JP3240182B2 - Manufacturing method of magnesium 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 made of a magnesium (hereinafter, referred to as Mg) alloy, and more particularly to a method of manufacturing a member made of magnesium.
The present invention relates to a method for obtaining a g-alloy member by forging.

[0002]

2. Description of the Related Art Mg alloys are the lightest among structural metals that have been put to practical use and have the property of high specific strength (proof strength / specific gravity). Widely used for parts of machinery. In general, Mg alloys have poor plastic workability when cold, but workability is significantly improved when the temperature is increased.
When such a part is manufactured by forging, it often depends on warm forging.

For example, AZ80 (ASTM standard, Al: 7.8 to 9.2), which is a highly versatile forging Mg alloy, is used.
%, Zn: 0.2-0.8%, Mn: 0.12-0.3
(5%, balance: Mg and impurities), a method is used in which a forged material is heated to 370 ° C. to 420 ° C. in an electric or gas furnace and forged. Conventionally, the heating temperature is set in this manner because if the temperature is lower than this temperature range, sufficient moldability cannot be obtained, and if the temperature is higher than this temperature, the surface of the material is oxidized violently.

[0004]

However, in this method, since the heat transfer medium is a gas, there is a problem that it takes too much time to raise the temperature of the Mg alloy material, and the method is exposed to a considerably high temperature for a long time. Therefore, the oxidation of the material surface is unavoidable, and the precipitates form a solid solution in the matrix during the temperature rise, resulting in a T4 structure (solution solution structure) in which the forged product has poor corrosion resistance. There was a problem that it would.

[0005] Regarding the above problems, for example, Mg
It is conceivable that the temperature rise time may be shortened by immersing the alloy material in a liquid such as a heated salt bath, but Mg alloy is extremely susceptible to oxidation in the salt bath and is currently heated to the above temperature range. No suitable heating medium (liquid) for heating has been found. With respect to the above problem, attempts have been made to prevent oxidation by heating and molding in a vacuum, but there is a drawback that productivity is extremely poor.

On the other hand, as a result of the use of Mg alloy members in various fields as parts, a large amount of chips generated by cutting or grinding work is also discharged. Means for reusing this include, for example, production of sintered parts using hot pressing (Japanese Patent Laid-Open No. 55-389).
No. 63), but in the case of Mg alloy chips, hot pressing alone does not sufficiently increase the strength. Therefore, they are inevitably incinerated, buried in the soil and disposed of, or collected and re-melted, which is not only a waste of resources and energy but also dangerous, and is now being regarded as a problem.

[0007]

SUMMARY OF THE INVENTION A method of manufacturing a member made of Mg alloy according to the present invention has been made to solve such various problems in the prior art. non-corrosive warm forging temperature for the functional life-and-death <br/> magnesium alloy material as a lubricant during warm forging
After being immersed in a lubricating liquid heated to a temperature and heated, warm forging is performed.
The product is solid solution in the matrix and the product after forging is T4 structure
The temperature is set to a value that does not result in (solution solution structure) . This warm forging can be performed at a temperature considerably lower than the conventional warm forging temperature of 370 ° C. to 420 ° C., for example, about 150 ° C. is selected.

[0008] The liquid for immersing and heating the Mg alloy material is non-corrosive to the magnesium alloy material, which can be heated to a warm forging temperature without oxidizing the Mg alloy.
Any lubricating liquid may be used, but an oil having lubricating properties such as engine oil is particularly preferable. The Mg alloy particularly suitable for the present invention is a so-called wrought Mg alloy, and contains about 2 to 11% of Al in order to improve strength. Further, in the method for manufacturing a member made of Mg alloy according to the present invention, a compression molded body of Mg alloy chips can be used as the Mg alloy material.

[0009]

It has been found that the formability of the Mg alloy has a close relationship with the size of the crystal grains, as will be specifically shown in Examples later. Then, in accordance with the manufacturing method of the Mg alloy member according to the present invention, by extruding before warm forging, destroying the initial coarse cast structure of the Mg alloy material and refining the crystal grains, thereby improving the forging formability. It can be significantly improved.

[0010] Extrusion molding requires about 20 casting materials.
What is necessary is just to heat it in the range of 0 degreeC-420 degreeC, and the temperature dependence of the effect of extrusion molding has little in that range. The setting of the extrusion temperature as described above is
If the temperature is less than 200 ° C, extrusion molding is difficult.
This is because, if it exceeds 300, oxidation of the surface of the Mg alloy material becomes severe, and the effect of extrusion molding is lost due to recrystallization. The extrusion ratio of the extrusion molding will be specifically described later in Examples, but in consideration of the initial crystal grain size of the casting material and the like, the necessary forging formability at the warm forging temperature is ensured. Is selected as appropriate.

By performing such extrusion before warm forging, forging at a low temperature of, for example, 150 ° C., which has never been considered conventionally, has become possible. And since the forging at low temperature became possible, in the present invention, the above-mentioned problem about the conventional example can be avoided. In addition, the above-mentioned problem has been solved by forging at a low temperature. That is, as described above, since the Mg alloy is very easily oxidized, it can be said that there is no liquid medium for heating the Mg alloy to a high temperature of 370 ° C. to 420 ° C. as in the conventional example. In this case, since heating at about 150 ° C. is sufficient, for example, a commercially available engine oil or the like can be used to heat the Mg alloy surface without causing oxidation.

[0012] Then, because it uses lubricating fluid of the engine oil or the like as the heating medium, the lubricating liquid is deposited on the entire surface of the Mg alloy material, which functions as a lubricant <br/> during the next warm forging Will do. Of course, the lubricating liquid medium is not limited to oil, and can be heated to a warm forging temperature without corroding Mg, such as wax or paraffin, and may be anything as long as it has a lubricating effect, or molybdenum disulfide or the like. Solid lubricants such as graphite may be dispersed and contained.

Further, in the present invention, since the forging at a low temperature is enabled, there is an additional effect that the life of the molding die is extended.

In the present invention, a compact of Mg alloy chips can be used as the Mg alloy material. That is, the Mg alloy chips are formed into a compression molded body by hot pressing and extruded. Originally, the compression molded body of the swarf has a smaller crystal grain size than the cast material. However, the extruded body is further refined to improve forging formability. In addition, the extrusion molding has an action of further firmly solidifying the compression molded body, so that a high-strength compression molded body can be obtained. In addition,
As the Mg alloy chips that can be used in the present invention,
Not only chips discharged by cutting and grinding of parts but also scraps or used wastes may be formed into chip-like strips by a crusher or the like.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described more specifically with reference to FIGS.

First, FIG. 3 shows the results of an upsetting test conducted at 350 ° C., and shows the relationship between the average crystal grain size of the AZ80Mg alloy casting and the critical upsetting rate.
Here, the limit upsetting ratio is defined as a value when a columnar test piece 3 is set up between the upper and lower dies 1 and 2 in the axial direction as shown in FIG. The height reduction rate means that the higher the rate, the better the forging formability of the material. The critical upsetting ratio is expressed as 100 × (H−H1) / H (%), where H is the initial height of the test piece and H1 is the height at which microcracks occur.

As shown in FIG. 3, the smaller the average crystal grain size of the Mg alloy, the higher the critical upsetting ratio and the better the formability.
An approximately linear relationship is established between the two. By the way, forging materials applied to various parts usually require formability with at least a limit upsetting rate of 60% or more. In the case of forging at 350 ° C., the condition is satisfied when the average crystal grain size is about 250 μm or less. However, a large Mg alloy casting generally used as a forging material has an average crystal grain size of 300 μm. This is often the case, and does not satisfy the condition of the limit upsetting rate of 60% or more. Therefore, if such a material is subjected to forging, there is a risk of cracking at 350 ° C., and it is necessary to heat the material to a temperature exceeding 350 ° C. to improve the formability. Conversely, a forging material having a small average grain size has a high critical upsetting ratio and good formability, so that predetermined forging can be performed even at a lower temperature.

In the present invention, the casting material is extruded before forging and the crystal grains are refined to improve the critical upsetting ratio, that is, the formability. To forge. Therefore, in the present example, the following test was performed to confirm the effect of the extrusion molding on the Mg alloy (see FIG. 1). That is, (1) AZ80Mg alloy mold castings (300 mmφ) having different average crystal grain sizes were prepared, and (2) extrusion molding was performed at 350 ° C. with various extrusion ratios to form test pieces. Next, (3) one test piece
It was immersed in an oil bath heated to 50 ° C. The oil used was engine oil (trade name, Mazda Golden Arrow), and the oil bath was heated by a throw-in heater. Finally, (4) the test piece was pulled out of the oil bath and immediately subjected to an upsetting test at 150 ° C.

FIG. 2 shows the test results. The horizontal axis represents the initial average grain size of the cast material, and the vertical axis represents the extrusion ratio.
The points at which a 60% critical upset at 50 ° C. is achieved are plotted and connected by a straight line. Further, the hatched side of the straight line is a region showing a critical upsetting ratio of 60% or more at 150 ° C.

As described above, even in the case of a cast material having a large average crystal grain size, the necessary formability could be provided at an extremely low temperature of 150 ° C. by extruding in advance. For example, when a cast material having an initial average crystal grain size of 300 μm is used, the critical upsetting ratio is less than 60% even at 350 ° C. when extruding is not performed (see FIG. 3). 3
By taking the above, the limit upsetting rate of the material after extrusion can be 60% or more at 150 ° C.

As shown in FIG. 2, the larger the initial average grain size of the cast material, the higher the extrusion ratio must be. Conversely, when the average crystal grain size is small, the extrusion ratio can be reduced, but in any case, the required extrusion ratio is determined by the average crystal grain size of the original cast material. However, the average crystal grain size is 120μ.
The AZ80Mg alloy cast material having a m of not more than m has a formability of a critical upsetting rate of 60% or more at 150 ° C. even without extrusion.

FIG. 2 shows the results of the upsetting test at 150 ° C. When the test is performed at a temperature higher than 150 ° C., the straight line in the figure shifts to the lower side of the extrusion ratio, and at a lower temperature. When performing, it goes without saying that it shifts to the side where the extrusion ratio is higher. Therefore, for example, assuming that the initial average grain size of the Mg alloy cast material is the same, if a higher warm forging temperature is selected, the extrusion ratio can be reduced, and a lower warm forging temperature is selected. If so, the extrusion ratio must be increased.

According to the present invention, since the formability is improved by extrusion, the degree of freedom in setting the forging temperature is considerably larger than in the prior art. For example, from the viewpoint that the upper limit of the forging temperature is within a range in which oxidation due to heating in a liquid medium is small and a structural change (a problem of the conventional example) does not occur.
The lower limit is determined from the viewpoint that a predetermined formability can be obtained by extrusion, and the actual forging temperature is appropriately selected from the viewpoint.

By the way, what has been shown in the above embodiment is AZ
Although it is for an 80Mg alloy cast material, the same effect can be obtained for other Mg alloy materials and also for a compression molded body of Mg alloy chips by performing extrusion before forging. . However, in the case of a compression molded body of cuttings, the extrusion ratio is preferably set to 4 or more because the extrusion molding also serves to further firmly solidify the compression molded body.

[0025]

As described above, in the present invention, by performing extrusion molding before warm forging,
Since the formability of the Mg alloy material can be greatly improved, warm forging can be performed at a considerably lower temperature than before. Thereby, without alloy material causes the tissue changes during the heating, or can be made to the surface of the Material is hardly oxidized. In addition, since a lubricating liquid is used as the heating medium, the time required to raise the temperature to the forging temperature can be greatly reduced , and the lubricating liquid can be used.
The body functions as a lubricant during warm forging. With lubricating liquid
Case, only functions as a lubricant during oil warm forging of using lubricating oil of the engine oil or the like by
It also prevents oxidation. Further, since the forging temperature can be lowered, there is also an effect that the life of the mold is extended.

Further, since the present invention can be applied to a compact obtained by compressing chips, it is possible to easily remove Mg alloy chips, scraps, used wastes, etc., which have not been effectively treated in the past. There is also an effect that it can be recycled.

[Brief description of the drawings]

FIG. 1 is a flowchart for explaining steps in an embodiment.

FIG. 2 is a diagram showing a relationship between an extrusion ratio that achieves a critical upsetting ratio of 60% or more at 150 ° C. and a crystal grain size.

FIG. 3 is a diagram showing a relationship between a critical upsetting ratio at 350 ° C. and an average crystal grain size.

FIG. 4 is a diagram illustrating an upsetting test.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // B21C 23/00 B21C 23/00 A (56) References JP-A-63-282232 (JP, A) JP-A-3-3 294036 (JP, A) JP-A-3-97824 (JP, A) JP-A-52-13551 (JP, A) JP-A-49-10850 (JP, A) JP-A-60-173898 (JP, A) JP-A-2-93036 (JP, U) JP-A-2-108536 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21J 1/00-13/14 B21J 17/00 -19/04 B21K 1/00-31/00 B22F 3/20 C22F 1/06

Claims (4)

(57) [Claims] 1. Extrusion of a magnesium alloy material, followed by addition of a warm forging temperature which functions as a lubricant during warm forging and is non-corrosive to magnesium alloy material.
After immersion in a heated lubricating liquid and heating, warm forging is performed.
The solution after forging does not form a solutionized structure due to solid solution inside
A method for producing a magnesium alloy member, wherein the temperature is set to a temperature . 2. The method for producing a magnesium alloy member according to claim 1, wherein the member is immersed in an oil bath and heated. 3. The method for producing a magnesium alloy member according to claim 1, wherein the magnesium alloy contains aluminum. 4. The method for producing a magnesium alloy member according to claim 1, wherein the magnesium alloy material is a compression molded body of magnesium alloy chips.