JP2006241548A - Al-Mg-Si ALLOY SHEET SUPERIOR IN BENDABILITY, MANUFACTURING METHOD THEREFOR, AND AUTOMOTIVE SKIN PLATE OBTAINED FROM THE SHEET - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al-Mg-Si alloy sheet which inhibits a crack from occurring when being bent after having been press-formed, and has enough superior bendability after having been press-formed to be applied to an automotive skin plate. <P>SOLUTION: This sheet is a T4-tempered material of a continuously cast-rolled plate of an aluminum alloy having a composition comprising 0.4-1.5% Si, 0.2-1.2% Mg, 1.0% or less Fe as an impurity, and the balance Al with unavoidable impurities; and includes an Al-Fe-Si compound coexisting with a Mg<SB>2</SB>Si compound in an amount of 50% or less by a ratio with respect to all Al-Fe-Si compounds existing in the sheet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is an aluminum alloy sheet T4 tempered material produced by a molten metal rolling method (also referred to as a continuous casting rolling method), particularly an Al—Mg—Si based aluminum alloy sheet material excellent in bending workability, and a method for producing the same. The present invention relates to an automobile outer plate obtained from the plate material.

  Conventionally, 5000 series alloys (Al-Mg series alloys) have been used as aluminum alloy sheet materials for automobile outer plates. 5000 series alloys are excellent in strength and ductility and show good formability. However, as the Mg content increases, hot workability deteriorates and SS marks (stretcher / strain marks) tend to occur during forming. In recent years, the use of 6000 series alloys (Al-Mg-Si alloys) has been expanding because of the appearance defects.

  The 6000 series alloy has excellent formability, and the strength is increased by performing the coating baking process, and the dent resistance is excellent, but there is a problem that the cost is higher than that of the cold-rolled steel sheet, and the range of use is limited. Limited. For this reason, in the 6000 series alloy, reduction of manufacturing cost has been an issue, and studies have been conducted on low-cost manufacturing processes that replace the conventional DC casting / hot rolling method.

As a process replacing the conventional DC casting / hot rolling method, the production of a plate material by a twin roll molten metal rolling method has been proposed. For example, the maximum length of a continuous crystallized material in the metal structure of the surface layer portion is 50 μm or less. By making it, the method (patent document 1) which obtains 6000 type | system | group board | plate material excellent in the moldability and surface property, and Al-Mg-Si alloy molten metal with which content, such as Mg, Si, and Mn, is prescribed | regulated is 150 degreeC. Continuous casting at a solidification rate of at least / sec. After cold rolling to a predetermined plate thickness, solution treatment is performed at 520 to 560 ° C., and quenching within 30 seconds is excellent in strength, formability, etc. A method for obtaining an Al—Mg—Si based alloy sheet (Patent Document 2) has been proposed. In addition, an Al—Mg—Si alloy containing a specific amount of Mg, Si, Fe, etc. is continuously cast, cold rolled after hot rolling, the maximum length of the insoluble compound is 2 μm or less, and its volume fraction By controlling the rate to 2.0% or less, the crack limit in press formability is high, the bake coating curability is excellent, and Al-Mg for automobile panels that can be applied to the continuous casting / direct rolling method. A technical technique for obtaining a Si-based alloy plate has also been proposed (Patent Document 3).
JP-A-10-130766 Japanese Patent Laid-Open No. 10-259464 Japanese Patent Application Laid-Open No. 07-252570

  However, the present inventors made a 6000 series aluminum alloy sheet according to the above-described technical technique and examined its characteristics. In general, although an aluminum alloy sheet having excellent formability is obtained, Special molding for use as an automobile outer plate, that is, if the bending process (also called hem processing) is performed so that the inner material is wrapped around the outer periphery after pressing, cracks occur on the surface of the bending process, and the outside of the automobile body It was recognized that there was a quality problem for use on the board.

In order to elucidate the above problems, the inventors have studied the crack generation mechanism during bending of a 6000 series aluminum alloy molten rolled material, and as a result, the Al-Fe-Si based compound present in the plate material has been studied. Among these, it has been found that an Al—Fe—Si based compound coexisting with the Mg ₂ Si compound acts as a crack propagation path during bending.

  The present invention was made as a result of further testing and examination based on the above knowledge, and its purpose is to suppress the occurrence of cracks in bending after press working, and can be applied as an automobile outer plate. An object of the present invention is to provide an Al—Mg—Si alloy plate material excellent in bending workability after press working, a manufacturing method thereof, and an automobile outer plate.

In order to achieve the above object, the Al—Mg—Si based alloy sheet material excellent in bending workability after press forming according to claim 1 of the present invention is Si: 0.4 to 1.5%, Mg: 0.00. 2 to 1.2% Fe containing 1.0% or less as an impurity, and a T4 tempered material of a rolled aluminum alloy sheet having a composition comprising the balance Al and inevitable impurities, Among the Al—Fe—Si compounds present in the above, the quantitative ratio of Al—Fe—Si compounds coexisting with the Mg ₂ Si compound is 50% or less.

  The Al—Mg—Si based alloy sheet excellent in bending workability according to claim 2 is the aluminum alloy sheet according to claim 1, wherein Mn: 0.3% or less, Cr: 0.3% or less, Zr: 0 It contains at least one of 15% or less.

  The Al—Mg—Si based alloy sheet material excellent in bending workability according to claim 3 is characterized in that, in claim 1 or 2, the aluminum alloy sheet material further contains Zn: 0.5% or less.

  The Al—Mg—Si based alloy sheet having excellent bending workability according to claim 4 is characterized in that in any one of claims 1 to 3, the aluminum alloy sheet further contains Cu: 1.0% or less. To do.

  The Al—Mg—Si-based alloy plate material excellent in bending workability according to claim 5 is the aluminum alloy plate material according to any one of claims 1 to 4, further comprising Ti: 0.1% or less and B: 50 ppm or less. It contains at least 1 sort (s) of this, It is characterized by the above-mentioned.

  Moreover, the manufacturing method of the Al-Mg-Si type alloy plate material excellent in the bending workability after the press work by Claim 6 is 500 degreeC after melt-rolling the aluminum alloy in any one of Claims 1-5. A homogenization treatment is performed at the above temperature for 1 hour or longer, and the temperature from the homogenization treatment temperature to 350 ° C. is cooled at an average cooling rate of 5 ° C./s or more, and then cooled to room temperature. It is characterized in that it is subjected to chemical treatment and quenching.

  According to a seventh aspect of the present invention, there is provided a method for producing an Al-Mg-Si based alloy sheet having excellent bending workability. The aluminum alloy according to any one of the first to fifth aspects is subjected to cold rolling after molten metal rolling, and then to 500 Perform a homogenization treatment for holding at a temperature of ℃ or more for 1 hour or more, cool from the homogenization treatment temperature to 350 ℃ at an average cooling rate of 5 ℃ / s or more, then cool to room temperature, and further cold rolling, It is characterized by solution treatment and quenching treatment.

  An automobile outer plate according to claim 8 is obtained by molding the Al—Mg—Si alloy plate material according to any one of claims 1 to 5.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the crack in the bending process after press work is suppressed, the Al-Mg-Si type alloy plate material excellent in the bending workability after press work applicable as a motor vehicle outer plate, its manufacturing method, and An automobile skin is provided.

  The present invention relates to a 6000 series aluminum alloy sheet material used in T4 tempering (solution treatment, quenching treatment, normal temperature aging treatment) produced by a molten metal rolling method (also referred to as a continuous casting rolling method), and its alloy composition is This is a range that can be suitably used as an automobile outer plate.

  First, the significance and reasons for limitation of the alloy components in the present invention will be described. Si functions to coexist with Mg to form an Mg-Si compound to improve strength and to provide high paint bake hardenability. The preferable content range of Si is 0.4 to 1.5%. If it is less than 0.4%, sufficient strength cannot be obtained by heating at the time of coating baking. May cause a problem in practical use. The more preferable content range of Si is 0.6 to 1.3%, and the most preferable content range is 0.8 to 1.2%.

Mg coexists with Si to form an Mg ₂ Si compound to improve the strength. The preferable content of Mg is 0.2 to 1.2%, and if it is less than 0.2%, sufficient strength cannot be obtained, and if it exceeds 1.2%, it coexists with an Al-Fe-Si compound. The quantitative ratio of the Mg ₂ Si compound increases and bending workability decreases. A more preferable range of Mg is 0.3 to 0.8%, and a most preferable range is 0.4 to 0.7%.

  Fe is basically contained as an impurity and forms an Al-Fe-Si-based crystallized product during casting. If the Al—Fe—Si based compound is excessively formed, the corrosion resistance is lowered and the bending workability is lowered. Therefore, the content is preferably 1.0% or less. A more preferable Fe content is 0.5% or less.

  Mn, Cr, and Zr are all elements that are selectively contained, and function to prevent rough skin during molding by crystal grain refinement. Preferable content ranges are Mn: 0.3% or less, Cr: 0.3% or less, and Zr: 0.15% or less. When the above ranges are exceeded, coarse intermetallic compounds are formed. Bending workability is reduced. Further preferable content ranges are Mn: 0.05 to 0.15%, Cr: 0.05 to 0.15%, Zr: 0.05 to 0.12%.

  Zn is an element that is selectively contained, but if contained in a range of 0.5% or less, it functions to improve surface treatment properties. If the content exceeds 0.5%, the corrosion resistance after coating is reduced. A more preferable content range is 0.3% or less.

  Cu is an element that is selectively contained, but if contained in a range of 1.0% or less, it functions to improve formability. When the content exceeds 1.0%, the corrosion resistance after coating is lowered and the bending workability is also lowered. From the viewpoint of moldability, 0.3 to 0.8% is preferable, and when corrosion resistance is important, 0.1% or less is preferable.

  Ti and B function to refine the cast structure and improve formability. Preferable contents are in the ranges of Ti: 0.1% or less and B: 50 ppm or less. When the content exceeds each of the above ranges, coarse intermetallic compounds increase and bending workability deteriorates.

In the present invention, among the Al—Fe—Si based compounds present in the plate material, it is important to suppress the quantitative ratio of the Al—Fe—Si based compound coexisting with the Mg ₂ Si compound to 50% or less. This improves the bending workability. When the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound out of the Al—Fe—Si compound present in the plate material exceeds 50%, the bending workability decreases, and the automobile outer plate When using as, there is a problem.

  Next, the manufacturing process will be described. First, an aluminum alloy having the above composition is melted and plate continuous casting is performed. As the continuous plate casting method, there are a twin roll method (TRC method) and a twin belt method (TBC method). In the present invention, either process may be used.

  The plate material produced by molten metal rolling is cold rolled, solution heat treated, quenched, and tempered at room temperature to become a T4 tempered material, but is homogenized before cold rolling or during cold rolling. I do. The homogenization treatment is preferably performed under a condition that the temperature is maintained at 500 ° C. or higher for 1 hour or longer.

Even if the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound out of the Al—Fe—Si compound present in the plate material in a state before the homogenization treatment exceeds 50%, By performing the homogenization treatment, it can be reduced to 50% or less. When the homogenization temperature is less than 500 ° C. or when the homogenization time is less than 1 hour, the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound cannot be reduced to 50% or less. There is. The more preferable temperature of the homogenization treatment is 540 ° C. or more, the most preferable temperature is 560 ° C. or more, the more preferable time of the homogenization treatment is 5 hours or more, and the most preferable time is 10 hours or more.

After the homogenization treatment, the material is cooled from the homogenization treatment temperature to 350 ° C. at an average cooling rate of 5 ° C./s or more, and then cooled to room temperature. In the cooling from the homogenization temperature to 350 ° C., when slow cooling is performed, the Mg ₂ Si compound tends to precipitate coarsely, and the coarsely precipitated Mg ₂ Si compound decreases bending workability. It is necessary to increase the cooling rate. For this reason, it cools from the homogenization process temperature to 350 degreeC with the average cooling rate of 5 degrees C / s or more. Especially when cooling at 350 ° C. or lower (from 350 ° C. to room temperature), the Mg ₂ Si compound does not precipitate coarsely and is decomposed by solution treatment even if it is slowly cooled at a cooling rate of less than 5 ° C./s. Speed is not specified.

  After the homogenization treatment, cold rolling is performed to a predetermined plate thickness. The workability of cold rolling is not particularly specified, but the larger the workability, the smaller the crystal grain size of the final plate material, and the rougher the surface during molding becomes less likely to occur. Generally, the workability of cold rolling is preferably 50% or more. Moreover, you may perform intermediate annealing as needed in the middle of cold rolling. By performing the intermediate annealing, it is possible to suppress the cracking of the edge portion of the plate in the cold rolling, and the productivity can be improved.

  After cold rolling, solution treatment and quenching treatment are performed. For the solution treatment and quenching, detailed conditions are not stipulated. However, for example, when solution treatment is performed, it is preferably performed in a high temperature range as long as the material does not dissolve. In the case of an Al-Mg-Si alloy Is preferably performed at 500 ° C. or higher and 580 ° C. or lower. In addition, as for the holding time of the solution treatment, a sufficient amount of solid solution can be obtained in a relatively short time in the case of a molten rolled material, so that it is sufficient to be 300 seconds or less. The temperature rising rate during the solution treatment is preferably 5 ° C./s or more, and the quenching rate is preferably 5 ° C./s or more.

  In addition, you may perform a preliminary aging treatment for the purpose of provision | providing bake hard property after a hardening process. As pre-aging treatment conditions, it is preferable to perform the treatment within 40 hours at a temperature of 40 ° C. to 120 ° C. within 60 minutes after quenching. Further, after the preliminary aging treatment, the restoration treatment within 60 seconds can be carried out at a temperature of 170 ° C. to 230 ° C. within 3 days, and the paint baking curability can be further improved by this restoration treatment.

In the present invention, it is important that the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound in the Al—Fe—Si compound present in the plate material is 50% or less. When the Mg ₂ Si compound coexists with the Al—Fe—Si compound existing in the inside, cracking occurs at the interface between the Al—Fe—Si compound and the Mg ₂ Si compound when bending is performed. It acts as a propagation path for cracks during bending. Bending workability is improved by making the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound 50% or less. A more preferable quantitative ratio of the Al—Fe—Si based compound coexisting with the Mg ₂ Si compound is 30% or less, and a most preferable ratio is 10% or less.

  Since the Al—Mg—Si based alloy sheet material according to the present invention obtained by the above-described process has excellent bending workability after press forming, it can be suitably used for an automobile outer sheet.

  Examples of the present invention will be described below in comparison with comparative examples, and the effects will be demonstrated based on the examples. These examples are for explaining a preferred embodiment of the present invention, and the present invention is not limited thereto.

Example 1
An aluminum alloy having the chemical components shown in Table 1 was melted, and molten metal rolling was performed at a casting speed of 1 m / min by a twin roll molten metal rolling method. At this time, the rising plate thickness of the molten metal rolling was set to 5.0 mm.

  The obtained molten rolled sheet material was subjected to a homogenization treatment that was maintained at a temperature of 560 ° C. for 10 hours, and then quenched with normal temperature tap water (average cooling rate from the homogenization treatment temperature to 350 ° C .:> 500 ° C. / s), and further cold-rolled to a plate thickness of 1.0 mm, heated to 550 ° C. at a rate of temperature increase of 25 ° C./s, and subjected to a solution treatment that was held at 550 ° C. for 20 seconds. It was water-quenched with tap water to obtain a T4 tempered material.

Using the obtained T4 tempered material as a test material, the following method was used to measure the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound 7 days after quenching, as well as tensile properties and bending work. And corrosion resistance were evaluated. The results are shown in Table 2.

Measurement of quantitative ratio of Al—Fe—Si based compound coexisting with Mg ₂ Si compound: A specimen for microstructure observation having a length of 10 mm and a width of 10 mm is cut out from a test material, and an L-ST cross section is observed (from the plate width direction). ), And after polishing with paper and buffing, the mapping image of Fe, Si, and Mg elements was measured by EMPA surface analysis, and the Al-Fe-Si compound coexisting with the Mg ₂ Si compound was measured. The quantitative ratio was measured.

  Evaluation of tensile properties: JIS No. 5 test piece was molded so that the tensile test direction coincided with the plate width direction, and the tensile strength (σB), proof stress (σ0.2), and elongation (δ) were determined according to JIS Z2241. taking measurement.

  Evaluation of bending workability: A test piece having a size of 25 mm in the rolling direction and a size of 200 mm in the plate width direction was cut out, and after 8% of tensile prestrain was introduced in the plate width direction according to JIS H 7701, the test piece was made 50 mm long. It cut | disconnected, 180 degree | times contact | adherence bending (the inner material was not inserted | pinched) was performed, and it evaluated by observing with the naked eye whether the crack of the outer side of a test piece curved part generate | occur | produced after a bending test.

  Corrosion resistance evaluation: The test material was subjected to zinc phosphate treatment and electrodeposition coating with a commercially available chemical conversion solution, cross cut reaching the aluminum base, and a salt spray test was conducted for 24 hours in accordance with JIS Z 2371, followed by 50 After being left in a moist atmosphere at -95% for 1 month, the maximum thread rust length generated from the crosscut portion is measured, and a maximum thread rust length of 4 mm or less is accepted.

As can be seen from Table 2, all of the test materials 1 to 9 according to the present invention have a high strength characteristic in which the quantitative ratio of the Al—Fe—Si based compound coexisting with the Mg ₂ Si compound is 50% or less. At the same time, no cracks were observed due to bending, and good corrosion resistance was exhibited.

Example 2
An aluminum alloy having the chemical components shown in Table 1 was melted, and molten metal rolling was performed at a casting speed of 1 m / min by a twin roll molten metal rolling method. At this time, the rising plate thickness of the molten metal rolling was set to 5.0 mm.

  The obtained molten rolled sheet material was cold-rolled to a thickness of 2.5 mm, subjected to a homogenization treatment that was held at a temperature of 560 ° C. for 10 hours, and then quenched with normal temperature tap water (from the homogenization treatment temperature to 350 ° C.). The average cooling rate to ℃:> 500 ℃ / s), and further cold-rolled to a plate thickness of 1.0 mm, then heated to 550 ℃ at a temperature increase rate of 25 ℃ / s and held at 550 ℃ for 20 seconds The solution was subjected to solution treatment and quenched with normal temperature tap water to obtain a T4 tempered material.

Using the obtained T4 tempered material as a test material, the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound 7 days after quenching was measured in the same manner as in Example 1, and the tensile properties were measured. The bending workability and the corrosion resistance were evaluated. The results are shown in Table 3.

As can be seen from Table 3, all of the test materials 10 to 18 have a high proportion of the Al-Fe-Si-based compound coexisting with the Mg ₂ Si compound, exhibiting high strength characteristics and bending. No cracking due to processing was observed, and good corrosion resistance was exhibited.

Example 3
An aluminum alloy having a chemical component of alloy A shown in Table 1 was melted, and molten metal rolling was performed at a casting speed of 1 m / min by a twin roll molten metal rolling method. At this time, the rising plate thickness of the molten metal rolling was set to 5.0 mm.

  The obtained molten rolled sheet material was subjected to homogenization treatment, cold rolling, solution treatment, and quenching under the conditions shown in Table 4 to obtain a T4 tempered material having a plate thickness of 1.0 mm.

Using the obtained T4 tempered material as a test material, the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound 7 days after quenching was measured in the same manner as in Example 1, and the tensile properties were measured. The bending workability and the corrosion resistance were evaluated. The results are shown in Table 5.

As can be seen from Table 5, all of the test materials 19 to 23 have an Al—Fe—Si-based compound coexisting with the Mg ₂ Si compound in a quantitative ratio of 50% or less, exhibit high strength characteristics, and bend. No cracking due to processing was observed, and good corrosion resistance was exhibited.

Comparative Example 1
Aluminum alloys having chemical components of Alloys I to S shown in Table 6 were melted, and molten metal rolling was performed at a casting speed of 1 m / min by a twin roll molten metal rolling method. At this time, the rising plate thickness of the molten metal rolling was set to 5.0 mm.

  The obtained molten rolled sheet material was homogenized by holding at a temperature of 560 ° C. for 10 hours, and then quenched with normal temperature tap water (average cooling rate from homogenization temperature to 350 ° C .:> 500 ° C./s ) And further cold-rolled to a plate thickness of 1.0 mm, heated to 550 ° C. at a temperature increase rate of 25 ° C./s, and subjected to a solution treatment for 20 seconds at 550 ° C. Water quenching was performed to obtain a T4 tempered material.

Using the obtained T4 tempered material as a test material, the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound 7 days after quenching was measured in the same manner as in Example 1, and the tensile properties were measured. The bending workability and the corrosion resistance were evaluated. The results are shown in Table 7.

As shown in Table 7, since the amount of Si exceeded the upper limit, the test material 24 was cracked by bending. The test material 25 has low strength because the Si amount is below the lower limit. Since the amount of Mg in the test material 26 exceeded the upper limit, the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound exceeded 50%, and cracking occurred during bending. Since the amount of Mg was less than the lower limit, the test material 27 has low strength. Since the test material 28 had an Fe amount exceeding the upper limit, cracking occurred during bending.

  Since each of the test materials 29, 30, and 31 exceeded the upper limit, the amount of Mn, Cr, and Zr was cracked during bending. Since the amount of Zn exceeded the upper limit of the test material 32, the corrosion resistance decreased. Since the amount of Cu exceeded the upper limit for the test material 33, cracking occurred during bending, and the corrosion resistance further decreased. In the test material 34, since Ti and B exceeded the upper limit, cracks occurred during bending.

Comparative Example 2
An aluminum alloy having a chemical component of alloy A shown in Table 1 was melted, and molten metal rolling was performed at a casting speed of 1 m / min by a twin roll molten metal rolling method. At this time, the rising plate thickness of the molten metal rolling was set to 5.0 mm.

  The obtained molten rolled sheet material was subjected to homogenization treatment, cold rolling, solution treatment, and quenching under the conditions shown in Table 8 to obtain a T4 tempered material having a sheet thickness of 1.0 mm.

Using the obtained T4 tempered material as a test material, the quantitative ratio of the Al—Fe—Si compound coexisting with the Mg ₂ Si compound 7 days after quenching was measured in the same manner as in Example 1, and the tensile properties were measured. The bending workability and the corrosion resistance were evaluated. The results are shown in Table 9.

As shown in Table 9, respectively test materials 35, 36, 37, the homogenization temperature is less than the lower limit, less than the homogenization treatment time is lower, the cooling rate after homogenization is less than the lower limit, Mg 2 _Si compound The quantity ratio of the Al—Fe—Si based compound coexisting with the sample exceeded 50%, and cracking occurred during bending.

Claims (8)

Si: 0.4 to 1.5% (mass%, the same shall apply hereinafter), Mg: 0.2 to 1.2%, Fe contained as impurities is 1.0% or less, the balance being Al and inevitable a T4 tempered material molten aluminum alloy rolled sheet having a composition consisting of impurities, among Al-Fe-Si based compounds are present in the plate material, Al-Fe-Si based compounds coexisting with _Mg 2 Si compound An Al—Mg—Si based alloy sheet having excellent bending workability, characterized in that the quantitative ratio of is less than 50%. The aluminum alloy molten rolled sheet material further contains one or more of Mn: 0.3% or less (excluding 0%, the same shall apply hereinafter), Cr: 0.3% or less, Zr: 0.15% or less. The Al-Mg-Si alloy plate material excellent in bending workability according to claim 1. 3. The Al—Mg—Si based alloy sheet excellent in bending workability according to claim 1, wherein the molten aluminum alloy sheet further contains Zn: 0.5% or less. The Al-Mg-Si-based alloy sheet excellent in bending workability according to any one of claims 1 to 3, wherein the molten aluminum alloy sheet further contains Cu: 1.0% or less. . The bending workability according to any one of claims 1 to 4, wherein the molten aluminum alloy sheet further contains at least one of Ti: 0.1% or less and B: 50 ppm or less. Excellent Al-Mg-Si based alloy sheet. After the aluminum alloy having the composition according to any one of claims 1 to 5 is melt-rolled, a homogenization treatment is performed at a temperature of 500 ° C or higher for 1 hour or more, and the temperature from the homogenization treatment temperature to 350 ° C is increased to 5 ° C / Production of an Al-Mg-Si alloy sheet having excellent bending workability, characterized by cooling at an average cooling rate of s or more and then cooling to room temperature, followed by cold rolling, solution treatment, and quenching treatment Method. The aluminum alloy having the composition according to any one of claims 1 to 5 is melt-rolled, cold-rolled, and then subjected to a homogenization treatment of holding at a temperature of 500 ° C or higher for 1 hour or more. Al-Mg- excellent in bending workability, characterized in that it is cooled to 5 ° C / s at an average cooling rate of 5 ° C / s or more, then cooled to room temperature, and further subjected to cold rolling, solution treatment, and quenching treatment. A method for producing a Si-based alloy sheet. An automobile outer plate obtained by molding the Al-Mg-Si alloy plate material excellent in bending workability according to any one of claims 1 to 5.