JP2006239748A - Method for producing magnesium alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a magnesium alloy sheet by which production cost can drastically be reduced by subjecting a continuously cast thin slab to an inline rolling reduction, thereby omitting or simplifying stages. <P>SOLUTION: A continuously cast thin slab (with a thickness of 5 to 50 mm) in a hot state is subjected to a multistage rolling reduction for two or more times in-line using a pair of rolling reduction rolls 3 whose surface part is heated to 250 to 400°C, and further, the draft as the percentage obtained by dividing a rolling draft A<SB>1</SB>(mm) per time by the thickness A<SB>0</SB>(mm) of the thin slab before the rolling reduction, [(A<SB>1</SB>/A<SB>0</SB>)×100(%)] is controlled to <15%, so as to be a sheet 5 with a thickness of ≤25 mm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnesium alloy manufacturing method in which a continuously cast thin slab is reduced in-line using its latent heat without reheating, thereby greatly omitting the manufacturing process and forming a thin plate.

  Magnesium alloys are the lightest among practical alloys and have excellent rigidity, and are therefore applied to aircraft, automobiles, mobile phones and the like. In particular, due to the rapid spread of mobile phones and the like, market needs for magnesium alloys are increasing more than ever, and it is desired to provide inexpensive and high-quality magnesium alloys.

  Magnesium alloys are highly reactive at high temperatures, are easy to oxidize, and easily absorb hydrogen. Therefore, if a molten magnesium alloy is present in the atmosphere at the time of melting and casting, oxidation is promoted to generate oxides, and oxygen and hydrogen are absorbed into the molten magnesium alloy, and their concentrations increase. become. Thus, when the oxygen concentration and hydrogen concentration in the magnesium alloy are increased, pores may be generated in the cast slab, or the mechanical properties required for the product may not be ensured.

  For this reason, after melting in an atmosphere shut off from the atmosphere, the magnesium alloy is manufactured by ingot casting or die casting, or a round billet or a slab which is a semi-finished product by continuous casting of a large cross section (slab thickness of about 150 mm). After manufacturing, a method has been adopted in which a final product is molded and machined to finish.

  However, in the manufacturing by the conventional ingot casting or continuous casting, there is a problem that the manufacturing cost increases because the product is manufactured through many processes such as rough rolling and hot rolling.

  In particular, when trying to obtain a thin plate of magnesium alloy, magnesium is inferior in workability at room temperature, so in the process from rough rolling to hot rolling, rolling and reheating must be repeated several tens of times. The large number of processes was the biggest factor that made it difficult to reduce manufacturing costs.

  As described above, even if the magnesium alloy is manufactured by ingot casting or die casting, or manufactured by continuous casting, many processes are required to obtain a final product, resulting in a large number of manufacturing steps. As a result, the manufacturing cost increases and the product delivery time is disadvantageous. For this reason, in the manufacture of a magnesium alloy, particularly a thin plate, a drastic countermeasure is desired.

  For example, Patent Document 1 proposes a method for producing a magnesium alloy in which ceramic powder is dispersed in a matrix alloy. In the proposed method, a step of producing a particle-dispersed master alloy in which ceramic powder is dispersed in a matrix alloy composed of a magnesium alloy, and after preheating the particle-dispersed master alloy at a temperature of 150 to 500 ° C., 750 ° C. or less A step of adding and stirring the molten metal of the parent phase alloy composition maintained at the temperature, solidifying by cooling the molten metal after stirring at a cooling rate of 10 ° C./second or more, and a drawing speed of 80 to 200 mm / min And a continuous casting process.

  However, in the proposed manufacturing method, a significant improvement in productivity cannot be expected as described in the casting speed of 80 to 200 mm / min, and since the casting has a relatively large cross section, the manufacturing process is aimed at cost rationalization. Even if it is attempted to omit (especially rolling and reheating steps), there is a limit. Furthermore, it is limited to the production of magnesium alloy bars.

  On the other hand, near net shaping (strip casting, etc.) is aimed at in order to drastically reduce the manufacturing cost, and development is being carried out aiming at practical use. However, it has not yet been put to practical use.

  As a technology related to this, in Patent Document 2, when supplying molten magnesium alloy into a mold, the magnesium alloy is solidified while applying vibration to the mold, and then immediately heated to a predetermined thickness using a pair of rolling rolls. A method for producing a magnesium alloy sheet is described, which is rolled and wound on a coiler, that is, a thin slab is hot-rolled in-line.

  According to this manufacturing method, a magnesium alloy thin plate can be manufactured with high productivity and low manufacturing cost by continuously casting a molten magnesium alloy and immediately hot-rolling the molten magnesium alloy into a thin plate. However, since the desired reduction ratio is large, for example, when an oscillation mark or a drawing mark on the surface of the slab is remarkable, cracking may occur at the start of the reduction.

JP-A-5-302137 JP 2003-340552 A

  The present invention has been made in view of the problem that the number of steps in manufacturing the above-mentioned magnesium alloy, particularly a thin plate, is increased, thereby increasing the manufacturing cost, and forming a near-net shape (thin slab casting + in-line reduction). The purpose of the present invention is to provide a method for producing a magnesium alloy that obtains a thin plate by efficiently suppressing the occurrence of cracking under in-line pressure.

  As described above, the problems in the method of manufacturing a magnesium alloy thin plate to be solved by the present invention are the suppression of cracking that is likely to occur when a continuously cast thin slab is reduced in-line, and the reduction efficiency. It is promotion.

  In order to reduce the slab being cast in-line, it is first important to reduce the slab surface without performing maintenance (that is, without maintenance). If surface care is carried out, it is possible to obtain a good rolled sheet, but it requires maintenance costs, costs for reheating the slab, and the like, which increases manufacturing costs.

  In that case, if the object to be reduced is steel that is continuously cast, the drawing mark on the surface of the slab formed at the time of drawing the slab is easily extended by the reduction, and usually problems such as cracking do not occur. However, as a result of investigations by the present inventors, when the object of reduction is a magnesium alloy, workability at normal temperature is poor and ductility is inferior, and therefore processing at high temperature is common. However, even when the slab temperature is high, it was confirmed that cracks may occur during the reduction due to unevenness such as a drawn mark formed on the surface of the slab. That is, it has been found that there is a critical rolling reduction rate of cracking, depending on the surface condition of the slab.

  Then, if the reduction after casting is performed by multistage reduction, and the reduction rate per pass is kept within the critical reduction rate of crack generation, it is possible to accumulate the reduction rate for each pass without causing cracks during reduction. As a result, it was confirmed that it was possible to secure a large reduction ratio in total. That is, it is possible to suppress the occurrence of cracks under uncleaned inline pressure.

  Furthermore, it has been found that it is effective to employ a roll under a heating pressure with the surface temperature increased. In other words, the surface temperature of the slab decreases due to heat release from the slab and heat removal by the reduction roll during continuous multi-stage reduction, but by using the heating reduction roll, it is possible to remove from the reduction roll during the reduction. When heat is suppressed and the slab temperature is lowered, heat can be applied during the reduction. This makes it possible to reduce the pressure more efficiently by taking advantage of the in-line reduction that enables the reduction without reheating using the latent heat of the slab during casting.

  This invention is made | formed based on such knowledge, The summary exists in the manufacturing method of the following thin plate of a magnesium alloy.

That is, a method for producing a magnesium alloy that obtains a thin plate by in-line rolling a continuously cast thin slab in a roll using a pair of rolling rolls, wherein the thickness of the cast slab after the casting is 5 to Using the above-described pair of rolling rolls having a surface portion heated to 250 to 400 ° C., the multi-stage rolling is performed twice or more, and the amount of rolling A ₁ (mm) per rolling of the thin slab before rolling is reduced. This is a method for producing a magnesium alloy in which a reduction ratio “(A ₁ / A ₀ ) × 100 (%)”, which is a percentage divided by a thickness A ₀ (mm), is less than 15%, and a thin plate having a thickness of 25 mm or less is obtained. In the following, “the manufacturing method of the magnesium alloy of the present invention” or simply “the manufacturing method of the present invention” means a manufacturing method of the magnesium alloy for obtaining a thin plate having a thickness of 25 mm or less.

  The magnesium alloy targeted by the present invention is a magnesium alloy prepared by adding an alloying element to pure magnesium metal, but also includes pure magnesium metal.

  The temperature of the “surface portion” in the “heating the surface portion to 250 to 400 ° C.” means the temperature of the surface of the reduction roll that is in contact with at least the thin cast slab during the reduction.

  According to the method for producing a magnesium alloy of the present invention, the production process is omitted and simplified by in-line rolling a thin slab that is continuously cast, and cracking is suppressed and efficiently reduced. A magnesium alloy sheet can be obtained. Thereby, the manufacturing cost can be significantly reduced.

  Below, the manufacturing method of the magnesium alloy of this invention is demonstrated with reference to drawings.

  FIG. 1 is a diagram schematically showing a configuration of a main part of an apparatus capable of carrying out the manufacturing method of the present invention. As shown in the figure, above the continuous casting mold 2, an immersion nozzle 1 for supplying the molten alloy to the mold 2 from a magnesium alloy molten metal supply device (not shown) is disposed. On the delivery side (lower side), a multistage reduction roll pair 3 for rolling a magnesium alloy whose surface portion is solidified in the mold 2 is disposed.

  The molten magnesium alloy 4 supplied to the continuous casting mold 2 through the immersion nozzle 1 is continuously discharged from below the casting mold 2 as a hot thin cast piece whose surface portion is solidified in the casting mold 2, and is subjected to multistage pressure reduction. The thin plate 5 is rolled down by the roll pair 3. As described above, magnesium alloy is highly reactive at high temperatures and easily oxidizes. Therefore, the melting, holding, and pouring of the magnesium alloy into the mold are blocked from the atmosphere, for example, in an argon gas atmosphere. Done.

The manufacturing method of the magnesium alloy of the present invention is such a method that the thickness of the cast slab after the casting is 5 to 50 mm and the surface portion is heated to 250 to 400 ° C., using the pair of rolling rolls 2 The rolling reduction ratio “(A ₁ / A ₀ ) is a percentage obtained by dividing the rolling reduction A ₁ (mm) per one time by the thickness A ₀ (mm) of the thin cast slab before rolling. ) × 100 (%) ”is less than 15%, and a thin plate having a thickness of 25 mm or less is obtained.

  The reason why the thickness of the thin slab is 5 to 50 mm is that when the thickness exceeds 50 mm, it is difficult to obtain a thin plate by in-line rolling, and it is necessary to repeat reheating and hot rolling. is there. On the other hand, it is technically difficult to obtain a thin slab having a thickness of less than 5 mm, and it is not practical if not impossible.

  Heating the surface portion of the pair of rolling rolls to 250 to 400 ° C. suppresses a decrease in slab temperature due to heat removal through the rolling roll during rolling, and reverses when the slab temperature decreases. This is because heat is applied to the slab during rolling. Such an effect is not remarkable when the temperature of the surface portion is less than 250 ° C., and heating above 400 ° C. is not necessarily a good idea in consideration of the effect, required energy for heating, and the like.

  A heating method using an induction heat generation method, a heat pipe method, or the like may be used for heating the reduction roll. The induction heating method is a heating method that has been used in many fields. In addition, the heat pipe method is a heating method in which a large number of pipes for enclosing and circulating ethylene are placed under the roll surface in the roll axis direction, and heated uniformly in the width direction and thickness direction of the roll. It has the feature that it can.

  As described above, the temperature of the “surface portion of the reduction roll pair” is at least the temperature of the surface of the reduction roll in contact with the thin cast slab. When heating by the above heat pipe method, the surface temperature of the rolling roll and the temperature inside the rolling roll are almost the same. For example, the pores reaching the site 20 mm deep from the surface at the center of the roll width of the rolling roll. It is possible to know the temperature of the surface portion of the reduction roll by measuring the temperature of the portion by providing a thermocouple in the pores in the axial direction and measuring the temperature of the portion. Actually, the relationship between the surface temperature and various conditions (setting voltage, current, etc.) for raising the temperature with the heating method to be used is known in advance, and indirect temperature management by the setting voltage etc. is performed. You may go.

  In the method for producing a magnesium alloy of the present invention, the multi-stage reduction is performed two or more times using the pair of reduction rolls. This is because the reduction rate per pass is reduced to suppress the occurrence of cracks, and the number of reduction passes is increased to ensure a large total reduction rate, thereby forming a thin plate inline.

  There is no particular upper limit on the number of reduction passes under multistage pressure. This is because the upper limit of the rolling reduction is determined as described below, and the number of roll pairs is naturally determined by the thickness of the thin cast slab and the thickness of the thin plate to be manufactured. For example, when a thin cast slab having a thickness of 35 mm is subjected to multistage pressing to form a thin plate having a thickness of 5 mm, 12 passes of reduction are required. That is, 12 roll pairs are arranged.

In the production method of the present invention, the reduction rate per one time under the multi-stage pressure of two or more times, that is, the reduction amount A ₁ (mm) is divided by the thickness A ₀ (mm) of the thin slab before reduction. The percentage “(A ₁ / A ₀ ) × 100 (%)” is less than 15%. By setting the rolling reduction to less than 15%, it is possible to suppress the occurrence of cracks during in-line rolling, as shown in examples described later.

  The lower limit of the rolling reduction is not particularly specified. In order to prevent the occurrence of cracking, the upper limit should be specified, so the rolling reduction is within the range of less than 15% in consideration of the thickness of the thin cast slab and the thin plate to be manufactured, the number of roll pairs installed, and the like. What is necessary is just to determine suitably.

  In the manufacturing method of the present invention, the thickness of the thin plate obtained is 25 mm or less, the number of rolling passes in in-line rolling is limited to 10 times or less, and the load on the rolling side (equipment cost increase) is reduced as much as possible. Because.

  The lower limit of the thickness of the thin plate is not specified. This is because of product needs. In practice, a thin plate having a thickness of 1 mm or less is often the object of manufacture as the final product. Further, for rerolling, a thin plate having a thickness of about 5 mm is also targeted.

  Using a thin slab cast under the conditions shown in Table 1, a multi-pass reduction test was conducted, and the presence or absence of cracking during reduction and the effectiveness of the heating roll was investigated.

  FIG. 2 is a diagram schematically showing the main configuration of the apparatus used in the multipass rolling test. This apparatus includes a pair of heating rolls 9 simulating a pair of rolling rolls, a heater 7 for heating the slab 6, and a lifter 8 that moves the slab 6 up and down while holding the lower end portion thereof.

  When performing the multi-pass reduction test, first, the slab 6 cast at a predetermined thickness is heated to a predetermined temperature (350 ° C. target) by the heater 7, and then the lifter 8 is lowered, and the slab 6 is heated by a heating roll. After clamping at 9, the first pass is reduced. In the second pass reduction, the slab 6 is released from the heating roll 9 and is raised to the first pass reduction start portion, and the slab 6 is clamped by the heating roll 9 again to perform the reduction. By repeatedly applying the reduction by such a method, a test simulating a multi-pass reduction in one direction can be performed.

  FIG. 3 shows the results of a survey on the presence or absence of cracks during rolling. In FIG. 3, the rolling reduction after 2 (that is, the second pass) in the number of rolling passes on the horizontal axis is not the cumulative rolling reduction but the rolling reduction for each pass. In addition, black marks (solid marks, ● and ■ marks in FIG. 3) indicate that cracking occurred during the reduction.

  FIG. 3 shows CASE 1 to CASE 7 in which the rolling reduction and the number of rolling passes are changed. From this figure, it can be seen that cracking may occur when the unsqueezed cast slab is reduced in one pass to an extent that the reduction rate exceeds 15%. In other words, cracks occur in the first pass of CASE 3 (marked with ●) and the third pass of CASE 4 (marked with ■) where the rolling reduction is over 15%. On the other hand, CASE 1, 2, 5 to 7 (examples of the present invention) are cases where multi-pass reduction is performed with a reduction rate of less than 15%. In this case, there is no cracking, and the total reduction amount can be increased. Is possible.

  FIG. 4 shows the relationship between the reduction load and reduction rate when a heating roll is used. In FIG. 4, ◯, ◇, Δ, and □ indicate cases where the roll surface temperature (Tr) is 25 ° C., 200 ° C., 300 ° C., and 400 ° C., respectively. The ◆, ▲, and ■ marks correspond to the ◇, △, and □ marks, respectively, and indicate that cracking occurred during rolling.

  As shown in FIG. 4, compared to the case where Tr is 25 ° C. (marked with ○), when a heated roll is used (marked with Δ and □), the rolling load for obtaining the same rolling reduction is greatly reduced (in the figure). Displayed with a white arrow). In particular, it is noticeable when the rolling reduction is 7.5% or more. This is because heat removal from the reduction roll is suppressed by using the heating roll, and the slab is kept at a higher temperature, and the use of the heating roll is effective in promoting reduction efficiency. I understand. Even when a heating roll was used, cracking occurred during the reduction when the reduction ratio exceeded 15%.

  The method for producing a magnesium alloy of the present invention is a method of obtaining a thin plate by continuously rolling a thin cast slab in a hot state at a predetermined reduction rate in-line. It can be efficiently reduced by use, omitting and simplifying the slab rolling process, and greatly reducing the manufacturing cost. Therefore, this method can be widely used as a method for producing a magnesium alloy thin plate.

It is a figure which shows typically the structure of the principal part of the apparatus which can implement the manufacturing method of this invention. It is a figure which shows typically the principal part structure of the apparatus used by the multipass rolling test. It is a result of an example and is a figure showing an investigation result about crack generation at the time of in-line reduction. It is a result of an example and is a figure showing the relation between a rolling load at the time of using a heating roll at the time of inline rolling, and a rolling reduction rate.

Explanation of symbols

1: Immersion nozzle 2: Mold 3: Reduced roll pair 4: Magnesium alloy molten metal 5: Thin plate 6: Slab 7: Heater 8: Lifter
9: Heating roll

Claims (1)

A magnesium alloy manufacturing method for obtaining a thin sheet by in-line rolling a continuously cast thin slab in a roll using a pair of rolling rolls, wherein the thickness of the cast slab after casting is 5 to 50 mm The surface portion is heated to 250 to 400 ° C., and the multi-stage reduction is performed twice or more, and the reduction amount A ₁ (mm) per time is the thickness of the thin slab before reduction. A method for producing a magnesium alloy, characterized in that a reduction ratio “(A ₁ / A ₀ ) × 100 (%)”, which is a percentage divided by A ₀ (mm), is less than 15% and a thin plate having a thickness of 25 mm or less is obtained. .

Images