JP3808757B2 - Manufacturing method of highly ductile Mg alloy material - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a highly ductile Mg alloy, and more particularly to a method capable of producing a Mg alloy having high ductility and excellent formability even at low temperatures with high productivity.
[0002]
In the present invention, “quasi-hydrostatic processing” refers to processing that deforms without changing the cross-sectional shape, although it is constrained in shape, and “quasi-hydrostatic warm processing” refers to the quasi-hydrostatic processing. Say what to do between.
[0003]
[Prior art]
Mg has a dense hexagonal structure and extremely low plastic deformability, so that it can hardly be formed with an ingot. Therefore, even complicated parts as well as parts with relatively simple shapes must be molded by a method that combines casting and cutting, and the processing cost is very expensive, so it is versatile. It was the biggest Kushiro.
[0004]
Under such circumstances, several studies have been conducted for the purpose of developing a highly ductile Mg alloy capable of secondary forming. For example, JP 2000-271631, 2000-271693, 2000-271695 A method disclosed in each publication is proposed.
[0005]
The basic principle of these methods is a method of first performing warming or hot extrusion processing with an extrusion ratio of about 10 and then performing warm quasi-hydrostatic processing [this method is, for example, a conceptual diagram of FIG. 1 is a test material, 2 is a die, 3 is a plunger, 4 is a pressurizing device, T ₁ and T ₂ are thermocouples, respectively), and ECAP (Equal Channel Angular Press) is often used (hereinafter, this method is referred to as “ecap processing” in this specification)], and the crystal structure is refined and the grain size of the intermetallic compound is refined. It gives a ductility of a level such as 220% or higher in elongation, and can be said to be an excellent technique in that it enables secondary forming of a difficult-to-work material Mg alloy.
[0006]
However, in these methods, in order to give a true strain that guarantees an elongation rate of 220% or more, it is necessary to give a very large strain such as 9 or more in the introduced true strain by the quasi-hydrostatic processing. For example, productivity must be very low because a large number of repeated shear deformations such as 8 or more must be applied.
[0007]
On the other hand, the inventors of the present invention have also been researching for the same purpose, and “Scripta Met.” Vol. 40, No. 4 (1999), p477 (Watanabe etc.) and “Mat. Trans. "JIM" Vol.40, No.8 (1999), p809 (Watanabe etc.), "Superplasticity & Superplastic Forming" (1998), p179 (Watanabe etc.) etc. were disclosed.
[0008]
However, the methods disclosed in these include:
(1) The extruding ratio during warming must be set to a very high value of about 100, for example, due to processing heat generated in the extrusion process, strong segregation parts such as Zn are liquified and are liable to cause processing cracks.
(2) If the extrusion speed is slowed to suppress the processing heat generation, the productivity will be extremely reduced.
(3) Since the extrusion ratio is very large (ie, when the extrusion ratio is 100, the cross-sectional size of the extruded product is 1/100 before processing), the final product (material) must be small and large. It becomes difficult to obtain processed products,
However, there is a need for improvement for practical use.
[0009]
[Problems to be solved by the invention]
The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is to combine a conventional warm extrusion and quasi-hydrostatic processing well, and to make an Mg alloy material excellent in formability into a conventional method. The aim is to establish a technology that can be efficiently manufactured as compared to a large-sized Mg alloy material that can be efficiently and easily obtained.
[0010]
[Means for achieving the object]
The method for producing a highly ductile Mg alloy material according to the present invention that has solved the above-mentioned problem is, for example, after warm-working an Mg alloy containing dispersion strengthened particles such as Zr at an extrusion ratio of 15 or more and 70 or less. The main point is that a quasi-isostatic pressure warm working is performed with a warm true strain of 0.5 to 3 inclusive.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
As described above, Mg is a dense hexagonal type and has a crystal structure with a small plastic deformability. Therefore, in the present invention, as a means for imparting workability to the Mg alloy, the plastic deformation ability is expressed by increasing the sliding system as a reoriented structure of random orientation by performing quasi-hydrostatic pressure warm working in an intermediate process. However, the basic idea itself is essentially the same as the method disclosed in the above publication.
[0012]
However, in the present invention, in order to easily obtain a large-sized Mg alloy material with fine crystal grains having a random orientation with good industrial productivity, an Mg alloy containing dispersion strengthened particles is selected as the Mg alloy. After the warm working at an extrusion ratio of 15 or more and 70 or less, a true strain of 0.5 or more and 3 or less is given by performing the quasi-isostatic pressure warm working in the second step.
[0013]
The reason why the extrusion ratio in the warm working in the first step is set to 15 or more is that an extrusion ratio of 15 or more must be given at least in order to obtain fine crystal grains of random orientation by the warm working. From the viewpoint of securing random fine crystal grains, the upper limit of the extrusion ratio at the time of warm working in the first step is not particularly limited. However, the larger the extrusion ratio, the smaller the size of the extruded product with respect to the raw material for extrusion, and a large member. Therefore, in order to make it possible to manufacture a large-sized material and increase the degree of freedom in size as a product, the extrusion ratio should be suppressed to 70 or less at the highest. The extrusion ratio in the first step is more preferably 25 or more and 40 or less in order to achieve both the securing of randomly oriented fine crystals and the production of large materials.
[0014]
In this way, by suppressing the extrusion ratio at the time of warm processing performed in the first step to the minimum necessary, processing heat generation at the time of extrusion processing can be suppressed, and a suitable extrusion temperature range is sufficiently secured, and a large size The material can be manufactured.
[0015]
In the present invention, after the first step of warm extrusion, the second step is subjected to quasi-isostatic pressure warm processing to give strain, thereby increasing the elongation rate (ductility), thereby achieving a high level of moldability. Is granted. In this step, in order to provide the level of plastic deformability intended by the present invention, that is, moldability, it is necessary to give a true strain of at least 0.5 or more, and more preferably a cumulative true strain of 1.0. It is desirable to give the above.
[0016]
Although the cold workability increases as the accumulated true strain increases, the ductility improvement effect due to the strain imparted by the quasi-hydrostatic warm working in the second step is used in the Mg alloy used in the present invention as will be clarified also in FIG. Is almost saturated at a cumulative true strain of about 3, and even if the cumulative true strain is increased beyond that, the ductility is hardly improved, and the productivity is reduced only by the infinite increase in the number of quasi-hydrostatic hot working. It will not pass. Therefore, considering the balance of productivity, it is desirable to suppress the cumulative true strain to 3 or less, more practically 2.0 or less.
[0017]
The “warm” temperature in performing the warming and quasi-hydrostatic warming performed in the first step and the second step described above destroys the cast structure of the Mg alloy to be used as well as crystal grains and metals. In order to prevent coarsening of the intermetallic compound, it should be set above the recrystallization temperature of the Mg alloy to be used, and the specific temperature varies slightly depending on the type of Mg alloy, that is, the type and content of the dispersion strengthened element. Typically, it is in the range of 250-360 ° C, more generally 300-350 ° C.
[0018]
As the Mg alloy used in the present invention, for example, a relatively small amount of a dispersion strengthened alloy element such as Zr, Ag, Al, Ga, Mn, Sn, Th, Ti, Zn, Y (0.1 to 1) is used. (Mass%, more preferably about 0.2 to 0.7% by mass).
[0019]
By the way, in the prior art described above, AZ (Mg—Zn—Al) or ZK (Mg—Zn—Zr) Mg alloys are used. Set the extrusion ratio to a high value, for example, about 100 to appropriately proceed with recrystallization in the process, or set the accumulated true strain due to the quasi-hydrostatic hot working in the second process to a very high value, such as 9 or more. It is presumed that it was unavoidable.
[0020]
On the other hand, in the present invention, since the Mg alloy containing the dispersion strengthened particles with reduced solid solution strengthening elements is selected as described above, both the first step and the second step are industrially versatile. We believe that high conditions can be set. Therefore, in the present invention, it is preferable to use a dispersion strengthened binary Mg alloy instead of a solid solution strengthening type, and even if a solid solution strengthening element is added, the recrystallization of Mg is not excessively suppressed. Alloy systems should be avoided.
[0021]
Thus, according to the present invention, an Mg alloy containing dispersion strengthened particles is selected, a relatively low extrusion ratio is employed in the warm working of the first step, and the quasi-hydrostatic warm working of the second step ( Ecap processing) can give a high level of ductility by giving less cumulative true strain than conventional techniques such as 0.5-3, and even with relatively large sizes, An Mg alloy having excellent formability can be produced with a small number of steps and high productivity.
[0022]
The Mg alloy material obtained by the present invention has many features such as 1) light weight and high specific strength, 2) high vibration absorption capability, and 3) good electromagnetic shielding properties. Therefore, taking advantage of these features, it can be effectively used as a material for various parts that require light weight and high rigidity, such as notebook computers, portable MD players, and video integrated cameras.
[0023]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be implemented with appropriate modifications within a range that can meet the gist of the preceding and following descriptions. Any of these may be included in the technical scope of the present invention.
[0024]
EXAMPLE A Mg-0.6% Zr ingot was machined into a round bar with a diameter of 60 mm and partly into a round bar with a diameter of 45 mm, and was extruded into a round bar with a diameter of 10 mm at 350 ° C. in the first step (each extruded The ratio is 36 and 20). Moreover, what was directly finished to a diameter of 10 mm by machining without preparing extrusion was also prepared.
[0025]
These alloy materials having a diameter of 10 mm were subjected to quasi-isostatic hot working (90 ° shearing) at 300 ° C. once, twice and four times. The processing strain given at that time is about 1.15 per time. A tensile test piece was cut out from the obtained material, and a tensile test was performed at 300 ° C. within a strain rate range of 3.3 × 10 ^{−5 to} 3.3 × 10 ⁻¹ .
[0026]
As a result, when the material formed into a round bar having a diameter of 10 mm by machining was subjected to quasi-isostatic pressure warm processing without performing the warm extrusion in the first step, the material was broken during the quasi-hydrostatic pressure warm processing. On the other hand, when the first step was performed at an extrusion ratio of 20 (extrusion from 45 mm to 10 mm in diameter), a material having a diameter of 10 mm was obtained without breaking during the quasi-hydrostatic hot working in the second step. As a result of a tensile test of the material, the elongation at a deformation temperature of 300 ° C. and a deformation speed of 3.3 × 10 ⁻⁴ was 120%.
[0027]
When the extrusion ratio in the first step was 36 (extruded from a diameter of 60 mm to 10 mm), the results shown in FIGS. 1 and 2 were obtained. That is, FIG. 1 shows the ductility (elongation rate) and tensile strength of a raw extruded material (first process material), and then a material (ecap material) subjected to quasi-isostatic pressure warm processing once in the second process. It is a graph showing the relationship between strain rates, and after performing only one quasi-hydrostatic pressure warm processing, a huge elongation of 420% is developed at a deformation rate of 3.3 × 10 ⁻⁴ , and only once Ductility has been drastically improved with processing (equivalent strain of about 1.15), that is, with a significantly smaller number of processing than in the prior art.
[0028]
FIG. 2 shows the improvement in ductility (elongation rate) by increasing the number of quasi-hydrostatic hot working (ecap processing) when a tensile test is performed at a deformation temperature of 300 ° C. and a deformation speed of 3.3 × 10 ^−3. It is the graph which showed the result of having investigated the ductility (elongation rate) improvement allowance per turn. As is clear from FIG. 2, the ductility improvement allowance by the first quasi-hydrostatic pressure hot working is about 90%, whereas the second quasi-hydrostatic temperature is high. Ductility improvement allowance by hot working is about 40%, ductility improvement allowance by the fourth quasi-hydrostatic hot working is about 20%, and ductility improves as the number of repetitions of quasi-hydrostatic hot working (ecap processing) increases. Teenagers will drop significantly. In other words, the ductility improving effect according to the present invention can obtain a high ductility improvement allowance in the first to second or third quasi-hydrostatic pressure warm processing performed after the warm extrusion, and the number of quasi-hydrostatic pressure warm processing times. If the amount is increased more than that, the ductility is hardly improved.
[0029]
Therefore, the number of times of quasi-hydrostatic pressure warm working is about 1 to several times (3 to 4 times), and about 3 or less, more preferably about 2.0 or less is sufficient in terms of true strain. The
[0030]
【The invention's effect】
The present invention is configured as described above, uses a dispersion strengthened Mg alloy, minimizes the extrusion ratio at the time of warm working in the first step, and performs quasi-hydrostatic pressure warm in the second step. By giving an appropriate cumulative true strain by processing, an Mg alloy material having a high level of formability can be produced with high productivity. In particular, in the present invention, by suppressing the extrusion ratio during the warm processing in the first step to a necessary minimum, it becomes possible to produce a large-size easily processable Mg alloy material and to minimize the processing heat generation. Temperature control is facilitated, and in the second step, a high level of ductility can be imparted by one to several quasi-hydrostatic hot working, so that productivity can be greatly increased.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the elongation (ductility) and strain rate of a Mg-0.6% Zr alloy.
FIG. 2 shows the effect of cumulative true strain given by quasi-hydrostatic warm working of Mg-0.6% Zr alloy on the elongation rate and ductility improvement allowance per quasi-hydrostatic warm working (ecap process). It is a graph to show.
FIG. 3 is a conceptual cross-sectional view illustrating a quasi-isostatic pressure warm working (ecap working) method.
[Explanation of symbols]
1 Specimen 2 Die 3 Plunger 4 Pressurizer T ₁ , T ₂ thermocouple

Claims (2)

The binary Mg alloys containing dispersion strengthened element 0.1 to 1 wt%, more than 15, 70 in the following extrusion ratio, after processing warm at a temperature range of 250 ° C. to 360 ° C., in true strain A process for producing a highly ductile Mg alloy material, wherein the ecap process is performed in a temperature range of 250 ° C. to 360 ° C. of 0.5 to 3 ° C. The method according to claim 1, wherein the dispersion strengthened element is Zr.

Images