Recycled 6xxx alloy sheet and manufacturing process
Patent Information
- Application Number
- EP2023720166
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-04-02
- Filing Date
- 2023-03-31
- Publication Date
- 2025-02-12
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Title: Recycled 6xxx alloy sheet and manufacturing process
[0003] Field of invention
[0004] The invention relates to the field of aluminum alloy sheets intended for the stamping manufacture of body parts for the body-in-white of motor vehicles.
[0005] State of the art
[0006] Aluminum alloys are increasingly used in automotive construction to reduce vehicle weight and thus reduce fuel consumption and greenhouse gas emissions.
[0007] It is also necessary to reduce greenhouse gas emissions during the production of these alloys. This reduction can be achieved by recycling aluminium alloy scrap and waste, which makes it possible to reduce or even avoid the use of primary aluminium produced by electrolysis and / or the addition of additives.
[0008] The best electrolysis plants, which use hydroelectricity, have a Carbon Footprint of 4 tonnes of CO2 equivalent (CO2 eq) per tonne of smelting plate considering the use of carbon anode. The typical Carbon Footprint for one tonne of aluminium electrolysis smelting plate produced in Europe is 7 tonnes of CO2 eq. The Carbon Footprint of one tonne of smelting plate obtained with only scrap and waste is 0.51 of CO2 eq per smelting plate. The CO2 equivalent emission is the emitted quantity of carbon dioxide (CO2) that would cause the same integrated radiative forcing, over a time horizon of 100 years, as an emitted quantity of a single greenhouse gas (GHG). The CO2 equivalent emission is obtained by multiplying the emission of a GHG by its global warming potential (GWP) for the time horizon of 100 years.In the case of a mixture of GHGs, the CO2 equivalent emission is obtained by adding the CO2 equivalent emissions of each of the gases. When a plate is produced using partly recycled alloys, the CO2 equivalent of this plate is evaluated by linear interpolation between an electrolysis plate mentioned above (0% recycling) and a plate obtained with only scrap and waste (100% recycling). The recycling or recycling rate is the ratio between the weight of the scrap and scrap aluminum alloy used to produce the plate and the weight of the plate, the rest of the alloy being primary aluminum and / or addition elements. Easy recycling consists of closed-loop recycling, i.e., scrap and scrap aluminum alloy are recycled to obtain the same alloy for which they were produced. However, there are products that cannot be recycled in this way.This is particularly the case for clad sheets as defined by EN 12258-1 (2012) in §2.6.26, especially when they contain very different alloys. The clad sheets used to make brazed heat exchangers are in this case because they generally consist of a central part in 3xxx series alloy, sometimes with a little Cu and / or Mg, with one or more claddings in 4xxx series alloy and / or 7xxx series and / or lxxx series and / or 3xxx series. Currently, these clad sheets are mostly recycled in castings for which 4xxx series alloys are usually used. However, the switch from internal combustion engine propulsion to electric propulsion will destabilize this recycling sector.Aluminium alloy sheets in vehicles, especially for bodywork and structural parts, are in the prior art made of 5xxx and 6xxx alloys which are not suitable for significant recycling of 4xxx series alloys given their composition. The evolution of alloys due to research and development also makes it difficult to recycle old scraps, which are scraps from products after their use according to EN 12258-1. This is the case of old scraps from the demolition of buildings with typical composition Si: 0.5%, Fe: 0.2%, Cu: 0.1%, Mn: 0.1%, Mg: 0.1%.
[0009] Application US20210108293 discloses an aluminum alloy sheet having a chemical composition containing Si: 2.3-3.8 mass%, Mn: 0.35-1.05 mass%, Mg: 0.35-0.65 mass%, Fe: 0.01-0.45 mass%, and at least one element selected from the group consisting of Cu: 0.0010-1.0 mass%, Cr: 0.0010-0.10 mass%, Zn: 0.0010-0.50 mass%, and Ti: 0.0050-0.20 mass%. The ratio of the Si content to the Mn content is 2.5 or more and 9.0 or less. Aluminum alloy sheet has an elongation of 23% or more and a work hardening exponent of 0.28 or more at a nominal strain of 3%. Such aluminum alloy sheet is well suited for press forming (stamping) applications, such as automotive body panel forming.
[0010] WO2018 / 175876 discloses techniques for casting metal products with high strength and formability from recycled scrap metal, without adding a substantial amount or even any primary aluminum. Additional alloying elements, such as magnesium, can be added to scrap metal, which can be cast and processed to produce a metal coil of a desired final thickness and having desirable metallurgical and mechanical properties, such as high strength and formability. Inexpensive, recycled scrap metal can thus be efficiently reused for new applications, such as automotive or as a raw material for beverage cans.
[0011] Application JP2005298922 addresses the problem of inexpensively providing an aluminum alloy sheet for forming, which has adequate bending formability, low bending anisotropy and superior bake hardening ability after coating, which has low room temperature aging and adequate line mark resistance.Its solution is an aluminum alloy sheet made of an Al-Mg-Si base alloy or an Al-Mg-Si-Cu base alloy; satisfying each condition of (C(sub l / 10)+C(sub l / 4)) / 2 > C(sub 1 / 2) and 30 < (C(sub l / 10)+C(sub 1 / 4)) < 500, when C(sub 1 / 10), C(sub 1 / 4) and C(sub 1 / 2) are defined as the orientation density of the cube at positions of 1 / 10, 1 / 4 and 1 / 2 depth from the sheet surface in the sheet thickness direction, respectively; has an orientation density {001} <210> in a range of 2 to 50, in a region of 1 / 10 to 1 / 4 depth in the direction of the sheet thickness; and has 0 degree and 90 degree hollowing rates of 5% or more. The manufacturing method includes strictly prescribed casting and hot rolling conditions. The conditions of metallographic structures in a cast plate and a sheet after being hot rolled, which are intermediate products, are prescribed.
[0012] Application WO2022 / 026825 discloses novel 6xxx aluminum alloys. In one approach, a novel 6xxx aluminum alloy may comprise 0.25-0.60 wt.% Fe, 0.8-1.2 wt.% Si, 0.35-1.1 wt.% Mg, 0.05-0.8 wt.% Mn, up to 0.30 wt.% Cu, up to 0.35 wt.% Zn, up to 0.15 wt.% Ti, up to 0.15 wt.% each of Cr, Zr, and V, with the remainder being aluminum, accessory elements, and impurities. The novel 6xxx aluminum alloys may be made from recycled aluminum alloys.
[0013] There is therefore a need to recycle scrap and waste from plated sheets to produce bodywork sheets for the automotive industry.
[0014] Problem posed
[0015] The problem to be solved is to develop a 6xxx series alloy sheet which aims for an excellent compromise between:
[0016] • Recycling of scrap and waste, preferably clad sheets. Clad sheets are generally made of very different alloys, for example a 3xxx series alloy for the central part, 4xxx series plating and / or 7xxx series plating. The average composition of a clad sheet is difficult to recycle into another sheet because it does not correspond to a known alloy. In addition, the recycling activity, particularly when it comes to old scraps from products after their use, is inseparable from the pollution phenomenon which results from the mixing with other materials, for example steel, and which can degrade the properties of the materials obtained after recycling.
[0017] • The formability of the sheet metal which is assessed in the T4 state after maturation, maturation corresponding to the duration of transport and storage between the quenching of the sheet metal and its stamping in the form of a part. The formability is characterized with the LDH (limiting dome height) test for the ability to deform and with the elastic limit for the force required to obtain said deformation.
[0018] • The properties necessary for the use of the part on a motor vehicle which are assessed on the finished part, therefore after stamping the sheet metal, painting and baking the paints. Baking the paints is also known to those skilled in the art as “bake hardening” because it allows at the same time the hardening, by tempering, of the stamped sheet metal to obtain the properties necessary for the use of the part on a motor vehicle. The suitability for use on a motor vehicle is characterized here by the elastic limit of the sheet metal after a deformation of 2% and a heat treatment of 170°C for 20 minutes, representative of the baking heat treatment of the paints. Industrially, baking the paints can last from 10 to 30 minutes at a temperature between 170 and 195°C.
[0019] • Corrosion which is assessed on the sheet after maturation. Corrosion is assessed by a filiform corrosion test of the sheet after a heat treatment of 170°C for 20 minutes.
[0020] Subject of the invention
[0021] An object of the invention is an aluminum alloy sheet of composition, in % by weight:
[0022] If: about 1.25% - about 1.55%,
[0023] Fe: <= approximately 0.60%,
[0024] Cu: <= approximately 0.37%,
[0025] Mn: about 0.22% - about 0.65%,
[0026] Mg: about 0.25% - about 0.55%,
[0027] Ti: <= approximately 0.15%,
[0028] Cr <= approximately 0.30%,
[0029] Cr + Mn +Fe: <= approximately 0.90%,
[0030] Zn <= about 0.15%, other elements: each < =0.05%, together < = 0.15%, remainder: Al.
[0031] Another subject of the invention is a method for manufacturing a rolled sheet of aluminum alloy according to the invention comprising the successive steps of: a. Production of an alloy, preferably comprising offcuts and waste, preferably clad sheets, b. Casting the alloy into a plate, preferably by semi-continuous vertical casting, c. Homogenization of the plate at a homogenization temperature, preferably between 540°C and 580°C, preferably above 550°C, d. Hot rolling of the plate, e. Cold rolling of the hot-rolled plate, f. Solution treatment then quenching, g. Pre-tempering at a pre-tempering temperature of 60 to 100°C for a period of 2 to 16 hours, preferably obtained by coiling then cooling to room temperature, h. Maturation of 72 hours to 6 months.
[0032] Description of figures
[0033] [Fig. 1]: This figure shows the LDH as a function of recyclability.
[0034] [Fig. 2]: This figure shows the LDH as a function of the alloy pollution in Fe, Mn and Cr.
[0035] [Fig. 3]: This figure shows the trade-off between LDH and yield strength at T4.
[0036] [Fig. 4]: This figure shows the trade-off between LDH and yield strength after paint baking simulation.
[0037] [Fig. 5]: This figure shows the yield strength in state T4 as a function of the recyclability for the sheets according to the invention.
[0038] [Fig. 6]: This figure shows the elastic limit after simulation of the baking of the paints as a function of the recycling suitability for the sheets according to the invention.
[0039] [Fig. 7]: This figure shows the filiform corrosion results as a function of Cu content.
[0040] [Fig. 8]: This figure shows describes the LDH measuring tool.
[0041] [Fig. 9]: The sheet according to the invention makes it possible to recycle plated sheets.
[0042] [Fig. 10]: The photograph shows examples of samples subjected to stringing, of class 1, 2 and 3 (1 average - 3 excellent). Description of the invention
[0043] All aluminum alloys referred to hereinafter are designated, unless otherwise stated, according to the rules and designations defined by the Aluminum Association in the Registration Record Series published by it from time to time. Unless otherwise stated, compositions are expressed in % by weight. The expression 1.4 Cu means that the copper content expressed in % by weight is 1.4%.
[0044] The metallurgical states in question are designated according to the European standard EN-515.
[0045] The static mechanical characteristics in tension, in other words the breaking strength Rm, the conventional elastic limit at 0.2% elongation Rp0.2, the elongation at necking Ag% and the elongation at break A%, are determined by a tensile test according to standard NF EN ISO 6892-1, the sampling and the direction of the test being defined by standard EN 485-1.
[0046] The work hardening coefficient n is evaluated according to the EN ISO 10275 standard.
[0047] The modulus of elasticity is measured according to ASTM 1876.
[0048] The Lankford anisotropy coefficient is measured according to EN ISO 10113.
[0049] The bending angles, called alpha norm, are determined by 3-point bending test according to standard NF EN ISO 7438 and procedures VDA 238-100 and VDA 239-200 version 2017.
[0050] Unless otherwise stated, the definitions of standard EN 12258 apply.
[0051] The LDH parameter is widely used to evaluate the formability of sheet metal. It has been the subject of numerous publications, including R. Thompson, “The LDH test to evaluate sheet metal formability - Final Report of the LDH Committee of the North American Deep Drawing Research Group”, SAE conference, Detroit, 1993, SAE Paper No. 930815. This is a stamping test of a blank held at the periphery by a retaining ring. The blank-holding pressure is adjusted to prevent slippage in the retaining ring. The blank, measuring 120 mm x 160 mm, is loaded in a mode close to plane deformation. The punch used is hemispherical. Figure 8 specifies the dimensions of the tools used to perform this test. Lubrication between the punch and the sheet is provided by graphite grease. The punch descent speed is 50 mm / min. The so-called LDH value is the value of the punch displacement at break, i.e. the limit depth of the drawing.It actually corresponds to the average of three tests, giving a 95% confidence interval on the measurement of 0.2 mm.
[0052] The standard for measuring intergranular corrosion is ASTM-G110. The standard for filiform corrosion is EN 3665.
[0053] Stringing is measured as follows. A strip measuring approximately 270 mm (crosswise) by 50 mm (rolling direction) is cut from the thin sheet. A tensile pre-strain of 15%, perpendicular to the rolling direction, i.e., along the length of the strip, is then applied. The strip is then subjected to the action of P800 type abrasive paper to reveal the stringing. The latter is then visually assessed and translated by classification on a scale of 1 (significant stringing) to 3 (complete absence of stringing). Examples of stringing corresponding to values 1 to 3 are illustrated in Figure 10.
[0054] Room temperature is any temperature compatible with human work from 5 to 35°C. Room temperature can be a temperature of 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C.
[0055] The term "approximately," when used in connection with a measurable numerical variable, refers to the stated value of the variable and all values of the variable that are within the experimental error of the stated value or within ±10 percent of the stated value, whichever is greater.
[0056] Detailed description
[0057] The invention is based on the observation made by the applicant that it is entirely possible, thanks to a suitable composition and manufacturing process, to produce sheets from recycled plated sheets having an acceptable suitability for stamping, good resistance to corrosion and mechanical properties suitable for the production of automobile bodywork
[0058] The typical composition of the alloy according to the invention is as follows (% by weight):
[0059] If: 1.25% - about 1.55%,
[0060] Fe: <= approximately 0.60%,
[0061] Cu: <= approximately 0.37%,
[0062] Mn: 0.22% - about 0.65%,
[0063] Mg: about 0.25% - about 0.55%,
[0064] Ti: <= approximately 0.15%,
[0065] Cr <= approximately 0.30%,
[0066] Cr + Mn +Fe: <= approximately 0.90%,
[0067] Zn <= about 0.15%, other elements: each < =0.05%, together < = 0.15%, remainder: Al.
[0068] The concentration ranges imposed on the constituent elements of this type of alloy are therefore explained by the following reasons:
[0069] Si: Silicon is, with magnesium, the first alloying element in aluminum-magnesium-silicon systems (AA6xxx family) to form the intermetallic compounds Mg2Si or MgsSig which contribute to the structural hardening of these alloys. A high Si content promotes the suitability for recycling given the use for plating of certain sheets plated with a Si-rich alloy such as AA4343, AA4045, AA4004 and other alloys whose Si content makes it possible to lower the melting point. The Si is in excess relative to the Mg in percentage by weight. Preferably, the excess of Si is at least 0.70% by weight, more preferably 0.80% by weight and preferably at most 1.20% by weight, more preferably 1.15% by weight. The purpose of this excess is to improve the ductility necessary for forming the sheet metal but in the field of the invention, the Si content has little influence on the formability measured by the LDH.The Si content is from 1.25% to about 1.55%. In one embodiment, the Si content is at most about 1.35%, preferably about 1.30%. This embodiment allows a low value of the yield strength in the T4 state, which reduces the drawing force. In one embodiment, the Si content is at least about 1.30%, preferably at least about 1.35%, preferably about 1.40%, preferably about 1.45% and / or the maximum is about 1.50%. This embodiment allows a high value of the yield strength after baking the paints.
[0070] In one embodiment, the Si content is at least 1.25%, and at most about 1.30% or at most about 1.35% or at most about 1.40% or at most about 1.45% or at most about 1.50% or at most about 1.55%. In one embodiment, the Si content is at least about 1.30%, and at most about 1.35% or at most about 1.40% or at most about 1.45% or at most about 1.50% or at most about 1.55%. In one embodiment, the Si content is at least about 1.35%, and at most about 1.40% or at most about 1.45% or at most about 1.50% or at most about 1.55%. In one embodiment, the Si content is at least about 1.40%, and at most about 1.45% or at most about 1.50% or at most about 1.55%. In one embodiment, the Si content is at least about 1.45%, and at most about 1.50% or at most about 1.55%.In one embodiment, the Si content is at least about 1.50%, and at most about 1.55%.
[0071] Fe: Iron is generally considered an undesirable impurity. The presence of intermetallic compounds containing iron is generally associated with a decrease in local formability. The maximum Fe content is about 0.60%, preferably about 0.50%, more preferably about 0.40%. Reducing the Fe content improves formability measured with LDH. However, very pure Fe alloys are expensive on the one hand and on the other hand, scrap and waste are naturally contaminated with Fe by mixing with steel. Preferably, the Fe content is therefore at least about 0.05%, preferably about 0.10%, more preferably about 0.15%, most preferably about 0.20%. The Fe content must also be controlled in combination with Mn and Cr taking into account the maximum pollutant content Cr + Mn + Fe: <= approximately 0.90% to control the LDH of the sheet according to the invention.
[0072] In one embodiment, the Fe content is at least about 0.25%, and at most about 0.30% or at most about 0.35% or at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60%. In one embodiment, the Fe content is at least about 0.30%, and at most about 0.35% or at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60%. In one embodiment, the Fe content is at least about 0.35%, and at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60%. In one embodiment, the Fe content is at least about 0.40%, and at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60%.In one embodiment, the Fe content is at least about 0.45%, and at most about 0.50% or at most about 0.55% or at most about 0.60%. In one embodiment, the Fe content is at least about 0.50%, and at most about 0.55% or at most about 0.60%. In one embodiment, the Fe content is at least about 0.55%, and at most about 0.60%.
[0073] Cu: In AA6000 alloys, copper is an element involved in precipitation hardening, which is beneficial for increasing the yield strength in the T4 state and after baking of paints. However, Cu is known to degrade corrosion resistance. The Cu content is a maximum of about 0.37%, preferably about 0.32%, preferably about 0.27%, more preferably 0.25% to ensure an acceptable level of filiform corrosion. Increasing the maximum Cu content improves the recyclability of clad sheets containing Cu, for example, as disclosed by application W002 / 40729. Increasing the Cu content also improves the formability characterized by the LDH test. This effect is advantageous because it allows to increase the pollutant content, in particular Mn, because the Cu content improves the LDH, which makes it possible to compensate for the degradation effect of the LDH which results from these pollutants.In one embodiment, the Cu content is therefore at least approximately 0.20%. In another embodiment, the Cu content is at most approximately 0.20%. This embodiment is advantageous because it makes it possible to avoid adding Cu, which is a more expensive metal than aluminum, for the recycling of clad sheets not containing Cu, such as for example clad sheets whose central part is made of AA3003, a reference alloy well known to those skilled in the art of clad sheets.
[0074] In one embodiment, the Cu content is at least about 0.05%, and at most about 0.07% or at most about 0.12% or at most about 0.17% or at most about 0.22% or at most about 0.27% or at most about 0.32% or at most about 0.37%. In one embodiment, the Cu content is at least about 0.07%, and at most about 0.12% or at most about 0.17% or at most about 0.22% or at most about 0.27% or at most about 0.32% or at most about 0.37%. In one embodiment, the Cu content is at least about 0.12%, and at most about 0.17% or at most about 0.22% or at most about 0.27% or at most about 0.32% or at most about 0.37%. In one embodiment, the Cu content is at least about 0.17%, and at most about 0.22% or at most about 0.27% or at most about 0.32% or at most about 0.37%.In one embodiment, the Cu content is at least about 0.22%, and at most about 0.27% or at most about 0.32% or at most about 0.37%. In one embodiment, the Cu content is at least about 0.27%, and at most about 0.32% or at most about 0.37%. In one embodiment, the Cu content is at least about 0.32%, and at most about 0.37%.
[0075] Mn: Manganese has a similar effect to iron through its contribution to common intermetallic precipitates. Decreasing the Mn content improves formability measured with LDH. Increasing the maximum Mn content improves the recyclability of clad sheet scrap and waste. In particular, it increases the recyclability of clad sheets containing an alloy with Mn such as AA3003 or the alloy disclosed by application WO02 / 40729. A compromise is a Mn content of at least 0.22% and at most 0.65%, preferably about 0.60%, preferably 0.55% and preferably the minimum Mn content is at least about 0.25%, preferably about 0.30%, preferably about 0.35%, preferably about 0.40%, preferably about 0.44%.The Mn content must also be controlled in combination with Fe and Cr taking into account the maximum pollutant content Cr + Mn + Fe: <= approximately 0.90% to control the LDH of the sheet according to the invention. Mn can slightly degrade the elastic limit in the T4 state, undoubtedly due, without this binding the inventors, to its polluting effect.
[0076] In one embodiment, the Mn content is at least about 0.22%, and at most about 0.25% or at most about 0.30% or at most about 0.35% or at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60% or at most about 0.65%. In one embodiment, the Mn content is at least about 0.25%, and at most about 0.30% or at most about 0.35% or at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60% or at most about 0.65%. In one embodiment, the Mn content is at least about 0.30%, and at most about 0.35% or at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60% or at most about 0.65%.In one embodiment, the Mn content is at least about 0.35%, and at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60% or at most about 0.65%. In one embodiment, the Mn content is at least about 0.40%, and at most about 0.45% or at most about 0.50% or at most about 0.55% or at most about 0.60% or at most about 0.65%. In one embodiment, the Mn content is at least about 0.45%, and at most about 0.50% or at most about 0.55% or at most about 0.60% or at most about 0.65%. In one embodiment, the Mn content is at least about 0.50%, and at most about 0.55% or at most about 0.60% or at most about 0.65%. In one embodiment, the Mn content is at least about 0.55%, and at most about 0.60% or at most about 0.65%.In one embodiment, the Mn content is at least about 0.60%, and at most about 0.65%. Mg: Generally, the level of mechanical characteristics of the alloys of the AA6xxx family increases with the magnesium content combined with silicon to form the intermetallic compounds Mg2Si or MgsSig, in particular after annealing of the paints, which is beneficial for reducing the thickness of the sheets and lightening the vehicles. Magnesium contributes to the increase in the yield strength in the T4 state, which increases the stamping force, as well as the yield strength after baking of the paints, which makes it possible to lighten the body part. In particular, Mg amplifies the baking response of the paints which is the difference between the yield strength after baking of the paints and the yield strength in the T4 state. Mg is comprised from about 0.25% to about 0.55%.In one embodiment, the Mg is at least about 0.30%, preferably about 0.35%, and / or at most about 0.50%, preferably about 0.45%. Limiting the Mg content makes it possible to maintain a low yield strength in the T4 state, which is favorable to formability by avoiding excessive stamping forces. In one embodiment, the Mg is at least about 0.45%, preferably about 0.50%. Adding Mg makes it possible to improve the response to paint baking and to obtain a higher yield strength after baking the paints. Increasing the Mg content makes it possible to improve the recyclability, in particular of plated sheets whose plating contains Mg, such as for example AA4004 or whose central part contains Mg, such as for example certain alloys disclosed by patent FR2797454.
[0077] In one embodiment, the Mg content is at least about 0.25%, and at most about 0.30% or at most about 0.35% or at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55%. In one embodiment, the Mg content is at least about 0.30%, and at most about 0.35% or at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55%. In one embodiment, the Mg content is at least about 0.35%, and at most about 0.40% or at most about 0.45% or at most about 0.50% or at most about 0.55%. In one embodiment, the Mg content is at least about 0.40%, and at most about 0.45% or at most about 0.50% or at most about 0.55%. In one embodiment, the Mg content is at least about 0.45%, and at most about 0.50% or at most about 0.55%.In one embodiment, the Mg content is at least about 0.50%, and at most about 0.55%.
[0078] Cr: It can be added to refine the grains and stabilize the structure. Reducing the Cr content improves the formability measured with LDH due to its polluting effect. A high content improves the recyclability of the alloy according to the invention. Indeed, scrap and waste can be polluted by mixing with steel with Cr. The Cr is at most about 0.30%. A compromise between formability and recyclability is Cr + M + Fe <= about 0.90%. In one embodiment to improve formability, the Cr is at most about 0.20%, preferably about 0.15%, preferably about 0.10%, preferably about 0.05%. In one embodiment, the Cr is an impurity.
[0079] Ti: A maximum content of approximately 0.15%, preferably 0.10%, is required to avoid the conditions for the formation of primary phases during vertical casting, which have a detrimental effect on all of the claimed properties. This element can promote solid solution hardening leading to the required level of mechanical characteristics and this element also has a favorable effect on ductility in service and corrosion resistance. In one embodiment, the Ti content is at least approximately 0.01%,
[0080] In one embodiment, the Ti content is at most about 0.05% or at most about 0.10% or at most about 0.15%. In one embodiment, the Ti content is at least about 0.01%, and at most about 0.05% or at most about 0.10% or at most about 0.15%.
[0081] Zn: The content is at most about 0.15%. Since Zn is an additive element in aluminum alloys, it is advantageous to accept it for the purpose of recycling aluminum scrap and waste, particularly from end-of-life vehicles. Indeed, Zn is used in certain plating alloys for certain plated sheets, in particular AA7072 with a plating of 10% of the thickness. Another plating alloy containing Zn is disclosed by application WO02 / 55256. Given the Zn content of AA7072 or the alloy of the aforementioned application, this content does not limit the use of such plated sheets to produce the alloy according to the invention. However, Zn is known to create sensitivity to corrosion. Limiting the Zn content can therefore improve corrosion resistance. In a preferred embodiment, the Zn is at most about 0.10%. In one embodiment, the Zn is at most about 0.05%.In one embodiment, Zn is an impurity.
[0082] The other elements are typically impurities whose content is kept less than or equal to 0.05%, preferably strictly less than 0.05%, the whole being less than 0.15%, the remainder being aluminum.
[0083] The pollution content consisting of Fe, Mn and Cr must be controlled. The term pollution is used to indicate that these elements may in certain cases be present in the alloy according to the invention due to recycling. However, without being linked to a theory, the present inventors note that the effect of these elements is not harmful and could have an unexpected favorable effect on the properties obtained in the claimed proportions. Increasing the pollution content makes it possible to increase the recyclability. Decreasing the pollution content makes it possible to increase the LDH. Preferably, a compromise is a pollutant content of at least about 0.64% to at most about 0.90%. In one embodiment, the pollutant content is from about Cu + 0.41% to about Cu + 0.59%, preferably from about 0.45% + Cu to about 0.55% + Cu. This embodiment is advantageous because it makes it possible to maintain a high LDH value.In a more preferred embodiment, the pollutant content is greater than about 0.70%, thereby increasing the recyclability for copper-containing plated sheets.
[0084] In one embodiment, the sheet according to the invention has an LDH less than or equal to 26.0 mm. The LDH is measured with a sheet 1 mm thick in the T4 state. Limiting the LDH is a compromise that makes it possible to improve the recyclability of the sheet according to the invention. Limiting the LDH is a compromise that makes it possible to increase the quantity of pollutants in the sheet according to the invention. Limiting the LDH is a compromise that makes it possible to increase the yield strength of the sheet according to the invention both in the T4 state and after baking the paints. In one embodiment, the sheet according to the invention has an LDH greater than or equal to 24.0 mm, preferably greater than or equal to 24.5 mm, more preferably greater than or equal to 25.0 mm, more preferably greater than or equal to 25.5 mm. Increasing the LDH value makes it possible to improve the formability during drawing.
[0085] In one embodiment, the sheet according to the invention has a minimum yield strength RpO,2 in the T4 state of 100 MPa, preferably 110 MPa, more preferably 115 MPa and / or has a maximum yield strength RpO,2 in the T4 state of 150 MPa, preferably 145 MPa, more preferably 140 MPa. Too low a yield strength in the T4 state will limit the yield strength after baking the paints. Too high a yield strength in the T4 state increases the drawing force. Limiting the maximum yield strength in the T4 state is a compromise that makes it possible to improve the formability measured with the LDH. In a sub-embodiment, the yield strength RpO,2 in the T4 state is a maximum of 135 MPa. This sub-embodiment is a compromise that makes it possible to increase the recyclability.
[0086] In one embodiment, the sheet according to the invention has a minimum yield strength RpO,2 after baking the paints of 200 MPa, preferably 210 MPa and / or has a maximum yield strength RpO,2 after baking the paints of 250 MPa, preferably 240 MPa. Increasing the yield strength after baking the paints is advantageous for reducing the thickness of the parts. In a sub-embodiment, the yield strength after baking the paints is a maximum of 220 MPa, preferably 215 MPa. This sub-embodiment is a compromise which makes it possible to increase the suitability for recycling.
[0087] In a preferred embodiment, the sheet according to the invention has excellent resistance to filiform corrosion of less than approximately 0.25 cm on average according to EN 3665 after painting and baking the paints. The painting includes all the operations known per se for surface preparation, cataphoresis and then painting. The baking of the paints, also known as bake hardening, can be simulated by treatment at 170°C for 20 minutes.
[0088] The method of manufacturing the sheets according to the invention involves casting a plate, preferably by vertical semi-continuous casting, followed by its homogenization.
[0089] The plate is cast with an alloy according to the composition previously described. The alloy is preferably produced in part with scrap and waste, preferably from plated sheets. These scrap and scrap of plated sheets can also be a finished product to be recycled (old scrap according to EN 12258-1) of which one part is made with a plated sheet. This is advantageous because these finished products are generally also made with parts of very different alloys, without all the components necessarily being plated, for example from alloys of the 3xxx series with alloys containing Zn, for example from the 7xxxx series or for example disclosed by application EP1446511. The scrap and scrap of plated sheets can be used for the production of the alloy either directly or indirectly.Indirect use is advantageous when the scrap and scrap of plated sheets are coated with paints or varnishes, or when the scrap and scrap of plated sheets are equipped with plastic parts. In these cases it is preferable to remelt them in specialized units, known to those skilled in the recycling art, where the coating or plastic parts will be properly treated, for example by filtering the fumes. Direct use is advantageous because it is simple and economical to organize since it consists of loading the scrap and waste directly into the melting furnaces to produce the alloy.
[0090] The recyclability is evaluated as follows. First, the average composition of the scrap or waste, preferably clad sheets, must be calculated, estimated or measured for each element. Then, for each element, the percentage ratio between the maximum of the alloy of the sheet according to the invention and the content of the element in the average composition of scrap and waste of clad sheets is calculated. The recyclability is the minimum value between all these ratios. This recyclability is therefore the maximum scrap and waste of clad sheets that can be put into the alloy of the sheet according to the invention, the composition of the alloy of the sheet according to the invention being obtained by the addition of primary aluminum and / or an additional element.
[0091] Increasing the recyclability makes it possible to reduce the amount of CO2 equivalent emitted to cast the plate. Preferably, the plate is produced with at least 10% of offcuts and waste, preferably at least 20%, preferably at least 30%, preferably at least 39%, preferably at least 46%, preferably at least 48%. In one embodiment, a maximum recyclability of 45% is a compromise which makes it possible to improve the yield strength in the T4 state or after baking the paints.
[0092] The preferred dimensions of the plates according to the invention are 200mm to 600mm thick, 1000 to 3000mm wide and 2000 to 8000mm long.
[0093] The plate is homogenized typically at a homogenization temperature above the solvus temperature of the alloy, while avoiding local melting or burning for a period of at least 2 hours, preferably 3 hours, more preferably 4 hours and at most 7 hours, preferably 6 hours, more preferably 5 hours. The homogenization temperature is preferably at most 580°C, preferably 570°C, more preferably 560°C, more preferably 555°C, and at least 540°C, preferably 550°C. Too high or too low a temperature degrades the mechanical properties of the sheet.
[0094] The plate is then transferred to the hot rolling mill. Optionally, it is directly transferred from homogenization to hot rolling, the temperature being able to decrease by 5 to 35°C naturally during this transfer. Optionally, the plate is cooled from the homogenization temperature to the hot rolling start temperature by forced cooling. This forced cooling is preferably carried out with a direct cooling rate of at least 150°C per hour. Advantageously, the direct cooling rate is at most 500°C / h. The cooling can typically be carried out by a machine such as that described by application WO2016012691. Preferably, this cooling is done in two stages, one of spraying and the other of uniformization. Optionally, this cooling can be carried out in two passes in the machine such as that described by application WO2016012691.
[0095] The homogenized plate is then hot rolled typically to a thickness of 4, preferably 3 mm, to 8 mm. The hot rolling start temperature is typically 520 to 550°C. Optionally, the hot rolling temperature after the aforementioned cooling is 390°C to 510°C or 490°C or 470°C or 450°C or 430°C or 410°C. Optionally, the hot rolling temperature after the aforementioned cooling is 410°C to 510°C or 490°C or 470°C or 450°C or 430°C. Optionally, the hot rolling temperature after the aforementioned cooling is from 430°C to 510°C or 490°C or 470°C or 450°C. Optionally, the hot rolling temperature after the aforementioned cooling is from 450°C to 510°C or 490°C or 470°C. Optionally, the hot rolling temperature after the aforementioned cooling is from 470°C to 510°C or 490°C. Optionally, the hot rolling temperature after the aforementioned cooling is from 490°C to 510°C.
[0096] The temperature change between the start and the end of hot rolling results from cooling by the usual heat exchange of the plate with the air at the ambient temperature of the factory, with the equipment of the hot rolling mill such as, for example, but not limited to, the cylinders or the conveyor rollers as well as with the usual lubrication or cooling fluids and the heating linked to the deformation energy. Preferably, the temperature at the end of hot rolling is 350°C to 450°C.
[0097] The hot-rolled plate is then cold-rolled, typically into a 0.7 to 1.5 mm sheet. Intermediate annealing may also take place between two cold-rolling stages. Annealing can take place in a static furnace or in a continuous furnace.
[0098] The sheet is then solution-treated typically at a solution temperature above the solvus temperature of the alloy, while avoiding local melting or burning, and then quenched, preferably in a continuous furnace. Too cold a solution and / or too short a solution degrade the mechanical properties of the sheet by insufficient solution treatment. Too hot a solution causes burns degrading the mechanical properties. Too long a solution degrades productivity. Preferably, the solution treatment lasts from 15 seconds to 300 seconds. The solution treatment temperature is preferably at least 530°C and at most 570°C.
[0099] The sheet is then quenched typically at a rate of more than 30°C / s and better at least 100°C / s with water or with air or with a successive combination of water or air. Preferably the sheet is quenched to a temperature of 60 to 100°C. An insufficient cooling rate degrades the mechanical properties of the sheet because the solution treatment is then incomplete.
[0100] The sheet is then reheated to achieve pre-tempering at a pre-tempering temperature of 60°C to 100°C for a period of 2 to 16 hours. Reheating is useful when the sheet undergoes a surface treatment between quenching and pre-tempering whose temperature is lower than that of pre-tempering. Pre-tempering is preferably obtained by coiling then cooling to room temperature, preferably for at least 40 hours. Pre-tempering improves the response to paint baking, which is the difference between the yield strength in the T4 state and the yield strength after paint baking.
[0101] The pre-tempered sheet is in the T4 state and then matures at room temperature for between 72 hours and 6 months. This step is a constraint linked to storage before forming. The sheet according to the invention can be formed despite maturation.
[0102] The sheet metal according to the invention is advantageously used for the production of automobile body parts. In one embodiment, the sheet metal according to the invention is a sheet metal for lining, such as for example door or hood linings. For automobile parts, in particular linings, the thicknesses are between 0.7 and 1.5 mm. A thickness of less than 0.7 mm is too thin to ensure the rigidity of the component containing the lining. A thickness greater than 1.5 mm makes the component containing the lining too heavy for the user and the vehicle. Since the linings are not visible parts from the outside of the vehicle, the sheets for linings do not have a surface condition in the delivered state and after painting comparable to that of the exterior parts of the vehicle body. In one embodiment, the cording of the sheet metal according to the invention at best 1.
[0103] Examples
[0104] The disclosure is further illustrated by the following examples. These examples are intended only to illustrate the invention and not to limit it.
[0105] Plates of different compositions were cast according to the alloys in Table 1. Alloy A is a typical alloy of application US20210108293. Alloy B is a typical alloy in production to provide AA6016 alloy body sheets. Examples according to the invention are identified E and counterexamples by CE in Table 1.
[0106] [Table 1]
[0107] The recyclability was evaluated with a plated sheet as disclosed by application W002 / 40729 by choosing a plating on each face of the core of 10%. In view of recycling such a sheet, the average composition of the plated sheet is calculated in the table below.
[0108] [Table 2]
[0109] The recycling suitability of the different alloys A to P is assessed by calculating the maximum quantity of the average composition calculated in Table 2 below for each element.
[0110] A value greater than 100% means that the clad sheet does not provide the quantity of the element considered, so there is no limit to the introduction of the clad sheet to produce the alloy for the element considered. A value less than 100% implies that the clad sheet provides too much of the element considered and that the introduction of the clad sheet to produce the alloy must be limited. It is therefore necessary to take into account only the minimum on all elements for each alloy evaluated to define its suitability for recycling. For Cr and Ti, the calculation of the suitability for recycling is not done with the Ti and Cr content of the alloys tested but with the value of 0.05% which corresponds to the conventional maximum of 0.05% of impurities.
[0111] [Table 3]
[0112] Plates A to N were homogenized at a temperature of 555°C for 4 hours, then hot rolled to a thickness of 6mm with a hot rolling start temperature of 550°C and then cold rolled into 1mm thick sheets. These sheets were then solution treated at a temperature above 530°C for 15s and then quenched to a temperature of 60°C. The sheets were then pre-tempered at 80°C for 16 hours.
[0113] The O and P plates were homogenized for 2 hours at 560°C and then cooled by forced cooling to the hot rolling start temperature of 400°C. The plate is hot rolled to a thickness of 3mm at a temperature of 305°C. The plate was then cold rolled to a thickness of 1.2mm and then solution treated with a PMT (peak metal temperature) of 560°C and then quenched. Pre-tempering is then carried out by reheating to a temperature of 65°C, then coiling which then cools naturally to room temperature.
[0114] The mechanical properties were tested in the T4 state. The results are in Table 4. The last column is the yield strength of these samples after 7 days of maturation after simulation of paint curing (Bake hardening or BH) with a heat treatment of 170°C for 20 minutes. The TL direction is the cross direction in the rolling direction.
[0115] [Table 4] Figure 1 shows that the sheets according to the invention K, L, M, N, O and P are a good compromise between formability and recyclability. In fact, sheet B is slightly better in formability but with very low recyclability. The other sheets may have better recyclability but with significantly reduced formability.
[0116] Figure 2 shows that the sheets according to the invention K, L, M, N, O and P are a good compromise between formability and the level of pollution in Fe, Cr and Mn. In fact, sheet B is a little better in formability but with a high purity alloy with a low pollution content. The other sheets contain a higher content of Fe, Cr and Mn pollutants but with a significantly reduced formability.
[0117] Figures 3 and 4 show that the sheets according to the compromise between LDH (formability) and RpO,2 in the T4 state (forming effort) and between LDH and RpO,2 after simulation of paint baking (BH or bake hardening). The K, L, M, N, O and P sheets have a better compromise than the other sheets (except sheet B but sheet B is not according to the invention due to its low content of one of the pollutants which is Mn). The K and L sheets have a similar level of formability to the M and N sheets thanks to the Cu content which compensates for the pollution level of Mn + Cr + Fe.
[0118] Figure 5 shows two different advantageous trade-offs between recyclability and yield strength in the T4 and after-baking conditions. Sheet N has better yield strengths in the T4 and after-baking conditions and slightly lower recyclability. Sheet L has better recyclability and slightly lower yield strengths in the T4 and after-baking conditions.
[0119] K and L sheets have better recycling suitability due to a higher Mn content than M and N sheets.
[0120] The N sheet allows to obtain the best yield strength after baking of the paints by increasing the Mg compared to the M sheet while maintaining a yield strength in the T4 state comparable to the M sheet by reducing the Si content. The Mn content lower than 0.50% makes it possible to compensate for the hardening effect in the T4 state to maintain the LDH level.
[0121] Sheets A to P were subjected to a filiform corrosion test according to standard EN3665. For this purpose, the samples underwent surface and painting treatments known to those skilled in the art. The samples then underwent the heat treatment of baking the paints at 170°C for 20 minutes. The samples were then scratched in the long rolling direction (L) and the long cross direction, perpendicular to the rolling direction. (TL). The results of the filiform corrosion test are given in the table below.
[0122] [Table 5] Only samples A, BD, H, K, LM, N, O and P with a copper content of less than 0.37% have resistance to filiform corrosion with an average length of less than 0.25 cm.
[0123] Sheets B, H, K, LM, N, O and P were also characterized after 90 days of maturation. The sheets remained relatively insensitive to maturation.
[0124] [Table 6]
Claims
Claims: Aluminum alloy sheet composition, in % by weight: If: 1.25% - approximately 1.55%, Fe: <= approximately 0.60%, Cu: <= approximately 0.37%, Mn: 0.22% - approximately 0.65% Mg: approximately 0.25% - approximately 0.55% Ti: <= approximately 0.15%, Cr <= approximately 0.30%, Cr + Mn +Fe: <= approximately 0.90%, Zn ≤ approximately 0.15%, other elements: each ≤ 0.05%, total ≤ 0.15%, remainder: Al. Sheet according to claim 1 characterized in that Cu ≤ approximately 0.32%, preferably approximately ≤ 0.27%, more preferably ≤ 0.25%. Sheet according to claim 1 or 2 characterized in that Mn ≥ approximately 0.30%, preferably approximately ≥ 0.35%, preferably approximately ≥ 0.40%, and / or Mn approximately ≤ 0.60%, preferably approximately ≤ 0.55%. Sheet according to any one of claims 1 to 3 characterized in that Mg ≥ approximately 0.30%, preferably approximately ≥ 0.35%, and / or Mg ≤ approximately 0.50%, preferably approximately ≤ 0.45%. Sheet metal according to any one of claims 1 to 4 characterized in that Cr ≤ about 0.15%, preferably ≤ about 0.10%, preferably ≤ about 0.05%. Sheet metal according to any one of claims 1 to 5 characterized in that Ti ≤ about 0.10%, preferably Ti ≤ about 0.05% or Ti ≥ about 0.01%.Sheet metal according to any one of claims 1 to 6 characterized in that Zn <= about 0.10%, preferably Zn <= about 0.05%. Sheet metal according to any one of claims 1 to 7 characterized in that Si <= about 1.50% and / or >= about 1.30%; preferably about >= 1.35%, preferably about >= 1.40%.
9. Sheet according to any one of claims 1 to 8 characterized in that the sheet has an LDH less than or equal to 26.0 mm and / or greater than or equal to 24.0 mm, preferably greater than or equal to 24.5 mm, preferably greater than or equal to 25.0 mm, the LDH being measured with a sheet of thickness of 1 mm in the T4 condition.
10. Sheet metal according to any one of claims 1 to 9 characterized in that the sheet metal has a minimum yield strength RpO,2 at state T4 of 100 MPa, preferably 110 MPa, more preferably 115 MPa and / or has a maximum yield strength RpO,2 at state T4 of 150 MPa, preferably 145 MPa, more preferably 140 MPa 11. A process for manufacturing sheet metal according to claims 1 to 10 comprising the successive steps: a. Preparation of an alloy, preferably comprising scrap and waste, preferably of clad sheets, b. Casting of the alloy into a plate, preferably by semi-continuous vertical casting, c. Homogenization of the plate at a homogenization temperature, preferably from 540°C to 580°C, preferably from 550°C to 580°C, d. Hot rolling of the plate, e. Cold rolling of the hot-rolled plate, f. Solution heating followed by quenching, g. Pre-tempering at a pre-tempering temperature of 60 to 100°C for a period of 2 to 16 hours, preferably obtained by winding and then cooling to ambient temperature, h. Curing from 72 hours to 6 months.