JP2010005659A - Method of manufacturing magnesium sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a magnesium sheet having excellent flatness. <P>SOLUTION: This invention relates to the method of manufacturing the magnesium sheet having excellent flatness by applying different circumferential speed rolling in the cold and at low temperature to the magnesium belt-like sheet, in the process in which a magnesium belt-like sheet is thinned by rolling in a coil shape, wherein in the final pass of the rolling, the upper and lower work rolls is made to have different circumferential speed, and in the range of 1.05-1.3 of a circumferential speed ratio, rolling in the cold and at low temperature is performed at the total draft of ≤25%. In this rolling, it is preferable that the temperature of a material is the room temperature to 180°C and the surface temperature of the work rolls is the room temperature to 180°C. Since shear deformation is generated in the vertical direction and the horizontal direction in the material and uniform stain is imparted to the full surface of the sheet, and the flatness is improved without bringing about the deterioration of characteristics by heating the material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an Mg plate having excellent flatness.

  Since Mg has a hexagonal close-packed structure, the sliding surface at room temperature is only the (0002) basal plane, the plastic workability at room temperature is poor, and it is necessary to heat to a high temperature when rolling. Moreover, in order to reduce the heat removal amount to the roll at the time of rolling, the method of heating and rolling the roll itself using the rolling roll which incorporated the heater is generally performed. If the heating of the material is insufficient, fine cracks and side cracks are likely to occur on the surface of the material, and in the worst case, the generated cracks and cracks propagate and may be caused by the fracture of the material. However, in hot rolling and warm rolling in which a material is heated and rolled, the shape of the material is likely to be defective due to the influence of the material temperature. For example, due to the influence of the thermal crown of the heating roll at the time of coil rolling, the position misalignment at the time of material feeding, etc., center berries and side berries are generated in the material, which is a factor that deteriorates the shape accuracy of the material. The shape accuracy of the material is indicated by flatness. In the case of a plate material, a good shape accuracy is a condition for a plate having a high accuracy as well as a dimensional accuracy. The poor flatness impairs the appearance of the product and causes a reduction in processing accuracy. Furthermore, in order to increase the speed of automation of processing, the accuracy of setting and feeding at the time of processing must be accurate, and for this reason, high flatness is required.

In addition, although the flatness of the material is relatively good, the shape after punching or other processing may vary, and the springback after bending may become uneven. Often due to the distribution of. The main purpose of correcting the material is to eliminate the defective shape, but it is also possible to make the distribution of residual stress uniform and to reduce it. Accordingly, the correction of the material is an indispensable process for increasing the accuracy of the thin plate, and the main correction methods for the continuous coil material are roughly classified into a roller leveler that uses repeated bending and a tension leveler that uses tension.
JP 2006-205173 A (paragraph 0020)

  In the above repeated bending straightening, straightening is performed by passing the material between the parallel rolls arranged in a zigzag shape alternately, and the bending is performed alternately. However, the Mg plate has a great effect because it has poor workability at room temperature. Is difficult to obtain. In addition, the tension straightening method is a method in which a tensile force is continuously applied by a pair of tension applying devices, but in the case of an Mg plate, it is necessary to carry out a heat treatment such as providing a furnace in the middle. Although the deformation resistance can be reduced by heating and the tension required for correction can be reduced, the material is heated again, resulting in grain growth under the influence of heat, leading to deterioration of material properties. Therefore, there is a need for a method for making the distribution of the residual stress of the material uniform and improving the flatness without causing deterioration of characteristics due to material heating.

  An object of the present invention is to improve the above-mentioned problems, and an object of the present invention is to improve quality by manufacturing an Mg plate having excellent flatness.

  The inventors of the present invention have conducted various studies to achieve the above-mentioned target, and as a result, by using different peripheral speed rolling for finish rolling, processing can be performed uniformly not only in the sheet width direction but also in the sheet thickness direction. The present invention can be completed.

  That is, among the manufacturing methods of the Mg plate of the present invention, the first present invention is different in the upper and lower work rolls in the process of thinning the Mg strip-like plate after hot rolling or warm rolling in a coil shape by rolling. The rolling speed is set to a peripheral speed, and the rolling speed ratio is in the range of 1.05 to 1.3, and cold rolling is performed at a total rolling reduction of 25% or less.

  In the manufacturing method of the Mg plate of the second aspect of the present invention, in the first aspect of the present invention, in the cold rolling step, the surface temperature of the work roll is set to room temperature to 180 ° C, and the material temperature is set to room temperature to 180 ° C. It is characterized by that.

In addition, the conditions prescribed | regulated with the manufacturing method of this invention are demonstrated below.
Peripheral speed ratio: 1.05-1.3
By performing different peripheral speed rolling as finish rolling, it is possible to improve the flatness by imparting shear deformation to the material in the vertical direction and the horizontal direction. Here, when the peripheral speed ratio is less than 1.05, a sufficient effect cannot be obtained. On the other hand, when different peripheral speed rolling is performed at a peripheral speed ratio exceeding 1.3, the processing force is too high. Therefore, the plate material is cracked.

Total rolling reduction: 25% or less When finishing rolling in which the total rolling reduction in the above-mentioned peripheral rolling is over 25%, strong work is repeatedly performed a plurality of times, so that cracks from the end of the material become large and sound. Mg plate cannot be obtained. The lower limit is preferably 3% or more, and there is no effect.

Work roll surface temperature: room temperature to 180 ° C
If the surface temperature of the work roll exceeds 180 ° C., the influence of the roll crown shape becomes too large, so that the shape of the Mg plate cannot be controlled and a center berry is produced.

Material temperature: Room temperature to 180 ° C
When the temperature of the material exceeds 180 ° C., the strength is affected. If the temperature is too high, the crystal grains are coarsened by heating a plurality of times, leading to a decrease in strength.

  That is, according to the manufacturing method of the Mg plate of the present invention, the upper and lower work rolls have different peripheral speeds in the process of thinning the Mg strip-like sheet after hot rolling or warm rolling in a coil shape by rolling. Since cold rolling is performed at a ratio of 1.05 to 1.3 and a total rolling reduction of 25% or less, the plate material processed by rolling at cold and low temperatures is a peripheral speed in the process of thinning in a coil shape. When passing through different upper and lower work rolls, not only the vertical reduction but also the horizontal shearing deformation occurs, so that a uniform strain is applied to the entire plate surface. As a result, the contact surface between the plate material and the roll has a uniform degree of processing, so an Mg plate with excellent flatness can be obtained.

Hereinafter, an embodiment of the present invention will be described.
In the present invention, an Mg strip that has been subjected to hot rolling or warm rolling is used. The Mg material used for the Mg strip is not particularly limited in composition, and an appropriate material can be selected. Moreover, the Mg strip | belt-shaped board should just pass hot rolling or warm rolling, and the manufacturing method in the front process is not specifically limited. For example, the billet may be hot-rolled and then hot-rolled or warm-rolled, or may be a direct hot casting or an Mg plate before hot-rolling manufactured by continuous casting.

  The production conditions for hot rolling or warm rolling to obtain the Mg strip are not particularly limited, and the rolling pass may include different circumferential speed rolling. In addition, warm rolling can be shown as a rolling process which makes material temperature more than 180 degreeC-300 degreeC.

In the cold rolling of the present invention performed after the hot rolling or the warm rolling, different circumferential speed rolling is performed within a circumferential speed ratio of 1.05 to 1.3. The total rolling reduction in the different peripheral speed rolling is 25% or less. The number of passes is not particularly limited as long as it is within the rolling reduction.
In the different peripheral speed rolling, the material temperature is set to 180 ° C. or lower, and similarly, the surface temperature of the work roll is set to 180 ° C. or lower.
By the different peripheral speed rolling, the material undergoes shear deformation in the vertical direction and the horizontal direction, a uniform strain is given to the entire surface of the plate, and the flatness is improved without causing deterioration of characteristics due to material heating.

Examples of the present invention will be described below.
A Mg strip-shaped plate made of JIS AZ31 alloy having a thickness of 5.4 to 5.7 mm was hot-rolled to a thickness of 2.0 mm, and homogenized at 400 ° C. for 16 hours. Thereafter, the thickness was reduced by warm rolling, and then the Mg strip was finish-rolled by an appropriate pass schedule, and the thickness was reduced to 0.6 mm while varying the rolling conditions. In the cold rolling during finish rolling, the material temperature was set to room temperature and the work roll surface temperature was 60 ° C. In the warm rolling during finish rolling, the material temperature was set to 250 ° C and the work roll surface temperature was 250 ° C.

The obtained Mg plate was placed on a surface plate and visually evaluated for flatness. The flatness was evaluated according to the following criteria, and the results are shown in Table 1.
A: Flat A: There are a few peaks when viewed from the side B: Mountains can be seen from above C: Mountains are large enough to be seen from above D: Mountain valleys that cannot be used as a product at all Is

As shown in Table 1, the best flatness was obtained when the peripheral speed ratio was 1.15 and the cold peripheral rolling speed was different. On the other hand, in the comparative example in which the different peripheral speed rolling was not performed, the flatness was C or D regardless of whether the finish rolling was performed by cold rolling or warm rolling. Moreover, when the peripheral speed ratio at the time of finish rolling exceeded 1.3, the flatness was B or C.
Furthermore, even by cold rolling with an appropriate peripheral speed ratio, the material cracked when the total rolling reduction exceeded 25%.

Claims (2)

  In the process of thinning the Mg strip after hot rolling or warm rolling in a coil shape by rolling, the upper and lower work rolls have different peripheral speeds, and the peripheral speed ratio is in the range of 1.05 to 1.3. A method for producing an Mg plate, comprising cold rolling at a rolling reduction of 25% or less.   In the said cold rolling process, the surface temperature of the said work roll shall be room temperature-180 degreeC, and material temperature shall be room temperature-180 degreeC, The manufacturing method of the Mg plate of Claim 1 characterized by the above-mentioned.