JP2000246414A - Manufacture of magnesium alloy formed parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and safety obtain the thin thickness formation and the uneven thickness formation at high production efficiency by charging a magnesium alloy having difficult-to-plastic work and difficult-to-forging work into a metallic mold for forming under state of heating-holding to the solid-liquid coexisting temp. in a specific-phase ratio and pressurize-forming. SOLUTION: The magnesium alloy under the state of heating-holding to the solid-liquid coexisting temp. of 30-80% solid-phase ratio, is charged into the metallic mold for forming in a forming press machine desirably heated to about 250 deg.C, and pressurize-formed. In this way, the forged-forming product of the magnesium alloy is easily obtd. At this time, as the magnesium alloy, the one which is rapidly cooled and solidified after heating and holding once to the solid-liquid coexisting temp. of 30-80% solid-phase ratio, is used and thus, reheating time at the pressurize-forming is shortened, or the forginability is improved by forming the crystal grain diameter at the initial stage to <=300 μm or the solid-phase grain is made fine with the recrystallization at the heat-up by giving the internal strain with the pressurize-deformation and thus, the forge- formability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a magnesium alloy molded part.

[0002]

2. Description of the Related Art Magnesium alloys are the lightest among practical alloys and have recently been employed in electronic equipment housings and the like as a material that can replace resin materials.

[0003] A commonly used magnesium alloy is a magnesium α phase having an hcp crystal structure (hereinafter referred to as α phase), so that it is difficult to carry out plastic working, and the forming method is a die casting method, a thixo casting method, or the like. A hot press method or the like is employed.

[0004] However, in the die casting method, it is necessary to handle a molten magnesium, and there is a problem with the danger of burning. Sulfur hexafluoride used as a flame retardant gas is a global warming gas. It is becoming unusable.

Further, in the thixocast method, it is necessary to apply mechanical stirring to the alloy in a semi-molten or semi-solid state to obtain a slurry in which the solid phase is made spherical, so that the production efficiency is poor.
In addition, there is a problem that danger of combustion is involved because a stirring atmosphere such as air is involved. Furthermore, even in the thixomolding method which does not require a slurry by using a cutting tip, the solid phase ratio at the time of molding is close to 0 at present, and the molten metal is substantially handled.

Furthermore, injection molding methods such as a die casting method and a thixo casting method are difficult to cope with thinning.
Since secondary processing such as deburring and surface finishing is required after molding, there is a problem that production efficiency is poor.

[0007] In press working such as hot pressing, an uneven thickness structure cannot be obtained, and even when partial strength is required, the entire structure must be thickened. Difficult to adapt to. In addition, since a mechanical portion such as a boss cannot be formed, its application is limited.

[0008] For this reason, forgeable magnesium alloys have been developed in some parts, and the forging has been put to practical use.
The deformation rate in one forging is small, and a plurality of forgings are required, and it is difficult to form a thin wall, for example, a shape like a housing of an electronic device.

Further, Japanese Patent Application Laid-Open No. 6-246384 discloses a method in which a magnesium alloy material is subjected to a heat treatment in a semi-molten state and forged. In this method, the solid phase ratio or the like at the time of molding is not specified, and if the semi-molten state, that is, the solid phase ratio is represented by Vf, processing is performed in the range of 0 <Vf <1.

However, in the above method, if the solid phase ratio is too low, the solid state becomes almost molten, so that the handling becomes difficult, and the flowability during forging is too good. When the solid fraction is too high, there is also a problem that the plastic deformability is low and forging cannot be performed.

[0011]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the present invention.
In the invention described, the magnesium alloy has a solid phase ratio of 30 to 80%.
A method for producing a magnesium alloy molded part, wherein the molded part is charged into a molding die while being heated and held at the solid-liquid coexistence temperature and then subjected to pressure molding.

Further, the invention according to claim 2 is characterized in that the magnesium alloy is once heated and maintained at a solid-liquid coexistence temperature of 30 to 80% and then rapidly solidified. 2. A method for producing a magnesium alloy molded part according to item 1.

The invention according to claim 3 is the method according to claim 1 or 2, wherein the initial crystal grain size of the magnesium alloy is 300 μm or less.

According to a fourth aspect of the present invention, there is provided the method of manufacturing a magnesium alloy molded part according to the first aspect, wherein the magnesium alloy is given an internal strain by pressurized deformation. .

According to a fifth aspect of the present invention, the magnesium alloy is extruded into a plate or a column while being heated and maintained at a solid-liquid coexistence temperature having a solid phase ratio of 30 to 80%. A method for manufacturing a magnesium alloy molded part according to claim 1, wherein:

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings.

Here, a casting magnesium alloy AZ91D (hereinafter referred to as AZ), which is generally considered to be difficult to perform plastic working.
91D), but is not limited to this, and other magnesium alloys may be used. Embodiment 1 Embodiment 1 will be described below.

First, in order to examine the relationship between the temperature and the solid fraction of AZ91D, AZ91D was completely melted at 700 ° C., then cooled to various temperatures at a cooling rate of 0.2 ° C./sec, and rapidly cooled in water. As a result, the tissue at each temperature was frozen and solidified. Then, the coagulated tissue was observed and measured, and the relationship between the temperature and the solid fraction was obtained. Figure 1 shows the results.
Shown in

Next, forging tests are performed on magnesium alloys having various solid fractions.

From the results shown in FIG. 1, 20%, 30%, 4%
The heating temperature (solid-liquid coexistence temperature) of the magnesium alloy having each of the solid fractions of 0%, 60%, 80%, 90%, and 100% is 590 ° C, 587 ° C, 585 ° C, 572 ° C, and 535 ° C, respectively.
It turns out that it is C, 493C, and 450C.

Therefore, the AZ91D ingot is set to 30 mm
A forged test piece 1 cut into a size of 30 mm x 20 mmt is
Heating and holding at each of the above-mentioned temperatures, and using a forging press machine as shown in FIG.
And pressurized to produce a forged product as shown in FIG. The mold temperature at this time was 250 ° C., and the material temperature was the solid-liquid coexistence temperature of each solid phase ratio.

Then, the thickness of the top surface of the forged product was measured, and the relationship between the solid fraction and the thickness of the top surface was examined. The result is shown in FIG.
Shown in

As is apparent from FIG. 4, a sufficient flow is obtained with a decrease in the solid fraction, and the thickness after forging becomes equal to the design value. However, when the solid phase ratio was 20% or less, it could not be set in a mold because it was almost liquid. On the other hand, when the solid phase ratio exceeded 80%, cracks occurred during pressurization, and forging could not be performed.

Next, when the solid-liquid coexistence temperature of the desired solid fraction was maintained, the time required to reach the desired solid fraction was measured.

First, an AZ91D ingot of the same dimensions as above was placed in a closed case made of iron, kept in a heat treatment furnace at a solid-liquid coexistence temperature (587 ° C.) of about 30% solid phase for 20 minutes, and then in water. Quenched. The solid-liquid coexistence treated sample thus prepared and a sample obtained by cutting out a normal ingot into the same size are sealed in an iron closed case, heated again to 590 ° C., held for a predetermined time, and then rapidly cooled in water. The relationship between the retention time and the solid phase ratio was examined by measuring the solid phase ratio. The result is shown in FIG.

As is apparent from FIG. 5, the sample subjected to the solid-liquid coexistence treatment reaches a desired solid phase ratio in a short holding time. That is, since the heating time until the solid-liquid coexistence state before forging can be shortened, the productivity is improved by cutting out the sample after performing the solid-liquid coexistence treatment on the ingot before cutting out for forging. be able to. Embodiment 2 Embodiment 2 will be described below.

First, the relationship between the particle size of the solid phase particles during forging and the forging formability was examined.

Initial crystal grain size is 100 μm, 300 μm
m, 500μm alloy ingot 30mm x 30mm
× 20 mmt, each having a solid fraction of 80%, 6
0%, 40% solid-liquid coexistence temperature (535 ° C, 572 ° C,
(585 ° C.), thereby obtaining a forged test piece 1. These forged test pieces 1 were inserted between the forming test dies 2 of the forging press machine shown in FIG. 2 and pressed to form a forged product as shown in FIG. The mold temperature at this time was 250 ° C., and the material temperature was the solid-liquid coexistence temperature of each solid phase ratio.

Then, the thickness of the top surface of the obtained molded product was measured. FIG. 6 shows the result.

As is clear from FIG. 6, when the solid phase ratio was 40%, the thickness after forging became equal to the designed value for any sample of any particle size, and no difference was observed. Particle size 5
It can be seen that the thickness of the sample having a thickness of 00 μm is slightly increased, and that the solid phase ratio is 80%. Therefore, if the solid fraction is 80% and the initial crystal grain size is large, good forgeability cannot be obtained,
To obtain the desired design thickness, the initial crystal grain size should be 30
It is necessary that the thickness be 0 μm or less.

Next, it was investigated how the crystal grain size of the initial alloy ingot changes by maintaining the solid-liquid coexistence state.

More specifically, the initial crystal grain size is 100 μm,
Samples of the alloy ingot adjusted to 300 μm and 500 μm were placed in an iron closed case, and the solid-liquid coexistence temperature (572%) of each solid phase ratio (60%, 40%, 20%) was set.
C., 585.degree. C., 590.degree. C.), hold for a predetermined time, quench in water, observe tissue, and examine how the particle size of solid phase particles changes during solid-liquid coexistence treatment. . The result is shown in FIG.

As is clear from FIG. 7, when the initial crystal grain size is 100 μm, the crystal grain size of the solid phase particles increases with the retention time at any solid phase ratio. In particular, when the solid phase ratio is 60%, the degree of increase is large.

When the initial crystal grain size is 500 μm, the grain size is reduced by dissolution at any solid phase ratio, and when the solid phase ratio is maintained at 60%, there is almost no change in the grain size. In the case of the solid phase ratio of 40 and 20%, it can be seen that there is a slight decreasing tendency.

When the initial crystal grain size was 300 μm, there was almost no change in the grain size regardless of the solid phase ratio.

In other words, in order to obtain good forgeability, when the initial crystal grain size is 300 μm or more, it is necessary to maintain the solid phase ratio for at least 30 minutes after reaching the desired temperature. It turns out that it is necessary.

When the initial crystal grain size is as small as 300 μm or less, it is desirable to set the holding time after reaching a desired temperature to 30 minutes or less in order to prevent coarsening due to grain growth. Third Embodiment A third embodiment will be described below.

The upsetting die 2 was attached to a forging press (the entire apparatus is not shown) as shown in FIG. 2, and an AZ91D ingot having an initial crystal grain size of 500 μm was placed in a size of 15 mm.
Cut to a thickness of 250 mm, mold temperature 250 ° C, material temperature 250
By pressurizing at ° C., it was deformed to a thickness of about 10 mm to give internal strain.

The sample thus prepared was placed in a closed case made of iron, and the solid-liquid coexistence temperature (57%) having a solid phase ratio of 60% was measured.
(2 ° C.) and then rapidly cooled in water, and the particle size of the solid particles was measured. As a result, the particle size of the solid particles was about 200 μm.

This is 500 μm for the initial ingot.
It is considered that the crystal grain size was recrystallized during the heating up to the solid-liquid coexistence temperature. That is, it can be seen that, by imparting an internal strain to the alloy ingot so as to be in a solid-liquid coexistence state, the particle size of the solid phase particles is reduced, and the forgeability is improved.

In order to confirm this, a forging test similar to that of Example 1 was performed, and good forgeability was confirmed. Embodiment 4 Hereinafter, Embodiment 4 will be described.

AZ91D having an initial crystal grain size of 500 μm
The ingot is charged in a container with an inner diameter of 200 mm,
Solid-liquid coexistence temperature of 20%, 30%, 40%, 60%, 70% of solid phase ratio (590 ° C, 587 ° C, 585 ° C, 572 ° C,
(558 ° C.) and extruded into a 30 mm × 30 mm square bar, and the particle size of the solid particles was measured. Table 1 shows the results.

[0043]

[Table 1] When the solid phase ratio was 20%, the flow was so strong that it could not be extruded into a square shape. When the solid fraction was 70%, extrusion was not possible due to poor flow.

In the case of solid phase ratios of 30%, 40% and 60%,
As a result of observing the structure, as shown in the remarks column of Table 1, the structure was a so-called slurry state in which solid phase particles were spheroidized and coexisted in a solid-liquid state. Further, the solid phase particles were finer than the initial crystal particle size due to the reduction in particle size due to dissolution and the shearing force during extrusion.

When a forging test similar to that of Example 1 was performed using these extruded materials, good forgeability was confirmed.

In this embodiment, extrusion was performed at an extrusion ratio of about 35, and such a result was obtained. However, when the extrusion ratio was changed, the ratio of solid phase that can be extruded was changed. Needless to say, it does not limit the invention.

[0047]

As described above, according to the first aspect of the present invention, a magnesium alloy is charged into a molding die while being heated and maintained at a solid-liquid coexistence temperature of 30 to 80% solids fraction. By performing pressure molding, a forged product can be easily obtained.

According to the second aspect of the present invention, the magnesium alloy is heated and maintained once at a solid-liquid coexistence temperature of 30 to 80%, and then rapidly solidified. When reheating sometimes, it is possible to reach a desired solid phase ratio in a short time, thereby improving the processing speed and the productivity.

According to the third aspect of the present invention, the forgeability can be improved by setting the initial crystal grain size of the magnesium alloy to 300 μm or less.

According to the fourth aspect of the present invention, since the magnesium alloy is given an internal strain by deformation under pressure, the solid phase particles are made finer by recrystallization at a temperature rise. And forgeability can be improved.

According to the fifth aspect of the present invention, the magnesium alloy is extruded into a plate or a column while being heated and maintained at a solid-liquid coexistence temperature having a solid phase ratio of 30 to 80%. Therefore, the solid phase particles can be made finer by the shearing force at the time of extrusion, and the step of cutting into the charged shape at the time of pressure molding can be simplified.

[0052]

[Brief description of the drawings]

[0053]

FIG. 1 is a view showing the results of measuring the temperature-solid fraction of a magnesium alloy for casting AZ91D.

[0054]

FIG. 2 is a schematic view showing a forming part of a forging device.

[0055]

FIG. 3 is a schematic diagram showing a forged product used for molding of the present invention.

[0056]

FIG. 4 is a view for explaining a difference in forgeability due to a solid phase ratio during forging.

[0057]

FIG. 5 is a diagram for comparing and explaining the time required for melting an untreated alloy ingot and an ingot subjected to solid-liquid coexistence treatment.

[0058]

FIG. 6 is a diagram showing a change in solid phase particle size due to an initial crystal particle size when the temperature is maintained at a solid-liquid coexistence temperature.

[0059]

FIG. 7 is a diagram for explaining a difference in forging formability depending on an initial crystal grain size and a solid phase ratio at the time of forming.

[0060]

[Explanation of symbols]

 1 Magnesium alloy forging test piece 2 Mold

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C22F 1/00 611 C22F 1/00 611 623 623 624 624 630 630 630K 681 681 683 683 690 690 694 694B

Claims (5)

[Claims] 1. A magnesium alloy having a solid phase ratio of 30 to 80%.
A method for producing a magnesium alloy molded part, wherein the molded part is charged into a molding die while being heated and held at the solid-liquid coexistence temperature and then subjected to pressure molding. 2. The magnesium alloy according to claim 1, wherein
The method for producing a magnesium alloy molded component according to claim 1, wherein the component is heated and maintained at a solid-liquid coexistence temperature of 80% and then rapidly solidified. 3. The method according to claim 1, wherein an initial crystal grain size of the magnesium alloy is 300 μm or less. 4. The method for manufacturing a magnesium alloy molded part according to claim 1, wherein said magnesium alloy is given an internal strain by pressurized deformation. 5. The method according to claim 1, wherein the magnesium alloy has a solid content of 30 to 30%.
The method for producing a magnesium alloy molded part according to claim 1, wherein the part is extruded in a plate shape or a column shape while being heated and held at a solid-liquid coexistence temperature of 80%.