IMPROVED METHOD FOR MANUFACTURING A STRUCTURE COMPONENT FOR A MOTOR VEHICLE BODY

Abstract

A method for manufacturing a rolled product for automobile bodywork or body structure with an alloy containing Si: 0.75-1.10, Fe: max 0.4, Cu: 0.5-0.8, Mn: 0.1-0.4, Mg: 0.75-1, Ti: max 0.15, Cr: max 0.1 and V: max 0.1 is disclosed with several process steps from casting the ingot to forming and painting a car body part. The various possibilities of pre aging of the sheet as well as of the heat treatment of the part offer advantageous material properties in forming, material strength and low sensitivity to the bake hardening process which can vary depending in the part location in the car body.

Claims

1. A method for manufacturing a rolled product for automobile bodywork or body structure, and/or a “body in white”, from an aluminium alloy, comprising: a. casting of an ingot with the following composition (% by weight): Si: 0.75-1.10; Fe: max 0.4; Cu: 0.5-0.8; Mn: 0.1-0.4; Mg: 0.75-1; Ti: max 0.15; Cr: max 0.1; V: max 0.1; inevitable elements and impurities at maximum 0.05% each, and total 0.15% maximum; remainder aluminium, b. homogenization of the ingot, c. hot rolling of the ingot, d. cold rolling into a sheet, e. solution heat treatment, quenching of the sheet, f. pre aging of the sheet, g. natural aging of the sheet.

2. The method according to claim 1, wherein the Cu maximum content of the ingot is 0.70% and/or the Cu minimum content is 0.55%.

3. The method according to claim 1, wherein the Mn maximum content of the ingot is 0.35% and/or the Mn minimum content is 0.15%, optionally 0.24% and optionally 0.25%.

4. The method according to any claim 1, wherein the Ti maximum content of the ingot is 0.05% and/or the Ti minimum content is 0.01%.

5. The method according to claim 1, wherein V is among the inevitable elements or impurities.

6. The method according to claim 1 wherein: b. homogenization of the ingot is at a temperature from 520 to 560° C. optionally during from 2 to 8 hours, and/or c. hot rolling of the ingot is to a thickness from 3 to 10 mm, and/or d. cold rolling into a sheet is to a thickness from 1 to 4 mm, and/or e. solution heat treatment temperature is from 540 to 580° C. optionally from 1 s to 5 minutes, and/or f. pre aging is during at least 8 hours at a temperature optionally from 50° C. to 120° C., optionally by coiling the sheet at a coiling temperature from 50° C. to 120° C., and/or g. natural aging is at ambient temperature, optionally from 72 hours to 6 months.

7. The method according to claim 1, wherein the casting a is a vertical semi continuous casting.

8. The method according to claim 6 wherein the pre aging is obtained by coiling the sheet at a coiling temperature from 70° C. to 95° C., 95° C. being excluded.

9. The method according to claim 6 wherein the pre aging is obtained by coiling the sheet at a coiling temperature between 50° C. and 70° C.

10. The method according to claim 6 wherein the pre aging is obtained by coiling the sheet at a coiling temperature above 95° C., and optionally preferably from 95° C. to 105° C.

11. A rolled product obtainable according to the method of clam 1.

12. A rolled product obtainable with the method of claim 8 wherein the tensile yield strength of the rolled product in a T4 temper is below 165 MPa and wherein the tensile yield strength of the rolled product in a T6B temper is at least 345 MPa.

13. The rolled product obtainable with the method of claim 9 wherein the tensile yield strength of the rolled product in T8A temper is at least 275 MPa.

14. The rolled product obtainable with the method of claim 10 wherein the tensile yield strength of the rolled product in T8C and T8D tempers and made from the same rolled product in T4 temper, differ by less than 5 MPa, and wherein the tensile yield strength of the rolled product in T6C and T6D temper and made from the same rolled product in T4 temper differ of less than 5 MPa and/or wherein T4 temper rolled product has a maximum tensile yield strength of 190 MPa and/or wherein the T6B temper rolled product has a minimum tensile yield strength of 340 MPa and/or wherein T8A temper rolled product has a minimum tensile yield strength of 280 MPa, optionally of 290 MPa.

15. The method according to claim 1 further comprising the following: g. Forming the rolled product, optionally by press stamping, into a shape, h. optionally artificial aging of the shape, i. painting and “bake hardening” of the shape into a part at a temperature from 150° to 190° C. and optionally from 170° to 190° C., during from 5 to 30 minutes, optionally from 15 to 30 minutes.

16. Part obtainable with the method according to claim 15.

17. A product comprising the part according claim 16 in a car as bodywork skin parts (or external bodywork panels) optionally front wings, roofs, bonnet, boot or door skins, and/or lining parts or bodywork structure components optionally door, bonnet, tailgate or roof linings or reinforcements, or, optionally, spars, bulkheads, load-bearing floors, tunnels and front, middle and rear pillars, and/or impact absorbers or “crashboxes”.

Description

DESCRIPTION OF THE FIGS

[0054] FIG. 1 depicts the device for “three-point bending test” consisting of two rollers R, and a punch B of radius r, for carrying out the bending of the rolled product T of thickness t.

[0055] FIG. 2 depicts the rolled product T after the “three-point bending” test with the internal angle β and the external angle, the measured result of the test: a is reported in the enclosed result. The maximum strength during the test procedure is also reported.

[0056] FIG. 3 depicts a specific embodiment for the method: [0057] 1: uncoiler [0058] 2: coiler [0059] 3: sheet [0060] 4: solutionizing furnace [0061] 5: quenching unit [0062] 6: surface treatment machine [0063] 7: pre ageing oven [0064] 8: stored coil

DESCRIPTION OF THE INVENTION

[0065] Unless defined otherwise within this description, the general terms are defined is the NF EN 12258-1. A sheet is a flat rolled product of rectangular cross-section with uniform thickness between 0.20 mm and 6 mm.

[0066] All aluminium alloys in question hereinafter are, unless indicated to the contrary, designated by the designations defined by the Aluminium Association in the Registration Record Series that it publishes regularly.

[0067] All the indications relating to the chemical composition of the alloys are expressed as a percentage by weight based on the total weight of the alloy.

[0068] The definitions of the metallurgical temper are indicated in the European standard EN 515 unless defined otherwise herein.

[0069] The static tensile mechanical characteristics, in other words the ultimate tensile strength R.sub.m, the tensile yield strength at 0.2% elongation Rp.sub.0.2, and the elongation at break A %, are determined by a tensile test in accordance with NF EN ISO 6892-1.

[0070] The bending angles are determined by a three-point bending test in accordance with NF EN ISO 7438 and the procedures VDA 238-100 and VDA 239-200.

[0071] The bendability is also measured with the norm ASTM E290-97a.

[0072] The inventors selected a set of composition of aluminium alloys in conjunction with suitable methods which offer to car manufacturer interesting properties to produce parts.

[0073] The subject of the invention is a method for manufacturing a rolled product for automobile bodywork or body structure, also referred to as “body in white”, from aluminium alloy, comprising the following steps. The casting of an ingot with the following composition: (% by weight): [0074] Si: 0.75-1.10. preferably the Si content maximum is 1.0% and more preferably, the maximum Si content is 0.95%. [0075] Fe: max 0.4. Preferably the minimum Fe content is 0.15% and/or the maximum Fe content is 0.30%. [0076] Cu: 0.5-0.8. Preferably, the Cu maximum content of the ingot is 0.70% and/or the Cu minimum content is 0.55%. More preferably, the maximum Cu content is 0.65%. Limiting the Cu to 0.8%, 0.70% or even 0.65% is interesting for economical reason as Cu is usually more expensive than aluminium. It is also advantageous to ease recyclability of the material. It may also improve the corrosion resistance. In another embodiment however the [0077] Cu minimum content is 0.65% in particular to increase strength. [0078] Mn: 0.1-0.4. Preferably the maximum Mn content is 0.35% and/or the minimum Mn content is 0.24% or preferably 0.25%. Addition of Mn improves in particular the bending behaviour. [0079] Mg: 0.75-1, preferably, the minimum content of Mg is 0.80% and/or the maximum Mg content is 0.90%. [0080] Ti: max 0.15, preferably the minimum Ti content is 0.01% and/or the maximum Ti content is 0.05%. [0081] Cr: max 0.1 and preferably the Cr is an inevitable element or an impurity. [0082] V: max 0.1, and preferably the V is an inevitable element or an impurity. [0083] And the inevitable elements and impurities at maximum 0.05% each, and total 0.15% maximum and the remainder is aluminium.

[0084] The casting can be made with various casting process. Continuous casting, which is usually a horizontal casting, is possible. It is also preferred to use a vertical semi continuous casting, which is also known under the name of direct chill casting. The vertical semi continuous casting is preferred because it more homogenous through the thickness of the sheet.

[0085] The ingot is homogenised, hot rolled and cold rolled into a sheet. The sheet is solution heat treated and quenched. Preferably the homogenization treatment of the ingot is at a temperature from 520 to 560° C. during preferably from 2 to 8 hours. Preferably the hot rolling rolls the ingot to a rolled intermediate product having a thickness from 3 to 10 mm. Preferably the cold rolling rolls the rolled intermediate product into a sheet having a thickness from 1 to 4 mm. The sheet is then solution heat treated typically at a temperature beyond the solvus temperature of the alloy while avoiding incipient melting. Preferably the solution heat treatment temperature is from 530° C., preferably 540° C. to 580° C. during preferably from is to 5 minutes. Quenching is then applied to the sheet. Water quenching is suitable with a temperature about 15 to 60° C., preferably 15° C. to 40° C. A pre ageing is applied during preferably at least 8 hours with preferably a temperature from 50 to 120° C. Natural ageing is then applied. Natural ageing is defined in NF EN 12258-1 and room temperature is defined in NF EN ISO 6892-1. Preferably the duration of the natural ageing is from 72 hours to 6 months.

[0086] The pre ageing step is preferably achieved by coiling of the sheet at a coiling temperature and cooling it in open air at the room temperature.

[0087] A convenient continuous annealing line device to realise the pre ageing is described by FIG. 3. The sheet 3 is uncoiled by uncoiler 1 and goes through the solutionizing furnace 4 and the quenching unit 5, then the sheet 3 enters the surface treatment machine 6, which is a very usual step for car body sheet, followed by a pre ageing oven 7 and finally coiled on the coiler 8 in open air. At the exit of pre ageing oven 7, the sheet is therefore hot and the sheet is coiled on the coiler 2 at a coiling temperature in open air. The coiled sheet 8 is hot and is stored at ambient temperature in the plant and cools down to ambient temperature. Pre ageing occurs during this cooling. Natural ageing starts after the end the cooling of the coiled sheet 8, preferably the pre-ageing duration is at least 8 hours.

[0088] Preferably, the pre ageing is obtained by coiling the sheet at a coiling temperature from 50 to 120° C., preferably from 60 to 120° C., followed by cooling the coiled sheet in open air, and its duration is 8 hours at least.

[0089] The rolled product of the invention comprises the product obtainable with the above method from casting to natural ageing. The temper of the rolled product after natural ageing is T4.

[0090] T4 temper rolled product tensile yield strength varies less than 5 MPa, preferably 3 MPa between the tensile yield strength in the transverse and 45° directions within the same rolled product. The same sheet is defined a rolled product made from the same ingot, same homogenization, same hot and cold rolling, same solution heat treatment, same quenching, same pre aging, same natural aging and the tensile testing samples are cut off from the rolled product as close as possible. This is a useful property for part stamping.

[0091] The rolled product in T4 temper can be characterized in 6 others specific tempers, T8A, T8C, T8D, T6B, T6C and T8D, which estimate the material properties of the part.

[0092] The T8A, T8C and T8D tempers are achieved by applying on the T4 rolled product a 2% strain followed each by a specific heat treatment. T8A temper uses a bake hardening heat treatment of 20 minutes at a temperature of 180° C. T8C temper uses a light and short bake hardening heat treatment of 5 minutes at a temperature of 160° C. T8D temper uses a light and long bake hardening heat treatment of 20 minutes at a temperature of 160° C.

[0093] The T6B, T6C and T6D tempers are achieved by applying on the T4 rolled product a specific heat treatment. T6B temper uses a heat treatment at a temperature of 225° C. during 30 minutes. T6C temper uses a light and short bake hardening heat treatment of 5 minutes at a temperature of 160° C. T6D temper uses a light and long bake hardening heat treatment of 20 minutes at a temperature of 160° C.

[0094] The T4 rolled product can then be formed, in particular by press stamping, in order to obtain a shape. Optionally, the shape is aged. The shape may be painted and bake hardened into a part at a temperature from 150 to 190° C., and preferably from 170 to 190° C., during from 5 to 30 minutes, preferably from 15 to 30 minutes.

[0095] An object of the invention is a part obtainable with the above method with the rolled product of the invention. The part can be used in a car as bodywork skin parts (or external bodywork panels) such as the front wings, roofs, bonnet, boot or door skins, and the lining parts or bodywork structure components such as for example door, bonnet, tailgate or roof linings or reinforcements, or, preferably, spars, bulkheads, load-bearing floors, tunnels and front, middle and rear pillars, and finally the impact absorbers or “crashboxes”.

[0096] In a first embodiment the coiling temperature is from 50° C. to 95° C., 95° C. being excluded, preferably from 60 to 95° C., 95° C. being excluded. The T4 temper rolled product of this first embodiment is characterized by a tensile yield strength lower than 165 MPa, which can be useful for customer formability at press stamping. The T6B temper rolled product of this first embodiment, as described formally, has a minimum tensile yield strength of 345 MPa and preferably a minimum tensile yield strength of 350 MPa.

[0097] A preferred composition for the method according to the first embodiment is [0098] Si: 0.75-1.10 and more preferably less 0.95%; Fe: max 0.4 and more preferably between 0.15% and 0.30%; [0099] Cu: 0.5-0.70 and preferably 0.5-0.65; [0100] Mn: 0.1-0.4; [0101] Mg: 0.75-1; [0102] Ti: 0.01-0.05; [0103] Cr: max 0.1; [0104] V: as an impurity; [0105] and the inevitable elements and impurities at maximum 0.05% each, and total 0.15% maximum and the remainder is aluminium.

[0106] With this preferred composition and with a coiling temperature from 50° C. to 95° C., 95° C. being excluded, preferably 60 to 95° C., 95° C. being excluded, the bendability of the T4 rolled product of the first embodiment is 0.19 maximum. This is advantageous in part forming.

[0107] A still more preferred composition of the first embodiment is [0108] Si: 0.75-1.10 and more preferably less 0.95%; [0109] Fe: max 0.4 and more preferably between 0.15% and 0.30%; [0110] Cu: 0.5-0.70 and preferably 0.5-0.65; [0111] Mn: 0.24-0.30 and preferably minimum 0.25%; [0112] Mg: 0.75-1; [0113] Ti: 0.01-0.05; [0114] Cr: max 0.1; [0115] V: as an impurity; [0116] and the inevitable elements and impurities at maximum 0.05% each, and total 0.15% maximum and the remainder is aluminium.

[0117] With this still more preferred composition, in conjunction with a coiling temperature from 50° C. to 70° C., preferably from 60 to 70° C., the VDA angle of the T4 temper rolled product is greater than 125°. The bendability of the T4 rolled product is still smaller than 0.19. This can be useful in some press stamping application.

[0118] In another preferred method of the first embodiment the coiling temperature is between 70° C. and 95° C. With this method, the T8A temper rolled product has a minimum tensile yield strength of 275 MPa. In a more preferred method of this embodiment, the T8A temper rolled product has a minimum tensile yield strength of 280 MPa with a coiling temperature between 70° C. and 95° C. and with a composition of [0119] Si: 0.75-1.10 and more preferably less 0.90%; [0120] Fe: max 0.4 and more preferably between 0.15% and 0.30%; [0121] Cu: 0.65-0.8; [0122] Mn: 0.1-0.4 and more preferably less than 0.24% and 0.15% minimum; [0123] Mg: 0.75-1 and more preferably less 0.95%; [0124] Ti: 0.01-0.05; [0125] Cr: max 0.1; [0126] V: as an impurity; [0127] and the inevitable elements and impurities at maximum 0.05% each, and total 0.15% maximum and the remainder is aluminium.

[0128] In a second embodiment of the invention the coiling temperature is from 95° C. to 120° C. and preferably from 95° C. to 105° C. with preferably the composition: Si: 0.75-1.10 and more preferably less 0.90%; [0129] Fe: max 0.4 and more preferably between 0.15% and 0.30%; [0130] Cu: 0.5-0.70 and preferably 0.5-0.65; [0131] Mn: 0.1-0.4 and preferably minimum 0.25% and preferably less than 0.35%; [0132] Mg: 0.75-1; [0133] Ti: 0.01-0.05; [0134] Cr: max 0.1; [0135] V: as an impurity; [0136] and the inevitable elements and impurities at maximum 0.05% each, and total 0.15% maximum and the remainder is aluminium.

[0137] The advantage of this second embodiment is in particular the low sensitivity of the yield strength of the part to a variation of the bake hardening treatment. The bake hardening conditions are dependent on the location inside the car body assembly, parts having a low sensitivity to bake hardening conditions are thus favourable because the car manufacturer has more flexibility. This low sensitivity can be assessed by comparing properties in T6C temper to those in T6D temper and/or properties in T8C temper to those in T8D temper which are obtained from the same T4 temper rolled product.

[0138] With rolled product obtained with the method of the second embodiment, the tensile yield strength of the rolled product in T8C and T8D tempers and made from the same rolled product in T4 temper, differ by less than 5 MPa. The T8C and T8D rolled product samples differs only by the duration of the bake hardening, the temperature of which is 160° C.

[0139] The T6C and T6D rolled product samples differs only by the duration of the bake hardening the temperature of which is 160° C. With rolled product obtained with the method of the second embodiment, the tensile yield strength of the rolled product in T6C and T6D tempers and made from the same rolled product in T4 temper, differ by less than 5 MPa.

[0140] More generally, the rolled product can be heat treated with a temperature from 150 to 190° C., and preferably from 170 to 190° C., during from 5 to 30 minutes, preferably from 15 to 30 minutes. The yield strength of the rolled product, heat treated at a given temperature in the above temperature ranges, during any duration in the above duration ranges, varies by less than 15 MPa, preferably 10 MPa and more preferably 5 MPa.

[0141] More generally, the 2% strained rolled product can be heat treated with a temperature from 150 to 190° C., and preferably from 170 to 190° C., during from 5 to 30 minutes, preferably from 15 to 30 minutes. The yield strength of the 2% strained rolled product, heat treated at a given temperature in the above temperature ranges, during any duration in the above duration ranges, varies by less than 15 MPa, preferably 10 MPa and more preferably 5 MPa.

[0142] With the second embodiment, the T4 temper rolled product has a maximum tensile yield strength of 190 MPa. With the second embodiment, the T6B temper rolled product has a minimum tensile yield strength of 340 MPa. With the second embodiment, the T8A temper rolled product has a minimum tensile yield strength of 280 MPa, preferably of 290 MPa.

[0143] Recyclability of any alloy is an important technical and economical parameter. Reducing the range any element is useful in order to strengthen recycling process as it gives predictability of the future melt. Reducing the maximum of the addition element is also advantageous as they can be more expensive than aluminium. Reducing Si content is advantageous for recycling because in many alloys, this element is not only an impurity but also detrimental to aluminium product properties. Therefore, an advantageous embodiment of the invention is to reduce the Si content to maximum of 0.95%. It is also an advantageous embodiment to reduce Fe maximum to 0.30% and/or to increase the Fe minimum to 0.15%. Another advantageous embodiment is to reduce the Cu maximum to 0.70% and preferably to 0.65% and/or to increase the Cu minimum to 0.55%. Another advantageous embodiment is to reduce the Mn maximum content to 0.35% and more preferably to 0.30% and/or to increase its minimum content to 0.15% and more preferably to 0.25%. Another embodiment is also to reduce the Ti maximum content to 0.05% and/or to increase the minimum content to 0.01%. Another embodiment is to classify the V as an impurity with a maximum of 0.05%

[0144] All those combinations of alloys composition and coiling temperature of the invention gives many possibilities for the car manufacturer with different forming properties. The car manufacturer can also optimize its processing and the design of its part. The shape ageing allows a high strength part but it requires a specific heat treatment of the shape ageing. High strength alloys are useful to lightweight part. If the part does not require high strength material, the car manufacturer can avoid the shape ageing, which is advantageous to simplify the production. Hence, the invention gives flexibility to car manufacturer.

EXAMPLES

[0145] Preamble

[0146] Table 1 summarises the chemical compositions (% by weight) of the alloys used during tests. The proportion of the others inevitable elements and impurities were lower than 0.05%, the total lower is than 0.15%, and the remainder is aluminium. Alloy G is an exemplary AA6111 alloy and alloy H is an exemplary of a modified AA6056.

TABLE-US-00001 TABLE 1 Alloy Si Fe Cu Mn Mg Ti Cr V A 0.81 0.21 0.68 0.20 0.7 0.04 <0.05 <0.05 B 0.81 0.21 0.70 0.20 0.8 0.03 <0.05 <0.05 C 0.81 0.20 0.58 0.20 0.7 0.03 <0.05 <0.05 D 0.80 0.20 0.58 0.20 0.9 0.04 <0.05 <0.05 E 0.83 0.19 0.56 0.29 0.8 0.03 <0.05 <0.05 F 0.82 0.20 0.58 0.29 0.9 0.10 <0.05 0.07 G 0.70 0.20 0.65 0.20 0.7 0.04 <0.05 <0.05 H 0.81 0.20 0.85 0.20 0.7 0.05 <0.05 <0.05

[0147] The rolling ingots of these various alloys were obtained by vertical semi-continuous casting. After scalping, these various ingots underwent homogenisation heat treatment at 540° C. during about 4 hours directly followed by the hot rolling to a 5 mm intermediate rolled product. The 5 mm intermediate rolled product was cold rolled to obtain sheets with a thickness of 2 mm.

[0148] The rolling steps were followed by a solution heat treatment followed by quenching. The solution heat treatment was at a temperature beyond the solvus temperature of the alloy while avoiding incipient melting. In this non limitating example the solutionizing temperature was 570° C. The solutionized sheet was then water quenched in a 20° C. water. The sheet samples were coiled with 3 coiling temperatures of 100° C., 80° C. and 60° C. for a pre ageing of 8 hours followed by a natural ageing. Two natural ageing were used: 7 days and 30 days at room temperature to obtain T4 temper rolled products.

[0149] The T4 rolled products were transformed into a T8A temper with a 2% strain and then heat treatment with a typical bake hardening heat treatment of 180° C. during 20 minutes. T8A samples were then characterized.

[0150] The T4 rolled product were also heat treated into a T6B temper with a heat treatment of 225° C. during 30 minutes. T6B samples were then characterized.

[0151] Tests Results

[0152] Tensile tests at ambient temperature were carried out in accordance with NF EN ISO 6892-1 with non-proportional test pieces, with a geometry widely used for sheets, and corresponding to the type of test piece 2 in table B.1 of Appendix B of said standard. These test pieces in particular have a width of 20 mm and a calibrated length of 120 mm. Tensile tests were done on rolled product in T4, T8A and T6B temper. The results obtained with a coiling temperature of 80° C. and 30 days of naturel ageing are presented in Table 2. The results obtained with a coiling temperature of 60° C. and 30 days of naturel ageing are presented in Table 3. The results obtained with a coiling temperature of 60° C., 80° C. and 100° C. and 7 days of naturel ageing are presented in Table 4.

TABLE-US-00002 TABLE 2 Coiling temperature 80° C. + 30 days natural ageing Measures in long transverse direction Bending radius three-point Tensile Yield strength, T4 radius bending test T4 T8A T6B WRAP T4 T4 T4 Alloy MPa MPa MPa mm r/t Angle α ° Fmax N A 140 268 336 0.3 0.15 127 5303 B 152 288 356 0.4 0.20 118 4911 C 138 255 339 0.2 0.10 121 4316 D 152 275 355 0.3 0.14 123 4972 E 149 279 353 0.3 0.15 122 4800 F 151 278 353 0.4 0.20 115 4766 G 129 254 325 0.3 0.14 129 4924 H 148 270 344 0.4 0.16 115 5453

TABLE-US-00003 TABLE 3 Coiling temperature 60° C. + 30 days natural ageing Measures in long transverse direction Bending radius three-point Tensile Yield strength, T4 radius bending test Refer- T4 T8A T6B WRAP T4 T4 T4 ence MPa MPa MPa mm r/t Angle α ° Fmax N A 140 230 334 0.3 0.15 133 5928 B 149 248 352 0.4 0.20 113 5295 C 138 238 337 0.2 0.10 128 4687 D 150 245 356 0.3 0.14 120 4826 E 150 241 351 0.3 0.15 135 5852 F 154 244 354 0.4 0.20 110 5080 G 135 221 326 0.3 0.14 133 5281 H 152 342 0.4 0.16 116 5679

TABLE-US-00004 TABLE 4 Coiling temperature + 7 days natural ageing Alloy 60° C. 80° C. 100° C. Tensile Yield Strength MPa Measures in long transverse direction, T4 temper A 142 137 B 148 149 C 133 136 D 146 149 E 154 147 174 F 152 149 G 124 125 H 149 146 170

[0153] The coiling temperature is an important parameter for T4 temper tensile yield strength. At 60 and 80° C. it allows to limit the T4 tensile yield strength below 165 MPa which can be advantageous for car manufacturer if it is needed to maintain stamping easiness.

[0154] Example alloys B, D, E and F, have a tensile yield strength minimum of 350 MPa in T8B temper. Those example alloys have a tensile yield strength minimum of 275 MPa in T8A temper.

[0155] Reducing the range of Ti to maximum 0.05%, the V to an impurity of 0.05% maximum and reducing Cu to less than 0.65% is also advantageous as exemplified by alloy E and D because it reduces the bendability to 0.15, which eases the manufacturability of the component independently of the coiling temperature.

[0156] In addition to the above reduced range of V, Ti and Cu, the optimized range of Mn from 0.25 to 0.35% offers with the 60° C. coiling temperature a very advantageous 3 points bending test with a high VDA angle which is good for formability. This is exemplified by alloy E with coiling temperature of 60° C.

Example 2

[0157] Rolled products manufactured with alloy E, with coiling temperatures 80° C. and 100° C. and after 7 days of natural ageing were used for others trials. Samples at both coiling temperature were split in 2 groups: in the first group a strain of 2% was applied and the second group there was not any strain. Then a bake hardening temperature of 160° C. was applied, with two different durations of 5 and 20 minutes.
Those results, provided in Table 5 for a coiling temperature of 80° C. and Table 6 for a coiling temperature of 100° C., show another advantageous embodiment: with a coiling temperature of 100° C., the rolled product tensile yield strength is nearly independent from bake hardening duration. This is an advantageous behaviour for parts which can be installed in the car body assembly either at the surface or deep inside a multiple parts assembly because their yield strength remains similar. This offer flexibility for part design for car manufacturer.

TABLE-US-00005 TABLE 5 Coilling temperature 80° C. Rp0, 2 Rm Alloy temper T° C. Tps, min Strain (%) (MPa) (MPa) E T4 147 293 E T6C 160 5 0 169 310 E T8C 160 5 2 215 321 E T6D 160 20 0 194 326 E T8D 160 20 2 235 333

TABLE-US-00006 TABLE 6 Coiling temperature 100° C. Rp0, 2 Rm Alloy temper T° C. Tps, min Strain (%) (MPa) (MPa) E T4 174 317 E T6C 160 5 0 203 336 E T8C 160 5 2 249 349 E T6D 160 20 0 204 337 E T8D 160 20 2 247 346

Example 3

[0158] An ingot of the following composition was cast

[0159] An ingot with the chemical composition in table 7 (% by weight) was cast using a vertical semi continuous casting. The proportion of the others inevitable elements and impurities were lower than 0.05%, and the total is lower than 0.15%, the remainder is aluminium.

TABLE-US-00007 TABLE 7 Si Fe Cu Mn Mg Cr Ti 0.86 0.21 0.66 0.28 0.85 0.01 0.04

[0160] The rolling ingot were heated at 554° C. during 4 hours. The ingot was directly hot rolled. The temperature of the ingot just before the start of hot rolling was 540° C. The thickness at the end of hot rolling was 5 mm. The thickness at the end of cold rolling was 2 mm. The sheet was split in three in order to solutionize at three different temperatures, 535° C., 544° C. and with each a different duration above 525° C.: 20s, 45s and 68s. The sheets were quenched in 22° C. water. The sheets were pre aged by coiling the sheets at a temperature of 96° C. and cooling in open air followed by a natural ageing at room temperature about 20° C. during 3 days to obtain T4 temper rolled products.

[0161] The T4 rolled products were transformed into a T8A temper with a 2% strain and then heat treatment with a typical bake hardening heat treatment of 180° C. during 20 minutes. T8A samples were then characterized.

[0162] The T4 rolled product were also heat treated into a T6B temper with a heat treatment of 225° C. during 30 minutes. T6B samples were then characterized.

[0163] Tensile tests were done in the rolling direction (L), in the transverse direction to the rolling direction (T) and direction at 45° the rolling direction (45′).

TABLE-US-00008 TABLE 8 Solution HT ° C. Direction Temper YS, MPa UTS, MPa Ag % A % 535 L T4 183 309 22 26 535 T T4 171 304 25 27 535 45° T4 172 302 25 27 535 L T8A 303 369 17 21 535 T T8A 293 361 17 21 535 45° T8A 297 362 17 21 535 L T6B 356 380 7 11 535 T T6B 345 376 8 12 535 45° T6B 346 375 8 11 544 L T4 180 308 21 27 544 T T4 168 301 24 26 544 45° T4 170 300 25 28 544 L T8A 307 373 17 21 544 T T8A 300 366 17 21 544 45° T8A 304 367 17 21 544 L T6B 356 380 8 11 544 T T6B 344 376 8 11 544 45° T6B 344 376 8 12 559 L T4 183 312 22 27 559 T T4 172 304 24 26 559 45° T4 175 304 26 28 559 L T8A 305 371 17 21 559 T T8A 298 366 17 21 559 45° T8A 302 366 17 21 559 L T6B 360 382 8 11 559 T T6B 350 381 8 12 559 45° T6B 349 379 8 11

[0164] Table 8 shows the solution heat treatment is reliable to process variation about temperature or duration to obtain the mechanical properties.

[0165] T4 temper tensile yield strength shows an anisotropy of less than 3 MPa between the tensile yield strength in the T and 45° directions within the same rolled product as it can be seen in table 8.

[0166] Bending radius was also measured on T6B temper to check the crash behaviour of the rolled product. Results are disclosed in table 9.

TABLE-US-00009 TABLE 9 Solution Bending HT ° C. Direction Temper radius r/t 535 L T6B 0.889 544 L T6B 0.889 559 L T6B 1.016