JP5356777B2 - Magnesium alloy forging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forging method of a magnesium alloy which is free from the generation of cracks upon forging, can be filled into a die at high precision, and can obtain a forged product having excellent mechanical strength. <P>SOLUTION: A cast body made of a magnesium alloy comprising, to the whole quantity, by weight, 6 to 10% aluminum, 0.4 to 2% zinc, 0.05 to 0.3% manganese and 0.4 to 1.5% calcium with inevitable impurities is cooled at a rate of 12 to 40&deg;C/s so as to form a magnesium alloy stock for first forging in which the dendrite arm spacing of resinous crystals is 0.5 to 15 &mu;m, and the grain size of crystallized products composed of Mg-Al intermetallic compounds is 1 to 10 &mu;m. The magnesium alloy stock for first forging is subjected to spare working at 250 to 450&deg;C at a working ratio of 20 to 70% so as to form magnesium alloy stock for second forging. The magnesium alloy stock for second forging is subjected to forging. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for forging a magnesium alloy.

  Aluminum alloys are used in parts such as wheels and suspension arms in order to reduce the weight of automobiles and reduce fuel consumption and exhaust gas. Further, in order to further reduce the weight of the automobile, it has been studied to use a magnesium alloy for the parts of the automobile. Magnesium has a specific gravity of 1.8, which is smaller than the specific gravity of aluminum of 2.7, and is known to be the smallest among the metal materials currently in practical use.

  Most of the magnesium alloys used for automobile parts are used as casting materials. This is considered to be because the magnesium alloy material for forging is difficult to obtain and is expensive.

  However, the magnesium alloy casting material may not have sufficient strength to be used for the automobile parts. Thus, attempts have been made to use a cast magnesium alloy material for forging. For example, a technique is known in which a magnesium alloy casting containing 6 to 12% by weight of aluminum is used as a magnesium alloy for forging (patent document). 1).

  In the said technique, as said magnesium alloy containing 6 to 12 weight% aluminum, it is supposed that the AZ80 alloy prescribed | regulated to JIS can be mentioned, for example. The AZ80 alloy is, for example, aluminum 8.0 wt%, zinc 0.67 wt%, manganese 0.21 wt%, silicon 0.042 wt%, iron 0.002 wt%, copper 0.005 wt%, nickel It contains 0.001% by weight, and the balance consists of magnesium and inevitable impurities.

  According to the technique, by forging the casting, the magnesium alloy has an average crystal grain size of 100 μm or less, and a member with fine crystal grains can be obtained. Since the pearlite structure formed in the crystal grain boundary becomes fine by further applying the T6 treatment after the forging, the member has a large amount of precipitation, and as a synergistic effect with the refinement of the crystal grains, It is said that mechanical properties such as tensile strength and elongation can be greatly improved.

However, the magnesium alloy for forging has the disadvantage that it cannot be filled with high precision without cracking when forged.
JP-A-6-172949

  The present invention eliminates such inconveniences and forges magnesium alloys that can be filled with high accuracy without cracking when forged, and can provide a forged product with excellent mechanical strength. It aims to provide a method.

In order to achieve this object, the magnesium alloy forging method of the present invention is based on the total amount of aluminum in the range of 6 to 10% by weight, zinc in the range of 0.4 to 2% by weight, and 0.05 to A casting which is a magnesium alloy comprising 0.3% by weight of manganese, 0.4-1.5% by weight of calcium, the balance magnesium and unavoidable impurities is 12-40 ° C./second. and cooled at a rate of dendritic JoAkira dendrite arm spacing in the range of 0.5 to 15 m, the particle size of the crystallized substances consisting of Mg-Al intermetallic compound is first in the range of 1~10μm The step of forming the magnesium alloy material for forging and the first magnesium alloy material for forging are preliminarily processed at a temperature in the range of 250 to 450 ° C. and a processing rate in the range of 20 to 70%. Magnesium for forging And a step of forging the second magnesium alloy material for forging.

In the forging method of the present invention, first, aluminum in the range of 6 to 10% by weight, zinc in the range of 0.4 to 2% by weight, and manganese in the range of 0.05 to 0.3% by weight with respect to the total amount. Then , a cast body which is a magnesium alloy composed of calcium in the range of 0.4 to 1.5% by weight, the remainder magnesium and unavoidable impurities is cast.

Before hearing Zotai are relative to the total amount, by the inclusion of aluminum in an amount ranging from 6-10 wt%, the cast structure and is miniaturized to prevent coarsening of crystal grains, further inhibiting the development of columnar crystals Effect can be obtained. Before hearing Zotai is based on the total amount in order to achieve the above effects, preferably contains aluminum in the range of 7-9 wt%. If the aluminum content is less than 6% by weight, it is not preferable because the cast structure is refined and the effect of suppressing the development of columnar crystals cannot be obtained. Further, if the aluminum content exceeds 10% by weight, it is not preferable because the cast structure is further refined and the effect of suppressing the development of columnar crystals cannot be obtained, and the forgeability is impaired.

Before hearing Zotai are relative to the total amount, by an amount of the zinc in the range of 0.4 to 2 wt%, it is possible to obtain the effect of improving mechanical strength, particularly yield strength. Before hearing Zotai in order to obtain the above effect, based on the total amount, preferably contains zinc in the range of 0.8 to 1.5 wt%. If the zinc content is less than 0.4% by weight, the effect of improving the mechanical strength cannot be obtained, and if it exceeds 2% by weight, the elongation becomes insufficient and the forgeability is hindered.

Before hearing Zotai it is relative to the total amount, by an amount of the manganese in the range of 0.05 to 0.3 wt%, and precipitated Mg-Mn intermetallic compound at the grain boundaries, mechanical strength An improving effect can be obtained. The front heard Zotai, by Mg-Mn intermetallic compound is precipitated in grain boundaries, it is also possible to obtain the effect of improving the mechanical strength at high temperatures. Before hearing Zotai in order to obtain the above effect, based on the total amount, preferably contains manganese in the range of 0.1 to 0.25 wt%. If the manganese content is less than 0.05% by weight, the effect of improving the mechanical strength cannot be obtained, and if it exceeds 0.3% by weight, the amount of crystallized substances increases and the forgeability is impaired.

Before hearing Zotai it is relative to the total amount, by the inclusion of calcium in an amount ranging from 0.4 to 1.5 wt%, and precipitated Mg-Ca intermetallic compound at the grain boundaries, mechanical strength As well as improving, the effect of improving creep resistance can be obtained. The front heard Zotai, by Mg-Ca intermetallic compound is precipitated in grain boundaries, it is also possible to obtain the effect of improving the mechanical strength and creep resistance at high temperatures. Before hearing Zotai in order to obtain the above effect, based on the total amount, preferably contains calcium in the range of 0.4 to 1.5 wt%. If the calcium content is less than 0.4% by weight, the effect of improving the mechanical strength and creep resistance cannot be obtained. If the calcium content exceeds 1.5% by weight, the viscosity of the magnesium alloy melt increases to obtain a cast body. Is not preferable, and high temperature cracking occurs in the obtained casting.

The forging method of the present invention, then cooled before the hearing Zotai at a rate in the range of 12 to 40 ° C. / sec. As a result, the composition has the above composition, the dendritic arm has a dendrite arm interval in the range of 0.5 to 15 μm, and the crystallized particle size of the Mg—Al intermetallic compound is in the range of 1 to 10 μm. 1 forging magnesium alloy material can be obtained.

  The first forging magnesium alloy material is excellent in that the dendrite arm spacing of the dendritic crystals is in the range of 0.5 to 15 μm, and the particle diameter of the crystallized material is in the range of 1 to 10 μm. Forgeability can be obtained, and a member having excellent mechanical strength when forged can be obtained. The first magnesium alloy material for forging is obtained by forging, if the dendrite arm spacing of the dendritic crystals exceeds 15 μm, or if the particle size of the crystallized material exceeds 10 μm, the forgeability is hindered. The mechanical strength of the remaining member cannot be improved. In the first magnesium alloy material for forging, it is technically difficult to set the dendrite arm interval of the dendritic crystal to less than 0.5 μm and the particle size of the crystallized material to less than 1 μm.

  By the way, the crystal grain size of the first magnesium alloy material for forging cannot be sufficiently reduced only by cooling the cast body at a speed in the range of 12 to 40 ° C./second. Therefore, in the forging method of the present invention, next, the first magnesium alloy material for forging is preliminarily processed at a temperature in the range of 250 to 450 ° C. and a processing rate in the range of 20 to 70%.

  As a result, a second forging magnesium alloy material in which the crystal grain size of the first forging magnesium alloy material is refined can be obtained. When the temperature of the preliminary processing is less than 250 ° C., the crystal grain size of the first magnesium alloy material for forging cannot be refined. On the other hand, if the temperature of the preliminary processing exceeds 450 ° C., the crystal grains may be partially coarsened or hot cracks may occur in the first forging magnesium alloy material.

On the other hand, even if the temperature of the preliminary processing is in the range of 250 to 450 ° C., the crystal grain size of the first forging magnesium alloy material cannot be refined when the processing rate is less than 20%. . In addition, it is economically disadvantageous that the processing rate of the preliminary processing exceeds 70%.

  Next, in the forging method of the present invention, forging is performed on the second magnesium alloy material for forging. Since the second forging magnesium alloy material has a fine crystal grain size as described above, it can be filled with high precision without cracking when it is forged. Forgings with sufficient strength can be obtained.

Further, in the forging method of the present invention, before hearing Zotai it is relative to the total amount, contain beryllium antimony or 0.006 to 0.2 wt% of the range of 0.01 to 0.3 wt% Is preferred. Before hearing Zotai includes antimony of the range may include both the beryllium of the range may include only one of.

Before hearing Zotai, by including beryllium antimony or the range of the range, and further refine the structure of the casting, it is possible to improve the mechanical strength of the resulting member by forgeability and Forging At the same time, the surface oxidation of the magnesium alloy melt can be prevented, and the surface skin of the cast body can be made beautiful.

  If the content of antimony is less than 0.01% by weight, the effect of further refinement of the structure of the cast body may not be obtained sufficiently, and if it exceeds 0.3% by weight, Mg—Sb intermetallic compound is precipitated. Thus, the forgeability and the mechanical strength of the member obtained by forging may not be sufficiently improved. Further, if the beryllium content is less than 0.006% by weight, surface oxidation of the molten magnesium alloy may not be sufficiently prevented. If it exceeds 0.2% by weight, the viscosity of the molten magnesium alloy will increase, resulting in a casting defect. Is likely to occur.

Further, the forging method of the present invention, before hearing Zotai are based on the total amount, preferably containing cerium in the range of 1.2 wt% or less.

Before hearing Zotai, by containing cerium of said range, by Mg 9 _Ce crystallizes which is an intermetallic compound in the grain boundary, it is possible to improve the mechanical strength at high temperatures, in particular 250 ° C. Heat resistance is improved in the following range. Although the cerium is contained in a small amount, it can obtain the effect of improving the mechanical strength at high temperature, but when the content exceeds 1.2% by weight, the effect of further improving the heat resistance is obtained. In addition, crystallization of the intermetallic compound may increase and sufficient forgeability may not be obtained. The cerium can be added to the magnesium alloy as a misch metal that is a mixture of rare earth metals.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

In the forging method of this embodiment, first, aluminum in the range of 6 to 10% by weight, zinc in the range of 0.4 to 2% by weight, and in the range of 0.05 to 0.3% by weight with respect to the total amount. A cast body which is a magnesium alloy composed of manganese, calcium in the range of 0.4 to 1.5% by weight, the remainder magnesium and unavoidable impurities is cast.

The front heard Zotai are based on the total amount, preferably contains 0.01 to 0.3 wt% of the antimony or from 0.006 to 0.2 wt% of the beryllium. Before hearing Zotai includes antimony of the range may include both the beryllium of the range may include only one of.

Furthermore, before hearing Zotai it is based on the total amount, preferably containing cerium in the range of 1.2 wt% or less.

The forging method of this embodiment, then, before the hearing Zotai cooled at a rate in the range of 12 to 40 ° C. / sec to obtain a first forging the magnesium alloy material.

Next, the cooling rate of the cast body in the first magnesium alloy material for forging obtained as described above, the dendrite arm dendrite arm interval (DAS), the crystallized particle diameter, and the crystal grains The relationship with the diameter is shown in FIG. From Figure 1, by a pre-listening Zotai cooled at 12 ° C. / sec or faster, 10 [mu] m with a particle size of the crystallized substances of the dendritic dendrite arm spacing of the crystal can be 15μm or less Obviously, it can be: In addition, it is clear that there is a correlation between the dendrite arm spacing of the dendrites and the particle size of the crystallized product.

On the other hand, from FIG. 1, be cooled before heard Zotai a 12 ° C. / sec or faster, it is clear that it is not possible to make the crystal grain size of the obtained forging the magnesium alloy material and 150μm or less .

  Here, the dendritic arm spacing of the dendritic crystal is obtained by taking a photograph by enlarging the sample 100 to 200 times with a metal microscope after micropolishing the sample, and determining the interval between the secondary branches of the dendritic crystal from the photographed image. Measured and calculated by multiplying the measured value by the magnification of the microscope. The crystal grain size of the crystallized product and the crystal grain size of the magnesium alloy material for forging are, for example, an arbitrary straight line drawn on a microphotograph image of 200 to 400 times, and the particle size of the crystallized product applied to the straight line or The crystal grain size of the forging magnesium alloy material was measured on a scale, and the actual value was multiplied by the magnification of the image.

  Therefore, in the forging method of the present embodiment, next, the first forging magnesium alloy material is preliminarily processed at a temperature in the range of 250 to 450 ° C. and a processing rate in the range of 20 to 70%. Thus, a second magnesium alloy material for forging is obtained.

  Next, as the first forging magnesium alloy material, three kinds of magnesium alloy materials having initial crystal grain sizes of 265 μm, 245 μm, and 150 μm, respectively, are prepared. Processing was performed while changing the processing rate in a range of ˜80%, and the crystal grain size of the obtained magnesium alloy material for forging was measured. The results are shown in FIG. From FIG. 2, it is clear that the crystal grain size can be reduced to 10 μm or less by setting the processing rate to 20% or more regardless of the initial crystal grain size.

  In the forging method of the present embodiment, a forged product as a final product is obtained by forging the second magnesium alloy material for forging.

  Next, the relationship between the crystal grain size, the tensile strength, and the elongation in the second magnesium alloy material for forging is shown in FIG. FIG. 3 clearly shows that the second magnesium alloy material for forging and the crystal grain size are refined to 10 μm or less, thereby providing excellent tensile strength and elongation.

  Since the second forging magnesium alloy material has excellent elongation as described above, in the forging method of this embodiment, by forging the second forging magnesium alloy material, The mold can be filled with high accuracy without causing cracks. Therefore, in the forging method of the present embodiment, a member having a complicated shape for automobiles and railway vehicles such as automobile pistons can be easily manufactured with fewer steps than in the past.

  Further, since the second forging magnesium alloy material has an excellent tensile strength as described above, by subjecting the second forging magnesium alloy material to forging, the piston for automobiles and the like A member requiring high strength for automobiles and railway vehicles can be manufactured.

  Next, examples and comparative examples of the forging method of the present invention are shown.

First, a first forging of samples 1 to 14 was performed by casting a casting that is a magnesium alloy having the composition shown in Table 1 and solidifying the obtained casting in one direction at a cooling rate of 15 ° C./second. Magnesium alloy material was manufactured.

  Next, of the first magnesium alloy material for forging, samples 1 to 8 are pre-processed at a processing rate in the range of 21 to 26% at a temperature of 400 ° C. as an example of the forging method of the present invention. The second forging magnesium alloy material was formed, and the crystal grain size of the second forging magnesium alloy material was measured. The results are shown in Table 1.

  On the other hand, among the first magnesium alloy material for forging, samples 9, 11 to 14 are used as a comparative example of the forging method of the present invention as a second magnesium alloy material for forging without any preliminary processing. The crystal grain size of the second magnesium alloy material for forging was measured. For sample 10, as a comparative example of the forging method of the present invention, preliminary processing is performed at a processing rate of 10% at a temperature of 400 ° C. to form a second magnesium alloy material for forging. The crystal grain size of the magnesium alloy material for forging was measured. The results are shown in Table 1.

表１から、第１の鍛造用マグネシウム素材に４００℃の温度下に、２１〜２６％の範囲の加工率で予備加工を施して、第２の鍛造用マグネシウム合金素材を形成した試料１〜８（実施例）においては、該第２の鍛造用マグネシウム合金素材の結晶粒径を４〜５μｍの範囲に微細化することができることが明らかである。従って、試料１〜８の第２の鍛造用マグネシウム合金素材（実施例）は、さらに鍛造加工を施すことにより、割れを発生することなく、高精度に型充満することができ、優れた機械的強度を備える鍛造品を得ることができることが明らかである。

From Table 1, Samples 1 to 8 in which the first magnesium alloy material for forging was formed by preliminarily processing the first magnesium material for forging at a processing rate in the range of 21 to 26% at a temperature of 400 ° C. In (Example), it is clear that the crystal grain size of the second magnesium alloy material for forging can be refined in the range of 4 to 5 μm. Therefore, the second magnesium alloy material for forging (Examples) of Samples 1 to 8 can be filled with high precision without cracking by further forging, and has excellent mechanical properties. It is clear that a forged product with strength can be obtained.

  On the other hand, from Table 1, the first forging magnesium material was not preliminarily processed at a temperature of 400 ° C. or preliminarily processed at a processing rate of 10%, and the second forging magnesium alloy material and In the samples 9 to 14 (comparative examples), the crystal grain size of the second magnesium alloy material for forging is in the range of 100 to 130 μm, and it is clear that the crystal grain size cannot be reduced. .

The graph which shows the relationship between the cooling rate of a casting, the dendrite arm space | interval (DAS) of a dendrite, the particle diameter of a crystallization thing, and a crystal grain diameter. The graph which shows the relationship between the processing rate in a magnesium alloy material for forging, and a crystal grain size. The graph shown in the relationship between the crystal grain diameter, tensile strength, and elongation in the magnesium alloy material for forging.

Explanation of symbols

  None.

Claims (3)

Aluminum in the range of 6-10 wt%, zinc in the range of 0.4-2 wt%, manganese in the range of 0.05-0.3 wt%, and 0.4-1.5 wt. cooling the% by weight of calcium in the range of the balance magnesium and casting a magnesium alloy consisting of unavoidable impurities at a rate in the range of 12 to 40 ° C. / sec, dendrite arm spacing of dendritic JoAkira 0.5 A step of forming a first forging magnesium alloy material having a particle diameter of 1 to 10 μm in a range of ˜15 μm and a crystallized product made of Mg—Al intermetallic compound;
The first forging magnesium alloy material obtained in the above step is preliminarily processed at a temperature in the range of 250 to 450 ° C. and a processing rate in the range of 20 to 70%. Forming the material;
And a second forging process for forging the magnesium alloy material for forging. The forging method of a magnesium alloy according to claim 1, wherein the cast body which is the magnesium alloy is 0.01 to 0.3% by weight of antimony or 0.006 to 0.2% by weight based on the total amount. A forging method of a magnesium alloy characterized by containing the beryllium. 3. The forging method of a magnesium alloy according to claim 1, wherein the cast body which is the magnesium alloy contains cerium in a range of more than 0 wt% and 1.2 wt% or less with respect to the total amount. To forge magnesium alloy.

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