KR20040075980A - Al-Si-Mg Alloy Metal For Motor Car Body Outer Panel - Google Patents

Abstract

A metal sheet for a motor vehicle body outer panel, having a thickness ranging between 0.8 and 1.2 mm, containing, in wt. %, Fe 0.25-0.40 and preferably 0.25-0.35; Si 0.90-1.20 and preferably 0.95-1.10; Cu 0.10-0.25 and preferably 0.15-0.20; Mg 0.35-0.50 and preferably 0.40-0.50; Mn 0.05-0.20 and preferably 0.08-0.15; other elements<0.05 each and <0.15 in total, the rest being aluminum. The sheet has, after solution heat treatment, quenching, pre-tempering or reversion, and maturation at room temperature for 3 weeks to 6 months, an L R0.2 direction yield strength less than 160 MPa, and preferably less than 150 MPa. A yield strength>180 MPa can be obtained on the body stamping part after the paint has been cured. The sheet of the invention enables a reduction in the thickness of parts while satisfying all the other required properties.

Description

Al-Si-Mg alloy sheet for car body exterior panel {Al-Si-Mg Alloy Metal For Motor Car Body Outer Panel}

Background of the Invention

The present invention relates to an Al-Si-Mg alloy sheet used for drawing and manufacturing body exterior panel members such as wings, doors, tailgates, bonnets and roofs, In particular it relates to the field of alloy sheets made of 6016 type alloys according to the Aluminum Association.

Prior art

Aluminum is increasingly used in automotive structures to reduce the weight of vehicles, thereby reducing fuel consumption and also reducing emissions of pollutants and greenhouse gases. In particular, a sheet is used in manufacturing a vehicle body exterior panel member (especially a door). This type of application requires a number of characteristics, but with the following contradictions:

-Good formability for drawing and hemming operations,

-Adjustable yield strength in the transport state of the seat to adjust the springback,

High mechanical strength after baking the paint to achieve good resistance to dent formation while minimizing the weight of the part,

Good resistance to corrosion of painted parts, in particular finishing corrosion,

Good surface quality after molding and painting,

Good behavior in various assembly processes used in automotive bodies such as spot welding, laser welding, gluing, clinching and riveting,

-Satisfactory price in case of large series production.

Al-Mg-Si alloys were selected in the 6000 series to meet the above requirements. In Europe, the most frequently used 6016 and 6016A alloys with thicknesses on the order of 1 to 1.2 mm are used for this application. The reason is that the 6016 and 6016A alloys have good compromise among various required properties, in particular good formability against hemming, and better against event corrosion than alloys with higher copper content, such as the 6111 alloy widely used in the United States. This is because it gives resistance. Alloy 6016 is described in French patent 2360684 to Alusuisse and applicant's European patent 0259332, and alloy 6111 is described in US Patent 4,614,552 to Alcan International Limited. Low iron (<0.2%) alloys similar to those described in Alcan International Limited's US Pat. Nos. 4,614,552 and 5,919,323 are also disclosed, and alloys of this type are registered as 6022. The compositions (% by weight of main component) of the 6016, 6016A, 6022 and 6111 alloys registered with the Aluminum Association are listed in Table 1.

Table 1

However, after baking the paint the mechanical strength of the 6016 alloy, i.e. resistance to flaw formation, is significantly lower than the corresponding value for the 6111 alloy case. The reason is that the baking temperature tends to be lowered so that the curing treatment becomes less effective during the aging treatment. This is because automobile manufacturers demand higher mechanical strength after painting.

In order to achieve the foregoing, the applicant has developed a new variant of the 6016 alloy, in particular the DR120 variant with a T4 hardness of about 120 MPa yield strength. These developments were published in Automotive Alloy 1999, "Optimum 6xxx Aluminum Alloy Sheets for Body Exterior Panels" (R. Shahani et al.), TMS Annual Symposium Journal (2000), pp.193-203, and IBEC held in Detroit. SAE technical paper 1999-01-3195 entitled "Development of 6xxx Alloy Aluminum Sheets for Body Exterior Panels-Bake Hardening, Formability and Trim Performance" by International Body Engineering Conference 1999 (D. Daniel et al.).

Alcan proposed a new variant of the 6111 alloy, called 6111-T4P, whose yield strength increased (typically 270 to 280 MPa) after baking the paint without reducing moldability at T4 hardness. In particular, such a product is described in the article "Characteristics and Characteristics of Two New Aluminum Automotive Exterior Panel Materials" (A. K. Gupta et al.) In SAE technical paper 960164. The article also mentions a so-called 61xx-T4P novel alloy, whose composition has not been published, has a similar reaction to paint baking and has a lower yield strength than the conventional 6111-T4 in the T4 state.

All of these new developments include an optimized pre-aging type of heat treatment performed after quenching to improve curing during baking of the paint. Without this type of heat treatment, the cure rate during baking decreases because the waiting time between quenching and baking at room temperature increases, and waiting weeks of industrial production are almost inevitable. This phenomenon is described in the "Pre-annealing of Aluminum-Magnesium-Silicon Alloys" by "Le Prerevenu des alliages aluminum-magnesium-silicium" (Dec. 1960, pp. 930-942) (M. Renouard and R. Meillat).

In order to prevent undesirable atmospheric effects, pre-aging by quenching stepwise, heat treatment immediately after quenching, storing metal in a non-universal freezer as a body part, or performing a reversion treatment It is necessary to do

Pre-aging temperatures and durations for 6000 alloys are described, for example, in section M 1290, “Heat Treatment for Aluminum Alloys” (R. Develay), Journal of Metallurgical Society No. 94, in Technologies de l'Ingenieur (1986). (1966 pp. 41-49) "Retard Aging in Aluminum-Magnesium-Silicon Alloys: Effects on Structural and Mechanical Properties" (DW Pashley et al.), And French Patent No. 1243877 (Surnitomo Light Metal) have. In addition, French Patent No. 1243877 (Cegedur) discloses a continuous furnace that can be used for pre-aging.

Given the increasing use of aluminum alloy sheets for mass-produced bodywork exterior panels, there is still a need for improved quality grades to reduce thickness without adversely affecting other properties. Thickness reduction is usually limited because of the lack of hardness of the molded part, which is equivalent to the thickness of an equivalent part made of steel 1.4 times. Therefore, the sheet will achieve resistance to flaw formation for molded parts after baking the paint at least equal to the resistance to steel parts with an aluminum / steel thickness ratio of 1.4 while maintaining good drawability and hemming performance. Can be.

Subject of Invention

It is an object of the present invention to have a composition suitable for regeneration, to have sufficient moldability for deep drawing and hemming under harsh conditions, to improve resistance to indentation compared to the 6016 type alloy sheet according to the prior art, It is also to provide a 6016 type alloy sheet for a car body exterior panel which adjusts springback with good adhesion properties, cuts without forming slivers, and has good resistance to eventual corrosion.

The above object of the present invention is a sheet for vehicle body exterior panel parts of 0.8 to 1.2 mm thickness, comprising the following composition (% by weight),

Fe: 0.25-0.40, preferably 0.25-0.35

Si: 0.90 to 1.20, preferably 0.95 to 1.10

Cu: 0.10 to 0.25, preferably 0.15 to 0.20

Mg: 0.35 to 0.50, preferably 0.40 to 0.50

Mn: 0.05-0.20, preferably 0.08-0.15

As other elements, the individual elements are <0.05 and the total elements are <0.15

The balance is aluminum,

Yield strength R _0.2 in the L direction less than 160 MPa after solution heat treatment, quenching, pre-ageing or reversal and aging at room temperature for 3 to 6 months It is achieved by a sheet for phosphor body exterior panel parts. The yield strength of the drawn part after heat treatment corresponding to baking of the paint is greater than 180 MPa, preferably 200 MPa.

Description of the invention

The present invention is based on a narrow composition range belonging to the definition of the 6016A composition registered with the Aluminum Association to obtain all necessary properties.

The silicon content is close to the bottom of the 6016A content range, while the magnesium content is in the middle of that range. This drop in silicon content is due to the more complete solution heat treatment of the alloy, which is desirable for formability. The iron content is maintained at 0.25% or more, which, unlike low grade iron such as 6022, allows the use of recycled metals and gives a better surface appearance after drawing.

The copper content is controlled within very narrow limits. That is, a content of at least 0.1%, slightly more than that for conventional 6016 or 6022 grades, contributes to mechanical strength, but more than 0.25% causes the risk of casual injury of the alloy. The alloy should contain at least 0.05% of manganese, chromium, vanadium or zirconium to control the particle diameter and to prevent the appearance of orange peels during extreme deformations, for example, hemming used for bonnets. In contrast, when the total content of such elements exceeds 0.20%, the moldability is poor.

The sheet manufacturing process according to the invention generally comprises casting of the plate, scalping of the plate and homogenization by simply heating it to a temperature of 400 to 570 ° C. for 6 to 24 hours. It is desirable to perform hot rolling at an input temperature of 510 ° C. or higher, which contributes to making the mechanical strength better than that which can be obtained at low input temperatures. The winding temperature of the hot rolled strip should be less than 350 ° C., preferably less than 300 ° C. to ensure mechanical properties and to prevent any indentation defects. The hot rolled strip is then cold rolled to the final thickness with intermediate annealing, if possible, at a temperature of 300 to 450 ° C. if carried out in a batch furnace and at a temperature of 350 to 570 ° C. if carried out continuously. The final cold rolled pass can be made, for example, into a cylinder organized by electron beam treatment (EBT), electro-erosion (EDT) or laser beam, which improves the formability and surface appearance of the parts formed after painting. do.

It is also possible to use strips obtained directly by continuous casting or twin roll casting or twin belt casting, and it is possible to perform cold rolling and subsequent work under the same conditions.

The solution heat treatment is performed at temperatures above the alloy solvates temperature while preventing overheating. The composition according to the invention allows for a very complete solution heat treatment, whereby in the differential enthalpy analysis diagram there is almost a silicon phase in the microstructure by very small peak areas of less than 1 J / g in the range of 565 to 580 ° C. The test was performed at a rate of temperature increase of 20 ° C./min.

After performing the solution heat treatment, the sheet is usually quenched with cold water or air. Quenching can be performed immediately by heat treatment in a pre-aging manner such as that described in the prior art to enhance the curing performance of the paint during baking.

Pre-aging does not require isothermal and its duration is temperature dependent. This can be considered by defining the equivalent time T _eq using the equation

Where T (in ° K) is the temperature, t is the pre-aging time and T _ref is the reference temperature of 373 ° K, ie 100 ° C. If pre-aging is sufficient, it should be carried out at a temperature of 50 ° C. or higher for 0.3 to 20 hours. If the equivalent time is insufficient, the cure rate of the paint decreases over time at ambient temperature during baking. On the other hand, if the equivalent time is too long, the mechanical properties increase too much during pre-aging and the formability of the sheet deteriorates. In the case of a 6016 type alloy, an equivalent time of 1 to 10 hours, preferably 3 to 6 hours is quite suitable. Sheets are typically stored for variable time periods at this stage, resulting in natural aging that increases yield strength over time. After three weeks of aging, the sheet thickness according to the invention is on the order of 0.9 to 1 mm and the yield strength in the L direction is on the order of 130 MPa, which is a high strength grade of DR100 and DR120 described in the above article by R. Shahani et al. It is higher than all 6016 variants, including slightly lower than that of the 6022 case. After 6 months of aging, the yield strength still remains below 160 MPa or even below 150 MPa, unlike the 6022 and 6111 alloys. This feature allows control over springback during molding, making it more difficult to control when thickness decreases and when yield strength increases, thus requiring multiple iterations when developing a stamping tool. Prior to molding, the sheet may be coated with a lubricant (oil or dry lubricant) suitable for drawing, assembly and surface treatment or for the part to be manufactured.

Sheets according to the present invention were superior to 6111 and 6022 alloys and obtained formability as high as 6016 grades as measured by the LDH ₀ ("limited dome height" in planar deformation) parameters.

The LDH parameter is used to evaluate the drawability of sheets of 0.5 to 2 mm thickness. A number of publications have been published, especially at the SAE conference in Detroit, 1993, SAE paper titled "LDH Test to Evaluate Sheet Metal Formability-Final Report of LDH Committee of North American Deep Drawing Research Group" (R. Thomson). There is an arc.

The LDH test is a pull test on a blank blocked by a retaining ring around its perimeter. The pressure of the blank clamp is controlled to prevent sliding within the retaining ring. The 120 × 160 mm blank is reinforced in a mode similar to planar deformation. Lubrication between the stamp and the sheet is achieved using plastic film and grease (Shell HDM2 grease). Punch lowering speed is 50 mm / min. The LDH value is the punch displacement at rest, ie the draw limit depth. The average of the three tests was measured, giving a 95% reliable range for measurements of ± 0.2 mm.

The sheet according to the invention has better crimpability than the 6111 or 6022 alloy sheet, and the crimpability is as good as the high strength 6016 alloy sheet according to the prior art. Hemming performance is evaluated by laboratory tests including 90 ° flange machining, 45 ° pre-hemming machining and final flat hemming.

Further, the sheet according to the present invention can be measured by the difference between the LDH in the peripheral case parallel to the rolling direction and the LDH in the peripheral case perpendicular to the rolling direction. This difference is less than 1 mm, preferably less than 0.6 mm.

Bodywork exterior panel parts are typically manufactured by cutting the blank into sheets, drawing the blank and trimming it with a press. During stamping processing, it is essential to prevent the occurrence of roping or indentation which may degrade the final paint appearance and reduce moldability in the case of severe deformation in the direction perpendicular to the rolling direction. As described in Applicant's European Patent No. 0259232, for this purpose, different means are provided for controlling the hot rolling discharge temperature, for example between 270 and 340 ° C. It is also important to prevent the occurrence of orange peel stamping, which contributes to appearance defects by the naked eye after painting. This is achieved by keeping the particle size smaller than 50 μm, and therefore, by the presence of a sufficient amount of manganese (or other element that plays a similar role, such as chromium, vanadium or zirconium) in the alloy, By temperature control and by a sufficient reduction of at least 30% by cold rolling. In the case of many parts, such as bonnets, the edges of the drawn blanks are flanged at 90 °, a lining stamping is inserted therein, pre-hemmed and then finally flat hemmed.

In addition, it is necessary to prevent sliver formation during the blank cutting and turning operations after the drawing process. Such slivers can cause defects that must be finished by hand. Cutting tools are important in this regard and have been recommended in the article by D. Daniel et al.

After stamping and hemming, the parts are coated with one or more paint coatings, followed by a baking step after each coating step. An important step is the baking of the electrophoretic layer, which is usually carried out at a temperature of 150 to 200 ° C. for 15 to 30 minutes. The baking temperature rarely exceeds 170 ° C. in the absence of electrophoresis. Paint baking aids in the aging process of the parts. The yield strength of the parts made from the sheet according to the invention baked at 165 ° C. for 20 minutes is at least 180 MPa or sometimes at least 200 MPa. Thus, for parts made from 0.9 mm thick sheets, the resistance to dynamic indentation is similar in value to parts made from conventional body steel sheets with yield strengths on the order of 250 to 300 MPa and 0.7 mm thickness. This is not the case for other 6016 grades.

The sheet according to the invention can be used to produce different bodywork panels such as hemming, clinching, riveting, spot welding, laser welding and bonding. In particular, hemmed joints used to make bonnets without performing chemical surface treatments such as chemical conversion or passivation, for example using phospho-chromic compounds or titanium, zirconium or silane based products. It is possible to glue them.

Parts made from the sheet according to the invention have good resistance to finishing corrosion after painting, which is superior to alloys with higher copper content, such as the 6111 alloy.

For economic reasons, it may be useful to combine steel structures with aluminum bodywork exterior panel parts for the same bodywork, such as wings, roofs and doors.

A prominent difficulty with this type of assembly is managing the difference in thermal expansion between the two materials when the paint is baked, especially during electrophoresis which is usually done at 160 to 200 ° C. It is essential to limit the residual deformation after baking processing to a level acceptable for the appearance of the vehicle.

The sheet according to the invention can limit these deformations regardless of the assembly mode selected and the geometry of the part. Thus, Applicant has demonstrated that a high yield strength at baking temperature, for example an yield strength greater than 140 MPa at 160 ° C. for an alloy according to the invention, has an advantageous effect on the deformation level if the assembly is made after baking. It is desirable to limit the baking temperature.

Other factors, such as the presence of ribs configured to reinforce aluminum panels or gaps between assembly points, can also limit deformation. Assemblies with continuous links, such as adhesives, may also be used with partial polymerization of the adhesive or transparent laser welding prior to baking.

Example 1

A 500 mm thick plate was cast from eight alloys A through I having the composition (% by weight) as shown in Table 1.

Composition A represents a conventional 6016 alloy, B is Applicant's grade DR100 described in the aforementioned articles, C and D are 6111 alloys, E is 6022 alloy, and F, G, H and I are in accordance with the present invention. Compositions I and Cu (F) or Mn (G and H) are alloys with similar compositions.

The plates were scalped and homogenized at 570 ° C. for 10 hours and then directly hot rolled directly with homogeneous heat over a reversible mill and then a tandem mill. The lamination start temperature was about 540 ° C and the hot strip winding temperature was about 310 ° C.

The hot rolled strip rolled to 3 mm is then cold rolled to a final thickness of 1 mm. “Batch” annealing for 10 hours in a coil heated to a temperature of 350 ° C., followed by a slow cooling after 2 hours of waiting time, or about 1 in a continuous furnace heated to a temperature of 400 ° C. An intermediate annealing treatment consisting of a process of "flash" annealing for a minute and immediately cooling is carried out to a thickness of 2.5 mm. Samples taken from the strip are subjected to solution heat treatment for less than 1 minute at a temperature of 570 ° C. and then quenched in cooling water. Samples made of alloys B, D, F, G, H and I are subjected to a complementary treatment for 2 hours at a temperature of 100 ° C. in an oil bath immediately after quenching to simulate industrial pre-aging.

After 3 weeks and 6 months of aging treatment at room temperature, yield strength (R _{0.2 in} MPa units) was measured, followed by aging treatment at 165 ° C or 185 ° C for 30 minutes to simulate a paint baking treatment. Formability was also measured (in mm) using an LDH parameter, with major deformations being horizontal and vertical with respect to the rolling direction, respectively. The results are shown in Table 2.

After three weeks of aging treatment, Sample I according to the present invention yielded the same level as conventional 6016 (Sample A) and significantly lower yields than the corresponding values of 6111 alloys (C and D) and 6022 alloy (E). It was confirmed to have strength. The position of yield strength of Sample I relative to other alloy samples did not change after 6 months of aging treatment.

The moldability measured by the LDH parameter is substantially superior to the moldability of the best alloy DR 100. In addition, the measured value of LDH in the rolling direction and in the direction perpendicular to the rolling direction is substantially the same, which is not always the case for other samples, which can provide good isotropy during molding.

Conversely, after baking the paint following pre-aging treatment, the value of yield strength of sample I is large, significantly greater than that of 6016 and DR100 alloys, the same as that of alloy F with high copper content, and It is the median of two 6111 grades that ensure high resistance to groove formation in the part.

In addition, the reaction during hemming was measured on a sheet having a thickness of 1 mm in a direction parallel to the rolling and in a direction perpendicular to the rolling, and was subjected to crushing treatment after phosphate treatment, electrophoresis and coating, and after drawing. The occurrence or lack of filament sliver was measured when cutting or trimming was performed.

The hemming test is carried out in three operations: flanging the edge at 90 ° C., pre-hemming at 45 ° C., and flattening the lining plate 0.7 mm thick. The hemmed edges are then classified by visual inspection as described in an article published in IBEC 99 by Daniel et al.

Resistance to finishing corrosion is assessed according to standard EN 3665 for samples of 150 x 60 x 1 mm which have been painted and scratched. The test procedure involves activating the corrosion by HCl vapor for one hour and then exposing it to a humid room for 1000 hours. The maximum length of the corroded filaments is measured, and in each case the average value of the three specimens is taken and classified as <2 mm = honor, 2-5 mm = medium, 5 mm = poor. Cleavage testing is described in a paper published in IBEC 99 by Daniel et al., Supra.

The clearance was 10% of the thickness and the cutting angle was 0 °.

The results are provided in Table 3.

A B C D E F G H I Heming Good Good crack crack crack orange peel Good Good Good Prehemming Good Good crack crack orange peel Orange peel Crack start orange peel Good Erosion Good Good Bad Bad Good middle Good Good Good Sliver none none filament filament Sliver none none none none

Since the behavior of Sample I satisfies the various criteria described above, it has been found that bodywork exterior panel parts with a perfect appearance can be manufactured.

Example 2

An aluminum alloy panel having the composition shown in Table 4 was fabricated using a manufacturing process similar to Example 1 but not necessarily including a heat treatment step and a pre-aging step after molding and before assembly, as mentioned in Table 4. Prepared. The panel measures 1.6 m x 0.9 m.

For each alloy, three panels of different geometries each containing ribs formed parallel to the short side of the rectangle by folding were tested.

These panels were riveted to a rectangular steel frame to simulate the case in which the vehicle body exterior panel sheet was made of aluminum alloy on the steel structure of the vehicle. Assembly is accomplished by riveting a pitch of 50 mm on the long side of the rectangle. The residual deformation of the panel was observed after heat treatment at 160 ° C. for 20 minutes to simulate electrophoretic baking. In addition, the mechanical properties (ultimate strength R _m and yield strength R _0.2 (in MPa)) of the panel at room temperature and a baking temperature of 160 ° C. were measured at a rate of temperature rise equal to about 20 ° C./min. The results are shown in Table 5.

Sample Panel 1 variant Panel variant Panel trivariate R _0.2 room temperature R _m room temperature R _0.2 160 ℃ R _m 160 ℃ J Extremely low 261 321 239 250 K that Extremely low Extremely low 160 282 148 208 L Go 164 309 137 220 M Go that Extremely low 142 263 127 186 N Extremely low 122 230 106 161

It has been found that the alloy according to the invention reduces the residual thickness after baking efficiently. The performance of the alloy is clearly correlated with the yield strength at baking temperatures. Finally, heat treatment prior to assembly and the addition of ribs is advantageous for reducing strain.

Example 3

An alloy according to the invention, produced according to the manufacturing process of the type shown in Example 1 which comprises pre-aging for 5 hours of evaluation time and heat treatment at different temperatures for 20 minutes to simulate baking of the paint. The resistance to dynamic indentation of a 1 mm thick sheet of 6016 DR100 alloy was evaluated and compared with the corresponding value of a 0.7 mm thick steel sheet having a yield strength equal to 290 MPa after baking the paint. After the baking process, the 290 MPa value of the yield strength of the steel sheet for use in the vehicle body corresponds almost to the average yield strength of the steel sheet used in the body exterior panels often used in European vehicles in recent years. The 1 mm thick aluminum sheet can withstand about 50% or more elongation compared to the 0.7 mm thick aluminum sheet.

The apparatus used for the indentation hardness test consists of a press-fitting body of 15 mm diameter and weighing 138 g, which is a sample sheet clamped between two steel sheets at a speed of about 16 km / h at a height of 1 m. Falls. Indentation depth (mm) is measured. The results are shown in Table 6.

Baking Temperature R _0.2 full invention R _0.2 DR100 R _0.2 steel Indentation Indentation DR100 Pressed steel 170 ℃ 193 161 290 1.55 1.80 1.45 185 ℃ 217 189 290 1.45 1.62 1.45 205 ℃ 230 207 290 1.38 1.46 1.45

At a paint baking temperature of 185 ° C., the 1 mm thick sheet according to the invention has the same resistance to groove formation as the 0.7 mm thick steel sheet. In the DR100 alloy, this is only realized at a paint baking temperature of 205 ° C. which is higher than the temperature typically employed in vehicle construction. Stronger alloys, such as 6111, will exceed the resistance to groove formation required by the market, but this can lead to loss of formability, especially during hemming.

Claims (14)

0.8-1.2 mm thick body exterior panel parts, It contains the following composition (% by weight), Fe: 0.25-0.40, preferably 0.25-0.35 Si: 0.90 to 1.20, preferably 0.95 to 1.10 Cu: 0.10 to 0.25, preferably 0.15 to 0.20 Mg: 0.35 to 0.50, preferably 0.40 to 0.50 Mn: 0.05-0.20, preferably 0.08-0.15 As other elements, the individual elements are <0.05 and the total elements are <0.15 The balance is aluminum, Yield strength R _0.2 in the L direction less than 160 MPa after solution heat treatment, quenching, pre-ageing or reversal and aging at room temperature for 3 to 6 months Seat for car body exterior panel parts. The method according to claim 1, the yield strength R _0.2 in the L direction less than 150 MPa after solution heat treatment, quenching, pre-aging or reversal and aging at room temperature for 3 to 6 months. Sheet. The method according to claim 1 or 2, wherein the solution heat treatment is performed so that the peak area is less than 1 J / g in the range of 565 to 580 ℃ in the differential enthalpy analysis diagram, and performing the test at a temperature increase rate of 20 ℃ / min Seat for body exterior panel parts. The method of claim 1, wherein the pre-aging is [Where T (° K) is the temperature, t is the pre-aging time, and T _ref is 373 ° K] at a predetermined temperature and time such that the equivalent time T _eq defined by The sheet for bodywork exterior panel parts to be carried out. The seat according to claim 4, wherein T _eq is between 3 hours and 6 hours. The sheet according to any one of the preceding claims, wherein the formable anisotropic LDH ₀ between the rolling direction and the perpendicular direction is smaller than 1 mm. The sheet according to claim 6, wherein the formable anisotropic LDH ₀ between the rolling direction and the right angle direction is smaller than 0.6 mm. The seat according to any one of the preceding claims, wherein the yield strength measured at 160 ° C. is greater than 140 MPa. The seat for vehicle body exterior panel parts according to any one of the preceding claims, wherein the particle size is smaller than 50 μm. The seat according to any one of the preceding claims, having a structured surface. The sheet for vehicle body exterior panel parts according to any one of the preceding claims, which is coated with a dry lubricant. The sheet according to any one of the preceding claims, wherein the yield strength R _0.2 (in the L or TL direction) in the artificially aged composition by solution heat treatment, quenching, natural aging, drawing and paint baking is greater than 180 MPa. Panel parts manufactured by The exterior panel part according to claim 12, wherein the yield strength R _0.2 (in the L or TL direction) in the artificially aged composition by solution heat treatment, quenching, natural aging and paint baking is greater than 200 MPa. In an exterior panel component made of the sheet according to any one of claims 1 to 11, The part is assembled to the steel structure prior to the paint baking process.