KR100510056B1 - Production technology of magnesium alloy slurries for semi-solid near-net shaping - Google Patents

Abstract

The present invention relates to a method for producing a magnesium alloy slurry required for reaction solidification of a magnesium alloy, and more particularly, the solid phase crystallized in advance when the liquid magnesium alloy is cooled to a solid / liquid coexistence zone. The present invention relates to a method for easily preparing a magnesium alloy slurry for reaction solidification by utilizing as a nucleation site. Method for producing a magnesium alloy slurry for reaction solidification according to the present invention comprises the steps of heating the solid magnesium alloy to form a single phase liquid magnesium; Cooling the single-phase liquid magnesium alloy to a liquidus temperature to form a solid crystal; And cooling the liquid magnesium alloy containing the solid crystal to a temperature between the liquidus temperature and the solidus temperature to form a magnesium primary by using the solid crystal as an inoculant. When using the method for producing a magnesium alloy slurry for reaction solidification according to the present invention, the spherical shape of the spherical particles is controlled by simple process variables such as the cooling rate, the content of the alloying elements included in the magnesium alloy, and the holding time at the solid-liquid coexistence temperature. It is possible to prepare a high-quality reaction high-molding magnesium alloy slurry in a state in which fine magnesium crystals are uniformly distributed in the liquid phase.

Description

Production Method of Magnesium Alloy Slurry for Reaction Molding {PRODUCTION TECHNOLOGY OF MAGNESIUM ALLOY SLURRIES FOR SEMI-SOLID NEAR-NET SHAPING}

The present invention relates to a method for producing a magnesium alloy slurry required for reaction solidification of a magnesium alloy, and more particularly, the solid phase crystallized in advance when the liquid magnesium alloy is cooled to a solid / liquid coexistence zone. The present invention relates to a method for easily preparing a magnesium alloy slurry for reaction solidification by utilizing as a nucleation site.

Semi-solid forming is the use of pseudoplastic and thixotropy properties, which are the rheological properties of semi-solid metals, to form and process semi-solid substrates with very low stress. Also there is an advantage that the deformation and molding of the base material can be.

Such reaction solidification includes rheo-forming for directly forming a semi-solid slurry formed during cooling of a molten metal, and thixo-forming, which is a technique for re-heating a solid metal into a solid / liquid coexistence region. There is). In the above Leo molding, the raw material of the solid / liquid coexistence region produced directly from the liquid alloy is called a slurry.

From the standpoint of formability, the solid phase in the slurry used as the raw material for the Leo molding is preferably as spherical fine particles as possible. In addition, the slurry must have a liquid phase fraction suitable for pressure molding, and the liquid phase fraction of the slurry can be appropriately controlled by the temperature of the solid / liquid coexistence region.

According to JP 249923/1997, the size of magnesium tablets is preferably as small as possible in reaction solidification, and the shape is required to be as spherical as possible. In normal reaction solidification, the average size of primary crystals should not exceed 200 µm, In addition, it is reported that irregular crystals such as dendritic phases of 300 µm or more should not occur.

The following are known as the prior art regarding the manufacturing method of the solid / liquid coexisting magnesium alloy slurry for Leo molding in which a magnesium primary tablet exists as a solid phase.

(1) A AZ91 magnesium alloy molten metal having a superheat degree of liquidus temperature (598 ° C for AZ91), that is, a melt superheat of less than 300 ° C, is brought into contact with a jig that is kept below the melting point of the alloy. A method of preparing a magnesium alloy slurry by crystallizing a fine tablet in a sugar alloy by injecting it into a container of a predetermined volume, cooling it to a temperature showing a predetermined liquidity rate, and maintaining it for 5 seconds to 60 minutes (JP 076051/1997).

(2) AZ91 magnesium alloy molten metal having a superheat degree of liquidus temperature (598 ° C for AZ91), that is, a melt superheat of less than 100 ° C, in a container of a constant volume maintained below the melting point of the alloy without the use of jig; A method of preparing a magnesium alloy slurry by crystallizing fine crystals in a sugar alloy in a liquid by injecting, cooling to a temperature showing a predetermined liquidity rate, and maintaining the mixture for 5 seconds to 60 minutes (JP 087770/1997).

(3) The method (1) and (2), wherein the jig and the container are vibrated, or the jig and the container are vibrated at the same time to promote magnesium crystal refinement.

(4) AZ91 magnesium alloy molten metal having a superheat degree of liquidus temperature (598 ° C for AZ91), that is, a molten metal superheat of less than 50 ° C, in a volume of a container kept below the melting point of the alloy without the use of jig; Method of applying vibration during cooling by inserting a vibrating rod into a container when preparing a magnesium alloy slurry by injecting and cooling to a temperature showing a predetermined liquidity rate and crystallizing a fine tablet in a sugar alloy in a sugar alloy (JP 140260/1998) .

(5) In the methods (2) and (4), 0.005% -0.1% Sr, or 0.01% -1.5% Si and 0.005% -0.1% Sr, or 0.05-0.3% Ca were added to refine the magnesium primary tablet. How to use magnesium alloy.

The above methods show that the tolerance of the melt superheat varies according to which cooling method is selected. That is, it can be seen that the greater the forced cooling capacity, the larger the allowable melt superheat. In the above methods, the magnesium primary produced in contact with the jig, container, vibrating rod, etc. is uniformly dispersed in the magnesium alloy liquid phase and cooled to the solid / liquid coexistence area. It can be seen that the key to producing a high-quality Leo molding slurry.

Recent studies using the devices disclosed in this patent (H. Kaufmann and PJ Uggowitzer, "Fundamentals of the new rheocasting process for magnesium alloys", Advanced Engineering Materials, vol. 3, no. 12 (2001) pp. 963-967. In order to produce a good magnesium alloy slurry by pouring the magnesium alloy liquid directly into the steel container, to prevent the constitutional supercooling to occur in order to allow the primary cell produced on the wall of the container to grow spherically. It is reported that the cooling rate should be well controlled. In addition, it is reported that when the superheat degree of molten metal is large, no primary crystal is generated on the wall of the container and disappears inside the container even when the primary crystal is generated.

Therefore, the above method has to properly control the production rate and dissolution rate of the magnesium primary tablet, there is a problem to precisely control the cooling pattern from the magnesium alloy molten metal to the solid / liquid coexistence zone.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a method for producing a high-quality reaction solid moldable magnesium alloy slurry in a state in which spherical fine magnesium crystals are uniformly distributed in a liquid phase with only simple process control.

In order to solve the above technical problem, the present invention, by producing a solid crystals in the liquid magnesium alloy first, and using the solid crystals as the inoculum of magnesium primary tablets, thereby simply preparing a magnesium alloy slurry for reaction molding Provide a way to do it.

Method for producing a magnesium alloy slurry for reaction solidification according to the present invention comprises the steps of heating the solid magnesium alloy to form a single phase liquid magnesium; Cooling the single-phase liquid magnesium alloy to a liquidus temperature to form a solid crystal; And cooling the liquid magnesium alloy containing the solid crystal to a temperature between the liquidus temperature and the solidus temperature to form a magnesium primary by using the solid crystal as an inoculant.

In an embodiment of the method for preparing a magnesium alloy slurry for reaction solidification according to the present invention, the size of the magnesium tablet in the slurry may be controlled by the content of the alloying element precipitated as a solid crystal. In this case, the lower limit of the content of the alloying element is determined in consideration of the ratio of solid phase crystallization acting as the inoculum of magnesium primary, and the upper limit thereof in consideration of the oxidation loss of magnesium in the process of melting the solid magnesium alloy into single phase liquid magnesium. Is determined.

In another embodiment of the method for preparing a magnesium alloy slurry for reaction solidification according to the present invention, the size of the magnesium primary in the slurry may be controlled by the rate of cooling the liquid magnesium alloy to the liquidus temperature. Increasing the cooling rate increases the nucleation density of the solid phase crystals used as a heterogeneous nucleation site of magnesium primary. This reduces the size of the magnesium primary in the slurry. For this reason, the cooling rate should be above a certain threshold in principle. On the contrary, when the cooling rate decreases, the size of solid crystals produced increases and the number decreases. In addition, the density of the solid phase precipitate is about three times greater than the density of the magnesium alloy liquid phase, the solid crystal formed in the magnesium alloy liquid phase is settled by the density difference to the bottom of the container. In addition, the residence time in the liquid phase of the solid crystals produced by the decrease in the cooling rate increases, so that a large amount of solid crystals settled to the bottom of the vessel before reaching the liquidus temperature at which magnesium crystals are formed. It will lose its effectiveness as an inoculum. In consideration of this, in order to obtain a good slurry, the magnesium alloy liquid phase should be cooled above a specific cooling rate.

In an embodiment of the method for producing a magnesium alloy slurry for reaction solidification according to the present invention, the spheroidization of magnesium primary in the slurry is such that the liquid magnesium alloy containing the solid crystal is maintained between the liquidus temperature and the solidus temperature. It can be adjusted by time. Increasing the retention time causes spheroidization to reduce the interfacial energy of the magnesium primary.

In addition, the spheroidization of magnesium primary tablets in the slurry can be controlled by increasing the amount of alloying elements precipitated as solid crystals. As the supersaturation increases due to the increase in the amount of alloying elements, nucleation of the solid phase crystallization is facilitated, and the size of the solid phase crystallization decreases at the same cooling rate. Increasing the supersaturation increases the amount of solid crystals and decreases the size, increasing the number of uneven nucleation sites of magnesium tablets decreases the size of individual magnesium tablets at the same liquidity. In solid phase filtrates, the uneven nucleated magnesium tablets initially grow spherical and later grow dendritic. The small size of the individual magnesium primary tablets means that the gap between dendrites is narrow, so that the diffusion distance decreases and spheronizes faster when maintained at the solid / liquid coexistence temperature.

It is known that the fraction of the liquid phase and the solid phase in the slurry can be controlled quantitatively and precisely by controlling the temperature at which the liquid magnesium alloy containing the solid crystal is cooled to a temperature between the liquidus temperature and the solidus temperature. .

In an embodiment of the method for preparing a magnesium alloy slurry for reaction solidification according to the present invention, the magnesium alloy is any one selected from AZ91, AM60, AM50, AS21, and AE42 as ASTM (American Material Standard). It may include Mn. The magnesium alloys are all three or more alloys, the specific composition of which is shown in Table 1 below. Except for the weight ratios of each ingredient listed in Table 1, magnesium consists of magnesium (see ASM Specialty Handbook, Magnesium and Magnesium Alloys, ASM International (1999) p. 17). Composition of Magnesium Alloy (wt%) Magnesium alloy Al Mn Zn Si Rare earth metals AZ91 8.3-9.7 0.13-0.50 0.35-1.0 - - AM60 4.4-5.4 0.26-0.50 - - - AM50 5.5-6.5 0.13-0.60 - - - AS21 2.2 0.1 - 1.0 - AE42 4.0 0.1 - - 2.5

Manufacturing Principle of Magnesium Alloy Slurry

Hereinafter, the production principle of the magnesium alloy slurry according to the present invention will be described step by step.

Forming single phase liquid magnesium:

According to ASTM (American Material Standard), any one magnesium alloy selected from AZ91, AM60, AM50, AS21, and AE42 containing Mn is heated to a certain temperature and completely melted.

This particular temperature is determined by the amount of Mn in the magnesium alloy that precipitates as a solid phase crystal during cooling of the single phase liquid magnesium alloy. Figure 1 shows the step-by-step temperature change process in the manufacturing process of the magnesium alloy slurry for reaction solidification according to the present invention. The specific temperature means a saturation temperature (T _sat , 2) corresponding to the content of Mn in the magnesium alloy.

As described above, the present invention is to prepare a magnesium alloy slurry using a solid crystallized product produced by the difference in solubility of Mn as a magnesium primary inoculum (nucleation site), so that the magnesium alloy is heated and melted ( T _m , 1) is preferably above the saturation temperature (T _sat , 2).

In other words, if the magnesium alloy is melted at a temperature lower than the saturation temperature T _sat , 2, the solid crystals containing Mn are already present in the liquid magnesium alloy. Since the density of the solid crystal is larger than that of the liquid magnesium (for example, the density of the Al ₈ (Mn, Fe) ₅ phase is 4.4 g / cm 3 and higher than that of the liquid magnesium, 1.6 g / cm 3), It is settled to the bottom of the crucible, and this solid precipitate is lost as an inoculant. Therefore, in order for the solid crystal containing Mn to function as a magnesium primary inoculum to the maximum, the melting temperature (T _M , 1) must be at or above the saturation temperature (T _sat , 2).

As shown in Table 2, in the magnesium alloy containing Mn, it can be seen that as the temperature increases, the saturation solubility of Mn increases. This in turn means that as the amount of Mn in the magnesium alloy increases, the temperature for complete melting of the magnesium alloy increases.

Solubility and equilibrium crystallization of Mn in liquid phase by magnesium alloy. (%, Weight percentage) Magnesium alloy Liquid line temperature (T _L , ℃) 650 ℃ 670 ℃ 690 ℃ Water prize AZ91 0.120% (598 ° C) ^* 0.248% 0.319% 0.400% Al ₈ (Mn, Fe) ₅ AM60 0.195% (615 ° C) ^* 0.311% 0.403% 0.513% Al ₈ (Mn, Fe) ₅ AM50 0.245% (620 ℃) ^* 0.361% 0.468% 0.603% α-AlMnFe AS21 0.178% (632 ° C) ^* 0.219% 0.277% 0.341% (Mn, Fe) ₅ Si ₃ AE42 0.126% (625 ℃) ^* 0.181% 0.245% 0.326% Al ₈ (Mn, Fe) ₄ RE

delete

However, when the melting temperature (T _M , 1) is excessive, there is a certain limit because the oxidation loss of the oxidizing magnesium alloy increases. Therefore, this also limits the content of Mn.

Formation of solid crystals:

In the present invention, the formation of a solid crystal that acts as an inoculant of magnesium primary tablet uses the difference in solubility according to the temperature of Mn in the liquid magnesium alloy.

In FIG. 1, when the liquid magnesium alloy is cooled from the melting temperature (T _m , 1) to the liquidus temperature (T _L , 3) of the alloy, the saturation temperature (T _sat , 2) and the liquidus temperature (T _L , Since the solubility of Mn in the liquid magnesium alloy decreases as the temperature decreases between 3), solid crystals 6 are formed in the magnesium alloy liquid phase 7. 5 of FIG. 1 is a figure which shows a figure in which the solid crystal | crystallization is formed.

It demonstrates using the AZ91 magnesium alloy of Table 2 as an example. For AZ91 magnesium alloy, Mn solubility is 0.12% at liquidus temperature (598 ° C), but Mn solubility increases to 0.4% as the temperature rises to 690 ° C. Therefore, when the AZ91 alloy containing 0.4% of Mn is dissolved at a temperature higher than 690 ° C. and then cooled, the supersaturated Mn is crystallized in the liquid AZ91 alloy when the liquid AZ91 alloy temperature is lower than 690 ° C. . When the liquid AZ91 alloy is further cooled to reach the liquidus temperature, the Mn solubility at this temperature is 0.12%, so Mn corresponding to 0.28% Mn is determined by the difference in solubility.

As shown in Table 2, when supersaturated Mn is crystallized, pure solid Mn is not produced, but is crystallized to Al ₈ (Mn, Fe) ₅ phase. The phase of the solid crystal is determined according to the type of alloy.

The amount of solid crystallization in this example is mainly determined by the amount of supersaturated Mn. This is because the Fe content in a typical magnesium die casting alloy is 50 ppm or less (ASTM B-94), because it is only about 1.8% of 0.28% of the Mn content change in the above example. Thus, the amount of crystallized Al ₈ (Mn, Fe) ₅ phase produced by supersaturated Fe can be ignored. On the other hand, since the concentration of Al in the Al ₈ (Mn, Fe) ₅ phase corresponds to 44% by weight percentage, Al is changed by 0.22% by 0.28% of Mn. That is, the precipitation of supersaturated Mn reduces the content of Al in the magnesium alloy by 0.22%. This change in Al content can satisfy the ASTM B-94 magnesium alloy component specification, and does not change the properties of magnesium alloy components manufactured by the reaction solidification process.

When a certain amount of solid crystallization is precipitated, the smaller the particle size of the solid crystallization, the more the nucleation site of the magnesium primary tablet, i.e., the number of solid crystallization is increased. Therefore, the smaller the size of the solid crystal is, the smaller the particle size of the magnesium primary tablet is. The size of the solid crystals can be adjusted by controlling the cooling rate between the saturation temperature (T _sat , 2) and the liquidus temperature (T _L , 3). According to nucleation theory, increasing the cooling rate decreases the size of the solid crystal formed from the supersaturated alloying element (Mn), and conversely, decreasing the cooling rate increases the size of the solid crystal.

The said cooling rate should just be a certain threshold or more from a principal point of view, Preferably it should just be 0.1 degree-C / s or more. If the cooling rate is further reduced, as described above, the residence time of the solid phase crystal in the magnesium alloy liquid phase increases, so that the settling amount of the solid phase crystal due to the density difference increases, which reduces the nonuniform nucleation site of the magnesium crystals, thereby reducing the quality. It is difficult to obtain a slurry.

Similarly, according to nucleation theory, the greater the degree of supersaturation, the easier the nucleation. Therefore, when the same cooling rate is maintained, in order to reduce the size of the magnesium primary in the slurry, it is possible to increase the number of solid crystals by increasing the alloying elements (Mn) in the magnesium alloy.

For example, in the AZ91 alloy containing 0.4% Mn, 5 g Al ₈ (Mn, Fe) ₅ phase is distributed in 1 kg AZ91 alloy liquid phase, while in the AZ91 alloy containing 0.22% Mn, 1.78 g Al ₈ ( The Mn, Fe) ₅ phase is distributed in 1 kg of AZ91 alloy liquid phase. Therefore, when the cooling rates are the same, the size of magnesium primary in AZ91 alloy slurry containing 0.4% Mn decreases because the amount of supernatant increases with increasing Mn content, and the amount of solid phase is also increased. do.

From the above it can be seen that by controlling the cooling rate to the liquidus temperature of the AZ91 alloy and the Mn content in the AZ91 alloy, it is possible to control the size of the magnesium primary in the AZ91 alloy slurry.

Steps to Form Magnesium Candles:

In this step, the liquid magnesium alloy containing the solid crystals is cooled and maintained to a temperature between the liquidus temperature and the solidus temperature to form magnesium primary by using the solid crystals as an inoculant.

As described above, 5 in FIG. 1 shows a state in which the solid crystals 6 containing Mn at the liquidus temperature are dispersed in the liquid magnesium alloy 7. When the liquid magnesium alloy 7 containing the solid crystals 6 is kept between the liquidus temperature T _L and the solidus temperature T _S , the magnesium primary 9 contains Mn or Zr. It is produced by using solid crystals as nuclei. 8 of FIG. 1 shows a state in which the magnesium primary tablet 9 is formed using the solid crystals 6 as a nucleus and dispersed in the liquid magnesium alloy 7.

The ratio of the liquid magnesium alloy 7 in state 8 of FIG. 1 can be theoretically obtained by changing the temperature 4 maintained to form the magnesium primary 9 (PJ Uggowitzer and A. Wahlen, 'On the formation of eutectic phase in magnesium alloys during cooling from the semi-solid state ', 6th International Conference Semi-solid processing of alloys and composites, Turin, Italy, Sep. 27-29, 2000, pp. 429-435).

If the temperature 4 forming the magnesium primary 9 is maintained for a long time, the magnesium primary 9 is spherical to reduce the interfacial energy.

In addition, when the content of Mn is increased, the magnesium primary 9 can be spherically easily even in a short holding time as described above.

Above, the principle of forming solid crystals in the liquid magnesium alloy by the difference in solubility according to the present invention, the principle of controlling the particle size of magnesium crystals in the slurry by controlling the content or cooling rate of the alloy elements to be crystallized, and magnesium primary formation process The principle of control of liquidus rate and particle spheroidization can be equally applied to AM60, AM50, AS21 and AE42 alloys as shown in Table 2.

Furthermore, in EQ21, EZ33, EK41, HK31, ZE41, ZE63, ZK51, ZK61, ZK40, ZK60, QH21, QE22, WE54, WE43, etc. which are magnesium alloys containing Zr, Zr also contains Mn and Similarly, Zr-containing crystals can be produced by the difference in solubility with temperature. Therefore, the same principle as described above may be utilized in the production of slurry for the reaction solidification of the magnesium alloy containing Zr.

Example 1 AZ91 Magnesium Alloy Slurry

The conditions employed in this example are shown in Table 3.

AZ91 Magnesium Alloy Slurry Manufacturing Conditions Mn content (wt.%) Cooling rate ¹⁾ (℃ / s) Melting temperature (℃) Retention time ²⁾ Surplus Mn ³⁾ (wt.%) Microstructure 0.17 1.5 670 1 minute 0.05 Picture 2 0.22 2.0 690 2 minutes 30 seconds 0.10 Picture 3 0.40 2.0 700 4 minutes 0.28 Picture 4 0.40 0.1 700 4 minutes 0.28 Picture 5 0.40 1.7 700 60 minutes 0.28 Picture 6

delete

1) Average cooling rate from melting temperature to liquidus temperature

2) Holding time of AZ91 alloy in solid / liquid coexistence area (580 ± 3 ℃)

3) Difference between Mn content in AZ91 alloy and Mn content (0.12wt.%) At liquidus temperature

First, 25 g of AZ91 alloy is placed in an iron crucible and melted using argon in a vertical tube furnace. In this embodiment, the AZ91 alloy contains up to 9% Al, 0.7% Zn, and 30 ppm Fe. In this case, the melting temperature should be high enough to dissolve all the solid crystals including Mn present in the AZ91 alloy.

The dissolution is complete and the AZ91 alloy in a uniform liquid phase is transferred upwards in a vertical column. The temperature of the upper part of the vertical tube furnace was 580 degreeC. Therefore, the AZ91 liquid phase moved to the upper part of the vertical tube is cooled to 580 ± 3 ° C., which is a solid / liquid coexistence area. The cooling rate from the melting temperature to the liquidus temperature ranged from 0.1-2 ° C./s. After holding for 1-60 minutes at 580 ± 3 ° C, AZ91 alloy in solid / liquid coexistence zone is quenched with ice water.

The microstructure of the AZ91 alloy slurry prepared in this manner is shown in FIGS. 2 to 6. To FIG hayeoteum, magnesium Primary inside Al ₈ (Mn, Fe) and present this crystallization water over _5, this Al ₈ (Mn, Fe) ₅ acts as a nucleation place of magnesium Primary As shown in Figures 2 to 6 Indicates.

2 to 4 are microstructures of the AZ91 alloy slurry obtained when the change in Mn content is 0.17%, 0.22%, and 0.4%, respectively, when the cooling rate is in the range of 1.5-2.0 ° C./s. As shown in the figure, it can be seen that the size of magnesium primary decreases as the content of Mn increases at a similar liquidity rate. At 0.6 liquidity, the initial average size is 110 μm when the Mn content is 0.17%, 102 μm at 0.22%, and 52 μm at 0.4%. This is because the amount of crystals in the Al ₈ (Mn, Fe) ₅ phase serving as the nucleation site of the magnesium primary increased with increasing Mn content as described above.

On the other hand, when the Mn content is low as 0.17% spherical and dendritic magnesium crystals are formed at the same time (Fig. 2), as the Mn content increases, magnesium primary crystals are spheroidized, which is advantageous for reaction molding. As the supersaturation increases due to the increase in Mn content and the heterogeneous nucleation sites of the magnesium tablet increase, the size of the individual magnesium tablet decreases at the same liquid rate. This narrows the spacing between the dendritic phases of the individual magnesium primary tablets, reducing the diffusion distance and forming more quickly when maintained at the solid / liquid coexistence temperature.

Figure 5 shows the microstructure of the AZ91 alloy slurry obtained at a cooling rate lowered to 0.1 ℃ / s when Mn content of 0.4%. According to Figure 5, compared with the case of Figure 4, the cooling rate is 2.0 ℃ / s increased the primary size, it can be seen that the shape also contains a lot of dendritic. The decrease in cooling rate increases the residence time of solid phase crystals in the magnesium alloy liquid phase. The sedimentation amount of solid phase precipitate due to the density difference increases, which increases the size of magnesium primary tablet and develops the dendritic phase.

FIG. 6 is a AZ91 alloy slurry microstructure when the Mn content is 0.4% and the cooling rate is 2.0 ° C./s, and is maintained at 580 ± 3 ° C. for 60 minutes in a solid / liquid coexistence range. According to Figure 6, compared with Figure 4, the retention time is 4 minutes, the initial tablet size increased from 52㎛ 105㎛ it can be seen that the tablet is more spherical.

As described above, it is desired that the size of magnesium tablets is as small as possible and that the shape is as spherical as possible in reaction solidification, but in normal reaction solidification, the average size of primary solids should not exceed 200 µm, and more than 300 µm. It is known that it is preferable that irregular amorphous crystals such as dendritic phase do not occur (JP 249923/1997).

In preparing the AZ91 alloy slurry according to the present embodiment, when the Mn content was 0.17% or more and the cooling rate was 0.1 ° C./s or more, the standard described in JP 249923/1997 was satisfied. As shown in Table 3, when the AZ91 alloy containing 0.17% Mn was cooled to liquidus temperature, 0.9 g of Al ₈ (Mn, Fe) ₅ phase per kg of AZ91 alloy was added with 0.05% excess Mn. This magnesium alloy is produced in the liquid phase. It can be seen that a magnesium alloy slurry suitable for reaction molding can be prepared by dispersing 0.9 g of Al ₈ (Mn, Fe) ₅ phase crystals per kg of AZ91 alloy. That is, the content of Mn is 0.05% more than the saturated solubility of Mn at the liquidus temperature, and the AZ91 alloy having such a composition may be used.

On the other hand, when the Mn content exceeds 1%, the melting temperature of the AZ91 alloy must be raised to 765 ° C in order to dissolve all the contained Mn. At this temperature, the oxidation loss of the highly oxidizable magnesium alloy is increased, so the Mn content is preferably 1% or less.

In addition, the holding time in the solid / liquid coexistence zone can be appropriately controlled according to the molding conditions of subsequent reaction solidification, but it is considered that about 60 minutes is fine. In order to reduce the interfacial energy as the holding time increases, the magnesium tablet becomes more spherical but the size of the magnesium tablet increases due to the growth of Ostwald. When considering the productivity of the reaction high-molding, holding for 60 minutes or more is meaningless, so the holding time is not set to 60 minutes or more in this embodiment. The lower limit was set under the condition that the average particle size of the solid phase in the slurry for reaction solidification became 200 µm or less as described above. Even if only one minute was maintained, this condition was satisfactorily satisfied, so the lower limit of the holding time was set to one minute. Below that, the holding time becomes difficult to control.

Example 2: AM60 Magnesium Alloy Slurry

The operating conditions for the production of AM60 alloy slurry can also be changed in the same way as for the AZ91 alloy. In this example, all the conditions are the same, and only the content of Mn shows the result.

Figure 7 shows the microstructure of the AM60 alloy slurry when the content of Mn is 0.25%, Figure 8 is 0.5%. The results in Figures 7 and 8 show that the cooling rate from the melting temperature of 700 ° C, from the melting temperature to the liquidus temperature (610 ° C) was 1.0 ° C / s, and the slurry production temperature and holding time were 600 ± 5 ° C and 5 minutes, respectively. will be.

As shown in Figures 7 and 8, a small Mn content of the spherical and dendritic magnesium crystals are formed (Fig. 7), while a high Mn content of a spherical magnesium primary crystals (Fig. 8). In addition, the initial average size at the Mn content of 0.25% is 105㎛ at the liquidity rate 0.6, but decreases to 70㎛ at the liquidity rate 0.61 when the Mn content is increased to 0.5%. This is because the amount of solid crystals containing Mn increased as described above.

On the other hand, when the AM60 alloy containing 0.25% Mn is cooled to the liquidus temperature, 0.9 g of Al ₈ (Mn, Fe) ₅ phase is crystallized per kg of AM60 alloy with 0.05% excess Mn as shown in Table 2. Water is produced in the liquid magnesium alloy. It can be seen that a magnesium alloy slurry suitable for reaction molding can be prepared by dispersing 0.9 g of Al ₈ (Mn, Fe) ₅ phase crystals per kilogram of AM60 alloy. That is, the content of Mn is 0.05% excess of the saturated solubility of Mn at the liquidus temperature, and an AM60 alloy having such a composition may be used. In addition, when the Mn content exceeds 1%, the melting temperature of the AM60 alloy must be increased to 750 ° C in order to dissolve all the contained Mn. At this temperature, the oxidation loss of the highly oxidizable magnesium alloy is increased, so the Mn content is preferably 1% or less.

In the present invention, since solid crystals containing Mn or Zr are used as the inoculum of magnesium tablets (nucleation sites), supercooling hardly occurs during solidification, and thus it is easy to control cooling from the liquid line to the solid / liquid coexistence zone. Do.

In addition, since only the cooling rate from the melting temperature to the liquidus temperature needs to be controlled, the superheat degree of the molten metal does not have to be strictly limited, and only the Mn content is controlled. There is an advantage to manufacture.

In addition, by controlling only the cooling rate of the magnesium alloy from the dissolution temperature of the magnesium alloy to the liquidus temperature, it is easier to obtain a high quality magnesium alloy slurry in which the spherical magnesium crystals are uniformly dispersed. For this purpose, the magnesium alloy liquid phase does not require a separate process such as stirring by applying mechanical or electromagnetic energy.

The magnesium alloy slurry used for reaction solidification is preferably as solid as possible in terms of formability and small in size.

Based on the principles of the present invention, increasing the number of Mn-containing crystallites per unit volume of the liquid magnesium alloy by controlling the supersaturation amount of Mn and the cooling rate to the liquidus temperature, the number of nucleation sites of the magnesium primary increases, thereby increasing the size of the magnesium primary. Can be reduced.

Based on the principles of the present invention, magnesium primary particles can be spherical by controlling the supersaturation amount of Mn and the holding time between the liquidus temperature and the solidus temperature. As the retention time increases, the magnesium tablet becomes spherical to reduce the interfacial energy. As the degree of supersaturation increases, the size of the magnesium primary decreases and the gap between dendritic phases narrows, resulting in spherical formation in a faster time. That is, when the supersaturation is increased by increasing the content of Mn, the size of the solid phase is small and the spherical reaction solidified magnesium alloy slurry can be obtained with a shorter holding time.

1 is a manufacturing principle of the reaction magnesium alloy slurry for molding according to the present invention.

Figure 2 is a microstructure of AZ91 magnesium alloy slurry prepared according to an embodiment of the present invention (50 ×, 0.17% Mn, cooling rate = 2 ℃ / s).

Figure 3 is a microstructure of AZ91 magnesium alloy slurry prepared according to another embodiment of the present invention (50 ×, 0.22% Mn, cooling rate = 2 ℃ / s).

Figure 4 is a microstructure of AZ91 magnesium alloy slurry prepared according to another embodiment of the present invention (50 ×, 0.40% Mn, cooling rate = 2 ℃ / s, holding time = 4 minutes).

Figure 5 is a microstructure of AZ91 magnesium alloy slurry prepared according to another embodiment of the present invention (50 ×, 0.40% Mn, cooling rate = 0.1 ℃ / s).

Figure 6 is a microstructure of AZ91 magnesium alloy slurry prepared according to another embodiment of the present invention (50 ×, 0.40% Mn, cooling rate = 2 ℃ / s, holding time = 60 minutes).

Figure 7 is a microstructure of the AM60 magnesium alloy slurry prepared according to another embodiment of the present invention (50 ×, 0.25% Mn, cooling rate = 2 ℃ / s).

Figure 8 is a microstructure of the AM60 magnesium alloy slurry prepared according to another embodiment of the present invention (50 ×, 0.50% Mn, cooling rate = 2 ℃ / s).

** Description of symbols for the main parts of the drawing **

1: melting temperature 2: saturation temperature of Mn

3: liquidus temperature 4: solid / liquid coexistence temperature

5: state of solid crystals in magnesium alloy liquid phase

6: solid phase crystal 7: liquid magnesium alloy

8: Magnesium Alloy Slurry 9: Primary Magnesium

Claims (5)

Any one of the solid magnesium alloys selected from the group consisting of AZ91, AM60, AM50, AS21 and AE42 is heated to a temperature higher than the saturation temperature (T _sat ) corresponding to the Mn content in the magnesium alloy, The produced single phase liquid magnesium alloy is cooled to a liquidus temperature (T _L ) at a cooling rate of 0.1 ° C./s or more to form a solid crystal, The liquid magnesium alloy containing the solid crystals is cooled to a temperature between the liquidus temperature and the solidus temperature of the alloy to form the magnesium crystals as a non-uniform nucleation site and hold for 1 to 60 minutes. A method of producing a magnesium alloy slurry for reaction molding, characterized in that to form a solid solution of magnesium solid solution. delete delete The method of claim 1, The content of Mn in the solid magnesium alloy is 0.05 to 1.0% by weight greater than the saturation weight of Mn at the liquidus temperature, the method of producing a magnesium alloy slurry for solidification molding. delete