.025; the remainder being aluminium and unavoidable impurities, each unavoidable impurity being present in a content of less than 0.05% by weight relative to the total weight of the aluminium alloy, and the total content of unavoidable impurities representing less than 0.15% by weight.

2. Alloy according to claim 1, in which the manganese content is between 0.25% and 0.50% by weight.

3. Alloy according to claim 2, wherein the manganese content is between 0.30% and 0.50% by weight.

4. Alloy according to claim 3, wherein the manganese content is between 0.35% and 0.50% by weight.

5. Alloy according to any one of claims 1 to 4, wherein the copper content is between 0.05% and 0.30% by weight.

6. Alloy according to claim 5, wherein the copper content is between 0.15% and 0.30% by weight.

7. Alloy according to any one of the preceding claims, wherein the magnesium content is between 0.20% and 0.50% by weight.

8. Alloy according to any one of the preceding claims, wherein the titanium content is between 0.05% and 0.20% by weight, preferably between 0.10% and 0.20% by weight.

9. Alloy according to any one of the preceding claims, having a dendritic microstructure with an interdendritic spacing (DAS) of less than 22 pm.

10. Method for producing a part comprising the following steps: a) supplying an aluminum alloy according to any one of claims 1 to 8, b) producing the part from the aluminum alloy supplied in step a) according to one of the casting processes among high pressure die casting (HPDC), low pressure die casting (LPDC) and counter pressure casting (CPC). 1 1. Method of implementation according to claim 10, further comprising the following step: c) carrying out a cataphoresis step on the part, including a baking carried out at a temperature between 160°C and 195°C, for a time between 15 and 25 minutes.

12. A method of implementation according to any one of claims 10 or 11, wherein the aluminum alloy supplied in step a) is a secondary melt alloy obtained at least partially by remelting of earlier parts and / or scraps.

13. Method of implementation according to claim 12, comprising, prior to step a), a step of adjusting the quantity of the chemical elements of the secondary aluminum alloy to obtain an aluminum alloy as defined in any one of claims 1 to 8.

14. Motor vehicle part comprising at least one aluminium alloy as defined in any one of claims 1 to 9.

15. Motor vehicle comprising at least one aluminium alloy as defined in any one of claims 1 to 9 and / or at least one part as defined in claim 14 and / or at least one part produced by a process according to any one of claims 10 to 13.