JP2010053386A - Magnesium alloy sheet material which is excellent in formability, and producing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium alloy sheet material having good formability even in a low temperature zone from room temperature to ≤150°C. <P>SOLUTION: In the magnesium alloy sheet material, the degree of the maximum accumulation at the bottom part is <10 and an r-value is 1.0-1.6. This magnesium alloy sheet material is obtained, by subjecting the base plate of the magnesium alloy sheet material to a heat-treatment at ≥450°C for ≥0.5 hr, then subjecting the base plate of the magnesium alloy sheet material to cold-rolling at circumferential speed ratio of 1.0-1.3 and rolling-reduction ratio of 2-10% (no heating to the material and roll), or to warm different circumferential speed rolling of 10-30% under condition of circumferential speed ratio of 1.05-1.6, the roll temperature of room temperature to 250°C, and material heating temperature of 180-300°C, and then, subjecting the base plate of the magnesium alloy sheet material to heat treatment of ≥380°C for ≥5sec. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnesium alloy sheet material used for electrical appliances, automobile parts, and the like, and a method for manufacturing the same.

Magnesium alloys are the lightest among practical alloys, and are widely used as housings for automobile parts, personal computers, mobile phones, and the like because they are excellent in recyclability, specific strength, dent resistance, and the like.
Conventionally, most of magnesium products are mainly produced by casting methods such as die casting and thixo, but wrought materials are attracting attention in terms of surface properties, corrosion resistance, yield, and the like.
However, in this wrought material, by performing hot rolling or warm rolling, heating and rolling are repeated, the crystal grain structure is coarsened, and press formability is reduced. On the other hand, the inventors of the present application continuously cast and roll a molten magnesium alloy, and perform warm rolling and hot rolling after homogeneous heat treatment, thereby reducing the number of heating and hot rolling, thereby reducing fine crystal grains. The manufacturing method which makes it a structure | tissue and intends to improve the press formability in warm as a result is proposed (refer patent document 1).
JP 2006-144043 A

However, in a magnesium alloy rolled sheet as a wrought material, the bottom texture formed during rolling is one factor that hinders formability at room temperature. In a magnesium alloy, since the critical shear stress at the bottom surface is as small as 1/100 or less of that at the non-bottom surface at room temperature, the deformation is limited to the bottom surface slip. As a result, when the bottom texture is formed by rolling, the deformation is limited to the RD and TD directions of the rolled surface in the low temperature region of the rolled sheet, and is difficult to deform in the ND direction of the sheet thickness. As a result, the formability in the low temperature region is remarkably poor in the magnesium alloy rolled sheet.
For this reason, in order to shape | mold a magnesium alloy rolled sheet, the warm shaping | molding which heated material temperature to 180 degreeC or more is required. When performing this warm forming, a heating device for materials and dies is required, which has become a foothold for popularizing magnesium alloy sheets. For this reason, when using a magnesium alloy rolled sheet, a material that can be molded in a low temperature region is required.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a magnesium alloy sheet having good formability in a low temperature range from room temperature to 150 ° C. and a method for producing the same.

  Among the magnesium alloy sheet materials of the present invention, the first invention of the present invention is characterized in that the bottom surface has a maximum integration degree of less than 10 and an r value of 1.0 to 1.6.

  The magnesium alloy sheet according to the second aspect of the present invention is the composition according to the first aspect of the present invention, wherein the composition is, by mass, Al: 0.5 to 7.0%, Mn: 0.1 to 0.5%. The remainder is made of Mg and inevitable impurities.

  The magnesium alloy sheet according to the third aspect of the present invention is characterized in that, in the second aspect of the present invention, the composition component further contains Zn: 2.0% or less by mass%.

  According to a fourth method for producing a magnesium alloy sheet of the present invention, a magnesium alloy sheet material is heat-treated at a temperature of 450 ° C. or more for 0.5 hour or more, and then a peripheral speed ratio of 1.0 to 1.3 and a reduction ratio of 2 to 2 are obtained. Cold rolling of 10% (both materials and rolls are not heated) or a peripheral speed ratio of 1.05 to 1.6, roll temperature of room temperature to 250 ° C., and material heating temperature of 180 ° C. to 300 ° C. % Warm different circumferential speed rolling, followed by heat treatment at 380 ° C. or more for 5 seconds or more.

  According to a fifth aspect of the present invention, there is provided a method for producing a magnesium alloy sheet material according to the fourth aspect of the present invention, wherein the magnesium alloy sheet material substrate is produced by a twin roll method having a cooling rate of 150 K / sec or more.

  The method for producing a magnesium alloy sheet according to the sixth aspect of the present invention is characterized in that the magnesium alloy sheet has the composition of the second or third aspect of the present invention.

Below, each condition prescribed | regulated by this invention is demonstrated.
<Maximum integration of bottom surface is less than 10>
By making the maximum degree of integration of the bottom surface less than 10, the crystal orientation is randomized, and the formability is improved by facilitating deformation in the plate thickness direction. If it is 10 or more, the degree of integration on the bottom surface is high and the anisotropy of deformation is increased, so that the workability is poor.
As will be described later, in the sample subjected to special rolling during the high temperature heat treatment, the maximum integration value is less than 10 from the bottom pole figure.
The method of creating the bottom pole figure is preferably performed by the Schulz reflection method by X-ray diffraction.
In addition, the value of the maximum accumulation degree of the bottom surface of the magnesium alloy sheet finished by general warm rolling is a large value exceeding 10 and has a strong bottom texture.

<R value of 1.0 to 1.6>
By randomizing the crystal orientation, the r value can be in the range of 1.6 or less to 1.0 or more, and the moldability is improved. On the other hand, if the r value is less than 1.0, the deformability in the RD and TD directions decreases.

<Magnesium alloy plate material composition>
The magnesium alloy composition constituting the magnesium alloy sheet is not limited to a specific one in the present invention. Preferably, Al: 0.5 to 7.0%, Mn: 0.1 to 0.5%, and optionally Zn: 2.0% or less, the balance being Mg and inevitable impurities Is exemplified.
With regard to a suitable alloy composition, as the Al content increases, the strength increases due to solid solution hardening and β-phase precipitation hardening. However, when Al exceeding 7.0% is added, segregation is likely to occur. When segregation is remarkable, the portion is re-dissolved during high-temperature heat treatment, and the probability of becoming a defect increases. Therefore, the preferable upper limit is set to 7.0%.
Regarding Mn content, Mn is effective for imparting corrosion resistance and suppressing crystal grain growth during heat treatment. If the content is less than 0.1%, the effect is insufficient. If 0.5% or more is added, coarse Mn alone is formed, and workability such as bendability is remarkably deteriorated.
As for Zn, Mg—Al—Zn-based compound is formed, and its precipitation hardening improves the strength in the same manner as Al, but the effect is saturated even if added over 2.0%. The positive addition amount is preferably 0.1% or more.
In addition, it is difficult to produce a substrate having a high Al addition amount with a rolled material or an extruded material from a slab. Therefore, it is preferable that the substrate to be used is manufactured by a twin roll method, and the cooling rate is 150 K / second or more.

Heat treatment to magnesium alloy sheet: 450 ° C or higher, 0.5 hour or longer Room temperature and randomization of crystal orientation (relaxation of bottom texture) to obtain magnesium alloy sheet with good formability in low temperature range of 150 ° C or lower Is effective. As a method for randomizing the crystal orientation, it is desirable to first heat-treat at a high temperature of 450 ° C. or higher for 0.5 hours or longer to coarsen the crystal grain size in the microstructure to 15 μm or more. By performing special rolling on the plate material whose crystal grains are coarsened by high-temperature heat treatment, relaxation of the bottom texture is achieved. In both cases of less than 450 ° C. and less than 0.5 hours, it becomes difficult to increase the grain size as intended, and it becomes difficult to relax the bottom texture by the subsequent special rolling. .
When the special rolling described later is combined with the high-temperature heat treatment, the crystal orientation randomization mechanism is preliminarily coarsened with crystal grains and the formation of twins.
If the crystal grain size is coarsened to 15 μm or more in the first heat treatment, twins are easily formed in the next special rolling stage. Twins contribute to randomization of crystal orientation as new nucleation sites during the final heat treatment.
As a mechanism for generating twins, when the crystal grain size is small, the activity of the non-bottom surface is relatively active in the vicinity of the grain boundary, though not as much as the bottom surface. Therefore, in a rolled plate having a small crystal grain size and a high grain boundary density, the non-bottom surface is also active and twins are not easily formed. Therefore, in such a sample, randomization of the crystal orientation cannot be expected in the end.

Special rolling method (1) Cold rolling with a circumferential speed ratio of 1.0 to 1.3 and a reduction ratio of 2 to 10% At this time, neither the material nor the roll is heated.
(2) Warm peripheral speed rolling with a rolling reduction ratio of 10 to 30% under conditions of a peripheral speed ratio of 1.05 to 1.6, a roll temperature of room temperature to 250 ° C, and a material heating temperature of 180 ° C to 300 ° C.

In the case of a sample with coarse crystal grains, twins are likely to be formed inside the particles in order to maintain the deformation. However, in normal warm rolling, since the material is heated to 180 ° C. or higher, grain boundary sliding and non-bottom sliding contribute to deformation, and twins are not easily generated.
It has been found that cold rolling at room temperature is effective as one method for generating many twins. The peripheral speed ratio at this time is 1.0 to l. 3. Since the material is not heated, many shear bands in which strain is introduced non-uniformly are formed, but twins are more likely to be generated. Furthermore, when the peripheral speed is changed, the apparent amount of strain increases due to shear deformation, and the generation of twins becomes prominent due to the deformation. However, if the peripheral speed ratio exceeds 1.3, the rolling reduction becomes too large and cracks occur during rolling. If the rolling reduction is less than 2%, sufficient strain cannot be introduced and there is no effect.

Moreover, in the warm different peripheral speed rolling, although the material is heated as in the normal warm rolling, many twins are generated due to the increase in the apparent amount of strain due to the application of shear deformation and the influence of the deformation mechanism, It is effective for randomization. If it is warm different peripheral speed rolling, since there is no change in roll temperature, it is easy to incorporate in the conventional rolling process. Further, since strain is easily introduced uniformly in the plate thickness direction, the final average crystal grain size becomes uniform and fine. The size is 40 μm or less including the case of cold rolling. Magnesium alloy rolled plate has a very large dependence on the grain size of the proof stress, but the grain size is set to 40 μm or less, and by suppressing the coarsening of the grains beyond that for randomization, a high strength can be obtained. can get.
In addition, as conditions for warm different peripheral speed rolling, the material heating temperature was set to 180 to 300 ° C. in order to obtain a desired reduction ratio in the warm condition. If it is lower than 180 ° C., there is a risk of producing cracks or large side cracks during rolling. Moreover, if it exceeds 300 degreeC, there will be no difference in rolling property and the effect will be saturated. When the roll temperature is higher than 250 ° C., the influence of the thermal crown of the roll becomes too great, and the shape of the material is remarkably deteriorated. If the peripheral speed ratio is less than 1.05, the effect of different peripheral speeds is small, and if it exceeds 1.6, the effect is saturated.

The magnesium alloy sheet subjected to the above special rolling is finally heat-treated at a high temperature of 380 ° C. or more for 5 seconds or more.
The twins generated by the rolling process by recrystallization by the heat treatment become recrystallization nuclei, and the crystal orientation is randomized. As a result, the bottom surface integration degree is lowered. Any effect of less than 380 ° C. and less than 5 seconds is insufficient.

As described above, according to the magnesium alloy sheet of the present invention, the maximum degree of integration of the bottom surface is less than 10 and the r value is 1.0 to 1.6, so that the crystal orientation is randomized. As a result, there is an effect that the moldability at room temperature and a low temperature range of 150 ° C. or lower is greatly improved.
Moreover, the manufacturing method of the magnesium alloy plate material of this invention is the heat treatment of the board | substrate of a magnesium alloy plate material at the temperature of 450 degreeC or more for 0.5 hour or more, Then, peripheral speed ratio 1.0-1.3, rolling reduction 2-10 % (Both materials and rolls are not heated) or rolling speed ratio of 1.05 to 1.6, roll temperature of room temperature to 250 ° C, material heating temperature of 180 ° C to 300 ° C, rolling reduction of 10 to 30% Thus, the magnesium alloy sheet of the present invention can be obtained with certainty because the heat treatment is carried out at a temperature of 380 ° C. for 5 seconds or more.

Preferably, an alloy containing Al: 0.5 to 7.0%, Mn: 0.1 to 0.5%, and optionally containing Zn: 2.0% or less, with the balance being Mg and inevitable impurities. Prepare a magnesium alloy plate material substrate by a twin roll method with a cooling rate of 150 K / second or more.
As described above, the base material is heat-treated at 450 ° C. for 0.5 hour or longer. The heat treatment can be performed using an appropriate heating furnace or the like, and the content of the apparatus is not particularly limited as the present invention. In addition, as a suitable upper limit, 520 degreeC and 4 hours can be shown.
The base material of the magnesium alloy sheet that has been subjected to the pre-rolling heat treatment is subjected to cold rolling or warm different peripheral speed rolling by the special rolling described above. The rolling can be performed appropriately with the number of passes, and it is desirable that the conditions such as the peripheral speed ratio are satisfied in each pass. The reduction ratio indicates the total reduction ratio.
After the special rolling described above, post-rolling heat treatment is performed at 380 ° C. or more for 5 seconds or more. The heat treatment can also be performed using an appropriate heating furnace, and it is efficient to perform heating using a continuous furnace. In addition, as a suitable upper limit, 520 degreeC and 4 hours can be shown.

  The magnesium alloy sheet obtained through the above steps has a characteristic that the maximum degree of integration on the bottom surface is less than 10 and the r value is 1.0 to 1.6, even in a low temperature range from room temperature to 150 ° C. or less. It has good moldability. The magnesium alloy sheet can be used for various applications that require good formability, and can be used for materials such as automobile parts, housings for electrical appliances such as personal computers and mobile phones.

Examples of the present invention will be described below.
A magnesium alloy having the composition shown in Table 1 (remainder Mg and inevitable impurities) was dissolved, and a base material for a magnesium alloy sheet was prepared by a twin roll method with a cooling rate of 400 K / sec. The substrate was subjected to heat treatment (high temperature heat treatment 1) under the conditions shown in Table 1, and then subjected to special rolling in cold or warm different peripheral speed rolling shown in Table 1. Heat treatment (high temperature heat treatment 2) was performed on the magnesium alloy sheet obtained by rolling under the conditions shown in Table 1. The final plate thickness was set to 0.6 mm.

For the magnesium alloy sheet after high-temperature heat treatment 2, the maximum degree of bottom surface integration and average grain size were measured, and the bottom base maximum degree of integration shown in Table 2 was created by a bottom pole figure by the Schulz reflection method using X-ray diffraction. From the bottom pole figure, the maximum degree of bottom surface integration was determined.
The average crystal grain size was determined by a cutting method.
Furthermore, the mechanical properties including the r value of the test material were measured and shown in Table 2.

  It has been found that the magnesium alloy sheet of the present invention has an Erichsen value of 5 or more, improved overhanging properties, and excellent formability at low temperatures.

Claims (6)

  A magnesium alloy sheet having a maximum bottom surface integration degree of less than 10 and an r value of 1.0 to 1.6.   2. The composition according to claim 1, wherein the composition contains, by mass%, Al: 0.5 to 7.0%, Mn: 0.1 to 0.5%, and the balance consisting of Mg and inevitable impurities. Magnesium alloy sheet.   The magnesium alloy sheet according to claim 2, further comprising, by mass%, Zn: 2.0% or less as a composition component.   After heat-treating the magnesium alloy sheet at a temperature of 450 ° C. or more for 0.5 hour or more, cold rolling with a peripheral speed ratio of 1.0 to 1.3 and a reduction ratio of 2 to 10% (both material and roll are not heated) Alternatively, the roll speed is 1.05 to 1.6, the roll temperature is room temperature to 250 ° C., and the material heating temperature is 180 ° C. to 300 ° C. A method for producing a magnesium alloy sheet material, comprising performing a heat treatment at 380 ° C. or more for 5 seconds or more.   5. The method for producing a magnesium alloy sheet according to claim 4, wherein the substrate of the magnesium alloy sheet is produced by a twin-roll method with a cooling rate of 150 K / second or more.   The said magnesium alloy board | plate material has the composition of the said Claim 2 or Claim 3, The manufacturing method of the magnesium alloy board | plate material characterized by the above-mentioned.