JP2012122112A - Cast magnesium alloy plate with excellent surface texture, method for producing the same, and magnesium alloy plate with excellent surface texture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cast magnesium alloy plate with an excellent surface texture, a method for producing the same, and a magnesium alloy plate.SOLUTION: The cast magnesium alloy plate contains 0.1-0.4 mass% of Mn, 0.5-2.7 mass% of Al, and at least one of Sr, Ca, and Re, wherein the total mass% of Al, Mn, Ca, Sr, and Re is in the range of 1.0-3.2 mass%, and the remainder has composition comprising Mg and inevitable impurities. The cast magnesium alloy plate has a value of detected Al quantity on the cell boundary in surface analysis by EPMA of 40 or less. When producing the cast magnesium alloy plate, a strip with a thickness of 2.5-10 mm is rolled by molten metal direct rolling from the magnesium alloy molten metal having the components, and the magnesium alloy plate is produced by subjecting the cast magnesium alloy plate to hot rolling or hot and warm rolling.

Description

  The present invention relates to a magnesium alloy cast plate that can be used for electrical products including personal computers and various mobile products, automobile parts, manufacturing apparatus parts, and the like, a method for manufacturing the same, and a magnesium alloy plate.

Magnesium alloy sheet is light and excellent in recyclability, specific strength, dent resistance, etc., so it is widely used as a housing for automobile parts, personal computers and mobile phones. Conventionally, AZ31, AZ61, AZ91, AM60 alloy and the like have been mainly used as the material for the plate material.
However, since the magnesium alloy sheet has poor formability in a low temperature region due to its crystal structure and the strong texture formed during rolling, the production of a sheet having a predetermined thickness is hot or hot and warm. Hot rolling is necessary. In that case, a plate material that uses a slab having a thickness of more than 100 mm as a base plate requires a very large number of man-hours and processes for rolling and heating the material, resulting in a problem that the manufacturing cost increases. Therefore, as a technique for reducing the manufacturing cost, thinning of the base plate by direct rolling of molten metal has attracted attention as a highly practical manufacturing method. In the molten metal direct rolling, not only can a wide range of alloy types be handled, but a plate material having a thickness of about 3 to 10 mm can be directly produced from the molten metal (see, for example, Patent Document 1).

JP 2006-144043 A

  Conventionally, since molten metal direct rolling provides a very fast solidification rate compared to other production methods, it is known that solute elements are easily dissolved, and are effective in increasing strength and refining the structure. . However, when the solidification rate is about several hundred K / sec, micro-segregation that occurs during solidification is significant, so that the concentration of solute elements in the final solidified portion becomes significant, and macro-segregation tends to occur. Among these, streaky surface segregation generated on the surface of the plate material causes a crack at the time of rolling if the degree is severe. In addition, even if the degree is light and cracks do not occur, surface treatment such as chemical conversion treatment will clarify the streak-like pattern, resulting in poor color unevenness after painting, or processing into the final product shape It may become a molding defect. Therefore, it is necessary to reduce the degree of segregation, but once macroscopic defects such as surface segregation cannot be resolved even after a long period of homogenization treatment, they are removed by mechanical operations such as polishing. However, it causes a decrease in yield and an increase in man-hours, and is not practical.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a magnesium alloy cast plate and a magnesium alloy plate material that are excellent in surface properties with little macrosegregation on the surface of the plate material, and a method for producing them.

  That is, among the magnesium alloy cast plates of the present invention, the first present invention contains, by mass%, Mn: 0.1 to 0.4%, Al: 0.5 to 2.7%, and Sr. , Ca, RE, and the total mass% of Al, Mn, Ca, Sr, RE is in the range of 1.0 to 3.2%, and the balance is composed of Mg and inevitable impurities. It has a composition, and the value of the Al detection amount on the cell boundary in the EPMA surface analysis is 40 or less.

  In the method for producing a magnesium alloy cast plate of the second aspect of the present invention, the magnesium alloy having the composition of the first aspect of the present invention is melted and the molten metal is rolled into a strip having a thickness of 2.5 to 10 mm by direct rolling of the molten metal. It is characterized by that.

  The magnesium alloy sheet excellent in surface properties of the third aspect of the present invention is manufactured by hot rolling or hot and warm rolling the magnesium alloy cast sheet of the first aspect of the present invention.

  The reasons for limiting the composition and the like specified in the present invention will be described below. In addition, all the content of each component in the following is shown by the mass%.

Mn: 0.1 to 0.4%
Mn has an effect of mitigating the influence of elements that lower the corrosion resistance. That is, by adding Mn, the influence of Fe, which is an impurity element that lowers the corrosion resistance, can be mitigated. However, if it is less than 0.1%, the effect is small, and if it exceeds 0.4%, the effect is saturated. For the same reason, it is desirable to set the lower limit to 0.25% and the upper limit to 0.35%.

Al: 0.5 to 2.7%
Al easily dissolves in a magnesium base, and has the effect of improving mechanical properties such as castability and strength and corrosion resistance. However, if it is less than 0.5%, sufficient castability, strength and corrosion resistance cannot be obtained, and if it exceeds 2.7%, the concentration of solute atoms becomes high, and it becomes easy to cause streak-like defects due to surface segregation on the cast plate. .

One or more of Sr, Ca, RE Sr, Ca, RE all form a compound with Al, and they crystallize on the grain boundary, contributing to the improvement of strength, so one or more of these elements including. For RE (rare earth), for example, La: 15%, Ce: 60%, Nd: 15%, Pr + Sm: 10%, etc. can be used, but the type of the present invention is particularly limited is not.

Total amount of addition of Al, Mn, Sr, Ca and RE: 1.0 to 3.2%
As the total mass% of the main additive elements increases, the solute atom concentration in the molten metal increases, so that macrosegregation such as surface segregation is likely to occur. On the other hand, the lower the total mass%, the lower the castability and strength, and the closer to pure Mg, the molten metal is activated and inclusions such as oxides are easily generated during casting.
From the above, it is specified that the total content of Al, Mn, Sr, Ca, and RE is in the range of 1.0 to 3.2%. More preferably, the lower limit value is 1.5% and the upper limit value is 2.7%.

The amount of Al detected on the cell boundary by EPMA surface analysis is 40 or less. Macrosegregation such as reverse segregation is caused by remarkable microsegregation. Therefore, if microsegregation is reduced, macrosegregation such as reverse segregation is also reduced. Is done. The degree of microsegregation can be known from the amount of Al detected on the cell boundary when EPMA surface analysis is performed on the cast plate. The amount of Al detected on the cell boundary here is analyzed under the conditions of EPMA surface analysis with an acceleration voltage of 20 kV, an irradiation current of 50 nA, a collection time of 20 ms, and a pixel count of 250 × 250 in an observation field range of 200 × 200 μm in SEM. It can be evaluated by the count number of the Al element. If the detected amount of Al exceeds 40 (no unit), remarkable microsegregation occurs at the cell boundary of the microstructure, so that they flow due to reduction during direct rolling of the molten metal, and macrosegregation such as surface segregation. Produce. Therefore, the Al detection amount is specified to be 40 or less.

  Next, the method for producing a magnesium alloy cast plate having excellent surface properties according to the present invention is characterized in that a magnesium alloy melt is rolled into a strip plate having a thickness of 2.5 to 10 mm by direct rolling of the melt.

The molten metal direct rolling step is a step of continuously casting and rolling a thin strip in a magnesium alloy molten metal having a predetermined composition. The molten alloy is usually melted in a melting holding furnace or the like to form a molten metal, and the molten metal is transferred to a casting and rolling mill.
Examples of the casting and rolling machine include a twin roll that casts and rolls a molten metal supplied between a pair of water-cooled rolls. In the present invention, an efficient magnesium alloy cast plate can be produced by a molten metal direct rolling process.

The method of transferring the molten metal from the melting and holding furnace to the casting mill is not limited to a specific method, and for example, a conventional tilting type of transferring method can be adopted. Moreover, the hot water can be transferred by a molten metal pump by rotating the impeller. In this method, since the molten metal can always be stirred by the impeller, the molten metal components in the melting and holding furnace and in the middle of the casting and rolling can be uniformly maintained even in the long-time casting and rolling, unlike the conventional tilting-type transferring method. It is possible. The molten metal component may be biased in the diffusion state in the molten metal due to the influence of gravity segregation. This bias can contribute to segregation during rolling. Therefore, stirring the molten metal with an impeller and maintaining the molten metal components uniformly is effective in suppressing segregation.
In addition, a method of stirring the molten metal with ultrasonic waves or electromagnetic stirring is also effective as a method for holding the molten metal component uniformly. However, these methods not only require special equipment, but are difficult to control.

  Such a magnesium alloy cast plate by direct rolling of the molten metal of the present invention or a rolled plate material using the same as a base plate is less likely to cause defects due to macrosegregation such as surface segregation, and a magnesium alloy plate material having excellent surface properties can be obtained.

  As described above, according to the magnesium alloy cast plate of the present invention, it contains Mn: 0.1 to 0.4%, Al: 0.5 to 2.7% by mass, and further Sr, Ca. A composition containing at least one kind of RE, the total mass% of Al, Mn, Ca, Sr, and RE being in the range of 1.0 to 3.2%, with the balance being Mg and inevitable impurities. In addition, since the value of the Al detection amount on the cell boundary in EPMA surface analysis is 40 or less, the surface has few defects due to macrosegregation such as reverse segregation, is low in cost, has high practicality, and has excellent surface properties.

  Further, according to the method for producing a magnesium alloy cast plate of the present invention, the magnesium alloy having the composition of the present invention is rolled into a strip-shaped plate having a thickness of 2.5 to 10 mm by direct rolling of the molten metal. Thus, it is possible to obtain a magnesium alloy cast plate having few defects due to macrosegregation, low cost, high practicality, and excellent surface properties.

  Further, according to the magnesium alloy plate having excellent surface properties of the present invention, it is produced by hot rolling or hot and warm rolling a magnesium alloy cast plate having the composition of the present invention, so that it can be obtained at low cost. Therefore, the surface has few defects due to macrosegregation such as reverse segregation, and has excellent surface properties.

It is a figure which shows the molten metal direct rolling apparatus used for the method of one Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described.
As shown in FIG. 1, a molten metal direct rolling apparatus for carrying out the method of the present invention includes a melting and holding furnace 1 that houses and melts a magnesium alloy, a bowl 2 that is supplied with molten metal from the melting and holding furnace 1, A molten metal pump 3 for transferring the molten metal of the melting and holding furnace 1 to the tub 2 is attached. The molten metal pump 3 includes an impeller 3a, and pumps up the molten metal by rotation of the impeller 3a. A molten water pump 3b having a tip facing the tub 2 is connected to the pumped side of the molten metal pump 3.
A nozzle 4 is provided at one end of the rod 2, and a water-cooled twin roll 5 including casting rolls 5 </ b> A and 5 </ b> B arranged above and below is arranged in front of the nozzle 4.

Next, a method for producing a magnesium alloy sheet using the above apparatus will be described.
In the present invention, by mass, Mn: 0.1 to 0.4%, Al: 0.5 to 2.7% is contained, and at least one of Sr, Ca, and RE is contained, and Al, Mn , Ca, Sr and RE are used in a total mass% of 1.0 to 3.2%, and the remainder is made of a magnesium alloy composed of Mg and inevitable impurities.
The magnesium alloy is accommodated in the melting and holding furnace 1 and melted, and the molten metal is supplied to the trough 2 through the molten metal pump 3 using the molten metal pump 3. At this time, the inside of the melting and holding furnace 1 is agitated by the rotation of the impeller 3a of the molten metal pump 3, and the molten metal components in the melting and holding furnace 1 and just before casting and rolling are made uniform.
The molten metal accommodated in the tub 2 is introduced between the twin rolls 5 through the nozzle 4 and solidifies between the twin rolls 5 which are cooled with water to form a belt-like plate 6. Although the cooling rate at the time of passing the twin roll 5 is not specifically limited, For example, 300-600 K / sec is mentioned. The strip plate 6 has a thickness of 2.5 to 10 mm, for example. The strip plate 6 corresponds to the magnesium alloy cast plate of the present invention.

  The strip 6 is further rolled to a product plate thickness through a homogenization heat treatment (not shown) and a rolling process (not shown) to obtain a magnesium alloy plate. The rolling process is performed by hot rolling or hot and warm rolling. Moreover, intermediate annealing can be interposed in the said rolling process. The intermediate annealing can be performed in the middle of hot rolling, or between the hot warming and the rolling process.

Examples of the present invention will be described below in comparison with comparative examples.
Magnesium alloy cast plate having a thickness of 6 mm is supplied from the furnace to the trough using the magnesium alloy melt (785 ° C.) having the alloy composition shown in Table 1 by the transfer method shown in Table 1 and by direct rolling of the melt using twin rolls. Was made. In addition, the pump in the hot water transfer method uses the molten metal pump provided with the impeller demonstrated in the said embodiment.
The rotation speed of the roll in the molten metal direct rolling was set to 1.2 m / min.
The following evaluation was performed about the produced magnesium alloy cast plate.

(Al detection amount by EPMA surface analysis)
A test piece was cut out from the specimen prepared as described above, a cross section with a thickness parallel to the rolling direction was taken out, this cross section was buffed and mirror-finished. Then, in the mirror-finished cross section, EPMA surface analysis was performed at a position 2 mm from the surface that was in contact with the upper roll during the direct rolling of the molten metal. JXA-8900RL manufactured by JEOL Ltd. was used as the apparatus. The analysis conditions were an acceleration voltage of 20 kV, an irradiation current of 50 nA, a collection time of 20 ms, and a pixel count of 250 × 250. The value of the detected amount on the cell boundary was obtained by the Al element count. The results are shown in Table 1.

(Surface properties)
About the test material produced by the above, both front and back surfaces were polished by 0.25 mm, subjected to pickling treatment in an aqueous solution of 10% nitric acid for 20 seconds, and surface properties were evaluated from visual observation of the surface. Those in which streak-like defects are observed on the surface are shown in Table 1 as “x”, nothing is observed and those showing good surface properties are indicated as “◯”.

  The obtained magnesium alloy cast plate was then subjected to hot rolling and warm rolling to produce an alloy plate having a thickness of 0.6 mm.

1 Melting and holding furnace 2 桶 3 Molten metal pump 4 Nozzle 5 Twin roll 6 Strip plate

Claims (3)

  In mass%, Mn: 0.1 to 0.4%, Al: 0.5 to 2.7%, and at least one of Sr, Ca, RE, and Al, Mn, Ca , Sr, RE total mass% is in the range of 1.0-3.2%, the balance is composed of Mg and inevitable impurities, the value of the amount of Al detected on the cell boundary in EPMA surface analysis is A magnesium alloy cast plate excellent in surface properties, characterized by being 40 or less.   A method for producing a magnesium alloy cast plate excellent in surface properties, comprising melting a magnesium alloy having the composition according to claim 1 and rolling the molten metal into a strip having a thickness of 2.5 to 10 mm by direct rolling of the molten metal. .   A magnesium alloy plate excellent in surface properties produced by hot rolling or hot and warm rolling the magnesium alloy cast plate of claim 1.

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