JP4252502B2 - Magnesium alloy molded part manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a molded part of a magnesium alloy.

Background Art and Problems to be Solved by the Invention

  Magnesium alloys are the lightest of practical alloys, and have recently been adopted in electronic equipment casings and the like as substitutes for resin materials.

  Generally used magnesium alloys are magnesium α-phase (hereinafter referred to as α-phase) with an hcp crystal structure, so plastic processing is difficult, and the die casting method, thixocasting method, hot press can be used as the forming method. Laws are adopted.

  However, the die-casting method has to handle molten magnesium, and there is a problem with the risk of combustion. Sulfur hexafluoride, which is used as a flame-retardant gas, cannot be used because it is a global warming gas. It is coming.

  Moreover, in the thixocast method, it is necessary to give a slurry in which the alloy is semi-molten or semi-solidified to obtain a slurry in which the solid phase is spheroidized, so that the production efficiency is poor, and the stirring atmosphere such as air is involved. There is a problem that there is a risk of combustion. Furthermore, even in the thixomold method that does not require slurry by using a cutting tip, the solid phase rate at the time of molding is close to 0, and the molten metal is substantially handled.

  Furthermore, injection molding methods such as die-casting and thixocasting methods are difficult to cope with thinning, and after processing, secondary processing such as deburring and surface finishing is required, so production efficiency is poor. There's a problem.

  Also, in press processing such as hot press, it is not possible to take an uneven thickness structure, and even if strength is partially required, the whole must be set thick, and it is suitable for weight reduction purposes It is hard to do. Moreover, since a mechanism part such as a boss cannot be built, the application is limited.

  For this reason, magnesium alloys that can be forged have been developed in some areas, and the forging has also been put to practical use. However, the deformation rate of one forging is small, and multiple forgings are required. It was difficult to mold a shape like a housing.

  Patent Document 1 discloses a method of forging by heat-treating a magnesium alloy material into a semi-molten state. In this method, there is no indication of the solid phase ratio at the time of molding, and if the semi-molten state, that is, the solid phase ratio is expressed as Vf, processing is performed in the range of 0 <Vf <1.

However, in the above method, if the solid phase ratio is too low, it will almost be in a molten state, which makes it difficult to handle, and the fluidity is too good during forging, so it will scatter before filling the mold cavity. In addition, when the solid phase ratio is too high, there is a problem that the plastic deformability is low and forging cannot be performed.
JP-A-6-246384

  Accordingly, the present invention has been made for the purpose of solving the above-mentioned problems of the present invention. The first invention is a solid-liquid coexistence temperature of a magnesium alloy having an initial crystal grain size of 300 μm or less and a solid phase ratio of 30 to 80%. A method for producing a magnesium alloy molded part, which is charged and molded in a molding die while being heated and held.

  Further, the second invention is to hold a magnesium alloy having an initial crystal grain size of 300 μm or more at a solid-liquid coexistence temperature with a solid phase ratio of 20 to 60% for 30 minutes or more, and thereafter, with a solid phase ratio of 30 to 80%. A method for producing a magnesium alloy molded part, comprising charging into a molding die while being heated and held at a liquid coexisting temperature, followed by pressure molding.

  In addition, the third invention provides a magnesium alloy in which the solid phase particle size is made smaller than the initial crystal particle size by applying internal strain to the magnesium alloy by pressure deformation and then heating and holding at a solid-liquid coexistence temperature. Is molded in a molding die while being heated and held at a solid-liquid coexistence temperature with a solid phase ratio of 30 to 80%, followed by pressure forming.

  The fourth aspect of the invention is that the solid phase particle size is made smaller than the initial crystal particle size by extruding the magnesium alloy into a plate shape or a column shape while being heated and held at a solid-liquid coexistence temperature of 30 to 60%. A magnesium alloy molded part manufacturing method, comprising: charging a formed magnesium alloy into a molding die in a state of being heated and held at a solid-liquid coexistence temperature with a solid phase ratio of 30 to 80%. .

According to a fifth aspect of the present invention, there is provided a magnesium alloy molding characterized in that the magnesium alloy is charged in a molding die while being heated and held at a solid-liquid coexistence temperature with a solid phase ratio of 30-80%. It is a manufacturing method of components.
The sixth invention is characterized in that, in the fifth invention, the magnesium alloy is once heated and held at a solid-liquid coexistence temperature of 30 to 80% and then rapidly solidified.
According to a seventh aspect, in the fifth or sixth aspect, the initial crystal grain size of the magnesium alloy is 300 μm or less.
The eighth invention is characterized in that, in the fifth invention, the magnesium alloy is provided with an internal strain by pressure deformation.
The ninth invention is the fifth invention, wherein the magnesium alloy is extruded in a plate shape or a column shape while being heated and held at a solid-liquid coexistence temperature with a solid phase ratio of 30 to 80%. It is characterized by.

According to the first invention, forging formability can be improved by setting the initial crystal grain size of the magnesium alloy to 300 μm or less.
According to the second invention, the solid phase particle diameter can be reduced and the forgeability can be improved.
According to the third invention, since the magnesium alloy is given internal strain by pressure deformation, the solid phase particles can be made fine by recrystallization at the time of temperature rise, and forging formability is improved. Can be made.
According to the fourth invention, the solid phase particles can be made fine by the shearing force at the time of extrusion, and the cut-out process to the charged shape at the time of pressure molding can be simplified.
According to the fifth invention, a magnesium alloy is easily forged by inserting it into a molding die while being heated and held at a solid-liquid coexistence temperature having a solid phase ratio of 30 to 80%, followed by pressure molding. Can be obtained.
According to the sixth invention, since the magnesium alloy is once heated and held at a solid-liquid coexistence temperature of 30 to 80% and then rapidly solidified, it is desired to reheat at the time of pressure forming. The solid phase ratio can be reached in a short time, and the processing speed and productivity can be improved.
According to the seventh invention, forgeability can be improved by setting the initial crystal grain size of the magnesium alloy to 300 μm or less.
According to the eighth invention, since the magnesium alloy is given internal strain by pressure deformation, the solid phase particles can be made fine by recrystallization at the time of temperature rise, and the forgeability is improved. Can be improved.
According to the ninth invention, since the magnesium alloy is extruded in the form of a plate or a column while being heated and held at a solid-liquid coexistence temperature with a solid phase ratio of 30 to 80%, the shearing force at the time of extrusion Thus, the solid phase particles can be made fine, and the cutting process into the charged shape at the time of pressure molding can be simplified.

Hereinafter, the present invention will be described in detail with reference to the drawings.
Here, a casting magnesium alloy AZ91D (hereinafter referred to as AZ91D), which is generally said to be difficult to be plastically processed, is used. However, the present invention is not limited to this, and other magnesium alloys may be used. Absent.

Example 1 will be described below.
First, in order to investigate the relationship between the temperature and the solid phase ratio of AZ91D, AZ91D was made into a completely molten state at 700 ° C., then cooled to various temperatures at a cooling rate of 0.2 ° C./second, and rapidly cooled in water. The tissue at each temperature was solidified while frozen. And the solidification organization was observed and measured, and the relationship of temperature-solid phase ratio was calculated | required. The result is shown in FIG.

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

  From the results of FIG. 1 above, the heating temperatures (solid-liquid coexistence temperatures) of the solid alloys of 20%, 30%, 40%, 60%, 80%, 90%, and 100% are 590 ° C., respectively. It turns out that it is 587 degreeC, 585 degreeC, 572 degreeC, 535 degreeC, 493 degreeC, and 450 degreeC.

  Therefore, the forging test piece 1 obtained by cutting the AZ91D ingot into 30 mm × 30 mm × 20 mmt is heated and held at each of the above temperatures, and used for a molding test using a forging press machine (not shown) as shown in FIG. A forged molded product as shown in FIG. 3 was produced by charging the mold 2 and applying pressure. 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 phase ratio and the top surface thickness was examined. The result is shown in FIG.

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

  Next, the time until the desired solid phase ratio was reached when the solid-liquid coexistence temperature of the desired solid phase ratio was maintained was measured.

  First, an AZ91D ingot having the same dimensions as above was placed in an iron sealed case, kept in a solid-liquid coexistence temperature (587 ° C.) with a solid phase ratio of about 30% in a heat treatment furnace, and then rapidly cooled in water. The solid-liquid coexistence treated sample prepared in this way and a sample obtained by cutting a normal ingot into the same dimensions are enclosed in an iron sealed case, heated again to 590 ° C., held for a predetermined time, and then rapidly cooled in water. Then, 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, it can be seen that the sample subjected to the solid-liquid coexistence treatment reaches the desired solid phase ratio in a short holding time. In other words, since the heating time until the solid-liquid coexistence state before forging can be shortened, productivity is improved by cutting the sample after subjecting the ingot before cutting for forging to the solid-liquid coexistence treatment. be able to.

Example 2 will be described below.
First, the relationship between the particle size of solid phase particles during forging and forging formability was examined.

  Alloy ingots having initial crystal grain sizes of 100 μm, 300 μm, and 500 μm were cut into 30 mm × 30 mm × 20 mmt, and solid-liquid coexistence temperatures (535 ° C., 572 ° C., 585 ° C.) with solid phase ratios of 80%, 60%, and 40%, respectively. The forged test piece 1 was heated and held at 0 ° C.). These forged test pieces 1 were placed between the molding test molds 2 of the forging press shown in FIG. 2 and subjected to pressure molding to produce a forged molded 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.

  And the thickness of the top | upper surface of the obtained molded article was measured. The result is shown in FIG.

  As can be seen from FIG. 6, when the solid phase ratio is 40%, the thickness after forging of the samples with any grain size is the design value, and no difference is seen. However, when the solid phase ratio is 60%, the grain size is 500 μm. It can be seen that, when the sample is slightly thicker and the solid phase ratio is 80%, the thickness increases as the particle size of the solid phase particles increases. Therefore, when the solid phase ratio is 80% and the initial crystal grain size is large, good forgeability cannot be obtained. Therefore, in order to form the desired design thickness, the initial crystal grain size should be 300 μm or less. It is necessary to.

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

  Specifically, a sample of an alloy ingot whose initial crystal grain size is adjusted to 100 μm, 300 μm, and 500 μm is placed in an iron sealed case, and the solid-liquid ratio of each solid phase ratio (60%, 40%, 20%). After reaching the coexistence temperature (572 ° C, 585 ° C, 590 ° C), hold for a predetermined time, quench in water, observe tissue, and how the particle size of solid phase particles changes during solid-liquid coexistence treatment I investigated. The result is shown in FIG.

  As can be seen 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. It can be seen that the degree of increase is particularly large when the solid phase ratio is 60%.

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

  Further, when the initial crystal grain size was 300 μm, there was almost no change in the grain size even when the solid phase ratio was maintained.

  That is, in order to obtain good forgeability, when the initial crystal grain size is 300 μm or more, it is necessary to hold for 30 minutes or more after reaching the desired temperature at any solid phase ratio. I understand that.

  When the initial crystal grain size is as small as 300 μm or less, it is desirable that the holding time after reaching a desired temperature is 30 minutes or less in order to prevent coarsening due to grain growth.

Example 3 will be described below.
The upset die 2 is attached to a forging press as shown in FIG. 2 (the entire apparatus is not shown), an AZ91D ingot having an initial crystal grain size of 500 μm is cut into a thickness of 15 mm, and a die temperature of 250 ° C. By applying pressure at a material temperature of 250 ° C., the film was deformed to a thickness of about 10 mm to give internal strain.

  The sample thus prepared was placed in an iron sealed case, heated and held at a solid-liquid coexistence temperature (572 ° C.) with a solid phase ratio of 60%, and then rapidly cooled in water, and the particle size of the solid phase particles was measured. . As a result, the particle size of the solid phase particles was about 200 μm.

  This is presumably because the crystal grain size, which was 500 μm in the initial ingot, was recrystallized during the temperature rise to the solid-liquid coexistence temperature. In other words, it can be seen that by applying internal strain to the alloy ingot to make it coexist in a solid-liquid state, the particle size of the solid phase particles is reduced and the forgeability is improved.

  In order to confirm this, the same forging test as in Example 1 was performed, and good forgeability was confirmed.

Hereinafter, Example 4 will be described.
An AZ91D ingot having an initial crystal grain size of 500 μm was charged into a container having an inner diameter of φ200 mm, and a solid-liquid coexistence temperature (590 ° C., 587 ° C., 20%, 30%, 40%, 60%, 70%) 585 ° C., 572 ° C., 558 ° C.) and extruded into 30 mm × 30 mm square bars, and the particle size of the solid phase particles was measured. The results are shown in Table 1.

  When the solid phase ratio was 20%, the flow was so intense that it could not be extruded into a square shape. When the solid phase ratio was 70%, the flow was so bad that extrusion could not be performed.

  When the solid phase ratio was 30%, 40%, or 60%, it was possible to extrude into a square shape. As a result of observing the structure, the solid phase particles were spheroidized as shown in the remarks column of Table 1. It was an organization of so-called slurry in a solid-liquid coexistence state. Further, the solid phase particles were finer than the initial crystal particle size due to the particle size reduction accompanying dissolution and the shearing force during extrusion.

  When these forging materials were used, the same forging test as in Example 1 was performed, and good forgeability was confirmed.

  In this example, extrusion was performed at an extrusion ratio of about 35, and such a result was obtained. However, when the extrusion ratio is changed, the extrudable solid phase ratio changes, so this example limits the present invention. It goes without saying that it is not what you do.

It is a figure which shows the result of having measured the temperature-solid phase rate of magnesium alloy AZ91D for casting. It is a schematic diagram which shows the shaping | molding part of a forging apparatus. It is a schematic diagram which shows the forge molded product used for shaping | molding of this invention. It is a figure for demonstrating the difference in forgeability by the solid-phase rate at the time of forging. It is a figure for comparing and explaining the time required for melt | dissolution of the unprocessed alloy ingot and the ingot which carried out the solid-liquid coexistence process. It is a figure for demonstrating the difference of the forge formability by the initial crystal grain size and the solid-phase rate at the time of shaping | molding. It is a figure which shows the change of the solid-phase particle size by the initial crystal grain size at the time of hold | maintaining at a solid-liquid coexistence temperature.

Explanation of symbols

1 Magnesium alloy forging specimen 2 Mold

Claims (1)

  A magnesium alloy having an initial crystal grain size of 300 μm or more is maintained at a solid-liquid coexistence temperature of a solid phase ratio of 20 to 60% for 30 minutes or more to reduce the crystal grain size, and then the solid phase ratio of 30 to 80%. A method for producing a magnesium alloy molded part, comprising charging into a molding die while being heated and held at a solid-liquid coexisting temperature, followed by pressure molding.

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