JP3281004B2 - Manufacturing method of Mg alloy member - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a member such as a wheel of an automobile using an Mg (magnesium) alloy.

[0002]

2. Description of the Related Art In recent years, automobile wheels have been manufactured from an Al (aluminum) alloy for the purpose of improving design and reducing weight. JP-A-59-67102 describes that a disk portion of a wheel is made of an Mg alloy. In this case, there is no particular problem in the case where only the disk portion is made of the Mg alloy as in the above publication, but if the entire wheel including the rim portion is to be made of the Mg alloy, it is described in the above publication. Like
If this is manufactured only by casting, the rim part supporting the tire will have insufficient strength,
When the entire wheel is formed by forging, the yield is significantly reduced.

[0003] In order to cope with this, first, the entire wheel is formed by casting, and thereafter, the rim portion of the cast material is forged, thereby improving the yield and providing the rim portion with a required strength. Is considered to be given.

[0004]

However, when forging is performed on a part of the casting material as described above, the required forging can be performed because the Mg alloy is generally poorer in formability by forging than the Al alloy. There is no problem. In order to enhance the formability, it is only necessary to increase the heating temperature during forging. However, in this case, the oxidation of the product surface progresses, or the structure near the forged part is affected by heat, and thus the structure is reduced. Is coarsened, and the problem that the strength is reduced occurs.

Accordingly, an object of the present invention is to realize a method for obtaining good formability while suppressing the heating temperature as low as possible when forging a predetermined portion of a casting material made of Mg alloy. .

[0006]

In order to solve the above problems, the present invention uses the following method.

First, the invention according to claim 1 of the present application (hereinafter referred to as “the invention”)
) Referred to as the first invention, provide Reinforced quenching at a site forging is performed in upon, after the step of casting a Mg alloy material by solidifying by injecting molten metal into a mold fine
It is characterized in that a dense structure composed of fine crystal grains is formed, and the quenched portion of the casting material is heated and forged.

The invention according to claim 2 of the present application (hereinafter referred to as “the invention”)
In the first invention, the Mg alloy member as the final product is an automobile wheel, and the forged portion is a rim portion of the wheel. A quenching process is performed on the rim portion, and the rim portion of the cast material is forged by spinning.

[0009]

According to the method having the above-described structure, the portion subjected to the quenching treatment at the time of casting the material is promoted to solidify the molten metal, thereby suppressing the coarsening of the microstructure and the fine crystal grains. A dense structure consisting of For this reason, the formability of the forging performed in the subsequent step on the part is improved, and accordingly, the heating temperature during the forging can be suppressed to be low.

According to the second aspect of the present invention, the rim portion of the wheel supporting the tire is subjected to a quenching process at the time of casting, so that forging for enhancing the strength of the rim portion is performed well. Since the heating temperature at that time is suppressed low, oxidation of the product surface is suppressed,
In addition, the adverse effect of heat on the outer peripheral portion of the disk portion near the rim portion of the wheel is reduced, and a decrease in strength due to coarsening of the tissue at the portion is prevented.

[0011]

Embodiments of the present invention will be described below.

First, the structure of an Mg alloy member as a final product according to this embodiment will be described.
2. A wheel of an automobile as shown in FIG. 2, wherein the wheel 1 has a disk portion 2 having a circular hole 2a in the center and a plurality of bolt holes 2b.
And a columnar rim portion 3 that continuously supports the tire.

Next, a method of manufacturing the wheel 1 will be described. First, a mold (die or sand mold) as shown in FIG.
20 forms a cast material made of Mg alloy. The mold 20 has a cavity 21 having a shape substantially corresponding to the wheel 1 as a final product, a runner 22 for injecting a molten Mg alloy into the cavity 21, and an outer peripheral surface of a rim portion in the cavity 21. The chiller 23 made of, for example, iron is buried in a portion corresponding to. Then, the mold 20 is heated to 250 ° C. in a chamber 24 in an atmosphere of a flameproof gas (for example, SF ₆ + CO ₂ ), and the cavity 21 is heated.
750 ° C. is poured into the molten alloy to solidify it. Here, in this embodiment, AZ80 is used as the Mg alloy.

As a result, a casting material 11 made of an Mg alloy as shown in FIG. 4 is formed. In this case, the outer peripheral portion 13a of the rim portion 13 in the material 11 is
By being deprived of heat by the chiller 23 buried in the mold 20, the solidification is promoted more rapidly than other parts by being rapidly cooled, so that in other parts, the average crystal grain size of 300 to 400 μm is about 200 μm, A dense structure will be formed.

Next, after removing the burrs and the sprue portion 14 of the casting material 11, the outer peripheral portion 13a of the rim portion 13 is forged and formed. In this forming, a spinning machine as shown in FIG. 30 is used.

The machine 30 includes a mandrel 31 fitted inside the casting material 11, a main motor 33 for rotating the mandrel 31 via a main shaft 32,
And a pair of saddles 3 disposed on both sides of the mandrel 31 and provided with rollers 36, 36 respectively.
7, 37.

After the casting material 11 is heated to about 270 ° C., the casting material 11 is heated with the mandrel 31 and the tailstock 35.
In this state, the mandrel 31, the material 11 and the tailstock 35 are integrally rotated by the motor 33, and the pair of rollers 36
1 against the outer peripheral surface of the rim. In this case, the rollers 36, 36 are pressed against the outer peripheral surface of the rim portion, and the copying apparatus 38,
38 moves the material 11 in a predetermined path in the axial direction of the material 11.

As a result, the outer peripheral surface of the rim portion is forged into a predetermined shape, and the strength of the rim portion is increased by the forging process. Since the structure is rapidly cooled at the time of casting and the structure is densified from other parts, forging can be favorably performed. In addition, as the forging property is improved, the heating temperature during forging is set to 2 as described above.
The heating temperature is set to about 70 ° C., and the heating temperature is suppressed to be lower than about 350 ° C. required for obtaining required formability when the structure is not densified.

By suppressing the heating temperature at the time of forging as described above, oxidation of the product surface is suppressed, and in particular, the outer peripheral portion of the disk portion close to the forged portion or the disk portion and the rim. The effect of heat on the continuation part (the part indicated by the symbol X in FIG. 4) and the like is reduced, and the tissue coarsening at the part and the reduction in strength due to this are prevented.

As described above, an intermediate product of a wheel having a rim portion which is well formed and has the required strength is obtained, and the intermediate product of the wheel 2a and the bolt holes 2b shown in FIGS. By forming 2b and the like by machining, the wheel 1 as a final product can be obtained. In this case, since the design as shown in FIG. 1 of the disk portion 2 of the wheel 1 is formed by casting, a final product can be obtained in a small number of steps.

Here, the relationship between the densification of the structure by the quenching treatment at the time of casting, the heating temperature at the time of forging, and the formability at the time of forging was confirmed by a test piece, and the results will be described.

The test piece 40 used in this confirmation experiment
Has a diameter of 16 mm and a height of 24 m, as shown in FIG.
It is a cylindrical body of m ± 0.05, and the material is AZ80 which is the same as in the above embodiment. As shown in FIG. 7A, the evaluation of the moldability was performed by using a test piece 4 in an infrared image furnace 50.
A load is applied in the axial direction by a press 51 while heating 0, and the temperature of the test piece 40 at that time is
As shown in FIG. 4B, when the test piece 40 has a crack 41 as shown in FIG.
The height H is measured. Then, a critical upsetting ratio R (%) defined by the following equation is obtained from the height H.

R = [(24−H) / 24] × 100 The result is as shown in FIG. 8 and FIG.
FIG. 8 shows that when the heating temperature is constant at 350 ° C., the smaller the average crystal grain size is, the higher the critical upsetting ratio (forging formability) is, which is generally desirable 60%.
The above-mentioned critical upsetting ratio is when the average crystal grain size is 270 to 280 μm.
m or less. And, in particular, the 20 obtained by the quenching process at the time of casting in
With an average grain size of 0 μm, a high critical upsetting of about 73% is achieved.

According to FIG. 9, the smaller the average crystal grain size, the higher the critical upsetting ratio can be obtained. If the average crystal grain size is constant, the higher the heating temperature during casting, the higher the critical upsetting ratio. The upsetting rate is shown to be higher. In particular, when the average grain size is 300 μm when the quenching process is not performed at the time of casting, it is necessary to heat to about 400 ° C. to obtain a critical upsetting rate of, for example, 60%. Is 440 μm, a critical upsetting rate of 60% cannot be obtained by heating to 400 ° C., which is the limit of heating, whereas a densification of 200 μm in average crystal grain size obtained by quenching during casting. In the case of the obtained structure, it was confirmed that a critical upsetting rate of 60% was obtained at a heating temperature of about 270 ° C.

When the quenched portion is heated to 270 ° C. during forging, the average crystal grain size is maintained at about 200 μm before heating, but the 350 ° C. required for conventional forging. If the heating temperature is
Due to the influence of this heating, the average crystal grain size is coarsened to about 350 μm. Then, the mechanical properties of the two cases were compared, and the results were described. As shown in FIG.
In the case where the heating temperature during forging was too high and the structure was coarsened (average crystal grain size: 350 μm), mechanical properties such as tensile strength, proof stress, elongation, etc. were higher than those in which the structure was not coarsened (the same: 200 μm). It was confirmed that all the properties deteriorated.

Therefore, as in the above-described embodiment, the rim portion subjected to the quenching treatment is heated to 270 ° C. for forging, thereby obtaining good formability and forging due to the excessively high heating temperature. Thus, a decrease in strength at a portion near the part is prevented.

In the case of a wheel made of Mg alloy, when it is attached to the axle of an automobile and tightened with a wheel nut,
There is a problem that a contact electromotive force is generated due to the pressure contact between the wheel and the iron nut, and the wheel is electrically corroded. Accordingly, a technique for preventing this electrolytic corrosion is disclosed in connection with the present invention.

As shown in FIG. 11, a metal pipe 60 having a conical seating surface with a nut C tightened is fitted into the inner periphery of the bolt hole B in the Mg alloy wheel A. The metal tube 60 has a double structure, the inner layer 61 side to which the nut C is crimped is formed of a high silicon Al alloy having excellent set resistance, and the outer layer 62 side fitted to the bolt hole B of the wheel A has Al6061 close to pure Al with excellent corrosion resistance
It is formed of an alloy.

The metal tube 60 is, for example, as shown in FIG.
First, as shown in FIG. 12, a tube 61 made of a high silicon-based Al alloy having an outer diameter substantially equal to the inner diameter is inserted into a tube 62 made of an Al6061 alloy as shown in FIG. At the same time, the tube having the double structure is cut into a predetermined size to form a short cylindrical material 63. next,
As shown in FIGS. 13A and 13B, the raw material 63 is formed by a hot or cold forging machine 70 having a die 71 and a punch 72 into a shape in which one end is opened in a conical shape. As shown in FIG. 14, serrations 64 are formed on the outer peripheral surface of the columnar portion. Then, the serrations 64 are pressed into the bolt holes B of the wheel A while crushing the serrations 64, and thereafter, the portion protruding from the end surface of the wheel A is deleted to finish as shown in FIG.

The metal tube 60 fitted to the inner periphery of the bolt hole B in this way prevents the sag of the seat surface due to the tightening of the nut C and the electrolytic corrosion of the wheel A due to the contact electromotive force. It becomes.

[0031]

As described above, according to the present invention, at the time of manufacturing a member made of an Mg alloy, a portion to be forged in a later step at the time of casting a material is subjected to a quenching treatment, and the forging is performed while heating this portion. Because it was molded, a dense structure consisting of fine crystal grains will be formed at the part where the quenching treatment was performed at the time of casting molding of the material,
The required strength is imparted to the portion, and the formability of forging formed in a later step is improved. Also,
With the improvement of the forging formability, it is possible to suppress the heating temperature at the time of the forging, so that the oxidation of the product surface is suppressed, and the influence of heat on the part near the forging part is reduced. Thus, the strength is prevented from being reduced due to the coarsening of the tissue at the site. In this way, according to the method of the present invention, a Mg alloy member having a good yield and excellent strength and formability is manufactured.

[Brief description of the drawings]

FIG. 1 is a front view of a wheel according to an embodiment of the present invention.

FIG. 2 is a sectional view of the wheel taken along line AA of FIG.

FIG. 3 is a schematic view showing a mold for blank casting.

FIG. 4 is a sectional view of a casting material manufactured by using the mold of FIG. 3;

FIG. 5 is a schematic view of a spinning machine for forging a rim portion of a casting material.

FIG. 6 is an external view of a test piece used in an experiment for confirming the relationship between the average crystal grain size, the heating temperature during forging, and the formability.

FIG. 7 is a schematic diagram showing an apparatus and an evaluation method used in the confirmation experiment.

FIG. 8 is a graph showing the relationship between the average crystal grain size obtained in the confirmation experiment and the critical upsetting ratio.

FIG. 9 is a graph similarly showing a relationship between a heating temperature and a limit upsetting rate.

FIG. 10 is a diagram showing a decrease in mechanical properties due to coarsening of a tissue.

FIG. 11 is a sectional view of a structure of a bolt hole of a wheel disclosed in connection with the present invention.

FIG. 12 is a perspective view showing a material of a metal tube in the structure of FIG. 11;

FIG. 13 is a view showing a forming step of the metal tube.

FIG. 14 is a view showing a press-fitting step of the metal pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wheel (Mg alloy member) 3 Rim part (forging part) 20 Mold 30 Spinning machine

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C22F 1/06 C22F 1/06 (56) References JP-A-3-86340 (JP, A) JP-A-62-220224 (JP) JP-A-2-41751 (JP, A) JP-A-3-236452 (JP, A) JP-A-3-184646 (JP, A) JP-A-54-19463 (JP, A) (58) Surveyed field (Int.Cl. ⁷ , DB name) B21H 1/04 B21J 5/00 B21J 5/12 B22D 15/00 B60B 3/02 C22F 1/06

Claims (2)

(57) [Claims] 1. A upon casting molding the Mg alloy material by solidifying by injecting molten metal into a mold, and facilities quenching process at a site forging in a later step are carried out fine crystals
A method for producing a member made of Mg alloy , wherein a dense structure composed of grains is formed, and the quenched portion of the casting material is heated and forged. 2. A member made of an Mg alloy is a wheel of an automobile, a portion to be forged is a rim portion of the wheel,
The method according to claim 1, wherein the forging is spinning.