JPH05223759A - Crystal grain fragmentation judgment device for magnesium alloy melt - Google Patents

Abstract

PURPOSE:To obtain a crystal grain fragmentation judgment device capable of simply and surely judging the crystal grain fragmentation effect for magnesium alloy melt before injection. CONSTITUTION:A judgment device of crystal grain fragmentation effect for magnesium alloy melt is provided with a means to detect a primary crystal coagulation temperature of the melt before fragmentation processing of the magnesium alloy and/or cooling rate just after the primary crystal coagulation initiation and a means to detect the primary crystal coagulation temperature of the melt after fragmentation processing of the magnesium alloy and/or cooling rate just after the initial crystal coagulation initiation. Also provided is a means to judge the degree of crystal grain fragmentation by comparing the detected primary crystal coagulation temperature of the melt before and after fragmentation processing and/or cooling rate just after the primary crystal coagulation initiation or the difference in the detected value and after fragmentation processing, with a standard value set in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal grain refining determination device for molten magnesium alloy, and more specifically, a magnesium alloy melt for reliably and easily determining the grain refining effect of molten metal before pouring. The present invention relates to a crystal grain refining determination device.

[0002]

2. Description of the Related Art The tensile strength of magnesium alloy castings decreases with increasing grain size. Therefore, in order to secure the strength of the casting to be cast, it is necessary to make the crystal grains fine. As the refining treatment of the magnesium alloy, for example, as a refining method of crystal grains of the Mg-Al alloy, 8
A method of heating the molten metal to a high temperature of 50 to 900 ° C. and quickly lowering the temperature to around 700 ° C., hexachloroethane (C ₂ C
Although the method of adding l ₆ ) is used, the latter method is generally used because of advantages such as ease of operation.

However, in a molten metal obtained by subjecting a magnesium alloy molten metal to a crystal grain refining treatment, the refining effect is weakened while the molten metal is held thereafter, and the crystal grain becomes coarser. Therefore, in order to ensure the quality of the casting, it is important to perform a reliable crystal grain refining treatment and to appropriately manage the molten metal. Therefore, there has been a demand for a method capable of easily determining the effect of the refinement treatment of the molten magnesium alloy.

Conventionally, as a method for determining the crystal grain refinement of these magnesium alloy melts, a method of observing the solidification structure of the cast product (first method) and a method of observing the fracture surface of the cast product (first method) 2 method) is performed.

[0005]

However, in the first method, although the effect of refining the crystal grains of magnesium casting can be accurately determined, the observation of the solidification structure is very cumbersome and time-consuming. Had. Further, although this method is effective for determining the crystal grain refinement of magnesium alloy castings, it is not possible to determine the crystal grain refinement of the molten metal of the alloy itself, so the determination cannot be performed at the melting treatment site. There was a problem.

Further, the fracture surface observing method of the casting according to the second method can be easily carried out, but since it is a subjective judgment, there are individual differences in the judgment and variations occur, and therefore it is not always quantitative and objective. There was a problem that it could not be said to be a proper determination method. Further, as in the case of the first method, there is a problem in that it is not possible to make a determination at the melting treatment site because the grain refinement of the molten magnesium alloy itself is not determined.

Therefore, the inventors of the present invention have earnestly studied to solve the above-mentioned problems of the prior art, and as a result of various systematic experiments, the present invention has been accomplished.

An object of the present invention is to provide a crystal grain refining determination apparatus which can easily and reliably determine the crystal grain refining effect of a molten magnesium alloy before pouring.

The present inventors have focused on the following problems with respect to the above-mentioned problems of the prior art. That is, none of the above-described conventional techniques determines the degree of crystal grain refinement of a magnesium alloy casting, and does not determine the crystal grain refinement effect of the molten alloy itself. Therefore, in order to determine the grain refining effect of the alloy even at the melting site, that is, in order to determine the grain refining effect of the magnesium alloy in front of the furnace, the alloy should be in the state of molten metal. It is necessary to judge the degree of crystal refinement. Therefore, attention was paid to the cooling behavior of the molten alloy during the grain refining process.

Then, the systematic experiments were conducted on the refined molten metal in which the crystal grains are coarsened and the refined molten metal in which the crystal grains are refined by thermal analysis and the like, and the phenomenon is clarified. The present invention has been accomplished by focusing on the fact that the degree of crystallization can be determined by the solidification behavior of the molten metal, that is, the primary crystal solidification temperature and / or the cooling rate.

[0011]

The crystal grain refining determination apparatus for molten magnesium alloy of the present invention is an apparatus for determining the crystal grain refining effect of molten magnesium alloy, which is before the refining treatment of the magnesium alloy. A means for detecting the primary crystal solidification temperature of the melt and / or the cooling rate immediately after the start of the primary crystal solidification; and the primary crystal solidification temperature of the molten metal after the refinement treatment of the magnesium alloy and / or the cooling rate immediately after the start of the primary crystal solidification. A means for detecting, the detected primary crystal solidification temperature before and after the refining treatment and / or the cooling rate immediately after the start of the primary crystal solidification, or the difference between the detected values before and after the refining treatment and a preset reference value. It is characterized by comprising means for comparing and determining the degree of grain refinement.

[0012]

In the crystal grain refining determination apparatus for molten magnesium alloy of the present invention, first, the primary crystal solidification temperature and / or the cooling rate immediately after the initiation of primary crystal solidification of the molten metal before the refinement treatment of the magnesium alloy are detected. Then, the primary crystal solidification temperature and / or the cooling rate immediately after the start of primary crystal solidification of the molten metal after the refinement treatment of the magnesium alloy are detected. Next, the detected primary crystal solidification temperature before and after the refinement treatment and / or the cooling rate immediately after the start of the primary crystal solidification, or the difference between the detected value before and after the refinement treatment and a preset reference value is calculated. calculate. The magnitude of the calculated value obtained from this indicates the presence or absence and the degree of the refinement effect of the alloy. Then, by comparing the calculated value with a preset value for the presence or absence of the refinement and a reference value for the extent thereof, it is possible to determine the degree of refinement of the crystal grains of the molten magnesium alloy.

[0013]

EFFECT OF THE INVENTION The crystal grain refining determination apparatus for molten magnesium alloy according to the present invention can easily and reliably determine the crystal grain refining effect of the molten magnesium alloy before pouring.

[0014]

EXAMPLES Hereinafter, specific examples of the present invention will be described.

A specific example of the present invention will be described in which AZ91 alloy melt is used as the magnesium alloy melt.

In this example, the grain refinement effect of the molten AZ91 alloy is determined by 1) performing a thermal analysis before the grain refinement treatment by the first molten metal state amount detecting means to refine the AZ91 alloy. Detecting the primary crystal solidification temperature of the previous molten metal and / or the cooling rate immediately after the start of primary crystal solidification, 2) The secondary crystal state amount detecting means, and the primary crystal solidification temperature of the molten metal after the refinement treatment of the AZ91 alloy and And / or detecting the cooling rate immediately after the start of primary crystal solidification, 3) by the crystal grain refinement determination means, the detected primary crystal solidification temperature before and after the refinement treatment and / or the cooling rate immediately after the start of primary crystal solidification, or The difference between the detected values before and after the refining process was compared with a preset reference value to determine the degree of crystal grain refining.

First, in the first molten metal state quantity detecting means,
The AZ91 alloy melt before grain refining is poured into a thermal analysis mold, and the AZ91 alloy in the melting process is subjected to thermal analysis. In addition,
In the mold for thermal analysis, a thermocouple is used in the center of the cavity with an organic resin as a binder, and the primary crystal solidification temperature of the melt before refining the AZ91 alloy and / or cooling immediately after the initiation of the primary crystal solidification are performed. A sensor for detecting a first state quantity such as speed is provided.

At this time, since the magnesium alloy melt is extremely easy to burn, it is preferable to create a sufficient flameproof atmosphere and pour the melt. The output from the first state quantity detection sensor such as a thermocouple after pouring the molten metal is recorded on a pen recorder or the like, or is input to a recording unit of a computer and recorded. The primary crystal solidification temperature and the cooling rate immediately after the initiation of the primary crystal solidification are read from the obtained cooling curve or data indicating this, or the information is calculated by a computer or the like, and the information is temporarily stored.

Since the cooling rate of the molten metal differs depending on the type of the molten metal and the size of the mold used for thermal analysis, it is preferable to take a cooling rate suitable for the type of the molten metal and the mold used. Further, in the cooling curve of the molten metal before the crystal grain refining treatment, the supercooling / reheating phenomenon appears immediately after the start of solidification of the primary crystals and the temperature becomes stagnant. The cooling rate of the AZ91 alloy refining melt immediately after the start of primary crystal solidification is about 0 ° C / s.

Next, in the second molten metal state quantity detecting means,
The AZ91 alloy molten metal after grain refinement is poured into a thermal analysis mold to perform thermal analysis of the AZ91 alloy. The thermal analysis molds used preferably have the same size. Further, a mold having a heating means is used as the thermal analysis mold, and after the first state quantity is detected by the first molten metal state quantity detecting means, the molten metal in the thermal analysis mold is kept in the molten AZ91 alloy. It is also possible to perform the crystal grain refining process and then detect the second state quantity by the second molten metal state quantity detection means. The output from the second state quantity detection sensor such as a thermocouple (may be the same as the first state quantity detection sensor) is recorded in a pen recorder or the like, or is input to a recording unit of a computer and recorded. The primary crystal solidification temperature and the cooling rate immediately after the initiation of the primary crystal solidification are read from the obtained cooling curve or data indicating this, or the information is calculated by a computer or the like, and the information is temporarily stored. It should be noted that the cooling rate is preferably an average cooling rate of the same time as the temperature stagnation time immediately after the start of solidification of the primary crystal of the molten metal before the grain refinement treatment.

Next, in the grain refinement determination means, the detected primary crystal solidification temperature before and after the refinement treatment and / or the cooling rate immediately after the start of the primary crystal solidification or the difference between the detected values before and after the refinement treatment. Is compared with a preset reference value to determine the degree of grain refinement. That is, the first state quantity and the second state quantity obtained by the first molten metal state quantity detecting means and the second molten metal state quantity detecting means, for example, the primary crystal solidification temperature before or / and after the refinement treatment of the magnesium alloy, The cooling rate immediately after the start of solidification of the primary crystals or the difference between these detected values before and after the refining process is compared with the reference value set corresponding to each value, and whether the degree of grain refining effect is sufficient. The degree of grain refinement is determined, such as whether the grain size is insufficient or insufficient.

A specific example of comparison / judgment with the reference value is as follows. First, as for the primary crystal solidification temperature, the value before the crystal grain refining treatment and the value after the crystal grain refining treatment are compared to obtain the difference in the primary crystal solidification temperature. Further, the cooling rate immediately after the start of primary crystal solidification before and after each grain refining treatment is used. Then, these values are compared with preset reference values for grain refinement. If the obtained value satisfies the reference value, it can be determined that this molten metal has a grain refining effect. However, when the standard value is not satisfied, it is determined that the grain refining effect is insufficient, and the grain refining process is required again. The molten metal subjected to the crystal refining treatment again, the grain refining was judged in the same manner as described above,
Confirm the effect of grain refinement.

The reference value required for determining the grain refinement is determined as follows. First, the same template as the template for thermal analysis is used. The molten metal is subjected to thermal analysis in a state in which the degree of crystal grain refining is different, such as by changing the amount of refining and addition of the crystal grain refining agent after refining, or changing the molten metal holding time after the crystal grain refining treatment. From the obtained cooling curve, the primary crystal solidification temperature and the cooling rate immediately after the start of primary crystal solidification are read, and at the same time, the solidification structure of the sample subjected to thermal analysis is observed,
Measure the crystal grain size. Then, the relationship between the change in the primary crystal solidification temperature and the cooling rate immediately after the start of the primary crystal solidification and the crystal grain size is obtained. The crystal grain size becomes smaller as the primary crystal solidification temperature of the melt after the crystal grain refining treatment becomes higher than the primary crystal solidification temperature of the melt before the crystal grain refining treatment, and the crystal grain size becomes constant when the temperature exceeds a predetermined temperature. Become. Further, as the cooling rate increases, the crystal grain size decreases, and the crystal grain size becomes constant at a predetermined rate or higher. By obtaining these relationships, the primary crystal solidification temperature at which the crystal grain size becomes fine and constant and the cooling rate before and after the start of primary crystal solidification are set as reference values for refinement.

Al-Si-Mg, Al-Si-C
In u-based alloys, an AE meter is used to determine the refinement of the eutectic structure due to Na, Sr, or the like. In this method, the molten metal is poured into a shell mold provided with a thermocouple, the eutectic solidification temperature of the obtained cooling curve is read, and the presence or absence of refinement is determined. However, Al-Si-Mg, Al-Si-C
Since the eutectic temperature of the u-based alloy also changes depending on the amounts of Si and Cu, just by directly reading the eutectic solidification temperature from the obtained cooling curve, the certainty of the refinement effect determination cannot be ensured. But,
In the present invention, as described above, the thermal analysis of the molten metal before the grain refining treatment, the thermal analysis of the molten metal after the grain refining treatment, the required value, using the same molten metal Since the degree of grain refining effect is judged by comparing with the reference value obtained by analyzing the thermal analysis data in advance, the precise grain refining effect is not affected by the difference in solidification temperature caused by the composition variation. Can be determined. Further, the composition change does not affect the cooling rate immediately after the start of the primary crystal solidification, and the effect can be accurately determined if the reference value for grain refinement is obtained in advance.

Thus, the judgment of the grain refining effect is
It is possible to determine the grain refining effect of the molten metal at either the primary crystal solidification temperature or the cooling rate immediately after the start of primary crystal solidification, but if these two are used as reference values at the same time, it is possible to determine the refinement effect. A double check can be performed, and reliability can be provided by determining the miniaturization effect.

The magnesium alloy includes Mg-Al-based alloys, Mg-Zn-R. E. There are many types of alloys such as Zr-based alloys. All of these alloys require a refinement treatment of crystal grains, and the determination of the effect is an important technique together with the melting method, and depends on a skilled melting engineer. According to the present invention, even if the alloy systems are different, if the reference value is set for each alloy, the grain refining effect can be determined easily and accurately by the same method in a short time.

In the above specific examples, when the molten magnesium alloy immediately after refining in the melting process is poured, the crystal grains of the solidified casting become remarkably coarse. However, on the other hand, when the molten metal is subjected to a refining treatment, the crystal grains of the casting become extremely fine.
However, if the molten metal is kept as it is for a long time after the crystal grain refining treatment, the crystal grain refining effect of the molten metal disappears, and the crystal grains of the casting become coarse. A thermal analysis of these melts and a detailed examination of the cooling curves obtained revealed that the primary crystal solidification behavior varied depending on the degree of grain refinement.

FIG. 1 shows the difference in cooling curves between the refined molten metal having coarse crystal grains and the molten metal immediately after the refining treatment in which the crystal grains are extremely fine. In the former cooling curve 11, there is a temperature stagnation for several seconds in which a supercooling / reheating phenomenon appears at the start of solidification of primary crystals. The latter cooling curve 12 shows that supercooling at the start of primary crystal solidification
The reheating phenomenon does not appear, but only an inflection point indicating the start of solidification appears.

From the difference in the cooling curves, the change in the primary crystal solidification temperature and the cooling rate immediately after the start of the primary crystal solidification was determined. It was confirmed that the temperature increased by 5 ° C, and the cooling rate for 5 seconds immediately after the start of solidification of the primary crystal increased from 0 ° C / s to 0.7 ° C / s.

That is, as shown in FIG. 2, as the effect of refining the crystal grains of the melt increases (the crystal grains decrease), the primary crystal solidification temperature increases and the cooling rate also increases.
However, the refining effect of the molten metal remains constant at an increase of 4 ° C or more in the primary crystal solidification temperature immediately after the start of the primary crystal solidification after the crystal grain refining treatment and a cooling rate of 0.4 ° C / s or more. Become. In this case, 4 ° C as a reference value of the difference between the primary crystal solidification temperature after the refinement treatment of the magnesium alloy and the primary crystal solidification temperature before the refinement treatment, cooling immediately after the start of the primary crystal solidification after the grain refinement treatment. 0.4 ° C / s is suitable as the reference value of the speed. Therefore, it is possible to determine the crystal grain refining effect of the molten metal by accurately reading the change in the cooling curve obtained by thermal analysis.

The crystal grain refining determination apparatus of this example is about 5
This is a thermal analysis of a small amount of molten metal of 0 to 100 g, and the thermal analysis time is as short as about 3 to 5 minutes, which is simple. Therefore, unlike the conventional method, a troublesome operation such as cutting, polishing, corrosion, and structure observation is not required, and therefore the time required for the determination can be significantly shortened. Further, since subjective factors such as fracture surface observation are eliminated, even a beginner can surely judge the grain refinement effect of the magnesium alloy melt immediately before pouring.

If it is determined that the grain refining effect is insufficient, the grain refining treatment can be performed again, the molten metal can be subjected to thermal analysis again, and the effect can be confirmed before pouring. In this way, the crystal grain refining effect of the melt immediately before pouring can be determined easily and reliably in a short period of time, which enables accurate melt control and reduces the strength of parts caused by crystal grain refining defects. And quality variations can be prevented.

In the above specific example, the molten magnesium alloy before and after the grain refinement is poured into a separately prepared thermal analysis mold, and the state quantity is detected by a state quantity detection sensor such as a thermocouple provided in the mold. An example in which the grain size is detected and the grain refinement is determined is shown. However, the state-quantity detection sensor is provided at an appropriate location of the magnesium alloy refining treatment apparatus or an apparatus or system including the refining treatment apparatus, and the thermal analysis template as described above is not used in real time. It is possible to determine the grain refinement of the molten magnesium alloy.
Further, the reference value can also be obtained from the obtained information instead of being preset as in the above-described specific example. In these cases, it is preferable to use a computer to detect the state quantity and / or determine the grain refinement. Further, the judgment result can be fed back using a computer to perform appropriate production control.

Examples of the present invention will be described below. First embodiment

Mg-9% Al-1% Zn alloy 150 kg
Was melted, and a grain refinement determination device was used to evaluate the device by a confirmation test of the grain refinement effect.

First, in the iron crucible in the burner heating furnace,
AZ91 magnesium alloy (Mg-9% Al-1% Zn
150 kg of the alloy) was sprayed, and the melting flux was sprinkled to dissolve the alloy. After the burnout, stirring and refining was performed for 20 minutes while adding the refining flux at a temperature of about 715 ° C. The molten metal that had been refined was subjected to thermal analysis to obtain the primary crystal solidification temperature as the first molten metal and the average cooling rate immediately after the start of primary crystal solidification.

The crystal grain refining determination apparatus used in the present embodiment is a template for thermal analysis in which a thermocouple is arranged, and a computer section for recording and calculating the output from the thermocouple, data, calculation results, etc. And a display unit for displaying. The electromotive force of the thermocouple is recorded in the computer section and the temperature change is drawn on the CRT of the display section. The first inflection point on the obtained cooling curve is read as the primary crystal solidification temperature. Then, the temperature 5 seconds after the start of solidification of the primary crystal is read, and the average cooling rate for 5 seconds is calculated. These two data are recorded / saved in the storage unit of the computer unit as they are.

After the first thermal analysis was completed, the temperature of the molten metal was raised to 740 ° C., hexachloroethane was added at the same temperature, and grain refinement treatment was performed. The molten metal that had undergone the grain refining treatment was held as it was, and when the mold was ready, thermal analysis was performed to determine the grain refining effect of the molten metal. The crystal grain size becomes finer with the increase of the primary crystal solidification temperature and the cooling rate, but in the present judgment apparatus, the increase of the primary crystal solidification temperature is set to 4 as a reference value for keeping the crystal grain size below 100 microns. ° C or higher, and the cooling rate was set to 0.4 ° C / s or higher.

Table 1 shows the crystal grain refining effect determination results of the molten metal when 150 kg of AZ91 alloy was melted for 10 charges. In the same table, the crystal grain size measured by the structure observation is also shown.

[0040]

[Table 1]

From Table 1, it was determined that the crystal grain refining effect was insufficient because the melts at the 3rd and 7th charges were below the standard value, but the crystal grain refining effect was insufficient. It was judged. When this determination result was confirmed by measuring the crystal grain size, the molten metal at the 3rd and 7th charges was 120,
The coarsening of the crystal grains proceeded at 150 microns, but the melts other than that were 100 microns or less and were sufficiently fine.

That is, according to the determination device of this embodiment,
Judgment can be made reliably when the grain size is 100 microns,
It was confirmed to be an extremely effective judgment method. The melts at the 3rd and 7th charges, for which the grain refinement effect was determined to be insufficient, satisfied the standard value as a result of performing the grain refinement treatment again.

From the above, by using the crystal grain refining determination apparatus of this embodiment to determine the crystal grain refining effect of the molten metal before pouring, the crystal grain refining of the casting to be reliably cast can be achieved, and the strength can be improved. It was found that it is possible to prevent variations in quality due to shortage. Second embodiment

A confirmation test of the duration of the crystal grain refining treatment effect was carried out by a grain refinement judging apparatus.

The thermal analysis template used was the same as that used in the first embodiment. Molten metal is AZ91 alloy 90kg
Was melted and subjected to refining and crystal grain refining treatment in the same manner as in the first embodiment. The thermal analysis was carried out by collecting the refined molten metal and the molten metal immediately after the grain refinement, and 30 minutes later.

FIG. 3 shows changes in the primary crystal solidification temperature and the cooling rate immediately after the start of primary crystal solidification. Also, in the figure, the change in the crystal grain size of the casting at that time is also shown. The primary crystal solidification temperature of the molten metal immediately after refinement of the crystal grains was 5 ° C higher than the primary crystal solidification temperature of the refined molten metal, and the cooling rate was as high as 0.7 ° C / s. This value satisfies the standard value. The primary crystal solidification temperature of the molten metal having a molten metal holding time of 120 minutes still rises by 5 ° C., and even in this state, there is still a crystal grain refining effect.
On the other hand, the cooling rate gradually decreased with the increase in the molten metal holding time, but it was 0.4 ° C even after holding for 120 minutes.
/ S, and it is judged that there is still a miniaturization effect. However, in the melt held for 150 minutes or longer, the rise of the primary crystal solidification temperature was 4 ° C or less, and the cooling rate was 0.4 ° C or less, which did not satisfy the standard value and the grain refining effect was lost. You can see that it is coming. When this is confirmed by the measured crystal grain size, the molten metal up to 120 minutes has a crystal grain size of 100 microns or less, but at 150 minutes or more, the crystal grain size is 10 microns or less.
It was found that the particle size was 0 micron or more, and even if the molten metal was kept for up to 120 minutes, there was an effect of refining the crystal grains of the molten metal.

For comparison, a fractured surface of a casting cast from the main melt was observed to determine the effect of refining the crystal grains. The unevenness of the fracture surface tended to become coarser with the increase in holding time, with the casting immediately after grain refinement being minimized, but the grain size 1
It was impossible to judge the miniaturization effect at the boundary of 00 microns.

As described above, by using the crystal grain refining determination apparatus of this embodiment, the determination of the crystal grain refining effect of the molten metal can be made simple and reliable in a short time, and is an extremely effective apparatus. It was confirmed.

[Brief description of drawings]

FIG. 1 is a diagram showing a cooling curve of molten metal in an example of the present invention.

FIG. 2 is a diagram showing a relationship between a primary crystal solidification temperature or a cooling rate of a molten metal and a crystal grain size in one specific example of the present invention.

FIG. 3 is a diagram showing the relationship between the molten metal holding time after the crystal grain refining treatment and the temperature, the grain size velocity and the crystal grain size in the second example of the present invention.

[Explanation of symbols]

 11 ・ ・ ・ Refined molten metal with coarse crystal grains 12 ・ ・ ・ Molten metal immediately after refining treatment

Front Page Continuation (72) Inventor Hatsuko Kusakabe, Nagakute-cho, Aichi-gun, Aichi-gun, Nagaminate Yokomichi 1 41, Toyota Central Research Institute Co., Ltd. (72) Inventor, Koji Yonekura, Aichi-gun, Nagakute-machi, Nagakute-machi No. 41 1 Toyota Central Research Institute Co., Ltd. (72) Inventor Takao Miyamoto 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Yukio Otsuka 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Vehicle Within the corporation

Claims (1)

[Claims] 1. A device for determining a crystal grain refining effect of a magnesium alloy melt, which detects a primary crystal solidification temperature and / or a cooling rate immediately after the start of primary crystal solidification of the melt before the refinement treatment of the magnesium alloy. Means for detecting the primary crystal solidification temperature and / or the cooling rate immediately after the start of primary crystal solidification of the molten metal after the refinement treatment of the magnesium alloy, and the detected primary crystal solidification temperature before and after the refinement treatment and / Or comparing the cooling rate immediately after the start of solidification of the primary crystal, or the difference between the detected values before and after the refining process and a preset reference value,
An apparatus for determining crystal grain refining of a molten magnesium alloy, comprising means for determining the degree of crystal grain refining.