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
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
• • 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
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
  • C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
• • 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
• • 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
  • C22F1/047—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 magnesium 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
  • C22F1/04—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
  • C22F1/05—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 of the Al-Si-Mg type, i.e. containing silicon and magnesium in approximately equal proportions
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
  • C30B25/18—Epitaxial-layer growth characterised by the substrate
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements

Definitions

• the present invention relates to an aluminum alloy sheet with excellent formability and paint bake hardenability and suitable as a material for transportation parts, in particular, as an automotive outer panel, and a method for producing the same.
• An automotive outer panel is required to have 1) formability, 2) shape fixability (shape of the press die is precisely transferred to the material by press working), 3) dent resistance, 4) corrosion resistance, 5) surface quality, and the like.
• Conventionally, 5000 series (Al—Mg) aluminum alloys and 6000 series (Al—Mg—Si) aluminum alloys have been applied to the automotive outer panel.
• the 6000 series aluminum alloy has attracted attention because high strength is obtained due to excellent paint bake hardenability, whereby further gage dawn and weight saving is expected. Therefore, various improvement have been made on the 6000 series aluminum alloy.
• the 6000 series aluminum alloy has problems relating to the surface quality after forming, such as occurrence of orange peel surfaces and ridging marks (long streak-shaped defects occurring in the rolling direction during plastic working).
• Surface quality defects can be solved by adjusting the alloy components, managing the production conditions, and the like.
• a method of preventing formation of coarse precipitates by homogenizing the alloy at a temperature of 500° C. or more, cooling the homogenized product to 450-350° C., and starting hot rolling in this temperature range has been proposed in order to prevent occurrence of ridging marks (see JP. 7-228956).
• the cooling rate is decreased when cooling the homogenized product from the homogenization temperature of 500° C. or more to the hot rolling temperature of 450° C., coarse Mg—Si compounds are formed. This makes it necessary to perform a solution treatment at a high temperature for a long time in the subsequent step, whereby production efficiency is decreased.
• the present inventors have examined for further improving formability, in particular, bendability of the 6000 series aluminum alloy.
• bendability of the 6000 series alloy is affected by the precipitation state of Mg—Si compounds and misorientation of adjacent crystal grains, and also found that bendability has a correlation with the Lankford value, and it is necessary to increase anisotropy of the Lankford values in order to improve bendability.
• bendability also has a correlation with the intensity ratio (random ratio) of cube orientation ⁇ 100 ⁇ ⁇ 001>of the texture, and it is necessary to allow the texture to have a high degree of integration of cube orientation in order to improve bendability.
• the present inventors have found that it is important to optimize the content of Si and Mg which are major elements of the 6000 series aluminum alloy, and to optimize the production steps, in particular, to appropriately control the cooling rate after homogenization of an ingot.
• An object of the present invention is to provide an aluminum alloy sheet having excellent formability which allows flat hemming, showing no orange peel surfaces and ridging marks after forming, having excellent paint bake hardenability capable of solving the problems relating to shape fixability and dent resistance, and with excellent corrosion resistance, in particular, filiform corrosion resistance, and a method for producing the same.
• An aluminum alloy sheet according to the present invention for achieving the above object is a 6000 series aluminum alloy sheet, with excellent bendability after a solution treatment and quenching, and has a minimum inner bending radius of 0.5 mm or less during 180° bending with 10% pre-stretch, even if the yield strength is further increased through natural aging.
• Specific embodiments of the aluminum alloy sheet are as follows.
• An aluminum alloy sheet comprising 0.5-1.5% of Si and 0.2-1.0% of Mg, with the balance consisting of Al and impurities, or comprising 0.8-1.2% of Si, 0.4-0.7% of Mg, and 0.1-0.3% of Zn, with the balance consisting of Al and impurities, in which the maximum diameter of Mg—Si compounds is 10 ⁇ m or less and the number of Mg—Si compounds having a diameter of 2-10 ⁇ m is 1000 per mm 2 or less.
• An aluminum alloy sheet comprising 0.4-1.5% of Si, 0.2-1.2% of Mg, and 0.05-0.3% of Mn, with the balance consisting of Al and impurities, in which the percentage of crystal grain boundaries in which misorientation of adjacent crystal grains is 15° or less is 20% or more.
• An aluminum alloy sheet comprising 0.5-2.0% of Si and 0.2-1.5% of Mg, with 0.7Si %+Mg % ⁇ 2.2%, and Si % ⁇ 0.58Mg % ⁇ 0.1% being satisfied and the balance consisting of Al and impurities, in which an anisotropy of Lankford values is more than 0.4.
• the anisotropy of Lankford values is (r0+r90 ⁇ 2 ⁇ r45)/2 (r0: r value of a tensile specimen collected in a direction at 0° to the rolling direction, r90: r value of a tensile specimen collected in a direction at 90° to the rolling direction, and r45: r value of a tensile specimen collected in a direction at 45° to the rolling direction).
• a method for producing an aluminum alloy sheet comprising homogenizing an ingot of an aluminum alloy having the above composition at a temperature of 450° C. or more, cooling the ingot to a temperature of 350-500° C. at a cooling rate of 100° C./h or more, starting hot rolling of the ingot at the temperature, cold rolling the hot-rolled product, and subjecting the cold-rolled product to a solution heat treatment at a temperature of 500° C. or more, and quenching.
• a method for producing an aluminum alloy sheet comprising homogenizing an ingot of an aluminum alloy having the above composition at a temperature of 450° C. or more, cooling the ingot to a temperature of less than 300° C. at a cooling rate of 100° C./h or more, heating the ingot to a temperature of 350-500° C. and starting hot rolling of the ingot, cold rolling the hot-rolled product, and subjecting the cold-rolled product to a solution heat treatment at a temperature of 500° C. or more, and quenching.
• a method for producing an aluminum alloy sheet comprising homogenizing an ingot of an aluminum alloy having the above composition at a temperature of 450° C. or more, cooling the ingot to a temperature of less than 300° C. at a cooling rate of 100 ⁇ C./h or more, cooling the ingot to room temperature, heating the ingot to a temperature of 350-500° C. and starting hot rolling of the ingot, cold rolling the hot-rolled product, and subjecting the cold-rolled product to a solution heat treatment at a temperature of 500° C. or more, and quenching.
• a method for producing an aluminum alloy sheet comprising homogenizing an ingot of an aluminum alloy having the above composition at a temperature of 450° C. or more, cooling the ingot to a temperature of less than 350° C. at a cooling rate of 100° C./h or more, hot rolling the ingot at the temperature, cold rolling the hot-rolled product, and subjecting the cold-rolled product to a solution heat treatment at a temperature of 450° C. or more, and quenching.
• a method for producing an aluminum alloy sheet comprising homogenizing an ingot of an aluminum alloy having the above composition at a temperature of 450° C. or more, cooling the ingot to a temperature of less than 350° C. at a cooling rate of 100° C./h or more, heating the ingot to a temperature of 300-500° C. and starting hot rolling of the ingot, cold rolling the hot-rolled product, and subjecting the cold-rolled product to a solution heat treatment at a temperature of 450° C. or more, and quenching.
• a method for producing an aluminum alloy sheet comprising homogenizing an ingot of an aluminum alloy having the above composition at a temperature of 450° C. or more, cooling the ingot to a temperature of less than 350° C. at a cooling rate of 100° C./h or more, cooling the ingot to room temperature, heating the ingot to a temperature of 300-500° C. and starting hot rolling of the ingot, cold rolling the hot-rolled product, and subjecting the cold-rolled product to a solution heat treatment at a temperature of 450° C. or more, and quenching.
• Si is necessary to obtain strength and high paint bake hardenability (BH), and increases strength by forming Mg—Si compounds.
• the Si content is preferably 0.5-2.0%. If the Si content is less than 0.5%, sufficient strength may not be obtained by heating during baking and formability may be decreased. If the Si content exceeds 2.0%, formability and shape fixability may be insufficient due to high yield strength during press working. Moreover, corrosion resistance may be decreased after painting.
• the Si content is more preferably 0.4-1.5%, still more preferably 0.5-1.5%, yet more preferably 0.6-1.3%, and particularly preferably 0.8-1.2%.
• Mg increases strength in the same manner as Si.
• the Mg content is preferably 0.2-1.5%. If the Mg content is less than 0.2%, sufficient strength may not be obtained by heating during baking. If the Mg content exceeds 1.5%, yield strength may remain high after a solution heat treatment or additional heat treatment, whereby formability and spring-back properties may be insufficient.
• the Mg content is more preferably 0.2-1.2%, still more preferably 0.2-1.0%, yet more preferably 0.3-0.8%, and particularly preferably 0.4-0.7%.
• Si and Mg are preferably added to satisfy the relations 0.7Si %+Mg % ⁇ 2.2%, and Si % ⁇ 0.58Mg % ⁇ 0.1% so that anisotropy of the Lankford values is more than 0.4 and bendability is improved.
• Si and Mg are preferably added to satisfy the relation 0.7Si %+Mg % ⁇ 2.2%.
• Zn improves zinc phosphate treatment properties during the surface treatment.
• the Zn content is preferably 0.5% or less. If the Zn content exceeds 0.5%, corrosion resistance may be decreased.
• the Zn content is still more preferably 0.1-0.3%.
• Cu improves strength and formability.
• the Cu content is preferably 1.0% or less. If the Cu content exceeds 1.0%, corrosion resistance may be decreased.
• the Cu content is still more preferably 0.3-0.8%. If corrosion resistance is an important, the Cu content is preferably limited to 0.1% or less.
• Mn, Cr, V, and Zr improve strength and refine crystal grains to prevent occurrence of orange peel surfaces during forming.
• the content of Mn, Cr, V, and Zr is preferably 1.0% or less, 0.3% or less, 0.29% or less, and 0.2% or less, respectively. If the content of Mn, Cr, V, and Zr exceeds the above upper limits, coarse intermetallic compounds may be formed, whereby formability may be decreased.
• the content of Mn and Zr is more preferably 0.3% or less and 0.15% or less, respectively.
• the content of Mn, Cr, V, and Zr is still more preferably 0.05-0.3%, 0.05-0.15%, 0.05-0.15%, and 0.05-0.15%, respectively.
• Mn is added in an amount of 0.05-0.3% as an essential component.
• Ti and B refine a cast structure to improve formability.
• the content of Ti and B is preferably 0.1% or less and 50 ppm or less, respectively. If the content of Ti and B exceeds the above upper limits, the number of coarse intermetallic compounds may be increased, whereby formability may be decreased. It is preferable to limit the Fe content to 0.5% or less, and preferably 0.3% or less as another impurity.
• Homogenization condition Homogenization must be performed at a temperature of 450° C. or more. If the homogenization temperature is less than 450° C., removal of ingot segregation and homogenization may be insufficient. This results in insufficient dissolution of Mg 2 Si components which contribute to strength, whereby formability may be decreased. Homogenization is preferably performed at a temperature of 480° C. or more.
• Cooling after homogenization Good properties are obtained by cooling the homogenized product at a cooling rate of preferably 100° C./h or more, and still more preferably 300° C./h or more. Since large-scale equipment is necessary for increasing the cooling rate, it is preferable to manage the cooling rate in the range of 300-1000° C./h in practice. If the cooling rate is low, Mg—Si compounds are precipitated and coarsened. In a conventional cooling method, the cooling rate is about 30° C./h in the case of cooling a large slab. However, Mg—Si compounds are precipitated and coarsened during cooling at such a low cooling rate, whereby the material may not be provided with improved bendability after the solution heat treatment and quenching.
• the cooling after homogenization must allow the temperature to be decreased to less than 350° C., and preferably less than 300° C. at a cooling rate of 100° C./h or more, preferably 150° C./h or more, and still more preferably at 300° C./h or more.
• the properties are affected if a region at 350° C. or more is partially present. Therefore, an ingot is cooled until the entire ingot is at 300° C. or less, and preferably 250° C. or less at the above cooling rate.
• the cooling start temperature is not necessarily the homogenization temperature.
• the same effect can be obtained by allowing the ingot to be cooled to a temperature at which precipitation does not significantly occur, and starting cooling at a cooling rate of 100° C./h or more.
• the ingot may be slowly cooled to 500° C.
• Hot rolling The ingot is cooled to a specific temperature of 350-500° C. or 300-450° C. from the homogenization temperature, and hot rolling is started at the specific temperature.
• the ingot may be cooled to a specific temperature of 350° C. or less from the homogenization temperature, and hot rolling may be started at the specific temperature.
• the ingot may be cooled to a temperature of 350° C. or less and heated to a temperature of 300-500° C., and hot rolling may be started at this temperature.
• the ingot may be cooled to a temperature of 350° C. or less, cooled to room temperature, heated to a temperature of 300-500° C., and hot-rolled at this temperature.
• the hot rolling start temperature is less than 300° C., deformation resistance is increased, whereby rolling efficiency is decreased. If the hot rolling start temperature exceeds 500° C., crystal grains coarsen during rolling, whereby ridging marks readily occur in the resulting material. Therefore, it is preferable to limit the hot rolling start temperature to 300-500° C.
• the hot rolling start temperature is still more preferably 380-450° C. taking into consideration deformation resistance and uniform microstructure.
• the hot rolling finish temperature is preferably 300° C. or less. If the hot rolling finish temperature exceeds 300° C., precipitation of Mg—Si compounds easily occurs, whereby formability may be decreased. Moreover, recrystallized grains coarsen, thereby resulting in occurrence of ridging marks. Hot rolling is preferably finished at 200° C. or more taking into consideration deformation resistance during hot rolling and residual oil stains due to a coolant.
• Cold rolling The hot rolled sheet is cold rolled to the final gage.
• Solution heat treatment The solution heat treatment temperature is preferably 450° C. or more, and still more preferably 500° C. or more. If the solution heat treatment temperature is less than 500° C., dissolution of Mg—Si precipitates may be insufficient, whereby sufficient strength and formability cannot be obtained, or heat treatment for a considerably long time is needed to obtain necessary strength and formability. This is disadvantageous from the industrial point of view. There are no specific limitations to the solution heat treatment time insofar as necessary strength is obtained. The solution heat treatment time is usually 120 seconds or less from the industrial point of view.
• Cooling rate during quenching It is necessary to cool the sheet from the solution treatment temperature to 120° C. or less at a cooling rate of 5° C./s or more. It is preferable to cool the sheet at a cooling rate of 10° C./s or more. If the quenching cooling rate is too low, precipitation of eluted elements occurs, whereby strength, BH, formability, and corrosion resistance may be decreased.
• Reversion treatment may be performed at a temperature of 170-230° C. for 60 seconds or less within seven days after final additional heat treatment. Paint bake harden ability is further improved by the reversion treatment.
• a sheet material with excellent bendability after the solution heat treatment and quenching can be obtained by applying the above production steps to an aluminum alloy having the above composition.
• the aluminum alloy sheet is suitably used as a lightweight automotive member having a complicated shape which is subjected to hemming, such as a hood, trunk lid, and door.
• the aluminum alloy sheet can be subjected to severe working in which the bending radius is small due to its excellent bendability after pressing the sheet into a complicated shape. Therefore, the aluminum alloy sheet widens the range of application of aluminum materials to automotive materials, thereby contributing to a decrease in the weight of vehicles.
• Aluminum alloys having compositions shown in Table 1 were cast by using a DC casting method.
• the resulting ingots were homogenized at 540° C. for six hours and cooled to room temperature at a cooling rate of 300° C./h.
• the cooled ingots were heated to a temperature of 400° C., and hot rolling was started at this temperature.
• the ingots were rolled to a thickness of 4.0 mm, and cold-rolled to a thickness of 1.0 mm.
• the cold-rolled sheets were subjected to a solution heat treatment at 540° C. for five seconds, quenched to a temperature of 120° C. at a cooling rate of 30° C./s, and additional heat treated at 100° C. for three hours after five minutes.
• the final heat treated sheets were used as test materials. Tensile properties, formability, corrosion resistance, and bake hardenability were evaluated when 10 days were passed after the final heat treatment, and the maximum diameter of Mg—Si compounds and the number of compounds having a diameter of 2-10 ⁇ m were measured according to the following methods. The tensile properties and a minimum bending radius for formability were also evaluated when four months were passed after the final heat treatment. The results are shown in Tables 2 and 3.
• Tensile property Tensile strength ( ⁇ B ), yield strength ( ⁇ 0.2 ), and elongation ( ⁇ ) were measured by performing a tensile test.
• Formability An Erichsen test (EV) was performed. A test material having a forming height of less than 10 mm was rejected. A 180° bending test for measuring the minimum bending radius after applying 10% tensile pre-strain was performed in order to evaluate hem workability. A test material having a minimum inner bending radius of 0.5 mm or less was accepted.
• EV Erichsen test
• Corrosion resistance The test material was subjected to a zinc phosphate treatment and electrodeposition coating using commercially available chemical treatment solutions. After painting crosscuts reaching the aluminum base material, a salt spray test was performed for 24 hours according to JIS Z2371. After allowing the test material to stand in a wet atmosphere at 50° C. and 95% for one month, the maximum length of filiform corrosion occurring from the crosscuts was measured. A test material having a maximum length of filiform corrosion of 4 mm or less was accepted.
• Bake hardenability Yield strength ( ⁇ 0.2) was measured after applying 2% tensile deformation and performing heat treatment at 170° C. for 20 minutes. A test material having a yield strength of 200 MPa or more was accepted.
• test materials Nos. 1 to 7 according to The present invention showed excellent BH of more than 200 MPa in the BH evaluation.
• the test materials Nos. 1 to 7 had excellent formability in which the forming height (EV) was more than 10 mm and the minimum inner bending radius was 0.5 mm or less.
• the test materials Nos. 1 to 7 exhibited excellent corrosion resistance in which the maximum length of filiform corrosion was 4 mm or less.
• Example 4 Aluminum alloys having compositions shown in Table 4 were cast by using a DC casting method. The resulting ingots were treated by the same steps as in Example 1 to obtain cold-rolled sheets with a thickness of 1 mm. The cold-rolled sheets were subjected to a solution heat treatment and quenching under the same conditions as in Example 1, and heat treatment at 100° C. for three hours after five minutes.
• the final heat treated sheets were used as test materials. Tensile properties, formability, corrosion resistance, and bake hardenability of the test materials were evaluated when 10 days were passed after final heat treatment, and the maximum diameter of Mg—Si compounds and the number of compounds having a diameter of 2-10 ⁇ m were measured according to the same methods as in Example 1. The tensile properties and the minimum inner bending radius for formability evaluation were also evaluated when four months were passed after the final heat treatment. The results are shown in Tables 5 and 6.
• test material No. 8 and test material No. 10 showed insufficient BH due to low Si content and low Mg content, respectively.
• Test material No. 9 and test material No. 11 had insufficient bendability due to high Si content and high Mg content, respectively.
• Test material No. 12 had inferior filiform corrosion resistance due to high Cu content.
• Test materials Nos. 13 to 16 had a small forming height (EV) due to high Mn content, high Cr content, high V content, and high Zr content, respectively. Moreover, these test materials showed insufficient bendability.
• Ingots of the alloys Nos. 1 and 3 of Example 1 were homogenized at 540° C. for eight hours.
• the ingots were cooled to the hot rolling temperature after homogenization, and hot rolling was started at the temperatures shown in Table 7.
• the thickness of hot-rolled products was 4.5 mm.
• the hot-rolled products were cold-rolled to a thickness of 1 mm, subjected to a solution heat treatment under the conditions shown in Table 7, quenched to 120° C. at a cooling rate of 15° C./s, and additional heat treatment at 90° C. for five hours after 10 minutes.
• Example 2 and Comparative Example 2 the ingots were cooled to the hot rolling temperature after homogenization, and hot rolling was performed at this temperature.
• the final heat treated sheets were used as test materials. Tensile properties, formability, corrosion resistance, and bake hardenability of the test materials were evaluated when 10 days were passed after final heat treatment, and the maximum diameter of Mg—Si compounds and the number of compounds having a diameter of 2-10 ⁇ m were measured according to the same methods as in Example 1. The tensile properties and the minimum bending radius for formability evaluation were also evaluated when four months were passed after the final heat treatment. Electro deposition coating was performed after applying 10% tensile deformation in the direction at 90° to the rolling direction. The presence or absence of ridging marks was evaluated with the naked eye.
• test materials Nos. 17 to 21 according to the present invention showed excellent tensile strength, BH, formability, and corrosion resistance, and maintained excellent bendability after natural aging for four months.
• Test materials Nos. 22, 23, and 26 had low tensile strength since the cooling rate after homogenization was low. Moreover, these test materials showed insufficient BH. Ridging marks occurred in test material No. 24 due to grain growth during hot rolling since the hot rolling temperature was high.
• Test material No.25 had a low tensile strength and inferior BH due to a low solution heat treatment temperature.
• Aluminum alloys having compositions shown in Table 10 were cast by using a DC casting method.
• the resulting ingots were homogenized at 540° C. for six hours and cooled to room temperature at a cooling rate of 300° C./h.
• the ingots were then heated to a temperature of 400° C. Hot rolling was started at this temperature.
• the ingots were hot-rolled to a thickness of 4.0 mm, and cold-rolled to a thickness of 1.0 mm.
• the cold-rolled sheets were subjected to a solution heat treatment at 540° C. for five seconds, quenched to a temperature of 120° C. at a cooling rate of 30° C./s, and additional heat treated at 90° C. for three hours after five minutes.
• the final heat treated sheets were used as test materials. Tensile properties, formability, corrosion resistance, and bake hardenability of the test materials were evaluated when 10 days were passed after final heat treatment, and the maximum diameter of Mg—Si compounds and the number of compounds having a diameter of 2-10 ⁇ m were measured according to the same methods as in Example 1. The tensile properties and the minimum bending radius for formability evaluation were also evaluated when four months were passed after the final heat treatment. The results are shown in Tables 11 and 12.
• test materials Nos. 27 to 32 according to the present invention showed excellent BH of more than 200 MPa in the BH evaluation.
• the test materials Nos. 27 to 32 had excellent formability in which the forming height (EV) was more than 10 mm and the minimum inner bending radius was 0.2 mm or less.
• the test materials Nos. 27 to 32 exhibited excellent corrosion resistance in which the maximum length of filiform corrosion was 2 mm or less.
• test material No. 33 and test material No. 35 showed insufficient BH due to low Si content and low Mg content, respectively.
• Test material No. 34 and test material No. 36 exhibited insufficient bendability due to high Si content and high Mg content, respectively.
• Test materials Nos. 37 and 38 exhibited inferior filiform corrosion resistance due to low Zn content and high Zn content, respectively.
• Test material No.39 had a small forming height (EV) due to high Fe content. Moreover, the test material No.39 showed insufficient bendability.
• Ingots of the alloy No.17 of Example 3 were homogenized at 540° C. for five hours.
• the ingots were cooled and hot-rolled to a thickness of 5.0 mm under conditions shown in Table 13.
• the hot-rolled products were cold-rolled to a thickness of 1.0 mm, subjected to a solution heat treatment under conditions shown in Table 13, quenched to 120° C. at a cooling rate of 150° C./s, and additional heat treated at 80° C. for two hours after five minutes.
• Example 4 and Comparative Example 4 the ingots were cooled to the hot rolling temperature after homogenization, and hot rolling was started at this temperature.
• the final heat treated sheets were used as test materials. Tensile properties, formability, corrosion resistance, and bake hardenability of the test materials were evaluated when 10 days were passed after final heat treatment, and the maximum diameter of Mg—Si compounds and the number of compounds having a diameter of 2-10 ⁇ m were measured according to the same methods as in Example 1. The tensile properties and the minimum bending radius for formability evaluation were also evaluated when four months were passed after the final heat treatment. Electrodeposition coating was performed after applying 10% tensile deformation in the direction at 90° to the rolling direction. The presence or absence of ridging marks was evaluated with the naked eye. The results are shown in Tables 14 and 15.
• test materials Nos. 40 to 42 according to the present invention showed excellent tensile strength, BH, formability, and corrosion resistance, and maintained excellent bendability after natural aging for four months.
• Test material No. 43 had low tensile strength and insufficient BH since the cooling rate after homogenization was low. Ridging marks occurred in test material No. 44due to texture growth during hot rolling, since the hot rolling temperature was high.
• Test material No. 45 had a low tensile strength and inferior BH due to a low solution treatment temperature.
• Aluminum alloys having compositions shown in Table 16 were cast by using a DC casting method.
• the resulting ingots were homogenized at 540° C. for six hours and cooled to room temperature at a cooling rate of 300° C./h.
• the ingots were heated to a temperature of 400° C., and hot rolling was started at this temperature.
• the ingots were hot-rolled to a thickness of 4.0 mm, and cold-rolled to a thickness of 1.0 mm.
• the cold-rolled sheets were subjected to a solution heat treatment at 540° C. for five seconds, quenched to a temperature of 120° C. at a cooling rate of 30° C./s, and additional heat treated at 100° C. for three hours after five minutes.
• Measurement of misorientation distribution of crystal grain boundaries The surface of the test material was ground using emery paper and mirror-ground by electrolytic grinding. The test material was set in a scanning electron microscope (SEM). The tilt angle distributions of the crystal grain boundaries were measured by measuring the crystal grain orientation at a pitch of 10 ⁇ m using an EBSP device installed in the SEM at an observation magnification of 100 times to calculate the percentage of crystal grain boundaries at 15° or less.
• SEM scanning electron microscope
• test materials Nos. 46 to 53 showed excellent BH of more than 200 MPa in the BH evaluation.
• the test materials Nos. 46 to 53 had excellent formability in which the forming height (EV) was more than 10 mm and the minimum inner bending radius was 0.2 mm or less.
• the test materials Nos. 46 to 53 exhibited excellent corrosion resistance in which the maximum length of filiform corrosion was 4 mm or less.
• Aluminum alloys having compositions shown in Table 18 were cast by using a DC casting method.
• the resulting ingots were treated by the same steps as in Example 5 to obtain cold-rolled sheets with a thickness of 1.0 mm.
• the cold-rolled sheets were subjected to a solution heat treatment and quenched under the same conditions as in Example 1.
• the quenched products were additional heat treated at 100° C. for three hours after five minutes.
• test material No. 54 and test material No. 56 exhibited insufficient BH due to low Si content and low Mg content, respectively.
• Test material No.55 and test material No. 57 exhibited insufficient bendability due to high Si content and high Mg content, respectively.
• Test material No. 58 and test material No. 59 showed inferior filiform corrosion resistance due to high Zn content and high Cu content, respectively.
• Test materials Nos. 60 to 63 had a small forming height (EV) and insufficient bendability due to high Mn content, high Cr content, high V content, and high Zr content, respectively.
• Test material No. 64 exhibited insufficient bendability since the percentage of crystal grain boundaries in which misorientation of adjacent crystal grains was 15° or less was less than 20% due to low Mn content.
• Ingots of the alloy No. 30 shown in Table 16 used in Example 5 were subjected to homogenization, hot rolling, cold rolling, solution heat treatment, additional heat treatment, and reversion treatment under conditions shown in Table 20 to obtain test materials Nos. 65 to 71.
• the ingots were cooled to the hot rolling temperature after homogenization, and hot rolling was started at this temperature.
• the homogenization time was six hours
• the thickness of the hot-rolled sheet was 4.0 mm
• the thickness of the cold-rolled sheet was 1.0 mm
• the period of time between quenching and additional heat treatment was five minutes.
• the test material No. 65 was subjected to the reversion treatment at 200° C. for three seconds after the additional heat treatment. The reversion treatment was performed when one day was passed after the additional heat treatment.
• Time material Alloy (° C.) (° C./h) (° C.) (° C.) (s) (° C./s) (° C.) (h) 65 30 540 300 400 550 5 30 100 3 66 30 520 300 400 550 5 30 100 3 67 30 540 200 400 550 5 30 100 3 68 30 540 300 450 550 5 30 100 3 69 30 540 300 400 520 30 30 100 3 70 30 540 300 400 550 5 10 100 3 71 30 540 300 400 550 10 30 60 5
• test materials Nos. 65 to 71 according to The present invention showed excellent tensile strength, BH, formability, and corrosion resistance. Moreover, occurrence of ridging marks was not observed at all.
• Ingots of the alloy No. 30 shown in Table 16 used in Example 5 were subjected to homogenization, hot rolling, cold rolling, solution heat treatment, additional heat treatment, and reversion treatment under conditions shown in Table 22 to obtain test materials Nos. 72 to 80.
• the ingots were cooled to the hot rolling temperature after homogenization, and hot rolling was started at this temperature.
• the homogenization time was six hours
• the thickness of the hot-rolled sheet was 4.0 mm
• the thickness of the cold-rolled sheet was 1.0 mm
• the period of time between quenching and additional heat treatment was five minutes.
• the test material No. 80 was subjected to the reversion treatment at 300° C. for 30 seconds. The reversion treatment was performed when one day was passed after the additional heat treatment.
• Time material Alloy (° C.) (° C./h) (° C.) (° C.) (s) (° C./s) (° C.) (h) 72 30 450 300 400 550 5 30 100 3 73 30 540 100 400 560 10 30 100 3 74 30 540 50 400 560 20 30 100 3 75 30 540 300 500 550 5 30 100 3 76 30 540 300 400 470 10 30 100 3 77 30 540 300 400 550 5 1 100 3 78 30 540 300 400 550 5 30 — — 79 30 540 300 400 550 5 30 140 72 80 30 540 300 400 550 5 30 100 3
• the test material No. 72 had low EV and insufficient bendability due to a low homogenization temperature. Moreover, the test material No.72 showed inferior BH. The test materials Nos. 73 and 74 showed insufficient bendability and inferior BH due to a low cooling rate after homogenization. Ridging marks occurred in the test material No. 75 due to inferior bendability since the hot rolling start temperature was high.
• the test material No.76 had low strength and low EV due to a low solution treatment temperature. Moreover, the test material No. 76 had low BH. The test material No. 77 showed insufficient EV, bendability, and corrosion resistance due to a low quenching rate after the solution heat treatment. Moreover, the test material No.
• the test material No. 78 had low BH since additional heat treatment was not performed.
• the test material No. 79 had low EV since the additional heat treatment was performed at a high temperature for a long period of time.
• the test material No. 80 had low strength and low BH since the reversion treatment temperature was high. Moreover, the test material No. 80 had low EV.
• Aluminum alloys having compositions shown in Table 24 were cast by using a DC casting method.
• the resulting ingots were homogenized at 550° C. for six hours and cooled to 200° C. at a cooling rate of 600° C./h.
• the ingots were cooled to room temperature, heated to 420° C., and hot-rolled to a thickness of 4.5 mm.
• the hot rolling finish temperature was 250° C.
• the hot-rolled products were cold-rolled to a thickness of 1.0 mm.
• the cold-rolled sheets were subjected to a solution heat treatment at 540° C. for 20 seconds and quenched to 120° C. at a cooling rate of 30° C./s.
• the quenched sheets were additional heat treated at 100° C. for three hours after three minutes.
• Tensile performance Tensile specimens were collected in three directions (at 0°, 45°, and 90° to the rolling direction), and subjected to a tensile test to determine average values of tensile strength, yield strength, and elongation as the tensile performance.
• Bake hardenability Yield strength was measured after applying 2% tensile deformation in the rolling direction and performing heat treatment at 170° C. for 20 minutes. A test material having a yield strength of 200 MPa or more was accepted.
• test materials Nos. 81 to 87 according to the present invention excelled in strength and BH, had anisotropy of the Lankford values of more than 0.4, and showed excellent minimum bending properties. Bendability after natural aging for four months was evaluated. As a result, the test materials of all the alloys had a minimum bending radius of 0.0 ⁇ 0.1.
• Aluminum alloys having compositions shown in Table 26 were cast by using a DC casting method. The resulting ingots were treated by the same steps as in Example 7. Tensile performance, anisotropy of Lankford values, bake hardenability (BH), and bendability of the aluminum alloy sheets were evaluated according to the same methods as in Example 7 when 10 days were passed after the final heat treatment. The results are shown in Table 27.
• test material No. 88 and test material No. 90 exhibited low strength and insufficient BH due to low Si content and low Mg content, respectively.
• Test material No. 89 had high strength due to high Si content, whereby anisotropy of Lankford values was decreased and bendability was insufficient
• Test material No. 91 had a small anisotropy of Lankford values since the value for (Si % ⁇ 0.58Mg %) was smaller than 0.1%, whereby minimum bendability was insufficient.
• Test material No. 92 had a small anisotropy of Lankford values since (0.7Si %+Mg %) exceeded 2.2%, whereby bendability was insufficient.
• Test materials No. 93 to 97 had a small anisotropy of Lankford values due to high Cu content, high Mn content, high Cr content, high V content, and high Zr content, respectively, whereby bendability was insufficient.
• the alloy No. 50 shown in Table 24 was cast by using a DC casting method.
• the resulting ingots were homogenized at 540° C. for 10 hours and cooled to 250° C. at cooling rates shown in Table 28.
• the ingots were then cooled to room temperature.
• the ingots were heated to the temperatures shown in Table 28 and hot-rolled to a thickness of 4.2 mm.
• the hot rolling finish temperature was 280° C.
• the hot-rolled products were cold-rolled to obtain sheets with a thickness of 1.0 mm. only test material No. 107 was cold-rolled to a thickness of 3.0 mm and subjected to process annealing at 450° C. for 30 seconds.
• the cold-rolled sheets were subjected to a solution heat treatment at 550° C. for 10 seconds and quenched to 120° C. at a cooling rate of 30° C./s.
• the quenched sheets were additional heat treated at 100° C. for three hours after three minutes.
• Tensile performance, anisotropy of Lankford values, BH, and bendability of the aluminum alloy sheets obtained by these steps were evaluated according to the same methods as in Example 7.
• test materials Nos. 98 to 102 according to The present invention excelled in strength and BH, had an anisotropy of Lankford values of more than 0.4, and showed excellent minimum bending properties.
• test material Nos. 103 and 104 due to a high hot rolling temperature.
• Test material No. 105 had a small anisotropy of Lankford values due to a low cooling rate after homogenization, whereby bendability was insufficient.
• Ridging marks occurred in test material No. 106 due to a high hot rolling temperature and a low cooling rate after homogenization.
• the test material No. 106 had a small anisotropy of Lankford values, whereby bendability was insufficient.
• Test material No. 107 had a small anisotropy of Lankford values since process annealing was performed, whereby bendability was insufficient.
• the alloy No. 50 shown in Table 24 was cast by using a DC casting method.
• the resulting ingots were homogenized at 550° C. for eight hours and cooled to 200° C. at a cooling rate of 500° C./h.
• the ingots were cooled to room temperature, heated to 400° C., and hot-rolled to a thickness of 4.2 mm.
• the hot rolling finish temperature was 260° C.
• the hot-rolled products were cold-rolled to obtain sheets with a thickness of 1.0 mm.
• the cold-rolled sheets were subjected to a solution heat treatment at 550° C. for four seconds and quenched to 120° C. at a cooling rate of 40° C./s.
• the quenched sheets were additional heat treated at 100° C. for two hours after two minutes.
• Aluminum alloys having compositions shown in Table 31 were cast by using a DC casting method.
• the resulting ingots were homogenized at 550° C. for six hours and cooled to 200° C. at a cooling rate of 450° C./h.
• the ingots were then cooled to room temperature, heated to 420° C., and hot-rolled to a thickness of 4.5 mm.
• the hot rolling finish temperature was 250° C.
• the hot-rolled products were cold-rolled to obtain sheets with a thickness of 1.0 mm.
• the cold-rolled sheets were subjected to a solution heat treatment at 540° C. for 20 seconds and quenched to 120° C. at a cooling rate of 30° C./s.
• the sheets were additional heat treated at 100° C. for three hours after three minutes.
• Intensity ratio of cube orientation The intensity ratio of cube orientation was calculated by a series expansion method proposed by Bunge using an ODF analysis device in which the expansion order of even-numbered terms was 22 and the expansion order of odd-numbered terms was 19.
• Bake hardenability Yield strength was measured after applying 2% tensile deformation and performing heat treatment at 170° C. for 20 minutes. A test material having a yield strength of 200 MPa or more was accepted.
• test materials Nos.108 to 114 according to The present invention excelled in strength and BH, had an intensity ratio of cube orientation of more than 20, and showed excellent minimum bending properties. Bendability after natural aging for four months was measured. As a result, the test materials of all the alloys had a minimum bending radius of 0.4 or less although the yield strength exceeded 160 MPa.
• Aluminum alloys having compositions shown in Table 33 were cast by using a DC casting method. The resulting ingots were treated by the same steps as in Example 10. Tensile performance, bake hardenability (BH), intensity ratio of cube orientation, and bendability of the aluminum alloy sheets were evaluated according to the same methods as in Example 10 when 10 days were passed after the final heat treatment. The results are shown in Table 34.
• test material No. 115 and test material No. 117 had low strength and insufficient BH due to low Si content and low Mg content, respectively.
• Test material No. 116 and test material No. 118 showed high strength since (0.7Si %+Mg %) exceeded 2.2% due to high Si content and high Mg content, respectively. As a result, the degree of integration of cube orientation was decreased, whereby bendability was insufficient.
• the alloy No. 67 shown in Table 31 was cast by using a DC casting method.
• the resulting ingots were homogenized at 550° C. for five hours and cooled to 250° C. at a cooling rate shown in Table 35.
• the ingots were heated to a temperature shown in Table 35 and hot-rolled to a thickness of 4.4 mm.
• the hot rolling finish temperature was 250° C.
• the hot-rolled products were cold-rolled to obtain sheets with a thickness of 1.0 mm.
• Annealing process was performed at 400° C. for two hours after hot rolling under a condition “t”.
• the sheets were subjected to a solution heat treatment at 550° C. for five seconds and quenched to 120° C. at a cooling rate of 30° C./s. The quenched sheets were additional heat treated at 100° C. for three hours after three minutes.
• Tensile performance, BH, intensity ratio of cube orientation, and bendability of the aluminum alloy sheets obtained by these steps were evaluated according to the same methods as in Example 10.
• ridging marks For the evaluation of ridging marks, tensile specimens were collected in the direction at 90° to the rolling direction and subjected to 10% tensile deformation and electrodeposition coating. The presence or absence of ridging marks was then evaluated.
• test materials Nos. 124 to 128 according to The present invention excelled in strength and BH, had an intensity ratio of cube orientation of more than 20, and showed excellent minimum bending properties.
• test material Nos. 129 and 130 due to a high hot rolling temperature.
• Test material No. 131 had a small degree of integration of cube orientation due to a low cooling rate after homogenization, whereby bendability was insufficient.
• Ridging marks occurred in test material No. 132 due to a high hot rolling temperature and a low cooling rate after homogenization.
• the test material No. 132 had a small degree of integration of cube orientation, whereby bendability was insufficient.
• Test material No. 133 had a small degree of integration of cube orientation since process annealing was performed, whereby bendability was insufficient.
• an aluminum alloy sheet having excellent bendability which allows flat hemming, excellent bake hardenability, and excellent corrosion resistance, and a method for producing the same can be provided.
• the aluminum alloy sheet is suitably used as a lightweight automotive member having a complicated shape which is subjected to hemming, such as an automotive hood, trunk lid, and door.

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