Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/043—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with silicon as the next major constituent

Definitions

• the invention relates to the field of aluminum alloy strips intended for the manufacture by stamping of bodywork parts for the body-in-white of motor vehicles.
• Aluminum alloys are increasingly used in automobile construction to reduce the weight of vehicles and thus reduce fuel consumption and greenhouse gas emissions.
• Aluminum alloy strips are used in particular for the manufacture of many "body-in-white” parts, among which are the body skin parts (or exterior body panels) such as the front fenders, roofs or roofs, skins hood, trunk or door.
• Application WO2013/037919 discloses a method for manufacturing a strip of AlMgSi alloy, consisting in casting a rolling plate from an AlMgSi alloy, in subjecting said rolling plate to homogenization, in carrying the rolling plate at the rolling temperature to hot roll it and then, optionally, cold roll it until the final thickness is reached.
• the objective of providing an improved process for manufacturing an aluminum strip in an AIMgSi alloy, making it possible to make the process for manufacturing AIMgSi aluminum strips having very good deformation properties more reliable, is achieved by producing a hot strip whose temperature is greater than 130°C, preferably between 135°C and at most 250°C, preferably does not exceed 230°C, when it leaves the last hot rolling pass for then winding said hot strip at this temperature.
• Application JP11172390 discloses an alloy having a composition consisting of, by weight, one or more types selected from 0.2-2.0% Mg, 0.3-3.0% Si, ⁇ +0.8% Cu, 0 0.01-10.4% Mn, 0.01-0.4% Cr, 0.01-0.4% Zr, 0.01-0.4% V, 0.03-0.5% Fe, 0.005 to 0.2% Ti and 0.01 to 3.0% Zn and the balance Al with unavoidable impurities.
• the cooling of the second stage is carried out until 35°C according to the inequality - l ⁇ log(R) ⁇ (0.0178T-1.289), where R is the cooling rate average (°C/h) at second stage cooling and T is the finishing temperature in °C of the first cooling stage.
• the invention aims to obtain an excellent compromise between all the properties sought and in particular between formability and corrosion resistance.
• the formability of the strip is assessed in the T4 state after maturation, the maturation corresponding to the duration of transport and storage between the quenching of the strip and its stamping in the form of a part. Corrosion is assessed on the finished part, so after stamping the strip, painting and baking the paintings.
• the baking of paints is also known to those skilled in the art as "bake hardening" because it simultaneously allows the hardening, by tempering, of the stamped strip to obtain the properties necessary for the use of the part on a motor vehicle. .
• An object of the invention is an aluminum alloy strip of composition, in% by weight:
• Another object of the invention is a method of manufacturing an aluminum alloy strip according to the invention comprising the steps of: a. Casting of a plate, preferably by semi-continuous vertical casting, in an alloy according to the invention, b. Homogenization of the plate preferably at a temperature between 500°C and 600°C, more preferably between 540 and 580°C and preferably between 1 hour and 12 hours, optionally followed by a second stage between 420°C and 550°C d a maximum duration of 4 hours, c. Cooling of the plate to the hot rolling start temperature between 350°C and 550°C at a cooling rate preferably greater than 150°C/h or cooling of the plate to room temperature then reheating of the plate to the temperature of said hot rolling start temperature, d.
• Hot rolling the plate into a strip at the hot rolling end temperature between 250°C and 450°C e.
• Cold rolling of the strip optionally in two parts separated by an intermediate annealing, preferably in a coil, f.
• Dissolution of the strip preferably between 500°C and 600°C for preferably 10s to 60s, followed by quenching, g.
• Another object of the invention is a body part a. Supply of an aluminum alloy strip according to the invention, b. Stamping, c. painting, d. Baking of the paints between 15 and 60 minutes at a temperature between 120 and 200°C, characterized in that the average length of the filiform corrosion filaments, after a corrosion test according to EN 3665, in the sanded area is less than 2 mm, preferably 1 mm or that the average length of the filiform corrosion filaments is in the unsanded zone, less than 1 mm, preferably less than 0.8 mm.
• FIG. 1 This figure is a photo of a strip sample after a lineage test.
• FIG. 2 This figure specifies the dimensions in mm of the tools used to determine the value of the parameter known to those skilled in the art as LDH (Limit Dome Height) characteristic of the ability to draw the material.
• LDH Limit Dome Height
• FIG. 3 This figure shows the variation of the elongation during the maturation time with the data of table 5.
• FIG. 4 This figure shows the variation of the work hardening coefficient during the aging period with the data in table 6.
• FIG. 5 This figure shows the variation of the elastic limit and the rupture limit during the time of maturation with the data of table 5.
• FIG. 6 This figure shows the variation of the bend angle during the ripening time with the data in Table 9.
• the metallurgical states in question are designated according to the European standard EN-515.
• the static mechanical characteristics in tension in other words the breaking strength Rm, the conventional yield strength 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 direction of the test being defined by standard EN 485-1.
• the work hardening coefficient n is evaluated according to standard EN ISO 10275.
• the modulus of elasticity is measured according to the ASTM 1876 standard.
• the Lankford anisotropy coefficient is measured according to EN ISO 10113.
• Filiform corrosion is characterized with the EN 3665 standard.
• the samples for this characterization are prepared in the following way: pre-traction of 2% in the transverse direction of rolling, sanding typical of a repair of a surface defect, then treatments usual automotive industry surface coatings and paint curing with the typical treatment of 180°C for 20 minutes. Sanding is done with a P150 grit paper for 10 seconds. Some samples are not sanded. Before the corrosion test, the painted samples are scratched with a width of 1 mm to expose the metal of the aluminum strip sample through the paint layer.
• alpha norm The bending angles, called alpha norm, are determined by 3-point bending test according to the NF EN ISO 7438 standard and the VDA 238-100 and VDA 239-200 version 2017 procedures.
• a thin strip or to simplify a strip, is a rolled product with a rectangular cross-section whose uniform thickness is between 0.20 mm and 6 mm.
• the LDH parameter is widely used for the evaluation of the drawability of strips. It has been the subject of numerous publications, in particular that of 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 blocked at the periphery by a rod. The blank holder pressure is adjusted to prevent slippage in the rod. The blank, with dimensions of 120 mm x 160 mm, is stressed in a mode close to plane deformation. The punch used is hemispherical. Figure 2 specifies the dimensions of the tools used to perform this test. The hemispherical punch has a radius of 50.8mm.
• the ring between the die and the side clamp has a diameter of 132.6 mm, the axis of which is common with the axis of the punch and the axis of a bore of the side clamp and the die.
• the bore of the side clamp and the die has a diameter of 101.6 mm.
• One 6.3 mm radius chamfer is placed on the die, around the bore and opposite the sidewall clamp.
• the lubrication between the punch and the strip is ensured by graphite grease, for example Shell HDM2 grease.
• the punch descent speed is 50 mm/min.
• the so-called LDH value is the value of the displacement of the punch at break, ie the limiting depth of stamping. The break is detected by a reduction in the drawing force of 20 daN.
• the so-called LDH value actually corresponds to the average of three tests, giving a 95% confidence interval on the measurement of 0.2 mm.
• the invention is based on the fact that it is possible, thanks to a suitable composition, tolerant to the presence of copper, to obtain strips combining excellent aptitude for drawing after solution treatment, quenching and maturation at the temperature ambient temperature and very good corrosion resistance after paint baking treatment.
• resistance to filiform corrosion is an important property for use on bodywork parts. These parts are exposed to scratches or accidental or even malevolent impacts. When the scratch or impact is deep enough in the paintwork, the metal is exposed to the external environment and filiform corrosion may appear. Filiform corrosion is a mode of corrosion that starts from the scratch or the impact and spreads to the surface of the metal under the paint. A small scratch or impact can therefore cause a large, particularly visible damaged surface.
• the strip according to the invention has excellent resistance to filiform corrosion after deformation, painting and baking paints.
• the deformation is 2% in the direction perpendicular to the rolling direction.
• Part of the surface of the samples is sanded because this corresponds to repairs for a surface defect during the production of the body parts.
• These sanded surfaces are generally more susceptible to filiform corrosion.
• the painting includes all the operations known per se of surface preparation, cataphoresis and then painting. Paint baking, also known as bake hardening, can be simulated by treatment at 180°C for 20 minutes.
• the average length of the filiform corrosion filaments in the sanded zone is less than 2 mm, preferably less than 1 mm.
• the average length of the filiform corrosion filaments is less than 1 mm, preferably less than 0.8 mm.
• the 0.7 to 1.0 mm thick aluminum alloy strip according to the invention in the T4 condition has a minimum LDH of at least 26.0 mm.
• the strip of thickness between 1.1 and 1.5 mm according to the invention in the T4 condition has a minimum LDH of at least 26.5 mm. This property is important for stamping complex geometries.
• the strip according to the invention in the T4 state is characterized by a strain hardening coefficient at relatively high deformations between 14 and 16% greater than 0.26.
• the strip according to the invention in the T4 state has a bend angle TT of at least 100°, preferably at least 120° or a bend angle TL of at least 120°, preferably of at least 145°.
• Si Silicon is, along with magnesium, the first alloying element of the aluminium-magnesium-silicon systems (AA6xxx family) to form the intermetallic compounds Mg2Si or Mg 5 Si 6 which contribute to the structural hardening of these alloys during the firing of metals. paintings.
• the Si content is between 1.2 and 1.5%. A higher content degrades the bendability and the mechanical strength after baking of the paints because the Si cannot be correctly put into solution. When the Si content is close to the maximum mentioned above, it is necessary to increase the duration of the solution treatment, which degrades the productivity, to ensure the correct solution treatment of the Si.
• a compromise between the formability and the productivity is a Si content of 1.25% to 1.45%, preferably 1.25% to 1.40%, more preferably 1.30% to 1.35%.
• the minimum Si content is 1.25% and the maximum is 1.50% or 1.45% or 1.40% or 1.35% or 1.30%.
• the minimum Si content is 1.30% and the maximum is 1.50% or 1.45% or 1.40% or 1.35%.
• the minimum Si content is 1.35% and the maximum is 1.50% or 1.45% or 1.40%.
• the minimum Si content is 1.40% and the maximum is 1.50% or 1.45%.
• the minimum Si content is 1.45% and the maximum is 1.50%.
• the Si content is in excess with respect to the Mg content to obtain the required formability.
• the excess of Si content over Mg content is the difference between the Si content minus the Mg content.
• the excess of Si content over Mg content is at least 0.95% by weight, preferably at least 1.00% by weight.
• Fe Iron is generally considered an undesirable impurity. The presence of iron-containing intermetallic compounds is generally associated with a decrease in local formability. However, very pure alloys are expensive.
• a compromise is an Fe content less than or equal to 0.25%, preferably less than or equal to 0.20% and preferably greater than or equal to 0.05%, more preferably greater than or equal to 0.10%.
• the Fe content is at least 0.05% and at most 0.25% or 0.20% or 0.15% or 0.10%. In another embodiment, the Fe content is at least 0.10% and at most 0.25% or 0.20% or 0.15%. In another embodiment, the Fe content is at least 0.15% and at most 0.25% or 0.20%. In another embodiment, the Fe content is at least 0.20% and at most 0.25%.
• Mn Manganese has an effect similar to iron in its contribution to common intermetallic precipitates.
• the maximum Mn content is 0.15%. In one embodiment, the Mn content is a minimum of 0.05% and a maximum of 0.15% or 0.10%. In another embodiment, the Mn content is at least 0.10% and at most 0.15%.
• Mg Generally, the level of mechanical characteristics of alloys of the AA6xxx family increases with the magnesium content. Combined with silicon to form the intermetallic compounds Mg2Si or Mg 5 SÎ 6 , magnesium contributes to the increase of the mechanical properties such as the mechanical resistance after the baking of the paints.
• the Mg content is between 0.20 and 0.45%. Too high a Mg content reduces the solubility of Si during solution treatment, which degrades the formability of the strip.
• a compromise between the solubility of Si and the increase in the mechanical resistance after baking of the paints is a content preferably less than or equal to 0.39%, more preferably 0.35%, more preferably 0.34%, more preferably 0, 33%.
• the Mg content is at least 0.25% and at most 0.45% or 0.40% or 0.35% or 0.30%. In one embodiment, the Mg content is at least 0.30% and at most 0.45% or 0.40% or 0.35%. In one embodiment, the Mg content is at least 0.35% and at most 0.45% or 0.40%. In one embodiment, the Mg content is at least 0.40% and at most 0.45%.
• Mg and Si are also important because, surprisingly, it allows the presence of Cu in the alloy, as described below.
• Cu In alloys of the AA6000 family, copper is an element participating in hardening precipitation but it is known to degrade corrosion resistance.
• the copper content is a maximum of 0.05%. Allowing the presence of copper in the alloy is economically advantageous because it makes it possible to recycle scrap and scrap aluminum which contains it.
• the presence of copper can come both from offcuts and waste as such, but may be due to accidental introduction. For example, during the dismantling of an end-of-life vehicle, it suffices inadvertently to leave a copper electric wire with the aluminum parts to pollute a plate obtained with recycled aluminum alloy.
• the Cu content is at least 0.01% and at most 0.05% or 0.04% or 0.03% or 0.02%.
• the Cu content is at least 0.02% and at most 0.05% or 0.04% or 0.03%. In one embodiment, the Cu content is at least 0.03% and at most 0.05% or 0.04%. In one embodiment, the Cu content is at least 0.04% and at most 0.05%.
• Ti This element can promote hardening by solid solution leading to the level of mechanical characteristics required and this element has moreover a favorable effect on the ductility in service and the resistance to corrosion.
• a maximum content of 0.15% for Ti is required to avoid the conditions of formation of the primary phases during vertical casting, which have a detrimental effect on all of the claimed properties.
• the Ti content is at least 0.01% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04 % or 0.03% or 0.02%.
• the Ti content is at least 0.02% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0, 04% or 0.03%.
• the Ti content is at least 0.03% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0, 04%. In another embodiment, the Ti content is at least 0.03% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0, 04%. In another embodiment, the Ti content is at least 0.04% and at most 0.15% or 012% or 0.10% or 0.08% or 0.06%. In another embodiment, the Ti content is at least 0.06% and at most 0.15% or 0.12% or 0.10% or 0.08%. In another embodiment, the Ti content is at least 0.08% and at most 0.15% or 0.12% or 0.10%. In another embodiment, the Ti content is at least 0.10% and at most 0.15% or 0.12%. In another embodiment, the Ti content is at least 0.12% and at most 0.15%.
• the Cr content is at least 0.002% and at most 0.09% because it serves as a hardening element. It can be added to refine the grains and stabilize the structure. In one embodiment, the Cr content is at least 0.002% and at most 0.09% or 0.08% or 0.06% or 0.04% or 0.03% or 0.02% or 0.01%. In another embodiment, the Cr content is at least 0.01% and at most 0.09% or 0.08% or 0.06% or 0.04% or 0.03% or 0, 02%. In another embodiment, the Cr content is at least 0.02% and at most 0.09% or 0.08% or 0.06% or 0.04% or 0.03%.
• the Cr content is at least 0.03% and at most 0.09% or 0.08% or 0.06% or 0.04%. In another embodiment, the Cr content is at least 0.04% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06%. In another embodiment, the Cr content is at least 0.06% and at most 0.09% or 0.08%. In another embodiment, the Cr content is at least 0.08% and at most 0.09%. Ni: The Ni content is at most 0.15%. The alloy is tolerant to the presence of nickel which can be introduced through recycling.
• the Ni content is at least 0.002% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04% or 0.03% or 0.02% or 0.01% or 0.005%. In another embodiment, the Ni content is at least 0.005% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04% or 0.03% or 0.02% or 0.01%. In another embodiment, the Ni content is at least 0.01% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0, 04% or 0.03% or 0.02%.
• the Ni content is at least 0.02% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0, 04% or 0.03%. In another embodiment, the Ni content is at least 0.03% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0, 04%. In another embodiment, the Ni content is at least 0.04% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06%. In another embodiment, the Ni content is at least 0.06% and at most 0.15% or 0.12% or 0.10% or 0.08%. In another embodiment, the Ni content is at least 0.08% and at most 0.15% or 0.12% or 0.10%. In another embodiment, the Ni content is at least 0.10% and at most 0.15% or 0.12%. In another embodiment, the Ni content is at least 0.12% and at most 0.15%.
• Zn The content is a maximum of 0.15% so as not to degrade the corrosion resistance. Since Zn is an additive element in aluminum alloys, it is advantageous to accept it for the purpose of recycling aluminum offcuts and waste, in particular from end-of-life vehicles. Indeed, Zn is used in certain alloys of certain components such as heat exchangers. In one embodiment, the Zn content is at least 0.001% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04% or 0 .03% or 0.02% or 0.01% or 0.005% or 0.002%.
• the Zn content is at least 0.002% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04% or 0.03% or 0.02% or 0.01% or 0.005%. In another embodiment, the Zn content is at least 0.005% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04% or 0.03% or 0.02% or 0.01%. In another embodiment, the Zn content is at least 0.01% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04 % or 0.03% or 0.02%.
• the Zn content is at least 0.02% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04% or 0.03%. In another embodiment, the Zn content is at least 0.03% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06% or 0.04 %. In another embodiment, the Zn content is at least 0.04% and at most 0.15% or 0.12% or 0.10% or 0.08% or 0.06%. In another embodiment, the Zn content is at least 0.06% and at most 0.15% or 0.12% or 0.10% or 0.08%. In another embodiment, the Zn content is at least 0.08% and at most 0.15% or 0.12% or 0.10%. In another embodiment, the Zn content is at least 0.10% and at most 0.15% or 0.12%. In another embodiment, the Zn content is at least 0.12% and at most 0.15%.
• the Zr content is at most 0.15%. Its content must be limited taking into account the effect on the grain size. Since Zr is an additive element in certain aluminum alloys, it is advantageous to accept it for the purpose of recycling aluminum scrap and waste.
• the minimum Zr content is 0.0005% and a maximum of 0.15% or 0.10% or 0.05% or 0.02% or 0.01% or 0.005% or 0.001 %. In another embodiment, the minimum Zr content is 0.001% and a maximum of 0.15% or 0.10% or 0.05% or 0.02% or 0.01% or 0.005%. In another embodiment, the minimum Zr content is 0.005% and a maximum of 0.15% or 0.10% or 0.05% or 0.02% or 0.01%.
• the minimum Zr content is 0.01% and a maximum of 0.15% or 0.10% or 0.05% or 0.02%. In another embodiment, the minimum Zr content is 0.02% and a maximum of 0.15% or 0.10% or 0.05%. In another embodiment, the minimum Zr content is 0.05% and a maximum of 0.15% or 0.10%. In another embodiment, the minimum Zr content is 0.10% and a maximum of 0.15%.
• the other elements are typically impurities whose content is kept below 0.05%, the whole being below 0.15%; the rest is aluminum.
• the process for manufacturing the strips according to the invention typically comprises the casting of a plate preferably by vertical semi-continuous casting, which is also known under the term Direct chili casting or DC casting, preferably the scalping of this plate to remove the layer foundry cortex, followed by its homogenization.
• the plate is cast with an alloy according to the composition described above.
• the preferred dimensions of the plates according to the invention are from 200 mm to 600 mm in thickness, from 1000 to 3000 mm in width and from 2000 to 8000 mm in length. The plates are then cut to length and scalped.
• the plate is then homogenized.
• a homogenization temperature that is too low and a time that is too short will make it necessary to increase the dissolution time. too long significantly degrades productivity. Too high a temperature can produce burns (incipient melting) which degrade the mechanical resistance after the paint has baked and the formability of the strip.
• the homogenization of the plate is carried out at a temperature between 500°C and 600°C.
• the homogenization time is advantageously at least 1 hour.
• An advantageous compromise is homogenization between 540° C. and 580° C. for a period of 1 to 4 hours.
• the homogenization temperature is between 520°C and 600°C or 580°C or 560°C or 540°C.
• the homogenization temperature is between 540°C and 600°C or 580°C or 560°C. In another embodiment, the homogenization temperature is between 560°C and 600°C or 580°C. In another embodiment, the homogenization temperature is between 560°C and 600°C.
• the homogenization time is advantageously at least 1 hour.
• the maximum homogenization time is 12 hours or 10 hours or 8 hours or 6 hours, or 4 hours or 2 hours.
• the maximum duration of homogenization is at least 2 hours and at most 12 hours or 10 hours or 8 hours or 6 hours, or 4 hours.
• the maximum homogenization time is at least 4 hours and at most 12 hours or 10 hours or 8 hours or 6 hours.
• the maximum duration of homogenization is at least 6 hours and at most 12 hours or 10 hours or 8 hours.
• the maximum homogenization time is a minimum of 8 hours and a maximum of 12 hours or 10 hours.
• the maximum homogenization time is at least 10 hours and at most 12 hours.
• Homogenization may optionally include a second level between 420° C. and 550° C. for a maximum duration of 4 hours.
• This second stage makes it possible to reduce the temperature of the plate towards its hot rolling temperature when there are production hazards which slow down production.
• this second stage has a maximum temperature of 550°C and 440°C or 460°C or 480°C or 500°C or 520°C or 540°C.
• this second stage has a maximum temperature of 540°C and 440°C or 460°C or 480°C or 500°C or 520°C.
• this second stage has a maximum temperature of 520°C and 440°C or 460°C or 480°C or 500°C.
• this second stage has a maximum temperature of 500°C and 440°C or 460°C or 480°C. In another embodiment, this second stage has a maximum temperature of 480°C and 440°C or 460°C. In another embodiment, this second stage has a maximum temperature of 460°C and 440°C. The usefulness of this second level is to avoid a double passing through the cooling machine which follows such as that described by application W02016012691.
• the direct cooling to the hot rolling start temperature is preferably carried out with a direct cooling rate of at least 150° C. per hour.
• the direct cooling rate is at most 500° C./h.
• the direct cooling can typically be carried out by a machine such as that described by application WO2016012691.
• this direct cooling is done in two stages, one of spraying and the other of standardization.
• this direct cooling can be carried out in two passes in the machine such as that described by application WO2016012691.
• the slab is then transferred at the hot rolling start temperature to the hot rolling mill.
• the hot rolling start temperature is between 350°C and 550°C.
• the hot rolling start temperature is between 500°C and 400°C. Limiting the too high temperature at the start of hot rolling causes the risk of cracks in the plate during hot rolling which can cause scrapping of the plate. Too low a hot rolling start temperature can make the hot rolling end temperature insufficient by making the plate too difficult to roll.
• the hot rolling start temperature is at least 350° C. and at most 500° C. or 480° C. or 460° C. or 440° C. or 420° C. or 400° C. or 380° C. vs.
• the hot rolling start temperature is at least 380°C and at most 550°C or 500°C or 480°C or 460°C or 440°C or 420°C or 400°C. In another embodiment, the hot rolling start temperature is at least 400°C and at most 550°C or 500°C or 480°C or 460°C or 440°C or 420°C. In another embodiment, the hot rolling start temperature is at least 420°C and at most 550°C or 500°C or 480°C or 460°C or 440°C. In another embodiment, the hot rolling start temperature is at least 440°C and at most 550°C or 500°C or 480°C or 460°C.
• the hot rolling start temperature is at least 460°C and at most 550°C or 500°C or 480°C. In another embodiment, the hot rolling start temperature is at least 480°C and at most 550°C or 500°C. In another embodiment, the hot rolling start temperature is at least 500°C and at most 550°C.
• the plate was rolled into a strip to the final hot rolling thickness between 3 and 10 mm. The temperature at the end of hot rolling is between 250°C and 450°C.
• the temperature at the end of hot rolling is at least 270° C. and at most 450° C. or 400° C. or 380° C. or 360° C. or 340° C. or 320° C. or 300° C. vs. In another embodiment, the temperature at the end of hot rolling is at least 300°C and at most 450°C or 400°C or 380°C or 360°C or 340°C or 320°C.
• the hot rolling end temperature is at least 320°C and at most 450°C or 400°C or 380°C or 360°C or 340°C. In another embodiment, the hot rolling end temperature is at least 340°C and at most 450°C or 400°C or 380°C or 360°C. In another embodiment, the hot rolling end temperature is at least 360°C and at most 450°C or 400°C or 380°C. In another embodiment, the temperature at the end of hot rolling is at least 380°C and at most 450°C or 400°C. In another embodiment, the temperature at the end of hot rolling is at least 400°C and at most 450°C.
• a first embodiment is the combination of a hot rolling start temperature of 400 to 450° C., preferably 400 to 430° C., a rolling end temperature of 350 to 450° C., preferably 350 to 420°C, cooling during hot rolling below 100°C preferably 70°C, and the absence of intermediate annealing during cold rolling.
• This combination makes it possible to obtain recrystallized states at the hot rolling exit which recrystallize during solution treatment to obtain a good surface quality after painting.
• a second embodiment is the combination of a hot rolling start temperature of 450 to 500°C, preferably 460°C to 500°C, a hot rolling end temperature of 250 to 350°C, preferably 260 to 320°C, cooling during hot rolling above 100°C, preferably above 125°C, more preferably above 150°C, and intermediate annealing during cold rolling.
• This combination makes it possible to obtain fibrous states at the hot rolling exit which recrystallize during solution treatment to obtain a good surface quality after painting.
• the first embodiment is preferred over the second because the intermediate annealing operation is absent, which is more economical.
• the strip is then cold rolled to the final thickness between 0.8 and 2 mm.
• the cold rolling is in two parts, separated by an intermediate annealing between 300°C and 500°C, preferentially between 300°C and 400°C, more preferentially between 340°C and 380°C.
• This intermediate annealing is preferably carried out on the strip wound in a coil instead of a continuous furnace because the furnace for annealing in a coil is simpler to build.
• the strip is then dissolved in a continuous furnace and then quenched.
• the solution temperature is between 500°C and 600°C.
• the solution temperature is at least 520°C and at most 580°C or 570°C or 560°C or 550°C or 540°C. In another embodiment, the solution temperature is at least 540°C and at most 580°C or 570°C or 560°C or 550°C. In another embodiment, the solution temperature is at least 550°C and at most 580°C or 570°C or 560°C. In another embodiment, the solution temperature is at least 560°C and at most 580°C or 570°C. In another embodiment, the solution temperature is at least 570°C and at most 600°C. The dissolution time is between 10s and 60s.
• a dissolution time of less than 10 s does not allow sufficient solution dissolution of the strip and the properties of the strip of formability and mechanical strength after the baking of the paints are not achieved. Too long a solution time degrades productivity and therefore production costs.
• Quenching is preferably done with air. Tempering with air is advantageous for the surface quality of the strip, which is an important characteristic for use for body skin parts. Quenching with water causes high cooling rates which deform the strip. The deformations which result from quenching with water then make it necessary to use a leveler which risks damaging the surface quality.
• the quenching rate up to the temperature of 100°C is at least 15°C/s, preferably more than 20°C/s, preferably more than 30°C/s. Considering the preferred quench with air, the preferred maximum quench rate is 95°C/s.
• Pre-tempering is obtained by winding the strip at a pre-tempering temperature between 50°C and 100°C followed by cooling to room temperature. This pre-tempering serves to stabilize the mechanical properties and formability of the strip during curing.
• the strip is reheated to the pre-tempered temperature and then coiled directly at said temperature. This reheating is advantageous for controlling the winding temperature. Indeed, on the one hand the temperature after rapid cooling such as quenching is difficult to control, the reheating makes it possible to finely control the obtaining of the temperature of the strip.
• the solution treatment and quenching machine is separated from the machine which carries out the reheating for the pre-tempering by an accumulator in which the strip continues its cooling which depends on the length of the accumulated strip.
• a surface treatment step known to those skilled in the art and useful for the use of the strip by the car manufacturer, often takes place after quenching and before pre-tempering. Reheating then makes it possible to choose a pre-temper temperature independently of the last temperature of the surface treatment.
• the pre-temper temperature is at least 60°C and at most 100°C or 95°C or 90°C or 85°C or 80°C or 75°C or 70°C or 65°C.
• the pre-temper temperature is at least 65°C and at most 100°C or 95°C or 90°C or 85°C or 80°C or 75°C or 70°C . In another embodiment, the pre-temper temperature is at least 70°C and at most 100°C or 95°C or 90°C or 85°C or 80°C or 75°C. In another embodiment, the pre-temper temperature is at least 75°C and at most 100°C or 95°C or 90°C or 85°C or 80°C. In another embodiment, the pre-temper temperature is at least 80°C and at most 100°C or 95°C or 90°C or 85°C.
• the pre-temper temperature is at least 85°C and at most 100°C or 95°C or 90°C. In another embodiment, the pre-temper temperature is a minimum of 90°C and a maximum of 100°C or 95°C. In another embodiment, the pre-temper temperature is a minimum of 95°C and a maximum of 100°C. The pre-tempering takes place during the natural cooling of the coil in the ambient temperature of the workshop for a period between 8 hours and 24 hours.
• Ambient temperature is a temperature compatible with human activity.
• the ambient temperature is typically a temperature of 0 to 45°C. Cooling the coil to a temperature of 45° C. at the pre-temper temperature is advantageous because it does not require the use of a cooling means such as an air conditioner during hot seasons.
• the band is therefore in the T4 state and matures at room temperature between 72 hours and 6 months. This period corresponds to the usual storage period before the manufacture of the bodywork parts.
• the strip is then used to manufacture a body part.
• the method of manufacturing the bodywork part therefore comprises the following successive steps
• the bodywork part has excellent resistance to filiform corrosion, following a corrosion test according to EN 3665.
• the average length of filiform corrosion filaments in the sanded area is less than 2 mm, preferably less than 1.
• the average length of the filiform corrosion filaments is less than 1 mm, preferably less than 0.8 mm.
• Sanding is representative of repairs to a surface defect that occurred during production of the part. These repairs by sanding are carried out by the workers in the production plants and they are well known to those skilled in the art.
• the plates were then cut to length and scalped then homogenized for 2 hours at 560°C.
• the homogenizing oven was then set to 540°C.
• the plates are taken out at 540° C. from the homogenization furnace and cooled to the start temperature of hot rolling according to Table 2.
• the cooling was carried out by a machine such as that described by the application W02016012691. Plates A, B and C required a double pass and the others passed only once through said machine.
• the cooling rate was about 350°C/h.
• the cooling was carried out in two stages, one of spraying followed by a standardization stage. The plates are then hot rolled into a strip.
• the temperatures at the start of the rolling of plates A, B and C are between 400 and 450°C, while the temperatures at the start of the rolling of the other plates are between 450 and 500°C.
• plates A, B and C have a temperature between 350 and 400°C while the other plates have an end of hot rolling below 300°C.
• the end hot rolling thickness of the strip is given in Table 2.
• the strip is then cold rolled to the intermediate cold rolling thickness.
• Certain tapes, according to Table 2 are heat treated at 350° C. in a reel for 1 hour.
• the strip is then rolled to the final thickness of Table 2. [Table 2]
• the strips were then put into solution and then air quenched in a continuous oven.
• the solution duration is given in Table 3.
• the strips were then tempered.
• the pre-tempering was carried out by winding the strip at the pre-tempering temperature, the resulting coil naturally cooling to room temperature in 12 hours. As these are strips produced under industrial conditions, the ambient temperature varied between 15 and 26°C.
• the pre-tempering temperatures are given in Table 3.
• the coils were then aged at room temperature and samples were taken for different characterizations.
• the stamping performance of strips in the T4 state is tested using the LDH (Limit Dome Height) test.
• the test specimens had a dimension of 120 x 160 mm for which the dimension of 160 mm was positioned either in the direction in the long direction, which is the direction of rolling, or the transverse direction, which is the direction perpendicular to the direction of rolling, and or the 45° direction between the two previous directions.
• the results are shown in Table 4.
• the coils according to the invention E and F have better drawability than the coil G and the latter does not deteriorate with the duration of maturation.
• Tables 5 and 6 give the results of mechanical characterizations after different maturing times. These results demonstrate the stability of the mechanical properties during maturation, an essential characteristic to allow forming, and in particular stamping, independently of the storage period of the strips.
• the static mechanical characteristics in tension are determined by a tensile test according to standard NF EN ISO 6892-1.
• Figure 3 shows the low time sensitivity of the elongations during maturation in Table 5.
• Figure 4 shows the low time sensitivity of the hardening coefficient at high elongation between 14 and 16% of table 6.
• Figure 5 shows the low sensitivity to maturation of the ultimate limit and the elastic limit of table 5.
• the anisotropy was also evaluated for the strip in the T4 state using the Lankford coefficient between 8 and 12% in the rolling direction, transverse to the rolling and at 45% between said directions.
• the average anisotropy as well as the plane anisotropy could therefore be calculated during the maturation.
• the results are shown in Table 8 and these characteristics remain stable for the duration of maturation.
• Lineage is measured as follows. A sample measuring approximately 270 mm (in the direction transverse to the direction of rolling) by 50 mm (in the direction of rolling) is cut from the strip. A pre-strain by tension of 15%, perpendicular to the rolling direction, ie in the direction of the length of the sample, is then applied. The sample is then subjected to the action of a P800 type abrasive paper in order to reveal the lineage. The lineage was measured on sample D, the result of which is shown in FIG. 1. The strip therefore has a satisfactory surface quality for the surface quality after painting of a part manufactured with this strip.
• Strips D, E and F have a bend angle TT of at least 120° and a bend angle TL of at least 145° in the long rolling direction.
• Figure 6 shows the low sensitivity to maturation of bend angles with the data in Table 9. [Table 9]

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• 2021
  • 2021-06-17 FR FR2106457A patent/FR3124196B1/fr active Active
• 2022
  • 2022-06-16 WO PCT/FR2022/051177 patent/WO2022263782A1/fr active Application Filing
  • 2022-06-16 KR KR1020247001537A patent/KR20240023116A/ko unknown
  • 2022-06-16 CN CN202280041990.6A patent/CN117480270A/zh active Pending
  • 2022-06-16 CA CA3221029A patent/CA3221029A1/en active Pending
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