KR20170132116A - High-strength aluminum alloy plate with superior bake-hardenability and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a high-strength aluminum alloy plate with superior bake-hardenability and a manufacturing method thereof, wherein when manufacturing a plate, pre-heat treatment is performed at 65-145C for 3-250 minutes after solution heat treatment. As such, during transportation and storage of the plate, a material property change due to natural aging is able to be restricted, and after forming and painting a vehicle body, strength is able to be improved by bake-hardenability. Moreover, a lightweight transport vehicle body having high strength is able to be manufactured.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength aluminum alloy plate having excellent hardening properties,

The present invention relates to a high-strength aluminum alloy sheet material excellent in hardening of the resin composition and a method for producing the same. More particularly, the present invention relates to a process for producing an aluminum-zinc-magnesium- A step of solubilizing the aluminum-zinc-magnesium-copper-based aluminum alloy sheet (step 2); And a preheating step (step 3) of maintaining the solution-treated aluminum-zinc-magnesium-copper-based aluminum alloy sheet at 65 to 145 ° C for 3 to 250 minutes and then cooling to room temperature To a method of manufacturing a high strength aluminum alloy sheet material.

Due to the tendency to improve fuel efficiency through the light weight of transportation equipment parts in domestic and abroad, there is a growing demand for materials with low density and high strength. Of these aluminum alloys, due to their excellent castability, processability and mechanical properties, Is rapidly increasing.

In the case of aluminum alloy sheets currently used in automobiles, 5000-grade (Al-Mg) alloy sheets having high strength and excellent formability are mainly used for inner plates requiring high processability. In order to cure paints after molding and painting (Al-Mg-Si based) alloy sheet material which can be expected to be improved in strength through paint bake-hardening carried out at a temperature of 170 to 190 ° C for 20 to 40 minutes is excellent in strength and dent resistance Resistance) is required. Table 1 shows the tensile properties of the 5000-series and 6000-series aluminum alloy sheets used as automotive aluminum alloy sheets.

[Table 1]

On the other hand, in order to use the alloy sheet material for the automobile shell, it takes time to transfer the aluminum sheet material after the solution treatment process to the automobile manufacturing company, and the natural aging phenomenon due to this time lag is caused by the original mechanical characteristics Resulting in unevenness in press molding as well as mechanical properties in a baking hardening step carried out by automobile manufacturing companies.

In order to solve such a problem, Korean Patent Registration No. 10-0213678 discloses a method for producing a 6000-series aluminum alloy sheet material having high-hardening property and solidification. Specifically, a stabilizing heat treatment is applied to a 6000-series (Al-Mg-Si-based) alloy sheet for a vehicle body sheathing member at a temperature of 100 to 160 ° C for 5 seconds to 15 minutes immediately after solution treatment in the manufacturing process There has been disclosed a method for manufacturing a high strength aluminum-magnesium-silicon alloy in which the change in physical properties due to the natural aging phenomenon at the time of transfer and storage of the plate material is suppressed and the strength is improved during the heat treatment of the resin composition after the body molding.

However, the 6000-series aluminum alloy sheet manufactured by the above method has a yield strength of 275 MPa and a tensile strength of 363 MPa even after the strength of the cement is improved, so that it is necessary to reinforce the thickness in order to secure rigidity , And when the thickness is reinforced, there is a problem that the lightening effect is reduced.

On the other hand, Al-Zn- (Mg, Cu) alloy, which is a 7000 series aluminum alloy among aluminum alloys, is a high-strength aluminum alloy with very high strength that is comparable to iron, and generally has a high non-strength such as aircraft, It is a heat-treated alloy used for the required structural materials and can be used for the body to lighten the transportation equipment. However, research on aircraft and other structural materials of 7000 series aluminum alloy has been actively carried out so far, It is true.

In the related art, US Patent Publication No. 2014-0069557 discloses a method for manufacturing a high strength 7000 aluminum alloy sheet material. More specifically 0.3 to 4.0 wt.% Of silicon, 0.35 wt.% Or less of iron, 0.3 to 1.2 wt.% Of zinc, 1.3 to 2.4 wt.% Of copper, 0.3 to 2.4 wt.% Of manganese, The aluminum alloy sheet including 0.1% by weight or less of titanium and the rest of aluminum was molded and assembled into a body part, followed by a bake hardening heat treatment to produce a high strength 7000 aluminum alloy sheet.

However, in the case of manufacturing the 7000-series aluminum alloy by the above-described manufacturing method, there is a problem that the increase in the strength after the baking hardening heat treatment is insignificant due to the natural aging caused by the time of transferring the aluminum plate material to the automobile manufacturing related company.

That is, the aluminum-zinc-magnesium-copper-based aluminum alloy is an age hardening type alloy and can improve the strength through formation of a precipitation phase during the artificial aging treatment after the solution treatment. In general, aluminum-zinc- The aging treatment of the aluminum alloy for automobile is carried out at a temperature of 170 to 190 DEG C for 20 to 40 minutes, There is a problem that the mechanical properties of the aluminum-zinc-magnesium-copper-based aluminum alloy deteriorate. In addition, there is a problem that the nucleation site of the precipitation phase is non-uniformly formed due to the natural aging during the time of allowing the solution treatment to be performed at room temperature until the bake hardening heat treatment is performed, so that sufficient strength improvement effect can not be obtained in the bake hardening heat treatment.

Accordingly, the present inventors have developed a 7000-grade aluminum alloy sheet manufactured by a method of performing a preliminary heat treatment after solution treatment in order to manufacture a 7000-series aluminum alloy sheet material having improved strength after the hardening heat treatment, .

Korean Patent No. 10-0213678 U.S. Published Patent Application No. 2014-0069557

An object of the present invention is to provide a high strength aluminum alloy sheet material excellent in hardening of the bake and a method of manufacturing the same.

In order to achieve the above object,

A step of producing an aluminum-zinc-magnesium-copper-based aluminum alloy sheet (step 1);

A step of solubilizing the aluminum-zinc-magnesium-copper-based aluminum alloy sheet (step 2); And

And a preliminary heat treatment step (step 3) in which the solution-treated aluminum-zinc-magnesium-copper-based aluminum alloy sheet material is maintained at 65 to 145 ° C for 3 to 250 minutes and then cooled to room temperature. A method of manufacturing an aluminum alloy sheet material is provided.

In addition,

A high strength aluminum alloy sheet excellent in hardenability after curing is characterized by having an aluminum-zinc-magnesium-copper-based aluminum alloy sheet produced by the above-described method and having a yield strength value of 400 MPa or more after a hardening heat treatment.

The method for producing an aluminum-zinc-magnesium-copper-based aluminum alloy sheet according to the present invention is characterized in that after the solution treatment, preliminary heat treatment is performed at a temperature of 65 to 145 ° C for 3 to 250 minutes, It is possible to further improve the strength by suppressing the change and by hardening the carcass after the car body is formed, and it is possible to manufacture a light-weight transportation vehicle body having high strength.

1 is a view showing a process for manufacturing an aluminum alloy sheet material according to the present invention,
FIGS. 2 to 5 are graphs showing the results of hardness measurement of the aluminum alloy sheet produced according to Examples and Comparative Examples before and after the baking hardening heat treatment,
6 is a graph showing the results of a tensile test before and after performing a bake hardening heat treatment on an aluminum alloy sheet produced according to Examples and Comparative Examples,
FIG. 7 is a transmission electron micrograph showing the microstructure before and after the calcining heat treatment of the aluminum alloy sheet produced according to Examples and Comparative Examples. FIG.

According to the present invention,

A step of producing an aluminum-zinc-magnesium-copper-based aluminum alloy sheet (step 1);

A step of solubilizing the aluminum-zinc-magnesium-copper-based aluminum alloy sheet (step 2); And

And a preliminary heat treatment step (step 3) in which the solution-treated aluminum-zinc-magnesium-copper-based aluminum alloy sheet material is maintained at 65 to 145 ° C for 3 to 250 minutes and then cooled to room temperature. A method of manufacturing an aluminum alloy sheet material is provided.

The high-strength aluminum alloy sheet material can be used as an aluminum alloy sheet for a vehicle body for lightweight transportation. In order to use the high-strength aluminum alloy sheet for a vehicle body, it is subjected to a process of forming, painting and hardening the sheet after the sheet material is manufactured. However, the mechanical properties of the aluminum alloy sheet material may be deteriorated through the above process. Accordingly, the production method of the present invention is a method for producing a high strength aluminum alloy sheet material having excellent curing ability for producing a plate material capable of improving mechanical properties in a baking hardening heat treatment process.

Hereinafter, a method of manufacturing a high-strength aluminum alloy sheet material excellent in hardenability for baking according to the present invention will be described in detail for each step with reference to the drawings.

In the method for producing a high strength aluminum alloy sheet material excellent in hardening of the bake hardenability according to the present invention, step 1 is a step of producing an aluminum-zinc-magnesium-copper-aluminum alloy sheet material.

The aluminum alloy sheet material may be prepared by re-dissolving the aluminum-zinc-magnesium-copper-based aluminum alloy ingot to a thickness of 4.5 mm after thin-plate casting, and the aluminum- zinc- The aluminum-zinc-magnesium-copper-based aluminum alloy sheet having a thickness of about 1.0 mm can be manufactured by sequentially performing annealing, hot rolling, secondary annealing and cold rolling. The method of manufacturing the aluminum-zinc-magnesium-copper-based aluminum alloy sheet is not limited to this, and other types of casting methods such as die casting and press casting can be applied, and other types of processing such as extrusion and forging Method may be applied.

Here, the molten metal may contain 4 to 8% by weight of zinc, 0.5 to 3.5% by weight of magnesium, 0.5 to 2.5% by weight of copper, and aluminum as the remainder. Both zinc (Zn) and magnesium (Mg) have a high solubility in aluminum and form a precipitation phase which contributes to an increase in strength at the time of simultaneous addition. Copper (Cu) also increases the strength of the aluminum alloy (Zn), magnesium (Mg), and copper (Cu) are contained in the aluminum alloy melt in the above content range, the strength of the aluminum alloy sheet produced from the molten alloy is improved.

In the method for producing a high-strength aluminum alloy sheet material excellent in hardening of hardening according to the present invention, step 2 is a step of solution-treating the aluminum-zinc-magnesium-copper-based aluminum alloy.

Wherein the solution treatment is a treatment for heating the alloy to a solid solution range and quenching the aluminum alloy to maintain the solid solution state at room temperature so that stress relief and supersaturation of the aluminum-zinc-magnesium- Can be carried out for the purpose of producing a super-saturated solid solution. At this time, the solution treatment may be performed by a heat treatment at 450 to 510 ° C for 5 minutes to 2 hours, followed by cooling to room temperature. However, the solution treatment is not limited thereto, and can be carried out at an appropriate temperature and time range in which the aluminum alloy becomes a completely solid solution.

In the method for producing a high strength aluminum alloy sheet material excellent in hardening of hardening according to the present invention, step 3 is a step of holding the solution-treated aluminum-zinc-magnesium-copper alloy aluminum alloy sheet at 65 to 145 DEG C for 3 to 250 minutes Followed by cooling to room temperature.

The preliminary heat treatment is carried out in order to eliminate the problem of deterioration of the mechanical properties in the case of the curing heat treatment in which the aluminum alloy sheet material is subsequently made to be manufactured into a car body.

The aluminum-zinc-magnesium-copper-based aluminum alloy is an age hardening type alloy, which is subjected to solution treatment and maintained at 120 ° C. for 24 hours. However, when the aluminum-zinc-magnesium-copper-based aluminum alloy is used for an automobile body, after the solution treatment, the bake hardening heat treatment is carried out at 170 to 190 ° C for 20 to 40 minutes, There is a problem that the mechanical properties are lowered and GP zone below the critical size is unevenly formed due to the natural aging during the standing at room temperature until the curing heat treatment is performed after the solution treatment so that the moldability is reduced, A sufficient strength and improvement in dent resistance may not be obtained during the heat treatment.

Accordingly, in the present invention, the solution-annealed aluminum-zinc-magnesium-copper-based aluminum alloy sheet is maintained at 65 to 145 ° C for 3 to 250 minutes and then cooled to room temperature to uniformly form the nucleation sites of the pre- And an aluminum alloy having improved hardness and yield strength after baking can be produced.

If the temperature for performing the preliminary heat treatment is less than 65 ° C, the diffusion rate of the elements may be low due to the low temperature, so that the nucleation site of the precipitation phase may not be generated uniformly. If the temperature exceeds 145 ° C, The diffusion rate of the elements is high due to the high temperature, so that the nucleation sites of the precipitation phase are coarsened or the precipitation phase is precipitated and the formability may be deteriorated.

On the other hand, when the preliminary heat treatment is performed at 65 to 105 ° C, the heat treatment time is preferably 25 to 250 minutes.

If the heat treatment time is less than 25 minutes in the temperature range of 65 to 105 캜, the nucleation of the precipitated phase is not performed and the effect of improving the strength during the heat treatment for sintering hardening may be small, If it exceeds 250 minutes, the degree of strength improvement is not greatly improved, and the economical efficiency of production may be deteriorated.

When the preliminary heat treatment is performed at 106 to 145 ° C, it is preferable to perform the heat treatment for 3 to 70 minutes.

In addition, when the heat treatment time is less than 3 minutes in the temperature range of 106 to 145 캜, nucleation of precipitation phase is not performed, and the effect of improving the strength in the heat treatment by baking hardening can be small, If it exceeds 70 minutes, there is a problem that the elongation before the baking hardening heat treatment sharply decreases and the formability is decreased.

The method may further include a step of subjecting the aluminum-zinc-magnesium-copper-based aluminum alloy sheet to a hardening heat treatment after the step 3, and further, before the hardening heat treatment of the hardening aluminum-zinc-magnesium- Based aluminum alloy sheet material.

Bake hardening heat treatment is a heat treatment process performed when a vehicle body is manufactured, and is a process which is performed to coat a plate after a forming process such as welding, joining and assembly, and finally to cure the paint. When the aluminum-zinc-magnesium-copper-based aluminum alloy sheet material is manufactured into a body, the final product is completed through the above-described molding process and coating process, and then finally subjected to a curing heat treatment for curing the paint.

At this time, the bake hardening heat treatment can be maintained at 170 to 190 ° C for 20 to 40 minutes, and after the preliminary heat treatment step, hardness and yield strength of the aluminum-zinc-magnesium-copper- have.

Through the manufacturing method of the present invention, the density after the baking hardening heat treatment is 8,000 / 탆 ² To 15,000 / ㎛ ² and comprises a deposition phase of size 2 to 12 ㎚.

The aluminum alloy sheet produced by the manufacturing method according to the present invention has a yield strength of not less than 400 MPa, which is improved by 1.26 to 1.50 times, after the heat treatment for bake hardening, compared with the case where the bake hardening heat treatment is performed without performing the preliminary heat treatment after the conventional solution treatment. Yield strength value.

The present invention also relates to

A high strength aluminum alloy sheet excellent in hardenability after curing is characterized by having an aluminum-zinc-magnesium-copper-based aluminum alloy sheet produced by the above-described method and having a yield strength value of 400 MPa or more after a hardening heat treatment.

Since the aluminum alloy sheet used for automobile bodywork can not be practically molded immediately after solution treatment, it is subjected to a natural aging process as it is left at room temperature. The natural aged sheet material is subjected to molding and painting processes, Curing heat treatment for curing the paint is performed at 170 to 190 캜 for 20 to 40 minutes.

There is a problem in that mechanical properties due to overexposure are reduced when the bake hardening heat treatment is carried out through natural aging after the solution treatment, which is a conventional method, for using an aluminum-zinc-magnesium-copper-aluminum alloy for an automobile body On the other hand, the high strength aluminum alloy sheet material having excellent bake hardenability of the present invention is a plate material subjected to preliminary heat treatment after solution treatment, and can further improve the strength after the bake hardening heat treatment.

The aluminum-zinc-magnesium-copper-based aluminum alloy sheet has a size of 2 to 12 nm and a density of 8,000 / 탆 ² To 15,000 / 占 퐉 ² , and exhibits an effect of improving the strength to 400 MPa or more by the bake hardening heat treatment, and can be used for the body of transportation equipment and can be used for a high strength and light transportation There is an advantage that an apparatus body can be manufactured.

The high strength aluminum alloy sheet material excellent in hardening of the bake hardenability according to the present invention maximizes the hardness and the yield strength after hardening the bake while maintaining the formability of the aluminum-zinc-magnesium-copper-based aluminum alloy through the preliminary heat treatment under predetermined conditions before the bake hardening So that it can be applied to the lightening of parts in the whole industry such as transportation equipment field, electronic product case, and the like.

Hereinafter, the present invention will be described in detail with reference to Examples and Experimental Examples.

However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following Examples.

≪ Example 1 >

A high strength aluminum alloy sheet excellent in hardening hardenability was produced through the following steps.

Step 1: The 7075 aluminum alloy ingot was remelted and an aluminum-zinc-magnesium-copper-based aluminum alloy sheet having a thickness of about 4.5 mm was prepared using a horizontal twin-screw casting apparatus. The copper-based aluminum alloy sheet material was annealed at 400 ° C for one hour, and then hot-rolled and cold-rolled were sequentially performed to produce an aluminum-zinc-magnesium-copper-based aluminum alloy sheet having a thickness of about 1.0 mm.

Step 2: The aluminum-zinc-magnesium-copper-based aluminum alloy sheet material was subjected to solution treatment by holding at 500 캜 for 1 hour.

Step 3: The solution-treated aluminum alloy sheet was pretreated at 90 캜 for 30 minutes and then cooled to room temperature to produce a high strength aluminum alloy sheet excellent in hardening hardenability.

≪ Example 2 >

A high strength aluminum alloy sheet excellent in hardening hardening was prepared by the same method as in Example 1, except that the preheating time of Example 3 was changed to 60 minutes.

≪ Example 3 >

A high strength aluminum alloy sheet excellent in hardening hardening properties was prepared in the same manner as in Example 1, except that the preliminary heat treatment time in Example 1 was changed to 120 minutes.

<Example 4>

A high strength aluminum alloy sheet excellent in hardening of hardening was prepared by the same method as in Example 1 except that the preheating time of Example 3 was changed to 240 minutes.

&Lt; Example 5 >

A high strength aluminum alloy sheet excellent in hardening of hardening was prepared by carrying out the same procedure as in Example 1 except that the preliminary heat treatment temperature in Example 1 was changed to 120 ° C and the heat treatment time was changed to 5 minutes .

&Lt; Example 6 >

A high strength aluminum alloy sheet excellent in hardening hardening was prepared by the same method as in Example 5, except that the preheating time of Step 3 in Example 5 was changed to 10 minutes.

&Lt; Example 7 >

A high strength aluminum alloy sheet excellent in hardening hardening was prepared by the same method as in Example 5 except that the preheating time of Step 3 in Example 5 was changed to 30 minutes.

&Lt; Example 8 >

A high strength aluminum alloy sheet excellent in hardening hardening was produced by the same method as in Example 5, except that the preheating time of Step 3 in Example 5 was changed to 60 minutes.

&Lt; Comparative Example 1 &

An aluminum alloy sheet was produced in the same manner as in Example 1 except that the preliminary heat treatment of Step 3 in Example 1 was not performed.

&Lt; Comparative Example 2 &

A high strength aluminum alloy sheet excellent in hardening hardening properties was prepared in the same manner as in Example 1 except that the preliminary heat treatment temperature in Example 1 was changed to 60 캜 and the preliminary heat treatment time was changed to 5 minutes .

&Lt; Comparative Example 3 &

A high strength aluminum alloy sheet excellent in hardening hardening properties was prepared in the same manner as in Comparative Example 2 except that the preliminary heat treatment time of Step 3 in Comparative Example 2 was changed to 10 minutes.

&Lt; Comparative Example 4 &

A high strength aluminum alloy sheet excellent in hardening hardening properties was prepared in the same manner as in Comparative Example 2, except that the preliminary heat treatment time of Step 3 in Comparative Example 2 was changed to 30 minutes.

&Lt; Comparative Example 5 &

A high strength aluminum alloy sheet excellent in hardening hardening was prepared by the same method as in Comparative Example 2, except that the preheating time of Step 3 in Comparative Example 2 was changed to 60 minutes.

&Lt; Comparative Example 6 >

A high strength aluminum alloy sheet excellent in hardening hardening properties was prepared in the same manner as in Comparative Example 2, except that the preliminary heat treatment time of Step 3 in Comparative Example 2 was changed to 120 minutes.

&Lt; Comparative Example 7 &

A high strength aluminum alloy sheet having excellent hardening properties was produced by the same method as in Comparative Example 2 except that the preheating time of Step 3 in Comparative Example 2 was changed to 240 minutes.

&Lt; Comparative Example 8 >

A high strength aluminum alloy sheet excellent in hardening hardening properties was prepared in the same manner as in Example 1, except that the preliminary heat treatment time of Example 3 was changed to 5 minutes.

&Lt; Comparative Example 9 &

A high strength aluminum alloy sheet excellent in hardening hardening properties was prepared in the same manner as in Example 1 except that the preliminary heat treatment time of Example 3 was changed to 10 minutes.

&Lt; Comparative Example 10 &

A high strength aluminum alloy sheet having excellent curing hardening properties was prepared in the same manner as in Example 5, except that the preheating time of Example 3 was changed to 120 minutes.

&Lt; Comparative Example 11 &

A high strength aluminum alloy sheet having excellent sinter hardenability was prepared in the same manner as in Example 5 except that the preliminary heat treatment time of Step 3 in Example 5 was changed to 240 minutes.

&Lt; Comparative Example 12 >

A high strength aluminum alloy sheet excellent in hardening hardening properties was prepared by carrying out the same procedure as in Example 1 except that the preliminary heat treatment temperature in Example 1 was changed to 150 캜 and the preliminary heat treatment time was changed to 5 minutes .

&Lt; Comparative Example 13 &

A high strength aluminum alloy sheet having excellent sinter hardenability was prepared in the same manner as in Comparative Example 12 except that the preliminary heat treatment time of Step 3 in Comparative Example 12 was changed to 10 minutes.

&Lt; Comparative Example 14 >

A high strength aluminum alloy sheet excellent in hardening hardening was prepared by the same method as in Comparative Example 12, except that the heat treatment time of Step 3 in Comparative Example 12 was changed to 30 minutes.

&Lt; Comparative Example 15 &

A high strength aluminum alloy sheet having excellent sinter hardenability was prepared in the same manner as in Comparative Example 12, except that the preliminary heat treatment time of Step 3 in Comparative Example 12 was changed to 60 minutes.

&Lt; Comparative Example 16 >

A high strength aluminum alloy sheet excellent in hardening of hardening was prepared by the same method as in Comparative Example 12, except that the preliminary heat treatment time of Step 3 in Comparative Example 12 was changed to 120 minutes.

&Lt; Comparative Example 17 >

A high strength aluminum alloy sheet having excellent curing hardening properties was prepared in the same manner as in Comparative Example 12, except that the preliminary heat treatment time of Step 3 in Comparative Example 12 was changed to 240 minutes.

The heat treatment conditions performed in the above Examples and Comparative Examples are shown in Table 2 below.

[Table 2]

&Lt; Experimental Example 1 > Comparison of hardness before and after hardening heat treatment (1)

The following experiment was conducted to confirm the hardness change of the aluminum alloy sheet produced by the manufacturing method of the present invention before and after the bake hardening heat treatment.

The aluminum alloy sheets prepared in Comparative Examples 2 to 7 were kept at 180 캜 for 30 minutes after coating, and the hardness before and after the bake hardening heat treatment was measured with a Vickers hardness tester. At this time, 11 hardness measurements were carried out using the test conditions of a load of 0.3 kg and a holding time of 5 seconds, and then the average of the remaining 9 hardness values except the maximum / minimum values was obtained. The results are shown in FIG.

As shown in FIG. 2, the hardness values of 125 to 135 Hv before performing the hardening heat treatment in Comparative Examples 2 to 7, and having a hardness value of 130 to 140 Hv after the hardening heat treatment were performed.

As a result, when the preliminary heat treatment is carried out at 60 ° C, the increase in hardness value at the time of baking hardening is insignificant to less than 10 Hv and the degree of improvement in strength and dent resistance is small.

&Lt; Experimental Example 2 > Comparison of hardness before and after hardening heat treatment (2)

The following experiment was conducted to confirm the hardness change of the aluminum alloy sheet produced by the manufacturing method of the present invention before and after the bake hardening heat treatment.

The hardness of the aluminum alloy sheet produced by Examples 1 to 4 and Comparative Examples 8 and 9 was measured at 180 DEG C for 30 minutes before and after the baking hardening treatment was performed under the same conditions as in Experimental Example 1, The results are shown in Fig.

3, Comparative Examples 8 and 9 had a hardness value of about 130 Hv before performing the bake hardening heat treatment and had a hardness value of about 140 Hv after the bake hardening heat treatment, 4 has a hardness value of about 135 Hv before performing the bake hardening heat treatment and has a hardness value of 155 to 165 Hv after the bake hardening heat treatment and the hardness value is improved as the heat treatment time is increased

It can be seen from this that, when the preliminary heat treatment is performed at 90 ° C, the hardness value after the heat treatment after the curing heat treatment is greatly improved when the heat treatment is performed for 10 minutes or more.

&Lt; Experimental Example 3 > Hardness comparison before and after hardening heat treatment (3)

The following experiment was conducted to confirm the hardness change of the aluminum alloy sheet produced by the manufacturing method of the present invention before and after the bake hardening heat treatment.

The hardness of the aluminum alloy sheet manufactured by Examples 5 to 8 and Comparative Examples 10 and 11 before and after the baking hardening heat treatment was maintained at 180 ° C for 30 minutes after coating was measured under the same conditions as in Experimental Example 1, The results are shown in Fig.

As shown in FIG. 4, in Examples 5 to 8, a hardness value of about 135 to 140 Hv before carrying out the bake hardening heat treatment, and a hardness value of 160 to 170 Hv after the bake hardening heat treatment, The hardness value after the curing heat treatment was greatly improved, whereas in the case of Comparative Examples 10 and 11, the hardness value before the curing hardening heat treatment was greatly improved. As a result, the aluminum alloy sheet manufactured by Comparative Examples 10 and 11 exhibited low molding You can expect to see sex.

As a result, when the preliminary heat treatment is carried out at 120 ° C, when the heat treatment is performed for more than 120 minutes, the formability is deteriorated.

&Lt; Experimental Example 4 > Hardness comparison before and after hardening heat treatment (4)

The following experiment was conducted to confirm the hardness change of the aluminum alloy sheet produced by the manufacturing method of the present invention before and after the bake hardening heat treatment.

The aluminum alloy sheets prepared in Comparative Examples 12 to 17 were kept at 180 캜 for 30 minutes after coating, and the hardness before and after the baking hardening treatment was measured with a Vickers hardness tester. The results are shown in Fig.

As shown in FIG. 5, the hardness values of 135 to 145 Hv before performing the bake hardening heat treatment in Comparative Examples 12 to 17 have a hardness value of 140 to 145 Hv after the bake hardening heat treatment.

As a result, it can be seen that, when the preliminary heat treatment is performed at 150 ° C, the degree of hardness improvement is small even after the preliminary curing heat treatment is performed.

&Lt; Experimental Example 5 > Evaluation of tensile properties before and after baking hardening heat treatment

In order to evaluate the tensile properties before and after the hardening annealing of the aluminum alloy sheet produced by the manufacturing method of the present invention, a tensile test was performed at room temperature by making a plate-like tensile specimen having a gauge length of 25 mm and a gauge width of 6 mm.

At this time, the aluminum alloy sheet materials prepared in Examples 1 to 8 and Comparative Examples 8 and 11 were subjected to the tensile test, and after the aluminum alloy sheet material was coated, heat treatment was performed at 180 ° C for 30 minutes, The results are shown in Fig.

As shown in FIG. 6, in the case of the elongation, the elongation was as high as 15.4 to 22.9% before the baking hardening heat treatment in Examples 1 to 8, And a yield strength of about 401 to 484 MPa, indicating high dent resistance and strength. These results show an improvement in yield strength at a level of 100 to 190 MPa as compared with the tensile properties after curing of the aluminum alloy produced by Comparative Example 1. [

&Lt; Experimental Example 6 >

In order to observe the microstructure of the aluminum alloy sheet produced by the manufacturing method of the present invention after the natural aging and the calcination heat treatment, the following experiment was conducted.

The aluminum alloy sheet prepared in Comparative Example 1 and Example 7 was subjected to a curing heat treatment to prepare a thin plate having a thickness of 80 占 퐉 or less and then subjected to jet polishing to prepare a specimen for transmission electron microscope and a transmission electron microscope And the microstructure was observed. The results are shown in FIG.

As shown in Figure 7, in the case of Comparative Example 1 subjected to the bake hardening heat treatment with no pre-aging, it is deposited on the density 3,200 / ㎛ ² And the average size of 10 ㎚ was between 5 and 16 ㎚. On the other hand, when the GP zone was stably distributed through the preliminary heat treatment for 30 minutes and then the bake hardening heat treatment was performed, in Example 7, the density of the precipitate was 10,500 / ㎛ ² and the average size was 6 ~ 12 nm. As a result, it can be expected that the baking hardening heat treatment after the preliminary heat treatment shows higher mechanical properties.

Claims (10)

(Step 1) of producing an aluminum alloy sheet comprising 4 to 8% by weight of zinc, 0.5 to 3.5% by weight of magnesium, 0.5 to 2.5% by weight of copper and aluminum of the remaining components;
A step of solubilizing the aluminum alloy sheet material (step 2);
A preliminary heat treatment step (step 3) of keeping the solution-treated aluminum alloy sheet material at 90 to 120 and then cooling it to room temperature; And
And a step (4) of subjecting the aluminum-zinc-magnesium-copper-based aluminum alloy sheet material to a bake hardening heat treatment,
Wherein the aluminum alloy sheet material having a yield strength value of 400 MPa or more is produced after the bake hardening heat treatment.
The method according to claim 1, wherein in the step 4, the hardening heat treatment is performed by heating the aluminum-zinc-magnesium-copper-based aluminum alloy sheet material at 170 to 190 ° C for 20 to 40 minutes after the step 3, &Lt; / RTI &gt;
The method of manufacturing a high strength aluminum alloy sheet according to claim 1, wherein the method further comprises molding the aluminum alloy before performing the bake hardening heat treatment.
The method of claim 1, wherein the manufacturing method of high-strength aluminum alloy plate bake curing is excellent, characterized in that for producing the aluminum alloy plate including the burn-hardening heat treatment since the density of 8,000 / ㎛ ² to 15,000 / ㎛ ² precipitation phase &Lt; / RTI &gt;
The method according to claim 1, wherein the aluminum alloy sheet material comprises a precipitate phase having a size of 2 to 12 nm after the bake hardening heat treatment.
The method according to claim 1, wherein the aluminum alloy sheet material has a relative yield strength improved by 1.26 to 1.50 times when the bake hardening heat treatment is performed without performing the preliminary heat treatment of the step 3 after the bake hardening heat treatment Wherein the high hardness aluminum alloy sheet has excellent hardening properties.
An aluminum alloy sheet comprising 4 to 8% by weight of zinc, 0.5 to 3.5% by weight of magnesium, 0.5 to 2.5% by weight of copper, and aluminum of the remaining components, produced by the manufacturing method of claim 1 and having a yield strength of 400 MPa or more Wherein the high hardness aluminum alloy sheet has an excellent curing property.
The high strength aluminum alloy sheet according to claim 7, wherein the aluminum alloy sheet has a precipitate phase having a density of 8,000 / 탆 ² to 15,000 / 탆 ² after the bake hardening heat treatment.
8. The high strength aluminum alloy sheet according to claim 7, wherein the aluminum alloy sheet comprises a precipitate phase having a size of 2 to 12 nm after the baking hardening heat treatment.
8. The high strength aluminum alloy sheet material according to claim 7, wherein the aluminum alloy sheet material is used for a vehicle body of a transportation equipment.

Images