JP4296158B2 - Method for producing Mg alloy - Google Patents

Description

  The present invention relates to a method for producing an Mg alloy containing, for example, 0.5 to 20% by mass of Y while suppressing component segregation.

Since Mg alloys are lightweight and have an appropriate strength, they are widely used in applications such as automobile parts. This Mg alloy is manufactured by a batch method or a continuous casting method in which a melting raw material is melted in a melting crucible and cast into a mold. For example, Patent Document 1 discloses a method of casting into a sand mold, and Patent Document 2 discloses a casting method using die casting.
In addition, in the Mg alloy, it has been proposed to add various elements for the purpose of improving the properties as an alloy. For example, Patent Documents 3 and 4 disclose Mg alloys to which rare earth elements such as Y are added.
Japanese Patent Laid-Open No. 06-279890 JP 2003-305554 A Japanese Patent Laid-Open No. 05-070880 JP 2004-099441 A

  However, when an Mg alloy containing an element having a large atomic weight such as Y is cast into a mold, a phenomenon occurs in which the Y component precipitates below the mold and the concentration difference of Y increases between the upper part and the lower part of the ingot. Recently, requirements for quality in applications using Mg alloys have been increasing, and Mg alloys whose quality has deteriorated due to the segregation of Y components cannot meet high product quality requirements.

  The present invention has been made against the background of the above circumstances, and when producing an Mg alloy containing Y, an ingot in which the component segregation is suppressed and the components are made as uniform as possible is obtained to obtain a high-quality Mg product. It aims at providing the manufacturing method which enables this.

  If the Mg alloy melt is solidified at a normal cooling rate, such as by casting into a mold as in the conventional case, the Y compound precipitates, and during the solidification, it precipitates at the bottom of the melt and causes segregation of components according to the solidification time. Therefore, in the present invention, after melting, the molten metal is solidified within a solidification time corresponding to the allowable amount of segregation of Y, so that segregation due to precipitation of the Y component or the like is suppressed within the allowable amount, and a product having a uniform component is manufactured. enable.

That is, among the manufacturing methods of the Mg alloy of the present invention, the invention according to claim 1 is that the Mg alloy containing Y is melted and injected into a mold and then allowed to stand and solidify within a solidification time of 200 seconds or less. Ingot.

  The method for producing an Mg alloy according to claim 2 is characterized in that the molten Mg alloy containing Y is stirred and allowed to stand, and then solidified within a solidification time of 200 seconds or less to form an ingot.

  The method for producing an Mg alloy according to claim 3 is the invention according to claim 1 or 2, wherein the Mg alloy contains 0.5 to 20% of Y by mass%.

  According to a fourth aspect of the present invention, there is provided a method for producing the Mg alloy according to any one of the first to third aspects, wherein the solidification time is 10 seconds or longer.

That is, according to the present invention, in the Mg alloy containing Y, solidification is advanced before the precipitation of Y becomes prominent at the time of manufacturing the ingot, thereby suppressing the precipitation of Y, thus preventing the segregation of the Y component. A uniform ingot can be obtained. At this time, if the solidification time exceeds 200 seconds, the effect of suppressing Y component segregation cannot be sufficiently obtained, and quality deterioration due to segregation becomes remarkable. In addition, if it is the solidification time within 200 seconds, it can be solidified according to segregation tolerance, and it can control to the segregation rate of 10% or less by setting it as the solidification time within 200 seconds. Here, the segregation rate is expressed by the following equation. However, when comparing the segregation rates, the absolute values are compared.
Segregation rate (%) = ((output) − (target content)) / (target content) * 100 (formula)
In order to obtain a segregation rate of 5% or less, it is desirable to set the solidification time within 100 seconds. The solidification time refers to the time from the start of solidification in the mold until the completion of solidification after releasing the temperature maintenance of the molten metal. In addition, it is desirable to stir the molten Mg alloy melt to make the components uniform before starting cooling. The molten metal stirring method is not particularly limited, and known methods such as stirring blades and electromagnetic stirring can be employed. After stirring the molten metal, it is allowed to stand to start the solidification. The end of solidification refers to the time when the solid phase ratio reaches 0.67.

  As a means for achieving the above-mentioned purpose, for example, the raw material was melted in a melting furnace, and after the molten metal was melted, the molten metal was sufficiently stirred and submerged, and then designed to solidify within the solidification time as shown above. Cast into mold. It is also possible to shorten the solidification time by casting into a sufficiently water-cooled mold.

  In addition, although content of Y in the said Mg alloy is not limited to a specific amount, in Y, it is desirable that the lower limit is 0.5% and the upper limit is 20% in mass ratio. By including Y in this range, mechanical strength can be improved. On the other hand, if it is less than 0.5%, the mechanical strength is not improved. If it exceeds 20%, the material becomes brittle, and segregation during casting becomes remarkable. For the same reason, it is more desirable to further set the lower limit to 1% and the upper limit to 15%.

  Moreover, although the said coagulation | solidification time has defined the upper limit as mentioned above, a lower limit is not limited to a specific thing as this invention. However, it is desirable to set a solidification time of 10 seconds as a lower limit for the purpose of reducing the manufacturing cost when manufacturing a large ingot. In the solidification time below the lower limit, a problem of an increase in production cost is likely to occur.

  As described above, according to the present invention, an Mg alloy containing Y is melted and then solidified within a solidification time of 200 seconds or less to form an ingot. There is an effect. For this reason, in the manufacture of an alloy or the like whose performance varies greatly depending on the component concentration, such as a functional material, a high-quality product can be manufactured with a high yield.

Hereinafter, an embodiment of the present invention will be described.
The Mg alloy used in the present invention contains at least Y, and the preferred content of Y can be 0.5% to 20% by mass ratio. When no other additive element is contained, the balance is Mg and inevitable impurities. Moreover, as this invention, you may contain another additive element. If this additive element is illustrated, in mass%, Zn: 0.1-10%, Zr: 0.1-2%, Al: 0.1-10%, Ca: 0.1-10%, Mn: 0.1 to 2%, Mm (Misch metal): 0.1 to 10%, Sr: 0.001 to 0.1%, Si: 0.1 to 2%, Sn: 0.1 to 10%, Ge : 0.1-10%, Ce: 0.1-10%, La: 0.1-10%, Nd: 0.1-10%, Gd: 0.1-10%, etc. are mentioned. The present invention is particularly suitable for suppressing component segregation in Mg alloys containing Zn, rare earth elements, and the like as components.

  As shown in FIG. 1A, the Mg alloy whose components have been adjusted is heated and melted, for example, in a melting furnace 1 to form a molten Mg alloy 2. The melting method of the Mg alloy is not particularly limited as the present invention, and for example, it can be performed by a known method using a known melting furnace. The molten Mg alloy is preferably stirred and mixed. The method and means for stirring and mixing are not particularly limited, and an appropriate one can be adopted. For example, as shown in FIG. 1 (b), the Mg alloy molten metal 2 is stirred by the stirring blade 3.

  As shown in FIG. 1 (c), the molten Mg alloy 2 is normally solidified in the mold 4 after being poured into the mold 4. In this case, the solidification rate of the molten metal and the time to solidification, depending on the components of the Mg alloy (the freezing point varies depending on the components), the temperature of the molten Mg alloy, the cooling ability of the mold, the mass effect of the Mg alloy, etc. That is, the coagulation time is determined. Since the component segregation rate of Y greatly depends on this solidification time, the longest solidification time is determined in accordance with the desired component segregation rate. When the segregation rate is within 10%, the solidification time is set within 200 seconds. When the segregation rate is within 5%, the solidification time is set within 100 seconds. It is necessary to determine the material and size of the mold, the temperature of the molten metal, the presence or absence of forced cooling of the mold, the method, and the like so that the solidification time is reached.

  After these conditions are determined, the ingot 5 is obtained by solidifying the Mg alloy melt 2 within a predetermined solidification time. In this ingot, the segregation rate of Y is not more than a predetermined desired segregation rate, and an ingot in which the components are homogenized can be obtained. By producing an Mg product using this ingot as a raw material, a product with less component segregation and excellent quality can be obtained. In addition, the process up to obtaining the Mg product using the ingot as a starting material is not particularly limited as the present invention, and a known processing method or the like can be adopted.

Examples of the present invention will be described below.
In order to reproduce the segregation of the Y component, a small dissolution test apparatus 10 as shown in FIG. 2 was prepared.
The melting test apparatus 10 is made of a heat-resistant material, and a furnace body 11 having a cylindrical inner space inside is vertically arranged with the axis being vertical, and a cylindrical heating element 12 is provided in the furnace body 11. Is disposed, and the core tube 13 is disposed concentrically inside the heating element 12. A crucible 14 is disposed as a melting furnace in the furnace core tube 13, and the crucible 14 is placed on a support table 13 a installed in the furnace core tube 13. The temperature of the crucible 14 is increased by operating the heating element 12 to heat the furnace core tube 13.

  Further, the upper and lower ends of the core tube 13 project outside the furnace body 11 and are closed by water cooling caps 15 and 16. The water cooling caps 15 and 16 are provided with cooling water introduction pipes 15a and 16a and cooling water discharge pipes 15b and 16b, respectively. The cooling water introduced from the cooling water introduction pipes 15a and 16a passes through the water cooling cap. Water is discharged from the cooling water discharge pipes 15b and 16b. The cooling water is passed during heating to prevent damage to the members in the water cooling caps 15 and 16.

The water cooling cap 16 is provided with an Ar gas introduction pipe 17 a, and the Ar gas introduction pipe 17 a communicates with the inside of the reactor core tube 13. Further, the water cooling cap 15 is provided with an Ar gas discharge pipe 17 b, and the Ar gas discharge pipe 17 b is also communicated with the reactor core tube 13.
By introducing Ar gas into the reactor core tube 13 from the Ar gas introduction tube 17a, the interior of the reactor core tube 13 can be made into an Ar gas atmosphere. When the Mg alloy is melted by the crucible 14, the alloy is oxidized. To prevent.
The furnace body 11 is provided with a furnace control thermometer 18 for measuring the temperature of the furnace body space, and the water cooling cap 15 is provided with a thermocouple 19 for measuring the temperature of the molten metal in the crucible 14.

  In the small melting test apparatus 10 described above, 90 g of Mg alloy containing 6.7% Y as a melting base material is inserted into the crucible 14, heated to 750 ° C. and melted, and solidified in a solidification time of 1000 seconds. When the sample was cut in the vertical direction and the structure of the cross section was observed (EPMA method), a phenomenon that the Y component was concentrated at the lower part of the ingot was observed as shown in FIG.

  Furthermore, the Y component analysis of the ingot center of the sample coagulated at various coagulation times was performed using the small dissolution test apparatus 10, and the correlation between the coagulation time and Y segregation was examined. The result is shown in FIG. As shown in FIG. 4, if the solidification time is long, the Y component is precipitated downward accordingly, so the Y component value at the center of the ingot is lower than the ladle value (molten component value), and the degree of Y segregation is low. It has become clear that there is a tendency to grow. On the contrary, it was found that when the solidification time was shortened to 10 sec, segregation of the Y component was suppressed as shown in FIG.

  Next, using a large melting furnace, 167 kg of raw material containing 6.7% Y (Y6.7 wt%, Zr 4.9 wt%, La 1.0 wt%, remaining Mg) is inserted into the crucible. By casting the molten metal into a square mold (320 × 490 × 440 mm), the relationship between the component segregation of Y in the mold casting material and the solidification time was examined. FIG. 6 shows the relationship between the component segregation of Y in each part of the ingot and the solidification time. The solidification time is calculated based on the distance from the ingot bottom. Therefore, the coagulation time and the distance from the ingot bottom have a one-to-one correspondence. Also in the mold casting material, as the solidification time becomes longer, the Y component precipitates at the lower part of the ingot, so the Y concentration increases at a position 20 mm from the bottom of the ingot, and conversely, the Y component value at the sampling position at the upper part of the ingot. Tended to decrease. The reduction ratio was found to be 5% at 100 sec, 10% at 200 sec, and 15% at 400 sec.

Next, in order to produce an ingot in which the component segregation of Y was suppressed to within 10%, the solidification time was judged from FIG. 6, and the mold was designed so that the solidification time was within 200 sec. The solidification time of a cylindrical mold having a thickness of 20 mm has a correlation with the inner diameter from solidification calculations, and from FIG. 7, it was determined that the air-cooled mold had a diameter of 230 mm or less. Based on this result, a mold having a diameter of 200 mm was manufactured.
Using a large melting furnace, a raw material of Mg alloy containing 6.7% Y was inserted into the crucible, and after melting, about 60 kg of molten metal was cast into a cylindrical mold of φ200 mm × H650 mm. FIG. 8 shows the relationship between the Y component segregation and the solidification time of each part in the ingot. The component segregation ratio of Y was suppressed to 10% or less, and a uniform ingot could be produced.

When manufacturing an ingot with Y component segregation suppressed to within 10%, in order to make the mold inner diameter larger than in the above embodiment, a water-cooled pipe is welded to the side of the mold and water is allowed to flow to sufficiently cool the mold. Prepare a water-cooled mold that can be used. From the calculation results shown in FIG. 7, it was found that the inner diameter of the cylindrical mold that can be solidified within 200 sec is expanded to φ350 mm or less in the water-cooled mold. When a raw material of Mg alloy containing 6.7% Y is inserted into a crucible using a large melting furnace and about 180 kg of molten metal is cast into a cylindrical mold of φ350 mm × H650 mm after melting, the component segregation ratio of Y is 10 %, And a uniform ingot can be produced.
As mentioned above, although this invention was demonstrated based on the said embodiment and Example, this invention is not limited to the range of the said description, It can change within the scope of the present invention.

It is process drawing in one Embodiment of this invention. Similarly, it is a figure which shows the melt | dissolution test apparatus used for an Example. It is a drawing substitute photograph of the test material obtained by the solidification test of the Example. It is a graph which shows the relationship between the solidification speed | rate of the test material obtained by the solidification test of the Example, and the shift | offset | difference of Y content. It is a drawing substitute photograph of the test material obtained by the solidification test of the Example. It is a graph which shows the relationship between the solidification speed | rate of the test material obtained by the solidification test of the Example, and the shift | offset | difference of Y content. It is a figure which shows the relationship between the internal diameter of a casting_mold | template and solidification time in the casting_mold | template obtained by solidification calculation. It is a figure which shows the relationship between Y segregation and the solidification time in the Example of this invention.

Explanation of symbols

1 Melting furnace 2 Mg alloy molten metal 3 Stirrer 4 Mold 5 Ingot

Claims (4)

A method for producing an Mg alloy comprising melting an Mg alloy containing Y , injecting it into a mold, and solidifying it in a solidification time within 200 seconds in a stationary state to form an ingot.   A method for producing an Mg alloy, comprising: stirring a molten Mg alloy containing Y and allowing to stand, and then solidifying the molten alloy within 200 seconds to obtain an ingot.   The Mg alloy production method according to claim 1 or 2, wherein the Mg alloy contains 0.5 to 20% by mass of Y. The said solidification time shall be 10 second or more, The manufacturing method of Mg alloy in any one of Claims 1-3 characterized by the above-mentioned.