JP2002266057A - Method for producing magnesium alloy sheet having excellent press formability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a magnesium alloy sheet which has excellent press formability with extremely high efficiency, and a magnesium alloy sheet which has excellent cost performance, and is press-formable into a complicated shape. SOLUTION: The production method for a magnesium alloy sheet contains a hot extrusion stage where a cast billet consisting of a magnesium alloy is worked into a sheet material for rolling; and a cold rolling stage where the sheet material for rolling is worked into the magnesium alloy sheet having a prescribed thickness. In the production method, a process annealing stage can be provided in the process of the cold rolling stage. As the magnesium alloy to be applied preferably has a composition containing, by weight, l to 6.5% Al, 0.2 to 2.5% Zn and 0.1 to 0.5% Mn, and the balance Mg with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a magnesium alloy sheet having excellent press formability.

[0002]

2. Description of the Related Art Since the crystal structure of a magnesium alloy is a dense hexagonal crystal, such a magnesium alloy is known as a material which is hardly plastically deformed at room temperature and has poor cold workability. For this reason, conventionally, a magnesium alloy plate having a predetermined thickness is manufactured by hot or warm rolling, in which the magnesium alloy is easily plastically deformed. Such a method is also disclosed in Japanese Patent Application Laid-Open No. 6-293944, in which a slab made of a magnesium alloy is repeatedly heated and rolled by hot rolling or warm rolling to produce a magnesium alloy plate having a desired thickness. ing.

[0003]

However, in the above-mentioned conventional method, heating and rolling for producing a magnesium alloy plate having a predetermined thickness are repeated, so that a great amount of time and labor is required. , Which also hindered productivity. This has been reflected in the manufacturing cost of the magnesium alloy sheet, and greatly affected the price of a press-formed product formed from the magnesium alloy sheet.

Further, in the conventional manufacturing method, since heating and rolling are repeated, the crystal structure of the obtained magnesium alloy sheet becomes coarse. Such a crystal structure is
The press formability when press forming the magnesium alloy sheet in a heated state is reduced. In particular, when the pressing speed is increased, the corner portion may be narrowed or cracked during drawing, and a desired shape may not be secured.

The present invention provides a method for manufacturing a magnesium alloy sheet excellent in press formability extremely efficiently, and provides a magnesium alloy sheet excellent in cost performance and capable of being press-formed into a complicated shape. Things.

[0006]

According to a first aspect of the present invention, there is provided a method for producing a magnesium alloy sheet having excellent press formability, comprising: a hot extruding step of processing a cast billet made of a magnesium alloy into a sheet material for rolling; And a cold rolling step of processing the sheet material into a magnesium alloy sheet having a predetermined thickness.

According to the present invention, the hot extruding step of processing a cast billet made of a magnesium alloy into a sheet for rolling and the cold rolling step of processing the sheet for rolling into a magnesium alloy sheet having a predetermined thickness are performed. As a result, a magnesium alloy sheet can be manufactured extremely efficiently as compared with the conventional method having a hot rolling step and a warm rolling step.
In particular, in the present invention, the hot-extrusion with a high working ratio causes the subsequent cold-rolling working ratio (reduction ratio).
There is an advantage that it is possible to extrude a rolling plate having an arbitrary thickness corresponding to the above. Also, as mentioned above,
Since a magnesium alloy plate can be manufactured by cold rolling, a magnesium alloy plate made of fine crystal grains can be manufactured. The magnesium alloy sheet thus obtained is excellent in press formability and can easily form a molded article having a complicated shape.

The invention according to claim 2 is characterized in that, in the method for producing a magnesium alloy sheet excellent in press formability according to claim 1, an intermediate annealing step is provided in the middle of the cold rolling step.

According to the present invention, an intermediate annealing step is provided in the middle of the cold rolling step for processing into a magnesium alloy sheet having a predetermined thickness, so that the cold rolling step and the intermediate annealing step allow the hot extrusion step to be performed. The processed rolling plate material can be processed into a magnesium alloy plate having a predetermined thickness.

According to a third aspect of the present invention, there is provided the method for producing a magnesium alloy sheet excellent in press formability according to the first or second aspect, wherein the magnesium alloy is Al: 1 to 6 by weight%. 0.5%, Zn: 0.2 to 2.5
%, Mn: 0.1 to 0.5%, balance: Mg and inevitable impurities.

According to the present invention, a magnesium alloy having this component composition is suitably applied to the characteristic production method of the present invention having the above-mentioned hot extrusion step and cold rolling step, and is extremely efficient. A magnesium alloy plate can be manufactured, and the manufactured magnesium alloy plate is excellent in press formability and cost performance, and can be easily press-formed into a molded article having a complicated shape.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A method for producing a magnesium alloy sheet having excellent press formability (hereinafter referred to as “magnesium alloy sheet”) according to the present invention will be described.

The method for producing a magnesium alloy sheet according to the present invention comprises a hot extrusion step of processing a cast billet made of a magnesium alloy into a sheet for rolling, and a cold extrusion step of processing the sheet for rolling into a magnesium alloy sheet having a predetermined thickness. And a hot rolling step.

The cast billet is formed by melting and casting a magnesium alloy described later. As the casting method, a conventional method can be applied and is not particularly limited. The shape of the cast billet is arbitrarily formed according to the container shape and the die shape of the hot extrusion device in the hot extrusion process described later.

The hot extruding step is a step of extruding the above-mentioned cast billet by a hot extruder and processing it into a rolling plate having a predetermined thickness. As the extrusion method, it can be applied regardless of direct extrusion and indirect extrusion,
Extrusion conditions can apply the conventional conditions in hot extrusion of a magnesium alloy.

As described above, the thickness of the rolled sheet material to be processed is arbitrary depending on the thickness of the magnesium alloy sheet to be manufactured, the number of times of cold rolling for rolling to the thickness, and the rolling reduction. Is set to

The cold rolling step is a step after the hot extrusion step, and is a step for processing a sheet material for rolling having a predetermined thickness into a magnesium alloy sheet having a desired thickness.
In the present invention, after the hot extrusion step, without providing a hot rolling step or warm rolling step, it is characterized by providing a cold rolling step, by such a manufacturing method, very efficient This enables the production of magnesium alloy sheets.

The rolling reduction in the cold rolling step is 30%
The following rolling reductions can be particularly preferably applied. The rolling reduction is not particularly limited, and may be rolling once (one pass) or rolling multiple times. When the rolling reduction exceeds 30%, cold rolling can be further performed after the intermediate annealing. It is particularly preferable that the cold rolling after the intermediate annealing is also performed at a rolling reduction of 30% or less. When cold rolling is required subsequently, such cold rolling and intermediate annealing can be repeatedly performed, and further cold rolling can be performed with the intermediate annealing interposed therebetween.

In the intermediate annealing step, the rolling reduction of the cold rolling is 30.
% Is preferably provided. Even if the rolling reduction in one cold rolling step is 30% or less, if the total rolling reduction in two or more cold rolling steps exceeds 30%, an intermediate annealing step is provided, followed by a cold rolling step. Preferably, a cold rolling step is provided.

According to the method for manufacturing a magnesium alloy sheet of the present invention, a magnesium alloy sheet having a desired thickness can be manufactured very efficiently. The manufactured magnesium alloy sheet has high strength with fine crystal grains, is excellent in press formability such as deep drawing, and can easily form a molded body having a complicated shape. As a result, it can be preferably applied to uses such as an electronic component case having a complicated shape.

Further, since it is a high-strength magnesium alloy sheet having fine crystal grains, it is possible to increase the efficiency of press forming by heating during press forming to an optimum state for press forming. is there. The magnesium alloy sheet according to the present invention can realize an optimal state for press forming by such a heating treatment, and can adjust, for example, a forming amount of a corner portion of a press formed product. As a result, it is possible to form a part having a high degree of difficulty, and it is possible to further improve the efficiency of press forming and improve the continuous formability.

Next, the component composition of the magnesium alloy will be described.

The magnesium alloy applied to the manufacturing method of the present invention is, by weight%, Al: 1 to 6.5% and Zn: 0.1%.
2 to 2.5%, Mn: 0.1 to 0.5%, balance: Mg and a component composition consisting of unavoidable impurities.

[0024] Al is preferably added in the range of 1 to 6.5%, more preferably in the range of 2 to 4%. Al is positively added for the purpose of improving mechanical properties such as strength and corrosion resistance, but when the added amount of Al exceeds 6.5%, the workability in the cold rolling step is reduced. May drop. If the amount of Al added is less than 1%, the corrosion resistance may decrease, and the strength may decrease. As a result, press formability may decrease.

It is preferable that Zn is added in the range of 0.2 to 2.5%. Like Al, Zn contributes to improvement of mechanical properties such as strength.
If the addition amount exceeds 2.5%, the corrosion resistance may decrease. If the amount of Zn is less than 0.2%, the strength may decrease, and as a result, the press formability may decrease.

Mn is preferably added in the range of 0.1 to 0.5%. Mn has an effect of mitigating the influence of elements that reduce corrosion resistance. That is, by adding Mn, the influence of Fe, which is an impurity element that lowers corrosion resistance, can be reduced,
By adding in the above range, the effect can be exhibited most.

[0027]

The present invention will be described below in more detail with reference to Examples and Comparative Examples.

(Example) A magnesium alloy having a composition shown in Table 1 was melted by a usual melting method, and a magnesium alloy having a diameter of 1
A 55 mm cast billet was made. The cast billet was extruded by a hot extruder into two types of rolling plates having a width of 100 mm, a thickness of 1.0 mm and a thickness of 0.7 mm. The hot extrusion at this time was performed at an extrusion speed of 5 to 10 m / min after heating to 350 ° C.

[0029]

[Table 1]

Next, the rolling plate was cold-rolled to obtain a magnesium alloy plate having a predetermined thickness. At this time, in the rolling plate having a thickness of 1.0 mm, the sheet was cold-rolled to a plate having a thickness of 0.7 mm, then subjected to intermediate annealing at 300 ° C. for 5 minutes, and then to a plate having a thickness of 0.6 mm After cold rolling to 300 ° C. × 5 minutes, the steel sheet is cold-rolled to a sheet having a thickness of 0.5 mm, and then subjected to intermediate annealing at 300 ° C. × 5 minutes. By cold rolling to 0.4 mm, a magnesium alloy sheet according to the present invention was obtained. Further, in the case of a 0.7 mm-thick rolling plate material, the thickness is 0.1 mm.
The magnesium alloy sheet according to the present invention was cold-rolled to 6 mm.

The two types of magnesium alloy sheets obtained in this way were 87 mm long × 84 mm wide × corner R10 m.
m was processed into a test sample for press molding.

(Comparative Example) A magnesium alloy having the composition shown in Table 1 was melted by a normal melting method, and a thickness of
A slab of 0 mm was produced. After heating this slab to 460 ° C., the thickness of the slab is reduced to 30% at a rolling reduction of 5 to 30% per pass.
The hot rolling was performed until the thickness reached mm. In the hot rolling at this time, the material temperature was maintained at 400 ° C. or higher.

Next, after grinding the hot-rolled sheet material,
The plate thickness is set to 340 to 38 by the heating furnace provided between the passes.
Rolling was performed while maintaining the temperature at 0 ° C., and processed into a plate material having a thickness of 3 mm. Furthermore, warm rolling at a temperature of 200 to 230 ° C. and a rolling reduction of 2 to 5% per pass was repeated to obtain a magnesium alloy plate having a thickness of 0.4 mm.

The thus obtained magnesium alloy plate was
It was processed into a test sample for press molding having a length of 87 mm x a width of 84 mm x a corner R of 10 mm.

(Evaluation of press formability) As a press mold for evaluating press formability, a 0.2 mm corner R
And a 7 mm deep square press mold having an embossed portion in the center of which can form an embossed character having a depth of 0.5 mm in a molded product.

In the press molding, the test samples for press molding obtained in the above Examples and Comparative Examples were held at a temperature shown in Table 2 for 120 mm by using the above press mold. Press molding at a press speed of / min. The heating of the test sample for press molding was performed by 1 kW × 4 heaters embedded in the press mold, and measured by a thermocouple embedded in the press mold closest to the surface of the test sample.

The press formability was evaluated based on whether or not cracks occurred at corners where the processing amount was the largest. When no cracks occurred, it was evaluated as ○, and when cracks occurred, it was evaluated as ×. The results are shown in Table 2.

[0038]

[Table 2]

(Evaluation Results) As is clear from the results in Table 2, the test samples for press molding (Examples) produced by the method for producing a magnesium alloy sheet of the present invention were subjected to press molding in a heated state. No cracking was observed when the test was performed. On the other hand, a test sample for press forming manufactured by a conventional method for manufacturing a magnesium alloy sheet (comparative example)
As for, cracking was observed when press molding was performed in a heated state.

[0040]

As described above, according to the method for producing a magnesium alloy sheet having excellent press formability of the present invention,
Since a magnesium alloy sheet having excellent press formability can be manufactured extremely efficiently, the productivity of the magnesium alloy sheet can be greatly improved.

Further, since the magnesium alloy sheet produced by the production method of the present invention can dramatically improve press formability, a molded body having a complicated shape which has been impossible in the past can be obtained. It can be press molded. As a result, the applicable range of a press-formed product made of a magnesium alloy can be significantly expanded, and a light-weight and high-strength molded product can be provided.

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Claims (3)

[Claims] 1. A hot extruding step of processing a cast billet made of a magnesium alloy into a sheet for rolling, and a cold rolling step of processing the sheet for rolling into a magnesium alloy sheet having a predetermined thickness. A method for producing a magnesium alloy sheet having excellent press formability. 2. The method for producing a magnesium alloy sheet having excellent press formability according to claim 1, further comprising an intermediate annealing step in the middle of the cold rolling step. 3. The magnesium alloy according to claim 1, wherein
l: 1 to 6.5%, Zn: 0.2 to 2.5%, Mn:
The method for producing a magnesium alloy sheet having excellent press formability according to claim 1 or 2, wherein 0.1 to 0.5%, balance: Mg and unavoidable impurities.