JP2009120883A - Magnesium alloy foil and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium alloy foil and its manufacturing method. <P>SOLUTION: A molten magnesium alloy, having a composition which consists of, by mass, 1 to 11.0% Al, 0.1 to 2.0% Zn, 0.15 to 0.5% Mn and the balance Mg with inevitable impurities and further contains, if necessary, 0.05 to 2% of one or more elements among Ca, Sr and RE and in which, among the inevitable impurities, the contents of Fe, Ni, Co and Cu are restricted to <50 ppm, respectively, and also the content of Cl is restricted to <20 ppm is used. The molten magnesium alloy is subjected, preferably, to continuous casting and rolling and worked into a strip-like magnesium alloy sheet. The sheet is used as a base material and formed into a magnesium alloy foil whose thickness is reduced to a foil thickness of 0.02 to <0.2 mm by plastic working such as rolling. In this way, the magnesium alloy foil in which the size of an Al-Mn compound is preferably <10 μm can be obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnesium alloy foil and a method for producing the same.

Magnesium has a specific gravity as small as 2/3 that of an aluminum alloy and 1/4 that of iron, has a high specific strength, and is excellent in recyclability. Therefore, it is effective in reducing the weight of structural products. Recently, magnesium alloy foil materials have been used as components for acoustic effects, taking advantage of magnesium thermal conductivity, attenuation performance, and electromagnetic shielding. Attenuation performance is the property of attenuating the impact inside the material when an impact is applied to the object. In the case of a speaker diaphragm, a large attenuation rate results in low-band reverberation and good sound quality.
However, most of the existing magnesium products are manufactured by casting methods such as die casting and thixo, and in the case of casting methods, complicated shapes can be easily obtained, but there is a problem in surface quality. In addition, a repairing process for polishing or filling the surface of the product is required, and it is difficult to cope with the reduction in thickness and size of the product. On the other hand, when a magnesium alloy wrought material is used, it is expected that it has excellent surface properties and can be applied to yield improvement, thinning, and enlargement.
Commonly used magnesium alloy foil is obtained by rolling a slab and an extruded material into a plate using a magnesium alloy adjusted to a composition containing appropriate amounts of Al and Mn in order to improve strength and corrosion resistance. It is normal. In addition, a method is also known in which a thin plate material is directly produced by a twin roll method and is rolled in the same manner to obtain an alloy plate (see, for example, Patent Documents 1 and 2).
These magnesium alloy foils cannot be said to have sufficient yield and press formability at the time of production, have difficulty in corrosion resistance, and are required to be subjected to surface treatment.
JP 2006-144043 A JP 2006-144059 A

  Conventional slabs, magnesium alloy foils with a thickness of 0.02 to less than 0.2 mm rolled onto a substrate, are easily observed with dotted holes (pinholes), and cracks are easily generated during press molding. As a result, there is a problem that the product yield is lowered.

  The present invention has been made against the background of the above circumstances, and it is an object of the present invention to provide a magnesium alloy foil that can improve product yield because pinholes are not observed and defects such as cracking are less likely to occur during press molding. .

  The inventors of the present application investigated and studied pinholes observed in the magnesium alloy foil and defects during press molding. As a result, the coarse Al-Mn compound formed in the magnesium alloy foil dropped out, causing pinholes. It was found that the phenomenon occurred and that it was the starting point of fracture during press molding.

  Magnesium alloy foils such as AZ (Mg—Al—Zn) and AM (Mg—Al) that are widely used are rolled slabs or extruded materials on a substrate, and in that case, in the microstructure of the rolled plate Are dotted with coarse Al-Mn compounds having a size exceeding 10 μm. These compounds adversely affect the surface properties and press moldability of the material thinned to a foil thickness of 0.02 to less than 0.2 mm.

  That is, the Al-Mn compound coarsened in a facet shape has a large volume occupied by the coarse compound in the thinned material with a foil thickness of less than 0.02 to 0.2 mm. As a result, when a coarse compound falls off, the portion becomes a cavity and becomes a pinhole. Furthermore, it becomes a starting point of crack generation at the time of press molding, and in the worst case, the crack propagates from the compound as a starting point and leads to fracture. Since the Al—Mn compound has high hardness and cannot be crushed and refined by rolling or the like, it remains in the material even if it is thinned.

  On the other hand, Mn is an additive element indispensable for reducing the amount of Fe that has an adverse effect on imparting corrosion resistance to a material as well as suppressing grain growth during heat treatment. Therefore, a method that does not produce a coarse Al—Mn compound is required, and an example thereof is a twin roll method. Casting and rolling by the twin roll method can suppress crystallization and growth of the Al—Mn compound and can be dispersed and refined due to rapid solidification by heat removal from the roll during continuous casting and rolling.

  As used herein, the twin roll method is a casting roll 4A in which a molten magnesium alloy 5 supplied from a nozzle 3 through a slag 2 from a melting furnace 1 is vertically arranged as shown in FIG. In this manufacturing method, the steel sheet is introduced between the twin rolls 4B and solidified between the water-cooled twin rolls 4 and then rolled into a cast and rolled plate 5a. The cast and rolled plate 5a thus obtained is cut into a sheet by cutting to a certain length with a shear or wound up as a coil.

  However, even in the twin roll method, the Al—Mn compound starts to crystallize when the molten metal temperature in the melting furnace during casting becomes less than 650 ° C., and the crystallized compound agglomerates and grows coarse when held at the low temperature. End up. Further, in the process of supplying the roll from the melting furnace, similarly, when the molten metal temperature falls below 650 ° C., the Al—Mn compound crystallizes and coarsens. If these coarse compounds are mixed in the cast plate during continuous casting and rolling, pinholes are formed as described above when the foil thickness is reduced to less than 0.02 to 0.2 mm by rolling or the like, resulting in defects in appearance. Cheap. Even at the time of press molding, a coarse Al-Mn compound may be a starting point of cracking during the pressing and cause fracture. An Al—Mn compound having a size of 10 μm or more generated during casting cannot be crushed even in the subsequent rolling process, and therefore needs to be controlled to be less than 10 μm during casting. Therefore, the inventors of the present application have obtained the knowledge that by suppressing the size of the Al—Mn compound to less than 10 μm, it is possible to suppress the generation of pinholes and to obtain a magnesium foil that is difficult to crack even during press molding. Thus, the present invention has been completed.

  That is, among the present inventions, the magnesium alloy foil of the first present invention has a foil thickness of less than 0.02 to 0.2 mm, and by mass%, Al: 1 to 11%, Mn: 0.15 to 0 .5%, and the balance is composed of Mg and inevitable impurities.

  The magnesium alloy foil of the second aspect of the present invention is characterized in that, in the first aspect of the present invention, the composition further contains Zn: 0.1 to 2.0% by mass.

  In the first or second aspect of the present invention, the magnesium alloy foil of the third aspect of the present invention may further contain 0.05% to 2% of one or more of Ca, Sr, and RE in the composition by mass%. It is characterized by containing.

  In the magnesium alloy foil of the fourth invention according to any one of the first to third inventions, Fe, Ni, Co and Cu are regulated to less than 50 ppm and Cl to less than 20 ppm, respectively, in the inevitable impurities having the above composition. It is characterized by doing. More preferably, the Fe content is regulated to Fe <40 ppm, Cu, Ni, Co, Cl <20 ppm.

  The magnesium alloy foil of the fifth aspect of the present invention is characterized in that, in any of the first to fourth aspects of the present invention, the maximum size of the Al—Mn compound is less than 10 μm.

  The manufacturing method for obtaining the magnesium alloy foil of the sixth aspect of the present invention is a method of manufacturing the magnesium alloy foil of any one of the first to fifth aspects of the present invention. The molten metal temperature is always maintained at 650 to 800 ° C. from the furnace to the roll, the molten metal is fed between the rolls at a molten metal temperature of 650 to 800 ° C., and the cooling rate of the plate material by the roll is 100 to 600 ° C. / It is characterized by continuous casting so as to be seconds. More preferably, 680-780 degreeC is desirable.

  In addition, in the degassing treatment of the magnesium alloy melt before casting with argon gas, the total amount (g) of argon gas blown into 1 kg of the magnesium alloy melt is set to 0.5 to 3.0, and then the melt is settled for 5 minutes or more. It is preferable to perform casting using a molten metal from which dross generated on the molten metal surface is removed.

  In addition, when the occupied area ratio of the Al-Mn compound is 1.0% or more from the viewpoint of the corrosion resistance of the material, a local battery is formed between the Al-Mn compound and the matrix even if the size of the Al-Mn compound is not coarse. Since the absolute amount to be formed increases, corrosion proceeds and yarn rust is likely to occur. For this reason, it is desirable that the occupied area ratio of the Al—Mn compound in the plate thickness surface layer portion is less than 1.0%. In addition, the occupation area ratio of the Al-Mn compound in the plate thickness surface layer portion is the ratio per unit area of the region occupied by the Al-Mn compound, specifically, when the surface layer cross-sectional portion of the magnesium alloy plate material is subjected to EPMA surface analysis. It can be evaluated by measuring the ratio per unit area of the region where Al and Mn elements are detected.

  Below, the composition, manufacturing method, etc. prescribed | regulated by this invention are demonstrated. In addition, all the following component amounts are shown by the mass%.

Al: 1 to 11%
Al is added for the purpose of improving mechanical properties such as castability and strength, and corrosion resistance. However, if the Al addition amount is less than 1%, sufficient castability, strength and corrosion resistance cannot be obtained. On the other hand, when the addition amount of Al exceeds 11%, the strength increase is saturated. On the other hand, if the Al content exceeds 6%, the workability in the rolling process gradually decreases, and if it exceeds 11%, rolling becomes difficult. For these reasons, the content range of Al is defined above. For the purpose of increasing strength, the lower limit is desirably 3%, and the upper limit is desirably 9% from the viewpoint of workability.

Mn: 0.15 to 0.5%
Since Mn has an effect of mitigating the influence of elements that lower the corrosion resistance, it is positively added. That is, by adding Mn, the influence of Fe, which is an impurity element that lowers corrosion resistance, can be mitigated. By containing 0.15% or more, this effect can be effectively obtained. However, if the content exceeds 0.5%, a coarse intermetallic compound is produced during production and the rollability deteriorates, so the Mn content is set to 0.15 to 0.5%.

Zn: 0.1 to 2.0%
Zn, like Al, contributes to improvement of mechanical properties such as castability and strength, and is thus contained as desired. This effect can be acquired by containing 0.1% or more. However, it may contain less than 0.1% as impurities. If the added amount of Zn exceeds 2.0%, the castability deteriorates, so the upper limit is made 2.0%.

If desired, one or more of Ca, Sr, RE may contain 0.05-2%:
Since Ca, Sr, and RE contribute to the improvement of flame retardancy and heat resistance, one or more kinds can be contained as desired. This effect can be obtained by containing 0.05 to 2% of each element. As RE (rare earth element), for example, yttrium, neodymium, lanthanum, cerium, misch metal (for example, La: 15%, Ce: 60%, Nd: 15%, Pr + Sm: 10%) can be used.

Fe, Ni, Co, Cu in unavoidable impurities <50 ppm each, Cl <20 ppm or less Fe, Ni, Co, Cu, Cl adversely affects the corrosion resistance of magnesium alloys. Therefore, it is desirable to regulate these elements to concentrations that are not harmful to corrosion resistance. Desirably, Fe, Ni, Co, and Cu are restricted to less than 50 ppm, and Cl is restricted to less than 20 ppm. More preferably, it is desirable that Fe <40 ppm, Cu, Ni, Co, Cl <20 ppm each.

Al—Mn compound: Less than 10 μm in maximum size When an Al—Mn compound with a maximum size of 10 μm or more is formed, pinholes are generated, surface properties are lowered, and cracks are likely to occur during press molding. It is desirable to limit the maximum size of the Mn compound to less than 10 μm. Preferably it is less than 5 μm. Note that the size of the Al—Mn compound can be evaluated by observing the microstructure of the cross section in the thickness direction with an optical microscope.

When producing a plate by the twin roll method, the molten metal temperature is always kept at 650 to 800 ° C. from the furnace to the roll, and the molten metal is fed between the rolls at a molten metal temperature of 650 to 800 ° C .:
Even in the twin roll method, the Al—Mn compound begins to crystallize when the molten metal temperature in the melting furnace during casting becomes less than 650 ° C., and the crystallized compound agglomerates and becomes coarse when held at the low temperature. . Further, in the process of supplying the roll from the melting furnace, similarly, when the molten metal temperature falls below 650 ° C., the Al—Mn compound crystallizes and aggregates and becomes coarse. If the molten metal temperature exceeds 800 ° C., a molten metal leaks during casting, and a sound cast and rolled sheet cannot be obtained. More preferably, 680-780 degreeC is desirable.

Cooling rate of plate material by roll: 100 to 600 ° C./second:
When the molten metal is supplied to the roll while maintaining the molten metal temperature described above, if the cooling rate of the plate material by the roll is less than 100 ° C./second, the time until the molten metal is solidified becomes long, and the Al—Mn compound is It becomes coarse. Moreover, although the upper limit of a cooling rate is not specified in particular, it is difficult to obtain a cooling rate exceeding 600 ° C./second in consideration of current facilities and actual manufacturing conditions. Preferably, it is 300 to 600 ° C./second. The cooling rate was calculated from the secondary dendrite arm spacing (DAS) at the cross-sectional surface in the thickness direction of the plate produced by continuous casting and rolling. The relationship between the secondary dendrite arm interval d (μm) and the estimated cooling rate V (° C./s) is expressed by the following equation (1).
d = 35.5V− ^0.31 (1)

In the degassing treatment of the magnesium alloy melt before casting with argon gas, the total argon gas blowing amount (g) with respect to 1 kg of molten metal is set to 0.5 to 3.0, and then the molten metal is calmed for 5 minutes or more. Cast using molten metal from which dross generated on the surface is removed:
The degassing treatment of the molten magnesium alloy before casting with argon gas has an action of removing inclusions and cleaning the molten metal. The effect appears when the total amount of argon gas blown into the molten magnesium alloy of 1 kg is 0.5 or more, and the effect is saturated when it exceeds 3.0. After the argon gas is blown, the molten metal is calmed for 5 minutes or more. However, the molten metal is not calmed for less than 5 minutes, and the effect of removing inclusions is reduced. Wait for objects to rise to the surface of the melt. The dross (inclusions) floating on the surface of the molten metal is removed with a jig such as a handle that has been dried in advance.

  As described above, the magnesium alloy foil of the present invention contains, in mass%, Al: 1 to 11%, Mn: 0.15 to 0.5%, Zn: 0.1 to 2.0%, Further, if desired, it contains 0.05 to 2% of one or more of Ca, Sr and RE, and the balance is composed of Mg and inevitable impurities, so the foil thickness is reduced to less than 0.02 to 0.2 mm. In this case, the effect of avoiding the occurrence of pinholes due to coarse Al—Mn compounds exceeding 10 μm and the problems during press molding can be obtained.

Hereinafter, an embodiment of the present invention will be described.
In mass%, Al: 1 to 11%, Mn: 0.15 to 0.5%, optionally Zn: 0.01 to 2.0%, and optionally Ca, Sr, RE Prepare a magnesium alloy containing 0.05 to 2% of one or more types, the balance being Mg and inevitable impurities, melting the magnesium alloy, and preferably by continuous casting and rolling at a cooling rate of 300 ° C./s or more Manufacture magnesium alloy sheets. A magnesium alloy sheet produced by continuous casting and rolling such as a twin roll method can suppress the growth of the Al-Mn compound due to rapid solidification by heat removal from the roll. Therefore, it is possible to suppress adverse effects such as occurrence of pinholes and defects during press molding. Furthermore, during continuous casting and rolling, it is necessary to control the molten metal temperature from the furnace to the roll, and by feeding the molten metal between the rolls at a molten metal temperature of 650 ° C. or higher at which the Al—Mn compound does not start to crystallize, The Al—Mn compound can be crystallized and aggregation coarsening can be suppressed.

The magnesium alloy sheet can be further rolled to a product foil thickness by a rolling process. As the product foil thickness, a foil material of 0.02 mm to less than 0.2 mm is assumed. In addition, the processing method used as product foil thickness is not limited to a rolling process, You may be based on other plastic processing. The magnesium alloy foil obtained by thinning the continuous cast rolled plate to the substrate by a rolling process or the like can make the size of the Al—Mn compound less than 10 μm.
A homogenization treatment can be performed before the rolling step or after hot rolling in the rolling step and before warm rolling. A homogenization process can be performed by heating at 370-470 degreeC for 1 hour or more, for example. This homogenization treatment can eliminate high-concentration segregation at the dendrite cell boundary and the center of the plate thickness of the solute elements in the rapidly solidified magnesium alloy plate, and the magnesium alloy foil with excellent rolling properties thereafter Can be obtained.

A rolling process can be performed by the process of performing warm rolling or hot rolling and warm rolling. In the rolling step, intermediate annealing can be interposed. The intermediate annealing can be performed between the hot rolling process and the warm rolling process, or can be performed in the middle of the warm rolling. When it exceeds 80%, it is preferably provided.
The intermediate annealing can be performed, for example, by heating at 200 to 350 ° C. for 1 hour.

  The final foil thickness of the magnesium alloy foil can be subjected to a surface treatment such as pre-coating. In the present invention, the conditions such as the surface treatment are not particularly limited, and can be performed under known conditions.

Examples of the present invention will be described below in comparison with comparative examples.
A magnesium alloy having the composition shown in Table 1 (remainder Mg and inevitable impurities) was melted and subjected to continuous casting and rolling by a twin roll method to obtain a cast and rolled plate (substrate). The rolled plate was subjected to a homogenization treatment at 400 ° C. for 20 hours, and then made into a foil having a thickness of 0.05 mm (50 μm) by hot rolling and warm rolling to obtain an inventive material and a comparative material. The inventive material and the comparative material were degassed with argon gas in the magnesium alloy melt before casting. In the degassing treatment, the total amount (g) of argon gas blown into 1 kg of molten magnesium alloy was set to 0.5 to 3.0, and then the molten metal was calmed for 10 minutes to remove dross generated on the surface of the molten metal.

  In addition, the molten metal temperature until a roll was measured at the time of the said continuous casting of each test material, and the result was shown in Table 1. The melt temperature fed between the rolls was determined by measuring the temperature of the melt flowing through the nozzle at a position 90 mm behind the nozzle tip.

  The microstructure of each obtained specimen was observed. The maximum size of the Al-Mn compound observed using an optical microscope was evaluated for the plate thickness surface layer portion of the plate cross section. The results are shown in Table 1, and the maximum size of the Al—Mn compound is 12.2 μm in the comparative material 20 in which the impurity elements Fe, Ni, Co, and Cu are restricted to less than 50 ppm and Cl is less than 20 ppm. On the other hand, as for this invention material, the maximum size of the Al-Mn compound was 5 micrometers or less. Regarding the comparative material 21, the maximum size of the Al—Mn compound is 2.5 μm, but the impurity element Fe exceeds 50 ppm.

  In addition, the number of pinholes observed on a 200 mm square foil was measured for each of the above test materials. Measurement of the number of pinholes was performed by irradiating the material surface with infrared light in a state where the sample was placed in a dark room, and evaluating the number of penetrating lights. Although the maximum size of the Al—Mn compound is less than 5 for the sample of less than 5 μm, the comparative material No. In 20, the number of occurrences increased.

  Next, the moldability of each test material was evaluated. Formability evaluation was performed by a two-stage process called stretch forming after deep drawing of the magnesium alloy foil by warm pressing. The molding test results are shown in Table 1. In addition, the symbol in a table | surface shows (circle): favorable, (triangle | delta): Occurrence of a crack occasionally, and x: Frequent crack generation. Good molding results have been obtained with samples whose maximum size of the Al—Mn compound is less than 5 μm.

  Further, each specimen was subjected to a salt water injection test for 24 hours with a 5% NaCl solution, and the corrosion rate was measured. The results are shown in Table 1. The inventive material had a low corrosion rate and excellent corrosion resistance. On the other hand, the comparative material had a high corrosion rate and was inferior in corrosion resistance.

  Next, the occupied area ratio of Mn in one visual field (195 μm × 195 μm) of the observation surface by EPMA surface analysis of each test material was evaluated. Since Mn forms a compound only with Al, it is estimated from the analysis of the occupied area ratio of Mn that the occupied area ratio of the Al—Mn compound is the same area ratio. The analysis location was randomly performed within a range of 150 μm from the cross section in the thickness direction. The evaluation results are shown in Table 1. The inventive materials all had an occupied area ratio of less than 1.0%. Invention No. Nos. 16 to 19 have better corrosion resistance than the comparative material, but the corrosion resistance was low among the inventive materials.

It is a figure which shows the principle of a twin roll method.

Explanation of symbols

1 Melting furnace 2 桶 3 Nozzle 4 Twin roll 5 Magnesium alloy melt 5a Cast and rolled plate

Claims (6)

  Magnesium alloy foil having a foil thickness of less than 0.02 to 0.2 mm and containing, by mass%, Al: 1 to 11%, Mn: 0.15 to 0.5%, with the balance being Mg and inevitable impurities A magnesium alloy foil having a composition comprising:   The magnesium alloy foil according to claim 1, wherein the composition further contains Zn: 0.1 to 2.0% by mass.   The magnesium alloy foil according to claim 1 or 2, further comprising 0.05 to 2% of one or more of Ca, Sr, and RE by mass% in the composition.   The magnesium alloy foil according to any one of claims 1 to 3, wherein Fe, Ni, Co, and Cu are each controlled to be less than 50 ppm and Cl is less than 20 ppm in the inevitable impurities having the composition.   The magnesium alloy foil according to claim 1, wherein the maximum size of the Al—Mn compound is less than 10 μm.   A method for producing a magnesium alloy foil according to any one of claims 1 to 5, wherein when producing a magnesium alloy sheet from a molten magnesium alloy by a twin roll method, the temperature of the molten metal is always maintained at 650 to 800 ° C. The magnesium alloy is characterized in that the molten alloy is fed between rolls at a melt temperature of 650 to 800 ° C., and a magnesium alloy plate is continuously cast so that the cooling rate by the roll is 100 to 600 ° C./second. Foil manufacturing method.

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