JP3821074B2 - Magnesium alloy plate and manufacturing method thereof - Google Patents

Description

【００４０】
このようにして得られた結果から、平均結晶粒径が10μm 以下であり、結晶粒径の80％以上が（平均結晶粒径±（平均結晶粒径×0.5)）μm の範囲にあるマグネシウム合金板は優れた温間成形性を有することが判明した。
【００４１】
(実施例２)
実施例１において得られたマグネシウム合金板のうち、圧延中に表面庇が見受けられた試料を供試材とし、表面庇部の表面最大粗さを測定し、これに有色塗装を行って有色塗装隠蔽性を評価した。
【００４２】
有色塗装隠蔽性の評価：
圧延、焼鈍後のマグネシウム合金板から90mm角の試験片を採取し、脱脂、下地処理後、有色塗装を実施した。有色塗装に関して、塗膜厚は下塗りと上塗りを合わせて40〜50μm とした。有色塗装隠蔽性の判定は有色塗装後、表面庇および表面模様が観察されないものを○、表面庇および表面模様が観察されるものを×とした。
【００４３】
結果は表２にまとめて示す。
【００４４】
【表２】

【００４５】
このようにして得られた結果から、表面疵が発生しても表面最大粗さが10μm 以下であれば、有色塗装後は良好な外観を呈することが判明した。
【００４６】
【発明の効果】
本発明によれば、温間成形性、有色塗装隠蔽性に優れたプレス加工用マグネシウム合金板を得ることができる。
【図面の簡単な説明】
【図１】マグネシウム合金板の製造装置の概略図である。
【図２】表１のNo.3の試料のミクロ組織写真である。
【図３】表１のNo.7の試料のミクロ組織写真である。
【符号の説明】
１：マグネシウムコイルアンコイラー
２：マグネシウムコイル巻き取りコイラー
３：加熱装置
４：圧延機
５：熱処理装置
６：放射温度計 (圧延機入側)
７：放射温度計 (熱処理装置出側)[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnesium alloy plate for press working and a method for producing the same. More specifically, the present invention relates to a magnesium alloy plate for press working excellent in warm formability and colored paint concealing property, and a method for producing the same.
[0002]
[Prior art]
Practical magnesium alloys, except for special ones that contain a large amount of Li, have a specific gravity in the range of 1.76 to 1.83, the smallest among practical metals, and have high specific strength and specific rigidity. Material.
[0003]
In particular, it is advantageous as a rigid design component for promoting miniaturization and low power consumption from the viewpoint of fuel efficiency reduction of automobiles and portability of electric and electronic devices.
Until now, however, only a few die cast products have been used. One of the causes is that the magnesium alloy is remarkably inferior in plastic workability as compared with practical metal materials other than the magnesium alloy.
[0004]
The crystal structure of most magnesium alloys is a dense hexagonal lattice, which is different from the cubic lattice of aluminum and copper alloys. In the dense hexagonal lattice, there are three sliding surfaces, that is, a bottom surface, a column surface, and a conical surface, but since only bottom surface sliding occurs at room temperature, the plastic workability deteriorates. However, when the temperature exceeds the recrystallization temperature, the slip surface increases and plastic working becomes possible. For this reason, the wrought material is pressed at the recrystallization temperature or higher. Generally, it is called a warm forming method, and the forming method of the magnesium alloy material is limited to this method.
[0005]
However, even in such a warm forming method, when deep drawing, bending, or the like is performed, the frequency of occurrence of cracks in the material is high and has become a problem.
Therefore, in order to obtain a magnesium alloy sheet having excellent ductility, Japanese Patent Application Laid-Open No. 2001-294966 discloses that the average crystal grain size is 0.1 to 30 μm. In order to obtain a magnesium alloy sheet excellent in ductility, strength, and deep drawability, JP-A-2001-200349 discloses that the crystal grain size is 10 μm or less.
[0006]
However, even if the average crystal grain size is adjusted within the above range, cracks that occur are reduced, but the level is not satisfactory in practice.
For these reasons, it has been strongly desired to establish a magnesium alloy suitable for the warm forming method and a method for producing the same.
[0007]
In addition, when commercializing a magnesium alloy, it is strongly desired to supply a magnesium alloy plate that does not require pre-treatment because surface treatment is performed after removing surface scratches caused by rolling or casting by surface polishing. It was.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a magnesium alloy plate for press working , which is industrially easy to handle in large quantities, inexpensive and excellent in formability, and a method for producing the same.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have conducted extensive research and, as a result, have obtained the following knowledge.
[0010]
1) Warm formability is likely to vary even if the average crystal grain size is the same.
2) This tendency tends to occur when some of the crystal grain size contains coarse grains.
3) Therefore, a material having a controlled crystal grain size is excellent in warm formability.
[0011]
4) In addition, the surface treatment of the magnesium alloy plate which is remarkably inferior in corrosion resistance is essential, and colored coating is generally used from the viewpoint of cost.
5) By the way, a magnesium alloy sheet having a surface with a maximum roughness Rmax of wrinkles exceeding 10 μm cannot be covered even with colored coating.
[0012]
6) Therefore, in order to hide the surface defects of the magnesium alloy plate, the maximum surface roughness Rmax must be 10 μm or less.
The present invention has been completed based on the above findings, and the gist thereof is as follows.
[0013]
(1) The alloy composition which is aluminum: 2.5-3.5%, zinc: 0.6-1.4%, manganese: 0.2-1.0%, and the balance magnesium and impurities by mass%. a, the average crystal grain size is 10μm or less, and more than 80% of the grain size, the press is characterized in that the range of the average grain size ± (average grain size × 0.5) [mu] m processing use magnesium alloy plate.
[0014]
(2) The magnesium alloy plate for press working as described in (1) above, wherein the maximum surface roughness Rmax is 10 μm or less.
(3) The alloy composition which is aluminum: 2.5-3.5%, zinc: 0.6-1.4%, manganese: 0.2-1.0%, and the balance magnesium and impurities in mass%. 1st rolling process which heats and heats the magnesium alloy material which has it to 250-350 degreeC is performed once or 2 times or more, and the rolled sheet obtained at this 1st rolling process is heated to 250-350 degreeC A method for producing a magnesium alloy sheet for press working, comprising: performing a second rolling step of performing cold rolling with a total rolling reduction of a plurality of passes of 12% or more after performing the heat treatment.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described.
FIG. 1 is a schematic view of an apparatus for producing a magnesium alloy sheet for press working according to the present invention.
[0016]
In FIG. 1, the magnesium alloy thin plate coil A continuously unwound from the uncoiler 1 is heated to a predetermined temperature by the heating device 3, then rolled by the rolling mill 4, and heated to the predetermined temperature by the heat treatment device 5. After being subjected to heat treatment, it is wound up by the coiler 2. If necessary, the rolling is repeated a plurality of times to obtain a rolled sheet having a predetermined thickness. At this time, the heat treatment apparatus 5 is not operated until the predetermined thickness is reached.
[0017]
The heating temperature by the heating device 3 is preferably 250 to 300 ° C. When the temperature is less than 250 ° C., the rolling is not sufficiently performed, and the variation in the crystal grain size cannot be sufficiently suppressed. Deformation resistance decreases, and width may shrink or break.
[0018]
Also, the heating temperature by the heat treatment apparatus 5 is preferably 250 to 300 ° C., and if it is less than 250 ° C., sufficient recrystallization cannot be realized, while if it exceeds 300 ° C., the crystal grains are coarsened as a whole. Finally, the average crystal grain size may not be 10 μm or less.
[0019]
For the heating device 3 and the heat treatment device 5, an induction heater is preferably used. The rolling temperature (temperature immediately before rolling) is measured by a radiation thermometer 6 provided at a position 400 mm before the rolling mill entrance side, for example, the center of the rolling mill entrance side. The heat treatment temperature (temperature immediately after the heat treatment) is measured by a radiation thermometer 7 provided at a position 400 mm behind the heat treatment apparatus exit side, for example, the center of the heat treatment apparatus exit side.
[0020]
The rolled material wound up by the coiler 2 is cooled and then unwound and then rolled again by the rolling mill 4 and rolled a plurality of times until the total rolling reduction becomes 12% or more. Preferably, 3-4 passes are performed at a rolling reduction of 4-6% per pass. The total amount of rolling reduction is preferably 20% or less from the viewpoint of occurrence of cracks and compression bands. Of course, in this case, the heating device 3 and the heat treatment device 5 are stopped.
[0021]
In cold rolling, if the total rolling reduction is less than 12%, sufficient fine graining cannot be realized, and if it exceeds 20%, cracks and compression bands may occur. In addition, in one cold rolling, the crystal grain size is not sufficiently uniform.
[0022]
That is, in the past, it was specifically intended to make fine particles, and the total reduction amount was required to be as large as possible, but in the present invention, heat treatment was performed prior to cold rolling for comparison. It is intended to minimize the variation of crystal grains by performing cold rolling with a small amount of rolling reduction a plurality of times.
[0023]
In the present invention, such warm rolling and cold rolling processes are hereinafter referred to as a first rolling process and a second rolling process, respectively, for convenience.
As another aspect, only the first rolling process may be performed in the apparatus of FIG. 1 and the second rolling process may be performed by a separately provided rolling apparatus.
[0024]
The number of repetitions of the first rolling step and the second rolling step is not particularly limited as long as it is 2 sets (times) or more, but preferably 2 to 3 sets (times). By performing a plurality of times of warm rolling and cold rolling as a set, the average crystal grain size is reduced and the variation is reduced simultaneously.
[0025]
Thus, according to the present invention, there is provided a magnesium alloy plate having an average crystal grain size of 10 μm or less and 80% or more of the crystal grain size in the range of average crystal grain size ± (average crystal grain size × 0.5) μm. can get.
[0026]
In the magnesium alloy sheet thus obtained, surface defects due to rolling, that is, surface roughness, are observed. In a preferred embodiment of the present invention, the surface roughness is limited to Rmax (maximum surface roughness) of 10 μm or less. . This is to ensure the color paint concealment. Such surface roughness can be adjusted by changing the surface roughness of the rolling roll and the rolling conditions.
[0027]
The alloy composition of the magnesium alloy plate for press working according to the present invention is a so-called practical magnesium alloy, and is not particularly limited. However, in a preferred embodiment, the mass ratio is aluminum: 2.5 to 3.5%. Zinc: 0.6-1.4%, Manganese: 0.2-1.0%, and the balance is substantially limited to magnesium, but such alloy composition is already specified in the standard, eg ASTM AZ31B In the present invention, such a known magnesium alloy is also included.
[0028]
Here, the reasons for limiting the alloy composition in the present invention are as follows. In the present specification, “%” indicating an alloy composition means “mass%”.
Al: Al is blended for improving corrosion resistance and mechanical properties. If it is less than 2.5%, the desired effect cannot be sufficiently exhibited, and if it exceeds 3.5%, the workability of the base material is lowered.
[0029]
Zn: Zn is blended for improving corrosion resistance and mechanical properties. If the content is less than 0.6%, the desired effect cannot be sufficiently exhibited. If the content exceeds 1.4%, the workability of the base material is lowered. Preferably, it is 0.8 to 1.1%.
[0030]
Mn: Mn is added to improve corrosion resistance and strength. If it is less than 0.2%, the desired effect cannot be fully achieved. If it exceeds 1.0%, workability is caused by cracks originating from MnAl intermetallic compounds. Decreases. Preferably, it is 0.3 to 0.8%.
[0031]
In addition, Fe, Si, Cu, Ni, and the like may be included as unavoidable impurities, but these are preferably limited to 0.050% or less as a total amount.
Next, the effects of the present invention will be described more specifically with reference to examples.
[0032]
(Example 1)
The magnesium alloy plate used in this example is AZ31B annealed material (Al: 3.02%, Zn: 0.88%, Mn: 0.50%, Mg: balance), and the dimensions are 2mm in thickness. The width was 150mm.
[0033]
The magnesium alloy sheet was rolled using the apparatus shown in FIG. First, the magnesium alloy sheet is continuously unwound from the uncoiler 1, each is heated and heated in the temperature range of 250 to 350 ° C. by the heating device 3, and the heat treatment is performed in the temperature range of 250 to 350 ° C. went. Such warm rolling was repeated until the plate thickness became 0.78 to 0.55 mm.
[0034]
Thereafter, cold rolling was repeated several times without heat treatment, and heat treatment was performed by heating to a temperature range of 250 ° C to 350 ° C. The total rolling reduction at that time was 5 to 20%. Two sets (times) of cold rolling repeated multiple times without heat treatment were performed, and the plate thickness was set to 0.5 mm.
[0035]
Table 1 summarizes the average crystal grain size and grain size distribution of the magnesium alloy sheet obtained at this time. The rolling speed was set to 4M / min.
“Grain size distribution” as used herein is a ratio in which the crystal grain size is in the range of (average crystal grain size ± (average crystal grain size × 0.5)), and the rolling direction of the plate thickness center portion and the plate thickness surface layer portion. The particle size was measured at an N number of 50 from each microphotograph.
[0036]
FIG. 2 is a microstructure photograph of the sample No. 3 (example of the present invention) in Table 1, showing a microstructure with an average particle size of 8 μm and a particle size distribution of 88%.
FIG. 3 is a microstructure photograph of the sample No. 7 (comparative example) in Table 1, showing a microstructure with an average particle size of 9 μm and a particle size distribution of 74%.
[0037]
The magnesium alloy sheet thus obtained was evaluated for warm formability.
Evaluation of warm formability:
Warm formability was evaluated by warm pressing. As the evaluation method, when commercial production was considered at a press speed of less than 30 mm / s, the press speed was slow, so the number of production was reduced, and therefore, x was assigned. Since the production number can withstand commercial production at a press speed of 30 mm / s or higher, it was marked as “Good”.
[0038]
A 40 mm square plate was taken from the magnesium alloy plate after rolling and annealing, and was pressed while changing the pressing speed. Test conditions are: mold set temperature: 250 ° C., punch set temperature: 250 ° C., press force: 2-3 Ton, wrinkle holding force: zero, punch shoulder: R = 2 mm, press depth: 15 mm, lubrication: molybdenum disulfide It was. The speed at which pressing was performed and cracks did not occur was defined as the critical pressing speed, and the results are also shown in Table 1.
[0039]
[Table 1]

[0040]
From the results thus obtained, a magnesium alloy having an average crystal grain size of 10 μm or less and 80% or more of the crystal grain size in the range of (average crystal grain size ± (average crystal grain size × 0.5)) μm The plate was found to have excellent warm formability.
[0041]
(Example 2)
Of the magnesium alloy plate obtained in Example 1, a sample in which surface flaws were observed during rolling was used as a test material, and the maximum surface roughness of the surface flaws was measured. Concealment was evaluated.
[0042]
Evaluation of color paint concealment:
A 90 mm square test piece was taken from the magnesium alloy sheet after rolling and annealing, and after degreasing and base treatment, colored coating was performed. For colored coatings, the coating thickness was 40-50 μm for both the undercoat and topcoat. The determination of the color paint concealment property was evaluated as “◯” when the surface wrinkles and surface patterns were not observed after the color coating, and “X” when the surface wrinkles and surface patterns were observed.
[0043]
The results are summarized in Table 2.
[0044]
[Table 2]

[0045]
From the results thus obtained, it was found that even if surface flaws occur, if the maximum surface roughness is 10 μm or less, a good appearance is obtained after colored coating.
[0046]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the magnesium alloy plate for press work excellent in warm formability and colored coating concealment property can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus for producing a magnesium alloy plate.
FIG. 2 is a microstructure photograph of a sample No. 3 in Table 1.
FIG. 3 is a microstructure photograph of a sample No. 7 in Table 1.
[Explanation of symbols]
1: Magnesium coil uncoiler 2: Magnesium coil winding coiler 3: Heating device 4: Rolling mill 5: Heat treatment device 6: Radiation thermometer (on the rolling mill)
7: Radiation thermometer (outside of heat treatment equipment)

Claims (3)

Having an alloy composition of, by weight, aluminum: 2.5-3.5%, zinc: 0.6-1.4%, manganese: 0.2-1.0%, and the balance magnesium and impurities , Magnesium alloy for press working, wherein the average crystal grain size is 10 μm or less, and 80% or more of the crystal grain size is in the range of average crystal grain size ± (average crystal grain size × 0.5) μm Board. The magnesium alloy plate for press working according to claim 1, wherein the maximum surface roughness Rmax is 10 µm or less. Magnesium alloy having an alloy composition of aluminum: 2.5-3.5%, zinc: 0.6-1.4%, manganese: 0.2-1.0%, and the balance magnesium and impurities in mass% A first rolling step of heating the material to 250 to 350 ° C. to perform rolling is performed once or twice or more, and a heat treatment for heating the rolled plate obtained in the first rolling step to 250 to 350 ° C. A method for producing a magnesium alloy sheet for press working, wherein the second rolling step of performing cold rolling with a total rolling reduction of a plurality of passes of 12% or more is performed twice or more.

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