JPH06145868A - Aluminum alloy sheet for high speed forming and its production - Google Patents

Abstract

PURPOSE:To produce an Al alloy sheet having high speed formability by subjecting an Al alloy contg. specified amounts of Mg and copper to specified annealing treatment. CONSTITUTION:The soft sheet of an Al alloy having a compsn. contg., by weight, 4.0 to 10.0% Mg or contg. 4.0 to 10.0% Mg and 0.1 ineritable impurities 0.5% copper and in which the content of both iron and Si as ineritable impurities is regulated to <=0.2%, and the balance Al is subjected to annealing treatment of executing heating to 300 to 450 deg.C at <=200C/h temp. raising rate and holding it to the same temp. for 0 to 6hr, by which the grain size of the metallic structure is regulated to <=60mum. In this way, its (m) value showing the dependency on the strain rate is regulated to <=-0.001, the average fracture strength in the three directions of 0 deg., 45 deg. and 90 deg. is regulated to >=280MPa and the maximum difference thereamong is regulated to >=5MPa.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an aluminum alloy sheet having excellent strength and ductility and having a good appearance after forming,
In particular, it has excellent high-speed formability with an average strain rate of 0.01 sec ^-1 or more.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been mainly used for automobile outer panels. However, since the demand for weight reduction of automobile bodies has recently been increasing, the use of aluminum alloy sheets has been studied.

Generally, materials for automobile outer panels are required to have excellent press formability and high strength. And as an aluminum material satisfying such characteristics, a JIS5052 alloy (Al-2.5wt% M
g-0.25 wt% Cr) and JIS5182 alloy (Al-4.5
Al-Mg based alloys such as wt% Mg-0.35 wt% Mn) were usually used.

[0004]

The JIS 5000 series alloy, which is the above-mentioned aluminum alloy, has a lower ductility than steel materials and has a drawback that it is easily cracked during forming. Therefore, in order to improve the ductility, measures such as addition of various elements and reduction of impurities have been studied, but the effect of sufficiently improving the ductility has not been obtained.

[0005]

As a result of various studies in view of this, the present invention positively utilizes the difference in deformation resistance of materials particularly in high-speed molding, and further improves shrinkage flangeability by texture of materials. The purpose of this is to develop an aluminum alloy sheet having substantially high formability regardless of the improvement of the apparent ductility.

That is, the aluminum alloy plate of the present invention is M
g: 4.0 to 10.0 wt% or Mg: 4.0 to 10.0 wt%
And Cu: 0.1 to 0.5 wt%, Fe and Si as unavoidable impurities to 0.2 wt% or less, and other impurity elements to 0.05 wt% or less. It is a soft plate, the grain size of the metal structure is 60μm or less, the m value showing the strain rate dependence is -0.001 or less, 0 ° to the rolling direction, 45
For high-speed molding with an average strain rate of 0.01 sec ^-1 or more, characterized in that the average breaking strength in the three directions of 90 ° and 90 ° is 280 MPa or more, and the maximum difference in the breaking strength in the three directions is 5 MPa or more. It is an aluminum alloy plate.

Further, the manufacturing method of the present invention uses Mg: 4.0-1
0.0 wt% or Mg: 4.0 to 10.0 wt% and Cu: 0.0.
1 to 0.5 wt% and Fe as an unavoidable impurity
And Si are both set to 0.2 wt% or less and other impurity elements are regulated to 0.05 wt% or less, and the aluminum alloy ingot composed of the balance Al is homogenized at a temperature of 480 ° C or higher and hot-worked. Rolling and cold rolling to give a rolled plate, and then subjecting the rolled plate to an annealing treatment of heating it to a temperature of 300 to 450 ° C at a heating rate of 200 ° C / h or less and holding it at that temperature for 0 to 6 hours. The crystal grain size of the metal structure is 60 μm
Below, the strain rate dependence m value is -0.001 or less, the average breaking strength in three directions 0 °, 45 °, 90 ° with respect to the rolling direction is 280 MPa or more, and the breaking strength in the three directions is Is a maximum difference of 5 MPa or more, and the average strain rate is 0.01 sec ^-1 or more.

[0008]

First, the reason why the alloy composition is limited in the present invention will be described.

When Mg forms a solid solution in Al, the strength is improved, and the work-hardening property is increased, so that the ductility is increased and the formability is improved. Further, the effect of fixing with dislocations is lowered at a high strain rate at the time of forming, so that it has a function of lowering the m value which is described below and which shows the strain rate dependency. And the content of Mg is 4.0-1
If the amount is less than 4.0 wt%, the above effect is small, while if it exceeds 10.0 wt%, the stress corrosion cracking resistance (SCC resistance) deteriorates and the hot workability deteriorates. This is because manufacturing becomes difficult.

Cu is applied to the GP zone, θ ', and
Since S phase is precipitated, it is added when it is desired to secure the strength after coating. However, its content is 0.1-0.5wt%
The reason is that if less than 0.1 wt%, the strength improvement is small,
This is because if it exceeds 0.5% by weight, the corrosion resistance decreases.

Fe and Si are usually contained as impurities of Al. However, Fe and Si easily form a compound with each other, and the compound becomes a starting point of a crack at the time of molding, which causes a decrease in ductility. This decrease in ductility is due to Fe, S
All of i become remarkable when more than 0.2 wt%. Therefore, their contents were both limited to 0.2 wt% or less.

Mn, Cr, T as other impurity elements
Although i, Ni, etc. are effective in making the crystal grains finer or improving the matrix strength, the ductility is lowered when the content is large, so both are limited to 0.05 wt% or less.

Next, the reasons for limiting the manufacturing method and the characteristics will be described. The homogenization treatment of the ingot is made of Mg, F formed during casting
It is necessary to carry out a sufficiently high temperature and a long time in order to form a solid solution of a compound such as e or Si in the matrix and reduce the amount. However, if the holding temperature is less than 480 ° C, the compound cannot be sufficiently dissolved in the solution during the actual operation, so a temperature of 480 ° C or higher is necessary.

Subsequent hot rolling and cold rolling may be carried out under normal conditions without any particular problem, and if necessary, intermediate annealing may be carried out during cold rolling.

Next, in the annealing at the final plate thickness after the completion of cold rolling, the holding temperature was set to 300 to 450 ° C. In some cases, recrystallization may not occur completely below 300 ° C., and when it exceeds 450 ° C. This is because the condition that the diameter is 60 μm or less cannot be achieved and sufficient breaking strength may not be obtained. The holding time is set to 0 to 6 hours because the effect of improving the characteristics is saturated even if the holding time is longer than 6 hours, which is economically disadvantageous. Further, the heating rate was set to 200 ° C / h or less in order to suppress the generation of random recrystallization nuclei, and if it exceeds 200 ° C / h, the maximum difference in rupture strength in 3 directions, which will be described later, of 5 MPa or more cannot be achieved. is there.

After completion of the above-mentioned annealing, if necessary, straightening by a tension leveler or the like, surface cleaning, etching, lubricating oil application, etc. are performed.

Further, the crystal grain size of the Al alloy plate material obtained by the above-mentioned manufacturing process is defined as 60 μm or less, because the larger the crystal grain is, the smaller the effect of fixing dislocations of the solid solution Mg atoms becomes, so that sufficient strength can be obtained. As it disappears, the effect of lowering the deformation resistance due to the increase in strain rate becomes smaller.
This is because an m value of 0.001 or less cannot be obtained.

Here, the m value will be described. This m
The value is 10mm / min. For a standard JIS-5 test piece.
Pull at a speed of 500 mm / min., Nominal strain at that time is 20%
When the stress at time is P ₁₀ and P ₅₀₀ respectively, m = ln (P
It is a value obtained by ₅₀₀ / P ₁₀ ) / ln ₅₀ and is an index showing strain rate dependence.

In a normal steel material, m> 0, and in this case, the higher the strain rate, the greater the stress and the greater the strength, that is, the harder. On the other hand, JIS 5000 series etc. Al
In the case of an alloy, m <0, and in this case, the higher the strain rate, the smaller the stress and the smaller the strength, that is, the softer. Therefore, in general, in the case of the above Al alloy, the strength of the locally deformed part is lowered and the part immediately breaks, so that the moldability has not been recognized as being good.

By the way, generally, in press molding, a part of the material comes into contact with the punch and bears the load, but even in the case of high speed molding, the material does not deform except for a slight sliding, so the strain rate of that part is small. . On the other hand, the portion flowing along the die has a strain rate proportional to the forming rate. Therefore, the higher the molding speed, the more the part that bears the load,
The difference in strain rate of the fluidized portion that is greatly deformed becomes large.

Therefore, in the case of high-speed forming of the above Al alloy, when the m value is negative, the higher the strain rate, the smaller the deformation resistance. Therefore, the difference between the deformation resistance of the portion that bears the load and the deformation resistance of the flowing portion becomes large. The present inventors have found that the formability is remarkably improved. Moreover, it was found that high-speed moldability was better when the m value had a larger negative value to some extent.

Therefore, in the case of molding with a strong drawing component, in addition to the conditions of the average value of breaking strength in three directions and the maximum strength difference in three directions, which will be described later, the m value for obtaining the effect of improving the moldability is
The condition that the average strain rate is 0.001 or less and the average strain rate is 0.01 sec-1 or more is indispensable. If this condition is not satisfied, sufficient formability cannot be obtained. The average strain rate is a value obtained by dividing the maximum strain (true strain) of the molded product by the time required for molding.

On the other hand, in drawing, high breaking strength is important to allow the material to flow in more than the ductility. And when actually forming, especially when using low-viscosity lubricating oil, as a result of experiments, it was found that the average breaking strength in three directions of 0 °, 45 ° and 90 ° with respect to the rolling direction should be 280 MPa or more. I found it. Further, it is important that the inflow resistance of the flange is low in the case of molding to obtain a high drawing height with a low drawing ratio, and it is also found that a texture having a maximum strength of 5 MPa or more in the above three directions is effective. It was If these conditions are not satisfied, cracking may occur in the case of molding with a strong drawing component. The average of the above three directions of intensity is 0
Add twice the strength in the 45 ° direction to the strength in the 90 ° and 90 ° directions,
It is a value divided by 4.

[0024]

EXAMPLE An Al alloy having the composition shown in Table 1 was melted and cast by a conventional method, and then the alloy and the manufacturing conditions shown in Table 2 are shown in Table 3.
The Al alloy plate material having a thickness of 1 mm was combined as shown in FIG. Then, a tensile test was performed on these plate materials to obtain tensile strength, proof stress and elongation, and m value was measured. As a forming test, blank drawing was performed with a blank diameter of 80 mm and a drawing ratio of 1.81 under the conditions of a wrinkle holding force of 3000 kgf and a low viscosity rust preventive oil coating. The moldability was evaluated by comparing the breaking height in the above molding test.

[0025]

[Table 1] In the table, * indicates each of the other impurity elements.

[0026]

[Table 2]

[0027]

[Table 3] In the table, the strength average of * 1 indicates the average value of tensile strength in three directions. * 2 Maximum strength difference indicates the maximum difference in tensile strength in three directions. The m value of * 3 indicates the average value in 3 directions.

As is apparent from Table 3, in the forming test, it is understood that the plate materials of the present invention all have a breaking height higher than the conventional level of 25 mm and have good formability. On the other hand, the plate materials according to the comparative examples each have a breaking height of 25 mm or less and are inferior in formability.

[0029]

As described above, the Al alloy sheet material of the present invention exhibits high formability in high-speed forming and is particularly suitable for mechanical presses and high-speed hydraulic presses that are frequently used in actual operations, and are suitable for automobile body sheets, pressure-resistant containers, and packaging containers. It has a remarkable industrial effect such that it is most suitable as a molding material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minoru Hayashi Minoru Hayashi 2-6-1 Marunouchi Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd. (72) Inventor Ryo Tokaibayashi 2-6-1 Marunouchi Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd.

Claims (2)

[Claims] 1. Mg: 4.0 to 10.0 wt%, or M
g: 4.0 to 10.0 wt% and Cu: 0.1 to 0.5 wt%, and 0.2 and 0.2 of Fe and Si as unavoidable impurities.
wt% or less, 0.05 wt% for all other impurity elements
Restricted to the following, a soft plate of aluminum alloy consisting of the balance Al, the crystal grain size of the metal structure is 60μm or less, the m value showing the strain rate dependence is -0.001 or less, with respect to the rolling direction The average breaking strength in three directions of 0 °, 45 ° and 90 ° is 280 MPa or more, and the maximum difference in breaking strength in the three directions is 5 MPa or more, and the average strain rate is 0.01 sec ^-1 or more. Aluminum alloy plate for high speed forming. 2. Mg: 4.0 to 10.0 wt%, or M
g: 4.0 to 10.0 wt% and Cu: 0.1 to 0.5 wt%, and Fe and Si both as unavoidable impurities of 0.2
wt% or less, 0.05 wt% for all other impurity elements
The aluminum alloy ingot containing the balance Al is homogenized at a temperature of 480 ° C or higher and hot-rolled and cold-rolled to form a rolled plate.
The crystal grain size of the metal structure is reduced to 60 μm or less by heating at 50 ° C. at a temperature rising rate of 200 ° C./h or less and holding at that temperature for 0 to 6 hours, and the strain rate dependence Value of -0.001 or less, 0 ° to the rolling direction,
The average breaking strength in 3 directions of 45 ° and 90 ° is 280 MPa or more,
A method for producing an aluminum alloy sheet for high-speed forming having an average strain rate of 0.01 sec ^-1 or more, characterized in that the maximum difference in breaking strength in the three directions is 5 MPa or more.