JPWO2005064025A1 - Method for producing Al-Mg-Si based aluminum alloy plate excellent in bake hardness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the strength and cost of an aluminum alloy plate and to improve press formability and bake hardenability.
SOLUTION: In addition to containing Mg: 0.3 to 1.0 wt%, Si: 0.3 to 1.5 wt%, Cu: 1.0 wt% or less (including 0%), Fe: 1.2 wt% or less (including 0%), The average cooling rate during solidification of an Al-Mg-Si based aluminum alloy melt containing Mn: 0.1 to 0.7 wt% and/or Cr: 0.1 to 0.3%, and the balance Al, if necessary, at 20°C/s or more As a twin belt casting, the temperature of the ingot coming out of the casting machine was set to 250°C or less, and then the sheet was rolled to the final plate thickness only by cold rolling without homogenizing treatment or hot rolling. A method for producing an Al-Mg-Si-based aluminum alloy sheet having excellent bake hardness, which is characterized by performing solution treatment at.
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Description

  The present invention relates to a method for manufacturing an Al-Mg-Si alloy plate. The present invention contains a predetermined amount of Mg, Si as an essential component in addition to Al, and optionally uses a predetermined amount of Fe, Cu, Mn and Cr Al alloy molten metal, when continuously casting this , Casting with an average cooling rate during solidification of 20°C/s or more, and the ingot temperature when coming out of the casting machine is 250°C or less, or casting within 2 minutes after pouring the molten metal into the casting machine The ingot is cooled so that the ingot temperature becomes 250°C or less, and then it is rolled to the final plate thickness only by cold rolling without homogenizing treatment or hot rolling, and then the solution is melted in a continuous annealing furnace. The present invention relates to a method for manufacturing an Al-Mg-Si-based aluminum alloy plate, which is characterized by performing a chemical treatment. The Al-Mg-Si alloy plate obtained by the present invention is excellent in bake hardness, so by taking advantage of its characteristics, it can be widely used as an outer plate material for automobiles, household appliances, etc., a building material, etc. be able to.

  For example, cold-rolled steel sheets have been conventionally used as automotive panel materials. However, recently, as a measure to reduce the weight of a vehicle body for the purpose of saving fuel consumption, reducing exhaust gas, etc., there is a rapidly increasing tendency to use an Al alloy material which is lightweight and has high specific strength and excellent formability. Among them, Al-Mg-Si alloys, which have excellent bake hardness, have attracted attention as Al-based alloy plates for automobiles that are often used after being coated for the purpose of improving the appearance. ing.

  By the way, as a method for producing an Al alloy sheet, conventionally, it is generally practiced that after subjecting an ingot produced by a semicontinuous casting method or the like to chamfering treatment or homogenizing heat treatment, hot rolling, cold rolling This is a method of sequentially performing rolling, annealing, and the like. The conventional Al alloy sheet manufactured through such steps has a good press formability and a good bake hardness, so that it has met the demands of consumers.

  However, in recent years, the demands of consumers have become more severe, and not only has there been a tendency to require even higher strength in order to improve weight reduction, but further improvement in moldability and bake hardness is also desired, Furthermore, there is an increasing demand for cost reduction by improving productivity.

As a relatively new Al alloy sheet manufacturing technology that meets these demands, a method of performing hot casting and cold rolling immediately after rolling into a moving strip by continuous casting (hereinafter, continuous casting/direct rolling method) However, a method of omitting chamfering and homogenizing heat treatment has been studied (JP-A-55-27497, JP-B-62-54182, etc.). According to this method, it is possible to reduce the cost by omitting the chamfering and homogenization heat treatment, and since the solid solution element that is solid-soluted to supersaturation in the casting step does not precipitate during the homogenization heat treatment, There is an advantage that the strengthening by melt strengthening is also promoted.
JP-A-55-27497 Japanese Patent Publication No. 62-54182

After continuously casting using an Al alloy molten metal, hot rolling, when further cold rolling to produce an Al alloy sheet, especially in a series of steps of continuous casting, hot rolling, cold rolling and intermediate annealing A method has also been proposed in which the precipitation of supersaturated solid solution elements is suppressed as much as possible, the strength of the final cold rolled product is increased, and the bake hardness and press formability are further improved (JP-A-7- 252616). This method uses, in particular, a molten Al alloy in which the content of alloying elements such as Mg, Mn, and Si is specified, and continuously hot-rolls this, and then cold-rolls the Al-Mg. -Si-based alloy sheet is manufactured.At that time, the cooling rate during continuous casting and after hot rolling is regulated, and the heat treatment condition after cold rolling that is performed thereafter is devised. It is intended to obtain an Al-Mg-Si based alloy sheet with improved formability and bake hardenability.
JP-A-7-252616

  The continuous casting method adopted in such continuous casting/direct rolling method is currently in practical use as a water-cooled continuous casting method (continuous casting that is formed into a plate shape from a fixed water-cooled continuous casting mold). A piece is directly cooled and solidified with cooling water and continuously cast), a twin roll casting method developed by Hunter Engineering Co., Ltd. (a molten metal is supplied between a pair of rotating cooling rolls, and solidified by cooling between the rolls). Continuous casting method), a belt-type continuous casting method developed by Hatherley Co. (supplying molten metal between two movable belt-like cooling members, continuously cooling and solidifying between the belts). Plate-shaped casting method), a block-type continuous casting method developed by Swiss Aluminum Co., Ltd. (molten metal is supplied between two movable block-shaped cooling members and continuously solidified while cooling and solidifying between the blocks). Plate-shaped casting method) and the like.

  However, in the continuous casting/direct rolling method currently in practical use, in the cold rolling process performed after continuous casting and hot rolling, in order to prevent processing cracks, etc. Although annealing is performed, precipitation of supersaturated solid solution elements occurs in this intermediate annealing step, and there is a problem in that the strength of the final cold rolled product is hindered. Further, the method as described above, specifically, Mg, Mn, using the Al alloy molten metal content of the alloying elements such as Si is specified, hot-rolled after continuously casting this, further cold rolling When producing an Al-Mg-Si alloy sheet, the cooling rate during continuous casting and after hot rolling is regulated, and by devising the heat treatment conditions after cold rolling that is performed thereafter, the press In the method of obtaining an Al-Mg-Si alloy plate with improved formability and bake hardness, hot rolling after continuous casting and heat treatment after cold rolling are required, resulting in high cost and continuous casting. There is a problem that the advantage cannot be utilized. Moreover, the obtained Al alloy sheet still has room for improvement in press formability and bake hardenability.

  The present invention has been made by paying attention to the above problems of the prior art, and when twin-belt casting Al-Mg-Si-based aluminum, the average cooling rate during solidification is 20° C./s or more and casting is performed. Then the ingot temperature coming out of the casting machine is 250°C or lower, or the ingot is cooled so that the ingot temperature becomes 250°C or lower within 2 minutes after the molten metal is injected into the casting machine, and then, An Al-Mg-Si system with excellent bake hardness, characterized in that it is subjected to solution treatment in a continuous annealing furnace after rolling to the final plate thickness only by cold rolling without homogenization treatment or hot rolling. The present invention relates to a method for manufacturing an aluminum alloy plate.

  The first invention for solving the above-mentioned problems is Mg: 0.3 to 1.0 wt%, Si: 0.3 to 1.5 wt%, Cu: 1.0 wt% or less (including 0%), Fe: 1.2 wt% or less (0% Average) during solidification of an Al-Mg-Si-based aluminum alloy melt containing the balance Al) and Mn: 0.1 to 0.7 wt% and/or Cr: 0.1 to 0.3%, and the balance Al. Twin belt casting is performed at a speed of 20°C/s or more, and the ingot temperature coming out of the casting machine is set to 250°C or less, and then the final plate thickness is obtained only by cold rolling without homogenizing treatment or hot rolling. It is a method for producing an Al-Mg-Si-based aluminum alloy sheet having excellent bake hardness, which is characterized by rolling to a continuous annealing furnace and solution treatment in a continuous annealing furnace.

  The second invention for solving the above-mentioned problems is Mg: 0.3 to 1.0 wt%, Si: 0.3 to 1.5 wt%, Cu: 1.0 wt% or less (including 0%), Fe: 1.2 wt% or less (0% Average) during solidification of an Al-Mg-Si-based aluminum alloy melt containing the balance Al and containing Mn: 0.1 to 0.7 wt% and/or Cr: 0.1 to 0.3% and the balance Al. Twin-belt casting is performed at a speed of 20°C/s or more, at which time the ingot is cooled so that the ingot temperature becomes 250°C or less within 2 minutes after pouring the molten metal into the casting machine, and then homogenized or hot-worked. It is a method for producing an Al-Mg-Si-based aluminum alloy plate with excellent bake hardness, which is characterized by rolling to the final plate thickness only by cold rolling without rolling and performing solution treatment in a continuous annealing furnace. ..

The reason for setting the average cooling rate to 20°C/s or more is that when the average cooling rate is less than 20°C/s, coarse Mg ₂ Si is likely to crystallize during solidification, and this coarse Mg ₂ Si is solution-treated by a continuous annealing furnace. This is because it is difficult to sufficiently dissolve in the treatment, and as a result, the bake hardness is poor.

The reason the ingot temperature when coming out of the casting machine is 250°C or lower is that when the temperature is higher than 250°C, Mg ₂ Si precipitates in the cooling process of the ingot, so that the final temperature in the continuous annealing furnace This is because the temperature and time required for solution treatment of the plate increase and, as a result, the bake hardenability deteriorates.

The reason for the not-rolled homogenization or heat, casting and crystallization in the cooling process Mg ₂ Si, be suppressed precipitation, for homogenization or when hot rolling Mg ₂ Si is re-precipitated, the solution This is because it becomes difficult to sufficiently dissolve it in the chemical treatment, and as a result, the baking hardness is poor.

The reason why we decided to cool the ingot so that the temperature would be 250°C or less within 2 minutes from the injection of the molten metal is that the precipitation of Mg ₂ Si occurs after 2 minutes, so the solution annealing of the final plate in the continuous annealing furnace This is because it becomes difficult to form a solid solution of Mg ₂ Si in the matrix, and as a result, the bake hardness is poor.

In order to keep the ingot temperature at the time of coming out of the casting machine at 250° C. or lower, it is necessary to remove from the ingot a heat amount of about 2200 MJ or more per 1 m ³ of the ingot volume in the casting machine. This means that when casting an ingot with a width of 1 m and a plate thickness of 1 cm at a casting speed of 8 m/min with a casting machine with an effective cooling length of 1 m, the average heat removal flow density in the casting machine is 3.0 MW/m ² or more. It is equivalent to casting.

In this way, the ingot temperature after casting should be 250°C or lower, or the ingot should be cooled to 250°C or lower within 2 minutes from the pouring of the molten metal, and then without homogenization treatment or hot rolling. By rolling to the final plate thickness only by cold rolling, it is possible to suppress the precipitation of coarse Mg ₂ Si, and Mg ₂ Si is easily incorporated into the matrix during the subsequent solution treatment by the continuous annealing furnace. Solid solution. With this, in combination with properly adjusting the component composition of the Al-Mg-Si alloy, a high strength of the cold rolled product is achieved, and the yield strength after the baking treatment performed thereafter is increased, Furthermore, an Al-Mg-Si-based alloy sheet with even better press formability is realized.

  Hereinafter, the component composition of the Al-Mg-Si alloy defined in the present invention and the manufacturing conditions including the cooling conditions during continuous casting and after hot rolling will be described in detail. First, the reason for defining the component composition of the Al-Mg-Si alloy used in the present invention will be described.

Mg (0.3-1.0 wt%) is an element that forms Mg ₂ Si and contributes to strengthening. To ensure the required strength as the outer plate material as described above, Mg (0.3 to 1.0 wt%) should be contained in an amount of 0.3 wt% or more. is necessary. However, if the content is too large, the formability is deteriorated, so it is also necessary to suppress the content to 1.0 wt% or less. The more preferable lower limit of Mg is 0.4 wt% and the more preferable upper limit thereof is 0.8 wt%.

Si (0.3 to 1.5 wt%) is an element that forms the above Mg and Mg ₂ Si and contributes to strengthening, and it is necessary to contain 0.3% or more in order to effectively exert its addition effect. .. However, if the content is too large, the press formability is adversely affected, so it is also necessary to suppress the content to 1.5 wt% or less. The more preferable lower limit value of Si is 0.6%, and the more preferable upper limit value thereof is 1.2 wt%. As described above, in the present invention, Mg and Si are added to G. It is an important element that forms an aggregate (cluster) of Mg ₂ Si composition called P zone or an intermediate layer and contributes to hardening by baking treatment.

  Cu (1.0 wt% or less) is not always essential, but since it has a precipitation strengthening effect, it is desirable to positively contain it when the demand for strength is high. However, if it is too large, the formability is adversely affected, so it must be kept to 1.0 wt% or less. Considering the balance between strength and formability, a more preferable Cu content is in the range of 0.4 to 0.9 wt %.

  Although Fe (1.2% wt or less) is not always essential, it also has the effect of increasing the strength, so it is desirable to positively contain it when the demand for strength is high. However, if it is too large, the formability is adversely affected, so it must be kept to 1.2 wt% or less. Considering the balance between strength and formability, the more preferable Fe content is in the range of 0.1 to 0.5 wt %.

  Mn (0.1 to 0.7 wt%) is an element effective as a solid solution strengthening element and a crystal grain refining element, and it must be contained at least 0.1 wt% or more in order to exert these effects effectively. However, if the amount becomes too large, the moldability tends to deteriorate due to an increase in the amount of Mn that cannot be completely dissolved, so it must be suppressed to 0.7 wt% or less.

  Cr (0.1 to 0.3 wt%) has an action as a grain refinement element, and in order to exert its effect effectively, it must be contained at a lower limit or more. However, if this content exceeds the above upper limit, an intermetallic compound is generated, and the formability is adversely affected. Considering these points, the preferable Cr content is in the range of 0.1 to 0.3 wt %.

  The balance component of the Al alloy in the present invention is composed of Al and unavoidable impurities, examples of the unavoidable impurities include Ni, Zn, Zr, V, Ti, Li and the like, but as long as they are inevitable impurities amount. However, there is no particular obstacle to securing the performance intended by the present invention. Next, conditions such as continuous casting and cold rolling using the above Al-Mg-Si alloy will be described.

  When the average cooling rate during solidification in continuous casting is specified as described above, the amount of crystallized substances derived from Fe and Si in the continuous cast structure is reduced by forced solid solution, and the crystallized substance size is 2 μm in average size. The size is reduced to below a certain level, and the press moldability and the bake hardenability are remarkably enhanced. However, if the average cooling rate during solidification during continuous casting is less than the above rate, not only the amount of crystallization of the intermetallic compound increases but also its size becomes coarse and satisfactory press formability cannot be obtained. , Bake hardness is also inferior.

  Further, after the above continuous casting, the ingot temperature when coming out of the casting machine is 250° C. or less, or casting is performed so that the ingot temperature becomes 250° C. or less within 2 minutes after pouring the molten metal into the casting machine. By adopting the rapid cooling in which the ingot is cooled and then rolled to the final plate thickness only by cold rolling without homogenizing treatment or hot rolling, precipitation of supersaturated solid solution components during ingot cooling can be prevented. The amount of supersaturated solid solution is suppressed, and a plate excellent in bake hardness can be manufactured. By the way, when the ingot temperature after casting exceeds 250°C, precipitation of supersaturated solid solution components occurs, and a plate having poor bake hardness is produced.

  After the final sheet thickness is obtained by cold rolling, solution annealing is performed in a continuous annealing furnace at a temperature in the range of 530 to 570° C., followed by quenching with warm water or water and then preliminary aging treatment. The solution treatment temperature at this time is determined as described above because the precipitation of the solid solution element during the solution treatment is suppressed to maintain a sufficient supersaturated solid solution amount, the strength is increased, and the solid solution element amount is increased. This is to improve the bake hardness. By the way, if the solution treatment temperature is lower than 530° C., the effect of improving the bake hard property becomes insufficient. On the other hand, when the temperature exceeds 570° C., the crystal grains become coarse and eutectic melting causes burning, which deteriorates the press formability.

  After the solution treatment, after quenching with hot water or cold water, by performing preliminary aging treatment, to obtain an Al-Mg-Si alloy plate having excellent press formability and bake hardness. be able to. Quenching conditions and aging heat treatment conditions at this time are not particularly limited, but preferable conditions are warm water quenching as quenching conditions, and aging heat treatment conditions at 60 to 200° C. for about 10 minutes to 8 hours.

  In the present invention, while specifying the component composition of the Al-Mg-Si alloy as described above, during continuous casting using the molten alloy, the average cooling rate during solidification is cast at 20°C/s or more, After that, the ingot temperature when coming out of the casting machine is 250 °C or less, or the ingot is cooled so that the ingot temperature becomes 250 °C or less within 2 minutes after pouring the molten metal into the casting machine, and then homogeneous It is characterized by rolling to the final thick plate only by cold rolling without heat treatment or hot rolling, and setting solution treatment conditions in a continuous annealing furnace. However, other preferable conditions will be described below.

  The present invention continuously casts the ingot to a temperature of 250° C. or lower, or cools the continuously cast slab to 250° C. or lower, winds it once, and then homogenizes or hot-rolls it. It is characterized in that it is rolled to the final thick plate only by cold rolling without performing, and the solution heat treatment conditions in the continuous annealing furnace are set, whereby it is temporarily wound after continuous casting and then cooled. Compared with the method in which homogenization treatment or hot rolling is further performed after that, heat loss is small, and it is also effective in improving productivity.

  Further, in carrying out the present invention, a plate-shaped slab with a wall thickness of usually about 4 to 15 mm is continuously produced by continuous casting, and after winding this, the wall thickness is 0.1 to by cold rolling. The aluminum alloy product sheet is preliminarily aged after solution heat treatment in a continuous annealing furnace to 1 mm. As the continuous casting method adopted here, a water-cooled continuous casting method, a twin roll type continuous casting method, a belt type continuous casting method, a block type continuous casting method or the like as described above may be appropriately selected and employed. You can

  Next, examples of the present invention will be shown, but the present invention is not limited by the following examples as well as the following examples, and it is of course possible to carry out appropriate modifications within the scope of the gist of the present invention. Both are included in the technical scope of the present invention.

Example 1
A twin-belt casting machine was used to cast a 1 cm thick ingot under the following conditions.

Effective cooling length of casting machine: 1m
Casting speed: 8m/Dispensing temperature: 700℃
Composition: Al, Mg: 0.6 wt%, Si: 0.8 wt%, Fe: 0.2 wt%, Mn: 0.2 wt%, Ti: 0.01 wt%

By changing the average heat removal flow density in the casting machine, ingots having different ingot temperatures immediately after casting were obtained.
Then, after cold rolling to a 1 mm plate, solution treatment of 545° C.×15 seconds→hot water quenching was performed, and preliminary aging at 85° C.×8 hours was performed to obtain a T4 material. For T6 material, natural aging was performed on T4 material for 1 week, and then artificial aging was performed at 170°C for 30 minutes. In order to evaluate the bake hardness, the proof stress of the T4 and T6 materials was measured, and the difference was defined as the bake hardness. The target bake hardness is 100 MPa or more. Furthermore, in order to see the effect of the presence or absence of homogenization treatment or hot rolling, as a comparative example, the bake hard property of a plate obtained by homogenizing the ingot or performing hot rolling was also measured.

*均質化処理： 560℃×6時間保持→炉冷
*熱間圧延： 560℃まで昇温した後、圧延開始温度を550℃として4mmまで熱間圧延。その後冷間にて1mmまで圧延した。

* Homogenization treatment: 560℃ x 6 hours hold → furnace cooling
* Hot rolling: After the temperature is raised to 560°C, the rolling start temperature is 550°C and hot rolling is performed to 4 mm. Then, it was cold rolled to 1 mm.

Example 2
A twin-belt casting machine was used to cast a 1 cm thick ingot under the following conditions.
Effective cooling length of casting machine: 1m
Casting speed: 8m/Dispensing temperature: 700℃
Composition: Al, Mg:0.6wt%, Si:0.8wt%, Fe:0.2wt%, Mn:0.2wt%, Ti:0.01wt%

A cooling device was attached to the outlet of the casting machine so that the ingot could be cooled immediately after casting. When the cooling device was operated, the ingot temperature, which was 357° C. immediately after casting, decreased to 230° C. two minutes after the molten metal was injected into the casting machine by passing through the cooling device. On the other hand, when the cooling rate was not operated, the ingot temperature 2 minutes after pouring the molten metal into the casting machine was still high at 330°C. Then, after cold rolling to a 1 mm plate, solution treatment of 545° C.×15 seconds→hot water quenching was performed and preliminary aging at 85° C.×8 hours was performed to obtain a T4 material. For T6 material, natural aging was performed on T4 material for 1 week, and then artificial aging was performed at 170°C for 30 minutes. In order to evaluate the bake hardness, the proof stress of the T4 and T6 materials was measured, and the difference was defined as the bake hardness. The target bake hardness is 100 MPa or more.

Claims (2)

(A) Mg: 0.3 to 1.0 wt%, Si: 0.3 to 1.5 wt%, Cu: 1.0 wt% or less (including 0%), Fe: 1.2 wt% or less (including 0%) and necessary. Depending on the, Mn: 0.1-0.7 wt% and / or Cr: 0.1-0.3%, Al-Mg-Si-based aluminum alloy molten metal consisting of the balance Al, the average cooling rate during solidification as 20 ℃ / s or more Twin belt casting,
(B) At that time, the ingot temperature coming out of the casting machine is set to 250° C. or lower,
(C) After that, the steel sheet is rolled to the final plate thickness only by cold rolling without homogenizing treatment or hot rolling,
(D) characterized by performing solution treatment in a continuous annealing furnace,
A method for producing an Al-Mg-Si-based aluminum alloy sheet having excellent bake hardness. (A) Mg: 0.3 to 1.0 wt%, Si: 0.3 to 1.5 wt%, Cu: 1.0 wt% or less (including 0%), Fe: 1.2 wt% or less (including 0%) and necessary. Depending on the, Mn: 0.1-0.7 wt% and / or Cr: 0.1-0.3%, Al-Mg-Si-based aluminum alloy molten metal consisting of the balance Al, the average cooling rate during solidification as 20 ℃ / s or more Twin belt casting,
(B) At that time, the ingot is cooled so that the ingot temperature becomes 250° C. or lower within 2 minutes after the molten metal is injected into the casting machine,
(C) After that, the steel sheet is rolled to the final plate thickness only by cold rolling without homogenizing treatment or hot rolling,
(D) characterized by performing solution treatment in a continuous annealing furnace,
A method for producing an Al-Mg-Si-based aluminum alloy sheet having excellent bake hardness.