KR20060135711A - Manufacturing method for al-mg-si aluminum alloy sheets with excellent bake-hardenability - Google Patents

Abstract

[PROBLEMS] The enhancement of strength, the improvement of press workability and bake-hardenability, and the production at a low cost, with respect to an aluminum alloy plate [MEANS FOR SOLVING PROBLEMS] A method for producing an Al-Mg-Si based aluminum alloy plate excellent in bake-hardenability, characterized in that it comprises providing an aluminum alloy melt having a chemical composition, in wt %, that Mg: 0.3 to 1.0 %, Si: 0.3 to 1.5 %, Cu: 1.0 % or less (inclusive of 0 %), Fe: 1.2 % or less (inclusive of 0 %), optionally further Mn: 0.1 to 0.7 % and/or Cr: 0.1 to 0.3 %, and the balance: Al, casting the alloy melt by the twin belt casting method with an average cooling speed during solidification of 20°C/s or higher, setting the temperature of the ingot at the outlet of a casting machine at 250°C or lower, then, without homogenation or hot rolling, subjecting the resultant ingot to cold rolling until the objective plate thickness, and subjecting the cold-rolled product to a solution treatment in a continuous annealing furnace.

Description

Manufacturing method of Al-Mg-Si-based aluminum alloy sheet having excellent bake hardenability {MANUFACTURING METHOD FOR Al-Mg-Si ALUMINUM ALLOY SHEETS WITH EXCELLENT BAKE-HARDENABILITY}

The present invention relates to a method for producing an Al-Mg-Si alloy plate. The present invention uses a molten aluminum alloy metal containing a predetermined amount of Mg, Si, and in some cases, a predetermined amount of Fe, Cu, Mn and Cr as an essential component in addition to Al, and the average cooling rate upon solidification during its continuous casting Is cast at 20 ° C./s or more, the temperature at which the ingot leaves the casting machine is 250 ° C. or less, or the temperature of the ingot is cooled to 250 ° C. or less within 2 minutes after the molten metal is injected into the casting machine. The present invention relates to a method for producing an Al-Mg-Si-based aluminum alloy plate, which is subjected to solution treatment after rolling only by cold rolling without homogenizing or hot rolling to the final thickness of the plate. The Al-Mg-Si-based alloy sheet thus obtained by the present invention has excellent bake hardenability, and by using this property, it can be widely used for exterior materials such as automobiles, home appliances, and building materials. .

For example, cold-rolled steel has been conventionally used as a vehicle panel material. Recently, however, as a method for reducing the weight of the vehicle body for the purpose of improving fuel efficiency and reducing exhaust gas, the tendency to use aluminum alloys that are light, high in strength, and excellent in metal forming processability is rapidly increasing. Among them, Al-Mg-Si-based alloys having excellent bake hardenability are attracting attention as automotive aluminum alloys which are often coated for improving aesthetics, and some of them have been put to practical use.

However, a method generally used for manufacturing an aluminum alloy plate is a semi-continuous casting method, and the like, and then hot rolling, cold rolling, and quenching are sequentially applied to the produced ingot after scaling or homogenizing. It was a way to lose. The aluminum alloy sheet produced by this process was good in press formability and the bake curability was also good to meet the needs of the consumer.

However, in recent years, the demands of consumers have become more stringent, and not only tend to seek higher strength to increase the weight reduction, but also require further improvement in formability and bake hardenability, and further, to reduce costs by improving productivity. Is increasing.

As a relatively recent aluminum alloy sheet manufacturing technology that satisfies these requirements, a method of manufacturing an ingot by a continuous casting method and directly sending it to a rolling press to perform hot and cold rolling (hereinafter referred to as continuous casting / direct rolling method). ), A method in which the surface treatment and the homogenization treatment are omitted is considered (Patent Publication No. 55-27497, Patent Publication No. 62-54182, etc.). According to this method, it is possible to reduce the cost by omitting the roughing and homogenizing treatment and to improve the strength of the aluminum alloy plate due to the solid solution strengthening because solid elements are not precipitated in the supersaturated solid solution during the homogenizing treatment. There is an advantage.

Precipitation of supersaturated solid elements during continuous casting, hot rolling, cold rolling and intermediate quenching during the production of aluminum alloy plates by continuous rolling using molten aluminum alloy followed by cold rolling. Has been proposed to increase the strength of the final cold-rolled product and to further improve the bake curability and press formability by controlling as much as possible (Patent Publication No. 7-252616). This method is a method of producing an Al-Mg-Si alloy sheet using a molten aluminum alloy containing a specific amount of Mg, Mn, Si, etc., and hot rolling after continuous casting, followed by cold rolling. In this case, the Al-Mg-Si-based alloy plate having improved press formability and bake hardenability is obtained by additionally controlling the cooling rate during continuous casting and after hot rolling, and further controlling the heat treatment conditions after cold rolling. .

As the continuous casting method employed in the continuous casting / direct rolling method, currently being practically used is a water-cooled continuous casting method (continuous casting slab [formed from a plate-shaped, fixed water-cooling continuous casting mold] directly cooled and solidified with cooling water, and continuously Casting method), twin roll casting method developed by Hunter Engineering Co., Ltd. (Method for continuous casting by supplying molten metal between a pair of rotating cold rollers to cool and solidify the rollers), Hazelett Belt type continuous casting method developed by Co., Ltd. (Method for casting molten metal into two belt-type cooling devices to cast continuous plate shape during cooling and solidification between the belts), Swiss Aluminum Block type continuous casting method developed by the company to supply molten metal to moving two block type cooling device. For example, the method of casting in the form of a block during the cooling and solidification between the blocks).

However, in the continuous casting / direct rolling method currently in practical use, in order to prevent process cracking, intermediate quenching is performed at a relatively low temperature of 350 ° C to 500 ° C, and precipitation of supersaturated solid elements during the intermediate quenching process There occurs a problem that inhibits the high strength of the final cold-rolled product. In addition, in the above-described method, in particular, a molten aluminum alloy in which the content of alloying elements such as Mg, Mn, and Si is specified is used, and after continuous casting, an Al-Mg-Si-based alloy plate which is hot rolled and then cold rolled In the case of manufacturing, a method of obtaining an Al-Mg-Si-based alloy plate having improved press formability and bake hardenability by controlling the cooling rate during continuous casting and after cold rolling, and additionally controlling the heat treatment conditions after cold rolling. In the case of hot rolling after continuous casting and heat treatment after cold rolling, there is a problem that the advantages of the continuous casting method cannot be put to practical use because the manufacturing cost is high. Furthermore, there is room for improvement in press formability and bake curability in the obtained aluminum alloy plate.

The present invention has been made in consideration of the above-described problems of the prior art, and in the twin belt casting method of Al-Mg-Si-based aluminum, the average cooling rate during solidification is 20 ° C / s or more, and the temperature of the ingot from the casting machine is 250 ° C or less. , Or within 2 minutes from when the molten metal is injected into the casting machine, the ingot is cooled to 250 ° C. or lower, and furthermore, the ingot is rolled to a final thickness by cold rolling without homogenizing or hot rolling, and then a continuous annealing furnace ( The present invention relates to a method for producing an Al-Mg-Si-based aluminum alloy plate having excellent bake hardenability, characterized by casting by solution treatment in a continuous annealing furnace.

The first invention to solve the above problems, Mg: 0.3 to 1.0% by weight, Si: 0.3 to 1.5% by weight, Cu: 1.0% by weight or less (including 0%), Fe: 1.2% by weight or less (including 0%) If necessary, Mn: 0.1 to 0.7% by weight and / or Cr: 0.1 to 0.3% by weight, the remainder of the Al-Mg-Si-based molten aluminum alloy made of aluminum, the average cooling rate during solidification Twin belt casting to cast 20 ℃ / s or more, in which the temperature of the ingot from the casting machine is below 250 ℃ and rolled to the final thickness by cold rolling without homogenizing or hot rolling and then used in continuous annealing furnace. It is a manufacturing method of the Al-Mg-Si type aluminum alloy plate excellent in the bake hardenability which makes it the summary subject to sieving process.

The second invention to solve the above problems, Mg: 0.3 to 1.0% by weight, Si: 0.3 to 1.5% by weight, Cu: 1.0% by weight or less (including 0%), Fe: 1.2% by weight or less (including 0%) If necessary, Mn: 0.1 to 0.7% by weight and / or Cr: 0.1 to 0.3% by weight, the remainder of the Al-Mg-Si-based molten aluminum alloy made of aluminum, the average cooling rate during solidification Twin-belt casting to cast 20 ℃ / s or more, in which the ingot is cooled to 250 ℃ or less within 2 minutes after the molten metal is injected into the casting machine, and cold-rolled without homogenizing or hot rolling. It is a manufacturing method of the Al-Mg-Si type aluminum alloy plate excellent in the bake hardenability which makes it a summary to carry out the solution treatment by the continuous annealing furnace after rolling to a final thickness by this.

The reason why the average cooling rate is 20 ° C / s or more is that if the average cooling rate is less than 20 ° C / s, coarse Mg ₂ Si precipitates during solidification, and the coarse Mg ₂ Si is a continuous annealing furnace. This is because it is difficult to dissolve sufficiently in the case of solution treatment at, resulting in poor bake hardenability.

The reason why the temperature of the ingot from the casting machine is 250 ° C. or lower is that if the temperature of the ingot exceeds 250 ° C., Mg ₂ Si precipitates in the process of cooling the ingot, so that the temperature required for the solution treatment of the final plate in the continuous annealing furnace is obtained. And time increase, and as a result, the bake curability is bad.

Why does not the homogenizing treatment or hot rolling, it becomes difficult enough to melt during solution treatment due to casting and cooling step, Mg ₂ Si is again precipitated even if the precipitation of Mg ₂ Si is suppressed during the homogenization process or the hot rolling in the This is because bake curability is bad as a result.

The reason for cooling the temperature of the ingot to 250 ° C or less within 2 minutes after the molten metal is injected into the casting machine is because, if 2 minutes have elapsed, Mg ₂ Si is precipitated and this Mg is dissolved in a continuous annealing furnace. difficult to dissolve the ₂ Si in the matrix is due as a result poor in bake hardening.

When the ingot is taken out from the casting machine, it is necessary to remove from the ingot about 2200 MJ of heat per 1 m 3 of the ingot volume in order to bring the temperature to 250 ° C or lower. This corresponds to casting with an average heat flow density of 3.0 MW / m 2 or more in the casting machine when casting an ingot 1 m wide and 1 cm thick at a casting speed of 8 m / min in a casting machine having an effective cooling length of 1 m.

After casting, the temperature of the ingot is lowered to 250 ° C or lower, or the molten metal is cooled to 250 ° C or lower within 2 minutes after the molten metal is injected into the casting machine, or further, the cold rolling is performed without subsequent homogenization and hot rolling. By rolling the plate to the thickness, the precipitation of the coarse particles of Mg ₂ Si can be reduced, and Mg ₂ Si can be easily dissolved in the matrix during subsequent solution treatment in a continuous annealing furnace. By doing so, in combination with appropriately adjusting the composition of the Al-Mg-Si-based alloy, the high strength of the cold rolled product can be achieved, and the yield strength increases after the subsequent baking treatment. Al-Mg-Si type alloy plate excellent in press formability can be put into practical use.

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

Mg (0.3 ~ 1.0% by weight), it is necessary to form Mg ₂ Si is contained as an element contributing to higher strength, more than 0.3% by weight in order to ensure the necessary strength as the above-mentioned external panel material. However, if the content is too large, it reduces the formability, so it is necessary to keep the content at 1.0 wt% or less. The minimum with more preferable Mg is 0.4 weight%, and a more preferable upper limit is 0.8 weight%.

Si (0.3 to 1.5% by weight) is an element that forms Mg ₂ Si and contributes to high strength in addition to the above-mentioned Mg, and in order to effectively exhibit its addition effect, it is required to contain 0.3% by weight or more. However, if the content is too high, it adversely affects the press formability, so it is necessary to maintain it at 1.5 wt% or less. The minimum with more preferable Si is 0.6 weight%, and a more preferable upper limit is 1.2 weight%. As described above, in the present invention, Mg and Si form important aggregates or intermediate layers of Mg ₂ Si components called GP zones in the aluminum alloy and are important elements that contribute to curing by baking.

Cu (1.0 wt% or less) is not necessarily required, but it is preferable to actively include it when the demand for strength is high for precipitation strengthening. However, if the content is too high, adverse effects may appear, so it should be kept at 1.0 wt% or less. The more preferable content of Cu in consideration of the balance between strength and formability is in the range of 0.4 to 0.9% by weight.

Fe (1.2 wt% or less) is also not necessarily necessary, but it is preferable to actively contain it when the demand for strength is high because it serves to increase the strength. However, if the content is too high, adverse effects may occur, so it should be kept at 1.2 wt% or less. The more preferable Fe content in consideration of the balance between strength and formability is in the range of 0.1 to 0.5% by weight.

Mn (0.1 to 0.7% by weight) is an element having a solid solution strengthening and crystal grain refining action, in order to effectively exhibit this action must contain 0.1% by weight or more. However, if the content is too high, the tendency to deteriorate formability may be due to an increase in the amount of Mn which cannot be dissolved in the solid solution, and therefore it should be kept at 0.7 wt% or less.

Cr (0.1 to 0.3% by weight) is an element having a crystal grain refining action, and in order to effectively exhibit such an action, it must contain at least a lower limit. However, when content exceeds the said upper limit, an intermetallic compound will be formed and a bad influence will appear. The content of preferable Cr in consideration of this point is 0.1 to 0.3 weight%.

Components constituting the remainder of the aluminum alloy of the present invention are aluminum and unavoidable impurities, and the unavoidable impurities include Ni, Zn, Zr, V, Ti, and Li, and the like. It is not particularly obstacled to securing. Next, each condition of continuous casting and cold rolling using the Al-Mg-Si-based alloy will be described.

When the average cooling rate during solidification in continuous casting is defined as described above, forced employment occurs so that the amount of Al-Fe-Si intermetallic compound in the continuous casting structure decreases, and in addition, the size of the Al-Fe-Si intermetallic compound It is refined to an average of about 2 μm or less, and press formability and bake curability are significantly increased. However, if the average cooling rate during solidification in the continuous casting is lower than the above-mentioned ratio, the amount of precipitation of the intermetallic compound increases, in addition, the particles become thicker, satisfactory press formability is not obtained, and the bake hardenability is also obtained. Worse

Further, after the continuous casting, the temperature of the ingot taken out from the casting machine is 250 ° C. or less, or the temperature of the ingot is cooled to 250 ° C. or less within 2 minutes from when molten metal is injected into the casting machine, and further, without homogenization treatment or hot rolling. By adopting rapid cooling, which is rolled to the final thickness by cold rolling, the precipitation of supersaturated solid solution is suppressed during the cooling of the ingot, the amount of supersaturated solid solution is preserved, and a plate having excellent bake hardenability can be produced. Incidentally, when the temperature of the ingot after casting exceeds 250 ° C, precipitation of supersaturated solid solution occurs, and a plate having inferior bake hardenability is produced.

After the final plate thickness was formed by cold rolling, the solution was treated in a continuous annealing furnace at a range of 530 to 570 ° C, quenched with hot or cold water, and then preliminary aging was performed. Do it. In this case, the reason for specifying the temperature of the solution treatment is to suppress the precipitation of the solid solution element during the solution treatment to maintain a sufficient amount of supersaturated solid element, increase the strength, and increase the amount of the solid element to bake hardenability. To increase. In other words, when the temperature of the solution treatment is lower than 530 ° C., the effect of improving the bake curability becomes insufficient. On the other hand, when the temperature of the solution treatment is higher than 570 ° C, the grains of the crystal become thicker, and further, burning occurs due to the generation of eutectic, and the press formability deteriorates.

In addition, after the solution treatment and after quenching with hot or cold water, preliminary heat treatment can be performed to obtain an Al-Mg-Si alloy plate having remarkably excellent press formability and bake curability. Hardening conditions and aging heat treatment conditions are not particularly limited, but preferable conditions are about 10 minutes to 8 hours at hot water quenching for quenching and 60 to 200 ° C. for aging treatment.

The present invention, in addition to specifying the composition of the Al-Mg-Si-based alloy, in the continuous casting method using the molten metal, the average cooling rate during solidification at 20 ℃ / s or more, the temperature of the ingot from the casting machine is 250 ℃, Alternatively, the ingot may be cooled to a temperature of 250 ° C. or less within 2 minutes from when the molten metal is injected into the casting machine, and furthermore, the ingot may be rolled to a final thickness by cold rolling without homogenizing or hot rolling, and then used in a continuous annealing furnace. Characterized by performing the casting process is characterized in that performing the casting, there is no particular restriction on other conditions, if there are other preferred performance conditions are as follows.

The present invention continuously casts the temperature of the ingot to 250 ℃ or less, or by cooling the continuous cast slab (slab) to 250 ℃ or less and rolled it up, and then rolled to the final thickness only by cold rolling without homogenization treatment or hot rolling And setting the solution treatment condition in the continuous annealing furnace, which results in less heat loss compared to the method of rolling up after the continuous casting, then cooling and then homogenizing or hot rolling. It is effective to increase productivity.

In addition, in the practice of the present invention, by continuously casting the slab slab of about 4 ~ 15mm thickness is continuously produced, rolled up and cold rolled to 0.1 ~ 1mm thickness, and further solution treatment in a continuous annealing furnace and By pre-aging, an aluminum alloy plate is produced. As the continuous casting method employed here, the above water-cooled continuous casting method, twin roll continuous casting method, belt continuous casting method, block continuous casting method and the like can be appropriately selected and adopted.

Next, embodiments of the present invention will be presented, but the present invention is not limited to the embodiments described hereinafter, and modifications deemed to be appropriate within the scope of the present invention can be carried out. It should of course also be included within the technical scope of the invention.

Example 1

A 1 cm thick ingot was cast in a twin belt casting machine according to the following conditions.

Effective cooling length of casting machine: 1m

Casting Speed: 8m / min

Injection temperature of molten metal: 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 flow density in the casting machine, ingots with different temperatures of ingots were obtained immediately after casting.

Subsequently, it was cold rolled to a plate of 1 mm, solution treated at 545 ° C. for 15 seconds, hot water quenched, and preliminary aging treatment at 85 ° C. for 8 hours to prepare a T4 material. In addition, T6 material was subjected to natural aging treatment for one week T4 material, then artificial aging treatment at 170 ℃ for 30 minutes. In order to evaluate the bake curability, the difference in strength of T4 and T6 was measured and these differences were adopted as bake curability. On the other hand, the target excellent bake curability is 100 MP or more. Further, in order to observe the effect of having a homogenization treatment or hot rolling, the bake curability of the plate subjected to the homogenization treatment or hot rolling was measured as a comparative example.

number One 2 3 4 Average heat flow density in the casting machine (MW / m ² ) 3.3 3.3 3.3 2.8 Temperature of ingot immediately after casting (℃) 197 197 197 330 Homogenization Never box Never Never Hot rolled Never Never box Never T4-YS (MPa) 110 105 106 109 T6-YS (MPa) 215 180 190 198 Bake Curable 105 75 84 91 Judgment ○ × × × Example Comparative example Comparative example Comparative example

-Homogenization treatment: furnace cooling after lasting 560 ℃ × 6 hours.

-Hot rolling: After increasing the temperature up to 560 ℃, hot rolling up to 4mm at 550 ℃ of rolling start temperature. After that, it was cold rolled to 1 mm.

Example 2

A 1 cm thick ingot was cast in a twin belt casting machine according to the following conditions.

Effective cooling length of casting machine: 1m

Casting Speed: 8m / min

Injection temperature of molten metal: 700 ℃

Composition: Al, Mg (0.6 wt%), Si (0.8 wt%), Fe (0.2 wt%), Mn (0.2 wt%), Ti (0.01 wt%)

A chiller was attached at the exit of the casting machine to allow the ingot to cool immediately after casting. When the chiller was operated, the temperature of the ingot, which was 357 ° C immediately after casting, passed through the chiller, dropping to 230 ° C within 2 minutes from when it was injected into the casting machine. In contrast, when the cooling device was not operated, the temperature was still high at 330 ° C even after 2 minutes had elapsed since the injection into the casting machine. Subsequently, cold rolling was carried out using a 1 mm plate, and solution treatment was performed at 545 ° C. for 15 seconds, followed by hot water quenching, and preliminary aging treatment at 85 ° C. for 8 hours to prepare a T4 material. In addition, T6 material was subjected to natural aging treatment for one week T4 material, then artificial aging treatment at 170 ℃ for 30 minutes. In order to evaluate the bake curability, the difference in strength of T4 and T6 was measured and these differences were adopted as bake curability. On the other hand, the target excellent bake curability is 100 MP or more.

number One 2 Average heat flow density in the casting machine (MW / m ² ) 2.7 2.7 Temperature of ingot immediately after casting (℃) 357 357 Chiller has exist none Temperature of ingot (℃) 2 minutes after molten metal injection 230 330 T4-YS (MPa) 108 107 T6-YS (MPa) 211 181 Bake Curable 103 74 Judgment ○ × Example Comparative example

Included in the above.

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% (including 0%), Mn: 0.1-0.7% by weight and / or Cr: 0.1-0.3% by weight, and the remainder of the Al-Mg-Si-based molten aluminum alloy made of aluminum has an average cooling rate of 20 ° C / s or more when solidifying To be cast by twin belt casting method, (b) At this time, the temperature of the ingot taken out from the casting machine is 250 ° C or less, (c) then rolled to the final thickness by cold rolling without homogenization or hot rolling, (d) A method for producing an Al-Mg-Si-based aluminum alloy plate having excellent bake hardenability, characterized by performing a solution treatment in a continuous annealing furnace. (a) Mg: 0.3 to 1.0% by weight, Si: 0.3 to 1.5% by weight, Cu: 1.0% by weight or less (including 0%), Fe: 1.2% by weight or less (including 0%), and Mn as necessary. : 0.1 to 0.7% by weight and / or Cr: 0.1 to 0.3% by weight, and the remainder of the Al-Mg-Si-based molten aluminum alloy, the average cooling rate of 20 ℃ / s or more during solidification Casting by twin belt casting, (b) At this time, the ingot is cooled so that the temperature of the ingot is 250 ° C. or less within 2 minutes from when the molten metal is injected into the casting machine. (c) thereafter, cold rolled to the final thickness without homogenization or hot rolling, (d) A method for producing an Al-Mg-Si-based aluminum alloy plate having excellent bake hardenability, characterized by performing a solution treatment in a continuous annealing furnace.