JP6035675B2 - Mg alloy continuous casting method, Mg alloy cast material, Mg alloy cast coil material, Mg alloy wrought material, and Mg alloy structure - Google Patents

Description

  The present invention provides a continuous casting method of Mg alloy for producing a cast material of Mg alloy (including pure Mg), a cast material of Mg alloy obtained by the method, and a cast material of the Mg alloy. The present invention relates to a Mg alloy cast coil material, a Mg alloy wrought material, and a Mg alloy structure.

  The plate-shaped cast material used as a material for the housing of electrical equipment is, for example, a twin roll method (twin roll method), a twin belt method (twin belt method), a wheel belt method (belt and wheel method) using a movable mold. It can produce by the continuous casting method. For example, in the twin-roll type continuous casting method, the molten metal is supplied between a pair of casting rolls rotating in opposite directions, and the molten metal is rapidly solidified between the casting rolls to obtain a plate-shaped cast material. Cast material produced by this twin-roll continuous casting method is usually wound on a take-up reel, cut when it reaches a predetermined length, and the take-up reel is transported to another work site or shipped. Or

  By the way, when the alloy to be cast is an Mg alloy (including pure Mg), the Mg alloy easily reacts with oxygen to produce magnesium oxide, and the magnesium oxide reduces the surface properties of the cast material of the Mg alloy. In addition, there is a risk of causing problems such as crack starting points during plastic working. Therefore, in Patent Document 1, the oxygen concentration in the casting atmosphere is reduced to 5% by volume or less.

JP 2009-174008 A

  2. Description of the Related Art In recent years, a housing for an electric device or the like has been actively produced using a lightweight and high-strength Mg alloy, and the demand for an Mg alloy casting material as a material for the housing has increased. In order to meet the demand, there is a demand for a continuous casting method of Mg alloy that can continuously produce a Mg alloy cast material with fewer defects than that of conventional production of magnesium oxide during casting.

  The present invention has been made in view of the above circumstances, and one of the objects of the present invention is to provide an Mg alloy continuous casting method capable of reducing the production of magnesium oxide during casting as compared with the conventional method, and the method thereof. The object is to provide a cast material of the obtained Mg alloy. Another object of the present invention is to provide an Mg alloy cast coil material obtained by winding the Mg alloy cast material of the present invention, and an Mg alloy cast material obtained by rolling the Mg alloy cast material or the cast coil material of the present invention. And a Mg alloy structure obtained by press-working the Mg alloy wrought material of the present invention.

  From recent studies by the present inventors, it is important to continuously control the oxygen concentration in the casting atmosphere near the pouring port of the casting nozzle in order to continuously produce a cast material of Mg alloy with few defects. I understood. Based on this finding, the present invention is defined below.

  The present invention provides an Mg alloy in which a molten Mg alloy is supplied from a casting nozzle between a pair of movable molds, and the molten alloy is rapidly cooled and solidified between the pair of movable molds to continuously produce a cast material of Mg alloy. This relates to the continuous casting method. In the continuous casting method of the Mg alloy of the present invention, the outer periphery of the casting nozzle is covered so that the atmosphere in the inner space of the covered portion can be made different from the atmosphere in the outer space of the covered portion. In such a state, the Mg alloy continuous casting method of the present invention continuously introduces an inert gas into the internal space, and monitors at least the oxygen concentration in the casting atmosphere near the pouring port of the casting nozzle. Then, continuous casting is performed while adjusting the casting atmosphere to be constant by adjusting the amount of inert gas introduced based on the monitoring result. The Mg alloy in the present invention includes pure Mg composed of 99.8% by mass or more of Mg and inevitable impurities.

Examples of the inert gas introduced into the internal space in the Mg alloy continuous casting method of the present invention include N ₂ gas and Ar gas. With these inert gases, it is possible to suppress changes in the chemical state of unnecessary Mg alloys. Here, if the introduction amount (flow rate) of the inert gas is too high, the molten Mg alloy is unnecessarily cooled, and if it is too low, the air in the internal space is not sufficiently expelled, and in the vicinity of the casting nozzle. It is difficult to control the casting atmosphere. The flow rate of the inert gas is preferably equal to or less than the volume of the internal space per minute. For example, if the internal space is 10 L, the flow rate of the inert gas is preferably 10 L / min or less.

  As in the configuration of the present invention, the outer periphery of the casting nozzle is covered, and the atmosphere of the inner space of the covered portion can be made different from the atmosphere of the outer space of the covered portion. By continuously introducing the inert gas, the oxygen concentration in the casting atmosphere can be easily managed. In addition, in the continuous casting method of the Mg alloy of the present invention, at least the oxygen concentration in the casting atmosphere is monitored, and the amount of inert gas introduced is adjusted as necessary to continuously control the casting atmosphere. Casting. Therefore, a cast material of Mg alloy with few defects can be produced continuously and stably.

  On the other hand, unlike the configuration of the present invention, for example, it is difficult to control the casting atmosphere to be constant only by spraying an inert gas around the casting nozzle, and the inert gas is once purged around the casting nozzle. Only the casting atmosphere may change. In any configuration, it is difficult to continuously and stably produce a cast material of Mg alloy with few defects. Moreover, although the continuous casting method of Mg alloy described in the said patent document 1 illustrated as a prior art makes the oxygen concentration in casting atmosphere the low oxygen state of 5 volume% or less, the oxygen concentration is made constant. Since the structure to control is lacking, it is expected that the longer the length of the cast material to be produced, the higher the possibility that defects will occur in the cast material.

  As one form of the Mg alloy continuous casting method of the present invention, by introducing an inert gas into the internal space, by controlling the oxygen concentration in the casting atmosphere in the vicinity of the pouring spout, contact between the molten Mg alloy and the movable mold The form which adjusts a position can be mentioned.

  The oxygen concentration in the casting atmosphere in the vicinity of the pouring gate in the above configuration can be adjusted by, for example, the flow rate of the inert gas introduced into the internal space. If the oxygen concentration in the casting atmosphere is lowered, the oxide film formed on the surface of the molten Mg alloy can be thinned, and as a result, the surface tension of the molten metal can be reduced. When the surface tension of the molten metal decreases, the contact position between the molten metal and the roll (movable mold) moves to the casting nozzle side. Here, in the rapid solidification in the twin roll type continuous casting method, the solidification start position, that is, the contact position between the molten Mg alloy discharged from the casting nozzle and the roll has a great influence on the quality of the cast material. . The contact position between the molten metal and the roll is determined by various factors such as the positional relationship between the casting nozzle and the roll, the feed pressure of the molten metal, and the surface tension of the molten metal. Among these factors, there is a limit to the adjustment of the positional relationship, and it is difficult to accurately control the molten metal feed pressure. On the other hand, according to the configuration of the present invention that controls the oxygen concentration of the casting atmosphere by introducing an inert gas, the surface tension of the molten metal can be finely adjusted relatively easily, and the molten metal accompanying the change in surface tension can be adjusted. Fine adjustment of the contact position between the roller and the roll can be performed.

  In addition, since the surface tension of the molten metal differs depending on the type of Mg alloy, the way of forming an oxide film on the surface of the molten metal differs depending on the type of Mg alloy. That is, a difference occurs in the contact position between the molten metal and the roll depending on whether the Mg alloy is pure Mg or what kind of additive element is included. It is possible to cope with such a change in the contact position between the molten metal and the roll due to the difference in alloy type by controlling the oxygen concentration in the casting atmosphere. This is because, as already described, it is relatively easy to adjust the contact position between the molten metal and the roll to a desired position by controlling the oxygen concentration in the casting atmosphere.

  As one form of the continuous casting method of Mg alloy of this invention, the form which controls the said casting atmosphere to 8 degrees C or less of dew points, 15 volume% or less of oxygen concentration, and the temperature of 65 to 450 degreeC can be mentioned. Needless to say, the dew point is a temperature at which condensation starts when a gas containing water vapor is cooled, and the lower the dew point, the more dry the gas.

  Recent studies by the present inventors have shown that molten Mg alloys may react with water vapor in the atmosphere to produce magnesium oxide even in a low oxygen atmosphere. In other words, it has been found that it is important to integrally adjust the oxygen concentration and humidity in the casting atmosphere in order to continuously produce a cast material of Mg alloy with few defects. Also, when adjusting the oxygen concentration and humidity by the flow of inert gas, it is possible to adjust the casting atmosphere temperature so that it does not become too high or too low. It is important to make.

  In a casting atmosphere having a dew point of 8 ° C. or less and an oxygen concentration of 15% by volume or less, Mg is very difficult to oxidize. Moreover, it can suppress that the molten metal of Mg alloy solidifies in a casting nozzle because the temperature of casting atmosphere shall be 65 degreeC or more. On the other hand, by setting the casting atmosphere to 450 ° C. or lower, it is possible to sufficiently secure the cooling rate of the molten Mg alloy discharged from the casting nozzle to the movable mold. As described above, by setting the dew point, oxygen concentration, and temperature in the casting atmosphere within the specified ranges, a cast material of Mg alloy with few defects can be continuously obtained.

  As one form of the continuous casting method of Mg alloy of this invention, the introduction of the inert gas in internal space can mention the form performed from the side of a casting nozzle and from the downward direction.

  When an inert gas is introduced into the internal space, it is preferable that the inert gas does not directly hit the molten metal or casting nozzle. This is because the molten metal and the casting nozzle are partially cooled and solidification unevenness may occur in the cast material. In addition, since the internal space is in an environment in which ascending airflow is likely to occur, if the inert gas is introduced from below, the ratio of the inert gas in the internal space can be naturally increased, and the casting nozzle in the internal space can be poured. The casting atmosphere in the vicinity of the gate can be set within the specified range.

  As one form of the continuous casting method of Mg alloy of this invention, the Mg alloy can mention the form which is a Mg alloy equivalent to ASTM standard AZ91.

  The Mg alloy (including pure Mg) in the present invention is not particularly limited, but an Mg—Al alloy in which Al is added as an additive element to Mg is preferable because it has excellent corrosion resistance. In particular, an Mg alloy corresponding to ASTM standard AZ91 contains Al in an amount of 8.3 mass% to 9.5 mass% and Zn in an amount of 0.5 mass% to 1.5 mass%, and has excellent corrosion resistance. The cast material of Mg alloy corresponding to AZ91 can be suitably used for various industrial products because of its corrosion resistance.

  On the other hand, the cast material of the Mg alloy of the present invention is obtained by the above-described continuous casting method of the Mg alloy of the present invention.

As already described, in the Mg alloy continuous casting method of the present invention, oxidation of the Mg alloy hardly occurs. Therefore, the Mg alloy cast material of the present invention obtained by the Mg alloy continuous casting method of the present invention has fewer surface defects and internal defects made of magnesium oxide than the conventional product. Specifically, when a cast material of Mg alloy having a width of about 200 mm to 600 mm and a thickness of about 3 mm to 5 mm is continuously produced, the surface properties and internal properties of the cast material of the Mg alloy of the present invention are determined by casting. The following values are satisfied in the state immediately after.
[Surface property] The number of surface defects due to magnesium oxide having a diameter of 0.5 mm or more is 0.1 or less per 1 m of the cast material.
[Internal properties] ... Internal defects due to magnesium oxide having a diameter of 20 μm or more are 0.1 or less per 1 mm ² in cross section of the cast material.

  Magnesium oxide generated by touching the casting atmosphere from the casting nozzle to the movable mold remains on the surface of the cast material, or is wound inside the molten metal while moving through the nozzle, or the molten mold is compressed by the movable mold. Or get caught inside the casting. Magnesium oxide entrained inside is divided when it is entrained and tends to be smaller than magnesium oxide remaining on the surface. For reference, a micrograph of an internal defect made of magnesium oxide in a cross section of a cast material of Mg alloy is shown in FIG. As shown in FIG. 4, the magnesium oxide produced in the cast material is like a burnt trace of tobacco, which is clearly different from the healthy structure around it, and can be visually confirmed. Note that magnesium oxide remaining on the surface of the cast material may fall off the cast material and form a hole in the surface of the cast material (see FIG. 2B of the embodiment described later). That is, it can be known that magnesium oxide is indirectly generated due to the presence of holes formed on the surface of the cast material.

  As described above, since the Mg alloy cast material of the present invention has fewer surface defects and internal defects made of magnesium oxide than conventional ones, defects such as cracks are present in the cast material even when bent or plastically processed. Not likely to occur. Therefore, the Mg alloy cast coil material formed by winding the Mg alloy cast material of the present invention into a coil shape, the Mg alloy cast material of the present invention or the Mg alloy cast coil material of the present invention is rolled. The Mg alloy wrought material obtained in this manner and the Mg alloy structure obtained by pressing the Mg alloy wrought material of the present invention are also industrial materials having few defects such as cracks.

  According to the Mg alloy continuous casting method of the present invention, it is possible to produce a cast material of Mg alloy having fewer surface defects and internal defects made of magnesium oxide than conventional ones.

FIG. 1A is a schematic cross-sectional view of a twin-roll continuous casting apparatus used in the embodiment, and FIG. 1B is a schematic vertical cross-sectional view of the twin-roll continuous casting apparatus. FIG. 2 (A) is a view showing a surface photograph of a cast material of Mg alloy having almost no surface defects due to magnesium oxide, and FIG. 2 (B) is a photograph of a surface of a cast material of Mg alloy having surface defects due to magnesium oxide. FIG. 3A is a view showing a cross-sectional photograph of a cast material of Mg alloy having few internal defects due to magnesium oxide, and FIG. 3B is a cross-sectional photograph of a cast material of Mg alloy having internal defects due to magnesium oxide. FIG. It is a figure which shows the enlarged photograph of the internal defect which consists of magnesium oxide in the cross section of the cast material of Mg alloy.

  Hereinafter, casting materials of Mg alloys were produced by changing the casting atmosphere in various ways, and surface properties and internal properties of the casting materials of the Mg alloys were examined.

  First, a casting apparatus used for manufacturing a cast material of Mg alloy will be described with reference to FIG. The casting apparatus of FIG. 1 includes a pair of opposing casting rolls 3U and 3D (movable mold 3) and a casting nozzle 2 for supplying molten alloy 4 'of Mg alloy between the casting rolls 3U and 3D. This is a so-called horizontal twin-roll continuous casting apparatus 1 for producing a cast material 4.

  The casting rolls 3U and 3D are cylindrical members, are arranged to face each other at a predetermined interval, and rotate in opposite directions as shown in FIG. The distance between the casting rolls 3U and 3D can be changed according to the thickness of the cast material 4 to be produced. The casting rolls 3U and 3D have a cooling mechanism in order to rapidly cool and solidify the molten metal 4.

  On the other hand, the casting nozzle 2 is provided with a pouring port 21 opened in a rectangular shape at the tip thereof, and the pouring port 21 is disposed so as to be inserted between the casting rolls 3U and 3D described above. The casting nozzle 2 includes side members 25 that define the width of the cast material 4 at both ends thereof. The side member 25 is disposed so as to be inserted between the casting rolls 3U and 3D, and also serves as a weir to prevent the molten metal 4 from leaking from the casting rolls 3U and 3D.

  Further, in the casting apparatus 1 of the present embodiment, the entire outer periphery of the casting nozzle 2 is covered, and the atmosphere of the inner space of the covered portion is different from the atmosphere (air atmosphere) of the outer space of the covered portion. It can be in a state. The state of the cover will be described in more detail. Of the nozzle support 2H that supports the casting nozzle 2, the portion located on the side of the casting nozzle 2 is the mold support 3H that rotatably supports the casting rolls 3U and 3D. In contact. On the other hand, leaf spring materials 2C, 2C wider than the casting nozzle 2 are attached to portions of the nozzle support 2H located above and below the casting nozzle 2, and the leaf spring materials 2C, 2C are cast rolls. 3U and 3D are in contact (see FIG. 1B). A felt material is attached to the leaf spring materials 2C and 2C at the contact points with the casting rolls 3U and 3D, and the leaf spring materials 2C and 2C directly contact the casting rolls 3U and 3D to damage the casting rolls 3U and 3D. It is supposed not to. In this way, the casting nozzle 2 is surrounded from all sides. The volume of the enclosed space (the space surrounded by the outer peripheral surface of the casting nozzle 2, the inner peripheral surface of the nozzle support 2H, the outer peripheral surfaces of the casting rolls 3U and 3D, and the inner peripheral surface of the mold support 3H. ) Was approximately 10 L.

  In addition, in the internal space of the covered portion, introduction pipes 2P and 2P for introducing an inert gas into the internal space are provided. Specifically, a pair of introduction pipes 2 </ b> P and 2 </ b> P are provided on both sides of the casting nozzle 2. The gas outlets of the introduction pipes 2P and 2P are open to the casting roll 2 side and slightly upward. Therefore, the inert gas introduced from the introduction pipes 2P and 2P flows in the direction from the casting nozzle 2 toward the casting rolls 3U and 3D and from the lower side to the upper side of the casting nozzle 2, and does not directly hit the casting nozzle 2. It is like that.

  The amount of inert gas introduced from the introduction pipes 2P, 2P into the internal space is controlled by a control mechanism (not shown). Specifically, the control mechanism adjusts the introduction amount of the inert gas based on the detection results of various sensors arranged in the vicinity of the width direction end of the pouring port 21 in the internal space. By adjusting the amount of inert gas introduced by this control mechanism, the casting atmosphere in the vicinity of the pouring gate 21 can be controlled to be constant. In this embodiment, a sensor for measuring the dew point, oxygen concentration, and temperature in the atmosphere is provided. A known configuration can be used for these sensors.

  With the configuration described above, the space in the cover is not completely sealed. However, as long as the inert gas is continuously introduced from the gas introduction pipes 2P and 2P, the atmosphere in the inner space of the covered portion is the cover. It becomes a state different from the air atmosphere outside the part.

  Using the casting apparatus 1 described above, a plurality of Mg alloy castings 4 having a length of 600 m, a width of 300 mm, and a thickness of 4 mm were produced by changing the atmosphere of the internal space of the covered portion. And the surface property and internal property of the obtained casting material 4 of Mg alloy were investigated. Table 1 shows the atmospheric conditions near the pouring port 21 of the casting nozzle 2 in the internal space and the evaluation results.

The flow rate in Table 1 is the flow rate of N ₂ gas introduced into the internal space. A flow rate of “0” indicates that N ₂ gas was not introduced (ie, atmospheric atmosphere). The dew point, oxygen concentration, and temperature in the atmosphere are values measured by various sensors arranged in the vicinity of the widthwise end of the pouring gate in the internal space.

  Further, the surface properties were evaluated by visually counting surface defects caused by magnesium oxide having a diameter of 0.5 mm or more formed on the surface of a 100 m cast material and measuring the number of defects per meter. FIG. 2 (A) is a view showing a surface photograph of a casting material in which surface defects due to magnesium oxide are almost absent, and FIG. 2 (B) is a casting having hole-like surface defects formed by dropping magnesium oxide. It is a figure which shows the surface photograph of material. In counting the surface defects, the hole-shaped surface defects shown in FIG. 2B and the surface defects made of magnesium oxide itself are counted.

On the other hand, the internal properties crossed the cast material at a position of about 10 m, 200 m, 400 m, 600 m from the start of casting, and the defects made of magnesium oxide having a diameter of 20 μm or more formed in the cross section were counted by SEM observation, The number of defects per 1 mm ² was evaluated. The width of the field of the observed cross section was 4 mm × 15 mm, and the number of fields was 6. FIG. 3 (A) is a view showing a cross-sectional photograph of a cast material having almost no internal defects made of magnesium oxide, and FIG. 3 (B) shows the internal defects made of magnesium oxide at a position slightly above and to the right of the drawing. It is a figure which shows the cross-sectional photograph of the casting material which has. In counting the internal defects, the internal defects made of magnesium oxide shown in FIG. 3B are counted.

From the results in Table 1, the number of magnesium oxide defects in samples E, F, and H produced in a casting atmosphere having a dew point of 8 ° C. or less, an oxygen concentration of 15% by volume or less, and a temperature of 65 ° C. to 450 ° C. In any case, it was much less than other samples. Specifically, the number of surface oxides of Samples E, F, and H was 0.1 piece / m or less, and the number of internal oxides was 0.1 piece / mm ² or less. In this way, if the specimens E, F, and H are almost free of defects on the surface and inside, it is expected that defects such as cracks will not easily occur in the cast material even if it is further bent or plastically processed. Is done.

  In addition, this invention is not necessarily limited to embodiment mentioned above, In the range which does not deviate from the summary of this invention, it can change suitably and can implement.

  The continuous casting method of the Mg alloy of the present invention can be suitably used for producing a cast material of Mg alloy which is a material for various industrial products.

1 Twin roll type continuous casting equipment (continuous casting equipment)
2 Casting nozzle 21 Pouring port 25 Side member 2H Nozzle support 2C Leaf spring material 2P Introducing pipe 3 Movable mold 3U, 3D Casting roll 3H Mold support 4 Mg alloy cast material 4 'Mg alloy molten metal

Claims (4)

Continuous casting of Mg alloy in which a molten alloy of Mg alloy is supplied from a casting nozzle between a pair of movable molds, and the molten metal is rapidly solidified between the pair of movable molds to continuously produce a cast material of Mg alloy. A method,
The outer circumference of the casting nozzle is covered, and the atmosphere of the inner space of the covered portion can be made different from the atmosphere of the outer space of the covered portion, and then an inert gas is continuously supplied to the inner space. Introduced
At least the oxygen concentration in the casting atmosphere in the vicinity of the pouring port of the casting nozzle is monitored, and the amount of inert gas introduced is adjusted based on the monitoring result, whereby the casting atmosphere is kept at a dew point of 8 ° C. or less and the oxygen concentration is 15 volumes. %, A continuous casting method of an Mg alloy that performs continuous casting while controlling the temperature at 65 ° C. to 450 ° C. With the introduction of the inert gas to the interior space, the watch by controlling the oxygen concentration in the casting atmosphere sprue vicinity of claim 1 for adjusting the contact position between the molten metal and the movable mold Mg alloy continuous casting method. The inner introduction of the inert gas into the space, the lateral side of the casting nozzle, and continuous casting method of the Mg alloy according to claim 1 or claim 2 carried out from below. The Mg alloy continuous casting method according to any one of claims 1 to 3 , wherein the Mg alloy is an Mg alloy corresponding to ASTM standard AZ91.