JP3525486B2 - Magnesium alloy casting material for plastic working, magnesium alloy member using the same, and methods for producing them - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesium alloy casting material for plastic working, a magnesium alloy member using the same, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Magnesium alloy has a specific gravity of about 1.8.
It is 2/3 of aluminum alloy and is promising as an alternative material for reducing the weight of various members. However, since the mainstream of parts production is die casting, most of the applied parts are parts with low strength such as cases and covers. Therefore, if materials and manufacturing methods applicable to high-strength parts at low cost are established, their industrial value will be great.

Magnesium alloys currently used generally have poor forgeability, and ZK60 alloy having relatively good formability is used for the forging. However, this alloy is expensive because it needs to contain a large amount of zirconium as an alloying element, and has the disadvantage of poor corrosion resistance.

On the other hand, A is used as a forging material having good corrosion resistance.
Materials that have undergone primary plastic working such as extrusion after casting of Z80 alloy are provided. These have already undergone heavy working and have relatively good forgeability due to the refinement of crystal grains, but they are also expensive, and mechanical properties after forging are not necessarily required for alloys of strength members such as wheels. It cannot be said that it is suitable. Moreover, a member such as a wheel requires an extruded material for a large forged part, which is difficult in reality.

In order to apply it to a wheel or the like, impact value is important in addition to tensile strength, elongation, etc. If this value is low, it must be thick to secure strength equivalent to that of an aluminum forged member. It is in the situation that the light weight effect is reduced. Therefore, in order to apply a magnesium alloy to a large strength member such as a wheel, it is necessary to provide a large-diameter continuous forged material obtained by forging an alloy having excellent mechanical properties after forging into a fine structure. Therefore, a method of refining the average crystal grain size of a magnesium alloy casting material (cast billet) is proposed. As one of the methods, JP-A-63-28
No. 2232, in particular, a method of continuously casting a molten magnesium alloy of AZ31 and AZ80 at a solidification rate of 25 ° C./sec or more and a magnesium alloy ingot of 220 to
A method of performing plastic working at a working rate of 25% or more under heat of 450 ° C has been proposed.

[0006]

However, when the molten metal is continuously cast at a solidification rate of 25 ° C./sec or more, the temperature gradient between the outer peripheral portion of the billet and the central portion tends to be large, and the predetermined purpose is stable. The billet diameter that can be realized is 5
It is extremely small to produce a large forged part of -100 mm, and a method of refining the average grain size of a magnesium alloy casting material (cast billet) at a normal cooling rate is desired.
Therefore, the present invention is a magnesium alloy casting material capable of producing a wheel, which is a large-sized forged component, with desired physical properties without using the ZK60 alloy casting material and the AZ80 alloy extrusion material, and the casting thereof. A primary object is to provide a method.

Further, the present invention uses such a casting material,
A second object of the present invention is to provide a large-sized forged part such as a wheel having physical properties comparable to those of an aluminum melt forged member and a method for manufacturing the same.

[0008]

According to the present invention, when a magnesium alloy is cast at a normal cooling rate, Al is used to control the average grain size of a casting material (cast billet).
When the content plays an important role and an alloy composition that is almost intermediate between the conventional AZ61 alloy and AZ80 alloy is selected and cast, it has excellent forgeability as it is, and it is forged and formed to have mechanical properties as a strength member and It was completed by discovering that it is possible to manufacture forged parts with excellent corrosion resistance. It contains the following alloying elements and the balance is Mg and unavoidable.
The magnesium alloy casting material for plastic working is made of a pure magnesium alloy and has an average crystal grain size of 200 μm or less and is excellent in forgeability. Al: 6.2 to 7.6 mass% Mn: 0.15 to 0.5 mass% Zn: 0.4 to 0.8 mass% Sr: 0.02 to 0.5 mass%

[0009]

According to the present invention, at least Al, Mn, Z
As shown in FIG. 22, the magnesium alloy casting material for plastic working containing n and Sr has an average crystal grain size of 200 when subjected to ordinary continuous casting at a cooling rate of about 7 ° C./sec.
It becomes μm or less, and a magnesium alloy casting material for plastic working which gives a limit upsetting rate of 60% or more to the casting material and can be directly subjected to forging (see FIG. 1). In particular, a casting material having an average crystal grain size of 80 μm or less is excellent in high speed forgeability (FIGS. 9 and 10).
reference). Therefore, Sr or CaNCN is used as a refiner.
When the cooling rate is about 3 ° C./sec, the average crystal grain size becomes 200 μm or less, and the cooling rate is 7 ° C./sec.
The average crystal grain size becomes 80 μm or less depending on the degree. Therefore, the present invention is a method for producing a magnesium alloy casting material for plastic working in which the average crystal grain size of the metal structure is 200 μm or less, and at least Al is 6.2 as an alloy element.
~ 7.6mass%, Mn 0.15-0.5mass
%, Zn of 0.4 to 0.8 mass% and a refiner are added to the magnesium alloy to perform casting at a cooling rate of 3 to 15 ° C./sec. It also seeks to provide a method. The refiner is either Sr or CaNCN, Sr is 0.02-0.5 mass%, CaNCN
Is effective for miniaturization by adding 0.3 to 0.7 mass%.

Next, the limitation of the composition of the alloy element will be described. When magnesium alloys are applied to strength parts, Al-Zn-Mn alloys are superior in consideration of corrosion resistance. However, there is a close relationship between the crystal grain size of this alloy and the strength characteristics (tensile strength, elongation, corrosion resistance, impact characteristics) and the amount of Al added, and it is necessary to select an appropriate value.
Therefore, if the amount of Al added is reduced, the elongation and impact value improve, but the corrosion resistance tends to decrease. On the other hand, a new finding was obtained that as the crystal grain size was made finer, the corrosion resistance was improved by the artificial aging treatment after the solution treatment (for example, T6 treatment). Therefore, it was decided to improve the strength and corrosion resistance by selecting an appropriate particle size. Since the present invention needs to have strength characteristics comparable to those of Al alloys (for example, JIS standard AC4C molten metal forgings and JIS standard 6061 forgings), AC4C molten metal forging in the range of 6-9 wt% aluminum addition The tensile strength and elongation of the material were compared. The result is shown in FIG. From FIG. 3, it was found that in terms of tensile strength, Al 6 to 8.5 wt% was good, that is, tensile strength equal to or higher than that of the AC4C molten metal forging was obtained. However, in terms of growth, AC4C
Al 6.2 wt% to obtain the above characteristics
As described above, it has been found that the amount needs to be 8% by weight or less.
The comparison of the properties here takes into consideration the improvement properties of the tensile strength and the elongation at the upsetting ratio of 60%, which are usually required for forging. Therefore, from the relationship between tensile strength and elongation, it is understood that the amount of Al added is preferably 6.2% by weight or more and 8% by weight or less.

On the other hand, when the Charpy impact value was examined, as shown in FIG. 4, it was found that when the Al addition amount exceeds 7.6 wt%, the Charpy impact value sharply falls below the AC4C molten aluminum forging material. Therefore, it was found that it is desirable that the upper limit of the component range of aluminum is defined by the Charpy impact value and the lower limit is defined by the tensile properties.
Therefore, the amount of Al added is 6.2 wt% or more, 7.6 wt%
Below.

Next, regarding the alloying element Zn, this is an element which, like Al, gives strength characteristics to the magnesium alloy. Casting by continuous casting is the only way to obtain a large-diameter forged billet. In this case, the crystal grain size can be adjusted by the cooling rate and the refining agent.
It is difficult to make the thickness below 00 μm. The average crystal grain size of the large diameter continuous cast material is usually about 200 μm. When a cast material having a relatively large grain size is forged as described above, the amount of Zn added affects the formability. Zn is Mg
As a compound of AlZn, it crystallizes in the alloy and contributes to the improvement of the strength of the magnesium alloy as described above, but if it is too much, the formability deteriorates and it becomes unfavorable for forging. Therefore, in order to obtain the required strength, the lower limit is set to 0.4% by weight or more, and the upper limit is set to 0.8% by weight or less in consideration of forgeability. That is, the Zn content in the chemical composition table of Table 3 was 0.
Considering the limit upsetting rate due to the change of the Zn amount by changing the range of 25 to 1.20% by weight, as shown in FIG. 11, when Zn exceeds 0.8% by weight, the limiting upsetting rate is 60%.
This is because it will be divided by%.

The alloying element Mn is as follows.
Mn mainly has an action of suppressing Fe content and is effective for the corrosion resistant structure of the material, but if it is less than 0.15% by weight, it has no effect, and if it exceeds 0.5% by weight, the forgeability is affected. is there. As other elements, Sr and CaNCN added as a refining agent remain, but especially Sr remains around 80% regardless of the amount of addition, as shown in FIG. When the residual amount is 0.02% by weight or more, the refinement effect of the cast structure of the magnesium alloy appears, but when it is 0.5% by weight or more, it forms a compound with Mg, Al, Zn, etc., which deteriorates the forgeability and forging. This is because it has an adverse effect on the later mechanical properties.

When the average crystal grain size of the material structure is 100 μm or less after plastic working of the casting material composed of the above alloy components, a magnesium alloy member having tensile properties of elongation 10% or more and tensile strength 300 MPa or more is obtained. Will be able to provide. In particular, when the average crystal grain size of the material structure is 50 μm or less, the Charpy impact value (50 J / cm ² ) is equal to or higher than that of the AC4C molten metal forging material.

In producing the forged member, a magnesium alloy material composed of the above alloy element components is cast so that the average crystal grain size is 200 μm or less, and the casting material is subjected to plastic working to obtain an average crystal grain size of 100 μm. It is preferable to carry out artificial aging treatment, especially T6 heat treatment together with solution treatment after forming the final product shape without having the following structure. As a result, the average crystal grain size of the metal structure is 50 μm.
When it is below, it will have corrosion resistance of AZ91D or more. When the plastic working is performed at 350 ° C. or higher, the same effect can be obtained by subjecting the final product to artificial aging treatment only.

The above casting is preferably carried out from a semi-molten state. This is because the mechanical properties after forging can be improved.

When performing forging as plastic working, the strain rate exceeding the critical upsetting ratio of 60% needs to be relatively low in the vicinity of the average crystal grain size of 200 μm, so the first time is low and the second time is It is preferable that the subsequent steps be performed at a higher speed than the first step.

[0018]

EXAMPLE Example 1 (Relationship between grain size and forgeability) A forging material (H42 mm, φ28 mm) was cast using a Mg alloy having the chemical composition (wt%) shown in Table 1 below, and FIG.
Upsetting (strain rate: low speed, about 10% / sec) was performed at the material temperature of 350 ° C by the test device shown in Fig. 3, and the crystal grain size and the limit upsetting rate (= original height H-height at the time of crack occurrence) H ′ / H × 100) was obtained.
The results are shown in Fig. 1. From this, it was found that the grain size needs to be 200 μm or less in order to obtain the forge formability that exceeds the critical upsetting ratio of 60% required for forging.

[Table 1]

Example 2 (Relationship between strain rate and formability) Forging material (H42 mm, φ28 mm) of Mg alloy having chemical composition (% by weight) shown in Table 2 below has an average crystal grain size of 200.
It was cast to a diameter of μm and the material temperature was 25
0 strain of 60% of the upsetting at 400 ° C. from the speed: slow, carried out at 10 ^0% / sec and a high-speed 10 ^3% / sec, was determined the change in the critical upsetting ratio. The results are shown in Fig. 8. From this result, the forgeability of the Mg alloy is affected by the strain rate (related to the working rate), and the average grain size is 20
It can be seen that even when the thickness is 0 μm or less, the formability is poor at high speeds and the manufacturing conditions such as forging temperature are limited.

Therefore, looking at the relationship between the strain rate and the formability (limit upsetting ratio) in Samples A, B and C having average crystal grain sizes of 125 μm, 200 μm and 250 μm at a forging temperature of 350 ° C., as shown in FIG. Is. From these results, it is necessary to slow down the strain rate in the vicinity of the average crystal grain size of 200 μm, and if it exceeds 200 μm, it is impossible to obtain a predetermined formability even at a low speed. Moldability of (upper limit upsetting ratio of 60% or more) can be obtained. Therefore, it is necessary to set the thickness to 200 μm when manufacturing a large forged part using a continuous cast material.

[Table 2]

Example 3 (Relationship between Crystal Grain Size and Formability at High Strain Rate) Mg alloys having the chemical composition (wt%) shown in Table 2 above were used as a forging material (H42 mm, φ28 mm) in average crystal grain size. Casting to 50 to 250 μm, and upsetting at a material temperature of 350 ° C. using a test apparatus shown in FIG.
It carried out at ³ % / sec, and the relationship between the average grain size and the limit upsetting rate was determined. The results are shown in Fig. 10. from this result,
It was found that the forging formability of the Mg alloy exceeds the critical upsetting ratio of 60% when the average crystal grain size is 80 μm or less at a high strain rate. This grain size is 20 as a casting material
When a material of 0 μm is used, it can be achieved by one forging (processing rate of about 50%).

Example 4 (Relationship between Zn Addition Amount and Formability) A forging material (H42 mm, φ28 mm) was made from a Mg alloy having the chemical composition (% by weight) shown in Table 3 below to have an average crystal grain size of 20.
It is cast to 0 μm and the material temperature is 3 by the test equipment shown in FIG.
Upsetting at 50 ° C Strain rate: 103% / s
ec was performed to determine the relationship between the Zn addition amount and the limit upsetting rate. The results are shown in Fig. 11. From these results, it is understood that the Mg alloy cannot secure the critical upsetting ratio of 60% when it exceeds 0.8 mass%, and therefore it is necessary to suppress it to 0.8 mass% or less.

[Table 3]

Example 5 A Mg alloy having the chemical composition (% by weight) shown in Table 2 above and a conventional AZ80 alloy shown in Table 4 below were used as a forging material (H42m).
m, φ28 mm) with an average crystal grain size of 200 μm,
Material temperature of 250 ° C and 35
Strain rate of upsetting at 0 ° C: 48 mm / se
Then, the relationship between strain and deformation resistance was obtained. The results are shown in Fig. 13. From these results, the Mg alloy of the present invention is
It can be seen that the forging load is lower and the forgeability is superior to the Z80 alloy.

[Table 4]

Example 6 (Relationship Between Al Addition Amount and Mechanical Properties) Forging material of Mg alloy A shown in Table 1 above was subjected to upsetting at a material temperature of 300 ° C. by a test apparatus shown in FIG. 2 (strain rate: Low speed, 10% / sec), 60
After processing at a upsetting rate of%, T6 treatment (400 ° C. × 15 hours air cooling, then 175 ° C. × 16 hours air cooling) was performed, and the relationship between the Al addition amount and changes in tensile strength and elongation before and after upsetting was determined. The results are shown in Fig. 3. From this, it was found that from 6.2% by weight to 8.0% by weight of Al, the physical properties equal to or higher than those of the AC4C molten metal forging material can be obtained. It should be noted that upsetting up to 60% was impossible with an Al addition of 9.0% by weight.

Example 7 (Relationship between Al Addition Amount and Charpy Impact Value) Upsetting of Mg alloy forging materials shown in Table 1 above at a material temperature of 300 ° C. by a test apparatus shown in FIG. 2 (strain rate: low speed) 10% / sec), and after processing at an upsetting rate of 60%, perform T6 treatment (400 ° C. × 15 hours air cooling, then 175 ° C. × 16 hours air cooling), and add Al to the Mg alloy after T6 treatment. The relationship between the dose and the Charpy impact property was determined and was as shown in FIG. The average crystal grain size at this time is about 50 μm, but it is understood that the amount of Al added must be 7.6% by weight or less in order to have a Charpy impact value of 50 J / cm ² which is equal to or higher than that of the AC4C molten metal forging material. From the above results, it can be seen that the highest tensile strength, elongation, and Charpy impact value can be obtained at 7.0% by weight of Al.

Example 8 (Relationship between crystal grain size and mechanical properties) Mg alloys having the chemical composition (% by weight) shown in Table 5 below were cast into a forging material (H42 mm, φ28 mm) and tested as shown in FIG. 60% of upsetting the stock temperature 350 ° C. the apparatus (strain rate: slow, 10 ^0% / about sec) charity, after performing the same T6 treatment as in example 1, the fatigue test Ono-type rotating bending Then, the rotational bending fatigue property was obtained. The result is shown in FIG. This is superior to the AC4C molten metal forging.

FIG. 6 shows the relationship between the average crystal grain size after T6 treatment, tensile strength (MPa), yield strength and elongation (%). From this, it can be seen that in order to provide the same or higher mechanical properties as the AC4C molten metal forging material, the average crystal grain size needs to be 100 μm or less, especially in consideration of the inflection point of the proof stress.

[Table 5]

Example 9 (Relationship between grain size and Charpy impact value) A forging material (H42 mm, φ28 mm) was cast from a Mg alloy having the chemical composition (% by weight) shown in Table 2 above, and the test shown in FIG. 60% upsetting of the material temperature 350 ° C. the apparatus (strain rate: slow, about 10 ^0% / sec)
And T6 treatment (after air cooling at 400 ° C for 10 hours, 175
Average crystal grain size (μm)
The relationship between the Charpy impact value (J / cm ² ) and the Charpy impact value is shown in FIG. 7. From this, it is understood that the crystal grain size needs to be 50 μm or less in order to obtain an impact value higher than that of the AC4C molten metal forging material.

Example 10 (Relationship between Crystal Grain Size and Corrosion Resistance) From the Al addition amount upper limit Mg alloy shown in Table 2 above and the Al addition amount lower limit Mg alloy shown in Table 6 below, a forging material (H42
mm, φ28 mm), subjected to 60% upsetting at a material temperature of 350 ° C. (strain rate: low speed, about 100% / sec) by the test device shown in FIG. 2, and T6 treatment (400 ° C. × 10 hours air cooling). Then, after air cooling at 175 ° C. for 16 hours), the average crystal grain size (μm) and corrosion resistance (mill
s / year) is as shown in FIG. From here, if the crystal grain size is made finer, it becomes 200μ
It can be seen from the vicinity of m that characteristics comparable to those of the AZ91D alloy F (non-heat treated) material, which has the best corrosion resistance among magnesium alloys, can be obtained.

[Table 6] Here, the corrosion test evaluated the corrosion resistance by the salt spray test.
The test conditions are a temperature of 35 ° C., a test time of 240 hours, a salt water concentration of 5 mass%, and the test piece shape has an emery surface.
The amount of corrosion was determined by the following formula with 600 × 50 × 90 × 5 mm.

[Equation 1]

Example 11 (Relationship Between Casting Cooling Rate, Plastic Working Rate and Crystal Grain Size) From the Mg alloys having the chemical components shown in Table 5 above, a forging material (H
42 mm, φ28 mm) when casting
When 0.5% by weight of aNCN was added and the relationship between the cooling rate and the average crystal grain size of the casting material was determined, it was as shown in FIG. Next, using the test device shown in FIG.
℃ upsetting in the processing (strain rate: slow, 10 ^0% /
(about sec.), and the relationship between the plastic working rate and the change in crystal grain size was determined. The results are shown in Fig. 15. It can be seen that the larger the plastic working ratio, the smaller the crystal grain size of the Mg alloy of the present invention.

Example 12 (Production of Forged Wheel) A columnar billet was produced by continuous casting using the Mg alloy having the chemical composition shown in Table 2 above, and this was subjected to rough forging as shown in FIG. Next, it is subjected to blocker forging, and then finisher forging to forge the wheel material,
Finally, spinning processing is applied and T6 treatment (400 ° C x 1
After air-cooling for 0 hours, air-cool for 16 hours x 175 ° C) to obtain the final product. Looking at the grain size distribution, it is as shown in FIG. 17, and fine grain sizes are distributed in the surface region. On the other hand, it is also possible to form the final product shape only by forging without performing the above spinning process. At this time, when a relatively large grain size is distributed in the surface region as shown in FIG. 19, it is preferable to subject the forging billet to plastic working such as roller working in advance as shown in FIG. Further, instead of the roller processing, the grain size of the surface region may be made finer by increasing the cooling rate in the forging step.

Embodiment 13 (Semi-melt casting and forging method) First, FIGS. 20 (A) to 20 (G) show each method of manufacturing a magnesium alloy automobile part (wheel) according to the embodiment of the present invention by the casting / forging method. The process is shown. First, a magnesium alloy material 2 having a composition of the above (Table 5), which is a light alloy material, is placed in a crucible 1 and heated from the surroundings by a heater to be in a semi-molten state, and a stirring rod 4 having a stirring plate 3 is placed on a motor. The mixture is agitated under the production conditions shown in the following (Table 7) by rotating and driving by No. 5.

[Table 7] In the heating and stirring of the magnesium alloy material 2 in the crucible 1 in this step, first, in the initial stage, the material 2 is heated to a temperature at which the material 2 is in an intermediate state between a solid phase (α phase) and a liquid phase. Then, in the same state, the stirring plate 3 is forcibly stirred under the above conditions (Table 7) (A in FIG. 20). As a result, the solid phase of the resinous crystals (dendrites) is crushed and becomes spherical. The solid fraction at this time is preferably 60% or less. Next, the solid phase ratio is 60% as described above.
The alloy material 2 in the semi-molten state in the crucible 1 as described below is placed in a sleeve 8 for die casting equipped with a plunger 9.
Inject from 0 (B) to 0 (B) (Fig. 2)
0 (B), (C)). Then, the sleeve 8 is fitted into the injection port of the die-casting die 20, and the plunger 9 is operated to inject the semi-molten alloy material 2 into the die-casting die 20 for casting (blank production). ) (Fig. 2
0 (D)). The alloy material 2 as an intermediate molded product, which has completed the semi-melt casting as described above, is taken out from the die-casting mold 20 ((E) in FIG. 20). The alloy material 2 which is an intermediate molded product formed by casting as described above is set as a casting material on the lower die 11 for forging, and forged with the upper die 10.
By performing (once), the final molding is performed and the mechanical strength is improved ((F) in FIG. 20). Then, for example, 400 ℃
Solution treatment by air-cooling for 4 hours at 180 ° C. and artificial aging treatment by air-cooling at 180 ° C. for 15 hours. After the T6 heat treatment, the jigs 12 and 13 are supported to perform detailed spin forge (spinning), and the final molded product 2
Is obtained ((G) in FIG. 20).

Example 14 (Effect of addition of refiner) A magnesium alloy having the composition shown in Table 8 below was prepared and melted, and the temperature was raised to about 780 ° C. Sample 1 was added with no refiner. In No. 2, Sr-Al alloy was added so that Sr remained 0.02 mass%, in Sample 3, 0.5 mass% of CaNCN was added and stirred, and the cooling rate was changed by the continuous casting method, and the metal structure after casting was changed. The relationship with the average crystal grain size of was investigated.

[Table 8] The results are shown in Fig. 22. In the case where no refining agent is added, the average crystal grain size of the metal structure becomes 200 μm or less by ordinary continuous casting at a cooling rate of about 7 ° C./sec. On the other hand, when Sr or CaNCN is added as a refining agent, the cooling rate becomes 3
The average crystal grain size is about 200 μm or less from about C / sec, and the average crystal grain size is about 80 μm or less from about 7 ° C./sec.

Example 15 (Residual Sr) Under the conditions shown in Table 9 below, Al: 6.9 mass% and Zn:
0.7 mass%, Mn: 0.38 mass%, balance M
When the casting material of g was melted and the temperature was raised to about 780 ° C., the Sr-10% Al alloy wrapped in aluminum foil was put into the molten metal, and after stirring, the temperature was lowered while cooling and the molten metal temperature was about 70.
When it reached 0 ° C, it was cast in a mold preheated to 70 to 85 ° C, and the Sr content in the cast material was investigated. The result is shown in FIG.
Shown in. The added Sr remains in the alloy and maintains the effect of refining even when it is redissolved. Further, a part of the added Sr forms an alloy with another alloy element such as Mg or Al and crystallizes.

[Table 9]

[0035]

As is apparent from the above description, according to the present invention, as shown in FIG. 21, a large-sized forged product is given the same tensile strength and elongation as the aluminum A6061 forged material, and the conventional Mg It has tensile strength and elongation exceeding that of alloy AZ80. Moreover, since such a Mg alloy material can be supplied by a continuous casting method, a Mg alloy suitable for application to large forged products such as automobile wheels can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a crystal grain size of a Mg alloy casting material and a critical upsetting rate.

FIG. 2 is an explanatory view of an upsetting test of a casting material.

FIG. 3 is a graph showing the relationship between the amount of Al added and the tensile strength and elongation in a forged product of the alloy of the present invention.

FIG. 4 is a graph showing the relationship between the amount of Al added and the Charpy impact value in a forged product of the alloy of the present invention.

FIG. 5 is a graph showing rotary bending fatigue characteristics of a forged product of the alloy of the present invention.

FIG. 6 is a graph showing the relationship between the average crystal grain size and tensile strength, proof stress, and elongation in a forged product of the alloy of the present invention.

FIG. 7 is a graph showing the relationship between the average grain size and the Charpy impact value in a forged product of the alloy of the present invention.

FIG. 8 is a graph showing the relationship between the material heating temperature and the critical upsetting rate due to low speed and high strain rate processing at an average crystal grain size of 200 μm of the casting material of the present invention.

FIG. 9: Average crystal grain size 125, 20 of the casting material of the present invention
It is a graph which shows the relationship between the strain rate at 0 and 250 μm, and the critical upsetting rate.

FIG. 10 is a graph showing the relationship between crystal grain size and livelihood under high strain rate.

FIG. 11 is a graph showing the relationship between the Zn content and the critical upsetting ratio of the casting material of the present invention.

FIG. 12 is a graph showing the relationship between the crystal grain size and the corrosion resistance of a forged Mg alloy product.

FIG. 13 is a graph showing the relationship between strain and deformation resistance of the casting material of the present invention and the conventional AZ80 alloy casting material.

FIG. 14 is a graph showing the relationship between the cooling rate and the crystal grain size during casting of the casting material of the present invention.

FIG. 15 is a graph showing the relationship between the plastic working rate and the crystal grain size of the casting material of the present invention.

FIG. 16 is a process drawing showing a process for forming a wheel from a continuously cast material of the alloy of the present invention.

FIG. 17 is a grain size distribution chart of the Mg alloy wheel manufactured in FIG. 16.

FIG. 18 is a schematic view showing an example of the case where the casting material of the present invention is plastically processed in advance.

FIG. 19 is a crystal grain size distribution chart of a wheel formed using the alloy of the present invention by a conventional method.

FIG. 20 is a process diagram in the case of manufacturing a wheel by a semi-melt forging method using the alloy of the present invention.

FIG. 21 is a graph showing a comparison between tensile strength and elongation of a forged product of the present invention and a conventional product.

FIG. 22 is a graph showing the relationship between cooling rate and average crystal grain size, which shows the effect of adding a refining agent to the cast material according to the present invention.

FIG. 23 is a graph showing the Sr addition amount of the cast material and the content in the cast material according to the present invention.

[Explanation of symbols]

1 ... crucible 2 ... The alloy material of the present invention 3 ... Stirrer plate 4 ... Stir bar 20 ... Die cast mold

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Yamamoto 3-3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) References JP-A-63-282232 (JP, A) JP-A-6 -279889 (JP, A) JP-A-7-109538 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 1/00-49/14 C22F 1/00-3/02

Claims (18)

(57) [Claims] 1. A magnesium alloy casting material for plastic working, which is made of a magnesium alloy containing the following alloy elements, the balance being Mg and inevitable impurities, and having an average crystal grain size of a metal structure of 200 μm or less and excellent in forgeability. Al: 6.2 to 7.6 mass% Mn: 0.15 to 0.5 mass% Zn: 0.4 to 0.8 mass% Sr: 0.02 to 0.5 mass% 2. The magnesium alloy casting material for plastic working according to claim 1, wherein the average crystal grain size is 80 μm or less. 3. The magnesium alloy casting material for plastic working according to claim 1, wherein the Sr is contained as an intermetallic compound. 4. A casting material containing the following alloy elements, the balance of which is Mg and inevitable impurities, is plastically worked. The average crystal grain size of the metal structure is 100 μm or less, the elongation is 10% or more, and the tensile strength is 300 MPa or more. A magnesium alloy member having the tensile properties of. Al: 6.2 to 7.6 mass% Mn: 0.15 to 0.5 mass% Zn: 0.4 to 0.8 mass% Sr: 0.02 to 0.5 mass% 5. The average crystal grain size of the metal structure is 50 μm.
The magnesium alloy member according to claim 4, which is as follows. 6. The magnesium alloy member according to claim 5, wherein the average grain size is 50 μm or less after being subjected to solution treatment and artificial aging treatment after plastic working. 7. The magnesium alloy member according to claim 5 or 6, which has a Charpy impact value of 50 J / cm ² or more . 8. A method for producing a magnesium alloy casting material for plastic working, wherein the average crystal grain size of the metal structure is 200 μm or less, wherein the magnesium alloy contains the following alloy elements and the balance is Mg and inevitable impurities, Sr as a refiner is 0.0
A method for producing a magnesium alloy casting material for plastic working, comprising adding 2 to 0.5 mass% and casting at a cooling rate of 3 to 15 ° C./sec. Al: 6.2-7.6 mass% Mn: 0.15-0.5 mass% Zn: 0.4-0.8 mass% 9. A method for producing a magnesium alloy casting material for plastic working, wherein the average crystal grain size of the metal structure is 200 μm or less, wherein the magnesium alloy contains the following alloy elements and the balance is Mg and inevitable impurities: Add 0.3-0.7 mass% of CaNCN as a refiner and add 3-15 ° C / sec
A method for producing a magnesium alloy casting material for plastic working, which comprises casting at a cooling rate of. Al: 6.2-7.6 mass% Mn: 0.15-0.5 mass% Zn: 0.4-0.8 mass% 10. The method for producing a plastically worked molten magnesium alloy casting material according to claim 8 or 9, wherein a continuous casting method is used for the casting. 11. The method for producing a magnesium alloy casting material for plastic working according to claim 8 or 9, wherein the casting is performed in a semi-molten state. 12. A method for producing a magnesium alloy member, wherein the final product has an average crystal grain size of 100 μm or less, wherein the average metallographic structure contains the following alloy elements and the balance is Mg and inevitable impurities. A method for producing a magnesium alloy member, which comprises subjecting a magnesium alloy casting material having a crystal grain size of 200 μm or less to plastic working. Al: 6.2 to 7.6 mass% Mn: 0.15 to 0.5 mass% Zn: 0.4 to 0.8 mass% Sr: 0.02 to 0.5 mass% 13. A method for producing a magnesium alloy member, wherein the final product has a metal structure having an average crystal grain size of 100 μm or less, which comprises the following alloy elements and compounds, and the balance is Mg and inevitable impurities. Average grain size of 200μm
A method for producing a magnesium alloy member, which comprises subjecting the following magnesium alloy casting material to plastic working. Al: 6.2-7.6 mass% Mn: 0.15-0.5 mass% Zn: 0.4-0.8 mass% CaNCN: 0.3-0.7 mass% 14. The method for producing a magnesium alloy member according to claim 12, wherein the final product is further subjected to solution treatment and artificial aging treatment. 15. An average crystal grain size of a metal structure comprising the following alloy elements, the balance being Mg and unavoidable impurities, and having an average crystal grain size of 20:
A method for producing a magnesium alloy member, characterized by subjecting a magnesium alloy casting material of 0 μm or less to plastic working at 350 ° C. or more to form a final product shape having an average crystal grain size of 100 μm or less, and further subjecting it to artificial aging treatment. . Al: 6.2 to 7.6 mass% Mn: 0.15 to 0.5 mass% Zn: 0.4 to 0.8 mass% Sr: 0.02 to 0.5 mass% 16. A magnesium alloy casting material containing the following alloy elements and compounds, the balance of which consists of Mg and unavoidable impurities, and whose average crystal grain size of the metal structure is 200 μm or less, is subjected to plastic working at 350 ° C. or more. , The average grain size is 1
A method for producing a magnesium alloy member, which is characterized in that a final product shape of 00 μm or less is formed, and further artificial aging treatment is performed. Al: 6.2-7.6 mass% Mn: 0.15-0.5 mass% Zn: 0.4-0.8 mass% CaNCN: 0.3-0.7 mass% 17. The method for manufacturing a magnesium alloy member according to claim 12, wherein the plastic working is forging. 18. The method for producing a magnesium alloy member according to claim 17, wherein the forging process includes at least two forging steps, and the second and subsequent steps are performed at a higher speed than the first step.