JP5419071B2 - Mg alloy forged product and its manufacturing method - Google Patents

Description

  The present invention relates to a magnesium alloy forged product obtained by forging a magnesium alloy in which a quasicrystalline phase or an approximate crystalline phase thereof is dispersed in a magnesium matrix into a predetermined shape, and a method for producing the same.

Magnesium is attracting attention as a lightweight material for electronic devices and structural members because it is lightweight and shows abundant resources. On the other hand, when considering the application to moving structural members such as railway vehicles and automobiles, high strength, high ductility and high toughness characteristics of the material are required from the viewpoint of safety and reliability in use.
Patent Documents 1 to 4 describe that quasicrystals developed in a magnesium matrix by addition of rare earth elements (particularly yttrium) are useful for high strength, high ductility, and high toughness characteristics. .
Patent Documents 5 and 6 show a forging technique of a magnesium alloy using high-speed superplastic behavior for a magnesium alloy in which a quasicrystalline phase cannot be expressed in a magnesium matrix. In any case, it is indicated that pinning particles are required to be dispersed in a magnesium matrix and have a fine crystal grain size in order to develop high-speed superplasticity during final forging.
In order to refine the magnesium matrix in advance, there are techniques such as using pinning particles with a high volume ratio to prevent coarsening of the magnesium matrix phase or to refine the initial structure by high strain processing. However, dispersion of general pinning particles at a high volume ratio tends to be a starting point of fracture, leading to deterioration of characteristics, particularly reduction of ductility. In addition, when high strain processing is used, there are problems such as shortening the life of molds and containers and increasing energy loss.
Unlike a general crystal phase, a peculiar phase that does not have a structure in which a predetermined arrangement of atoms is repeatedly arranged (translational order), that is, a quasicrystalline phase is Mg—Zn—RE (RE = Y, Gd, Dy, It was noticed that it appears in an alloy of Ho, Er, Tb) or Mg—Zn—Al. Since the quasicrystalline phase has good matching with the crystal lattice of the parent phase, the interface between the parent phase and the quasicrystalline phase is strongly bonded to form a matching interface.
Therefore, dispersing the quasicrystalline phase in the magnesium matrix is known to inhibit dislocation movement during plastic deformation and contribute to higher strength, but is less likely to become the nucleus or starting point of fracture.
In addition, a magnesium alloy subjected to straining (stretching) such as rolling or extrusion has a problem of so-called yield anisotropy in which the compressive yield stress is lower than the tensile yield stress due to the formation of the texture.
However, wrought quasicrystalline particle-dispersed magnesium alloy reduces the strength of the texture (the degree of accumulation on the bottom surface), improves the compression characteristics while maintaining a high tensile strength level, and is used for structural component design. Undesirable yield anisotropy can be eliminated. Further, the quasicrystal-dispersed magnesium alloy that has been subjected to the stretch processing exhibits superplastic behavior and is excellent in secondary formability. On the other hand, in order to develop superplastic behavior, it is necessary to show fine and equiaxed crystal grains, and there is little change in the microstructure of the magnesium alloy used for forming and the microstructure after processing. It is important. Large structural changes lead to deterioration of mechanical properties such as strength and ductility, and the molding process is greatly restricted, impeding its practicality.
For this reason, even if the quasicrystalline phase is dispersed, it is premised on cutting that does not affect the structure, and forging, especially warm forging, is impossible.

  In view of such problems, an object of the present invention is to provide a magnesium alloy forged product that can be formed by forging and that does not lose its quasicrystalline phase characteristics.

The magnesium alloy forged product of the invention 1 is a magnesium alloy forged product obtained by forging a magnesium alloy in which a quasicrystalline phase or an approximate crystalline phase thereof is dispersed in a magnesium matrix into a predetermined shape. The chemical composition of (100-XY) at. % Mg-Xat. % RE-Yat. % Zn alloy (RE = Y, Gd, Dy, Ho, Er, Tb), and the composition range formed by the quasicrystalline phase consisting of Mg—Zn—RE or its approximate crystalline phase in the magnesium matrix is 0. .2 ≦ X ≦ 1.5, 5X ≦ Y ≦ 7X, X and Y are atomic%, and the magnesium matrix phase in which the quasicrystalline phase or its approximate crystalline phase is dispersed is equiaxed. Features.
A magnesium alloy forged product according to a second aspect of the present invention is a magnesium alloy forged product obtained by forging a magnesium alloy in which a quasicrystalline phase or an approximate crystalline phase thereof is dispersed in a magnesium matrix into a predetermined shape. The chemical composition is expressed by mass% and is a (100-ab) Mg-aAl-bZn alloy not containing rare earth elements, and a quasicrystalline phase composed of Mg-Zn-Al, or an approximate crystalline phase thereof. The composition range formed in the magnesium matrix is 3 ≦ a ≦ 15 and 6 ≦ b ≦ 12, 2 ≦ a ≦ 15 and 12 <b ≦ 35, a and b are mass%, and the quasicrystalline phase Alternatively, the magnesium matrix phase in which the approximate crystal phase is dispersed is equiaxed.
Invention 3 is characterized in that in the magnesium alloy forged product of Invention 1 or 2 , the aspect ratio of the magnesium matrix phase is 2.5 or less.
Invention 4 has a complex shape in which the concavo-convex portion is formed at least in part in the magnesium alloy forged product according to any one of the first to third aspects , and the magnesium matrix is equiaxed in the concavo-convex portion. It is characterized by being.

Invention 5 is a method for producing a magnesium alloy forged product according to Invention 1 , wherein the magnesium alloy is forged by a press die having a predetermined shape as an inner die by warm forging performed by heating the magnesium alloy at 450 ° C. or less. It is characterized by becoming.
Invention 6 is a method for producing a magnesium alloy forged product according to invention 2 , wherein the magnesium alloy is closed forged by a press die having a predetermined shape as an inner die by warm forging performed by heating the magnesium alloy at 350 ° C. or less. It is characterized by becoming.

The magnesium alloy forged product having the above-mentioned structure can be cut into a shape after forging, and can efficiently realize a high-strength magnesium alloy product processed into a free shape.
Moreover, since it can also be achieved by utilizing a forging means that has been generally known, it has extremely high feasibility.

The fine structure observation photograph by the optical microscope of the sample for forging of Example 1. FIG. Appearance photograph and sectional view after forging and forming of Example 1 The fine structure observation photograph by the optical microscope of the forging molding material (gear vicinity part) of Example 1. FIG. The fine structure observation photograph by the electron beam backscattering diffraction method of the forging molding material (forging center part) of Example 1. FIG. Nominal stress-nominal strain curve for tension and compression of the forged material of Example 1 FIG. 3 is an example of X-ray diffraction measurement of the forged molded material of Example 1. FIG. The microstructure observation photograph by the optical microscope of the sample for forging of Example 2. FIG. The fine structure observation photograph by the optical microscope of the forging molding material (gear vicinity part) of Example 2. FIG. The microstructure observation photograph by the electron beam backscattering diffraction method of the forging molding material (forging center part) of Example 2. FIG.

Add a rare earth element (100-XY) at. % Mg-Xat. % RE-Yat. In the% Zn alloy, the composition range in which the quasicrystalline phase composed of Mg—Zn—RE or its approximate crystalline phase forms in the magnesium matrix is 0.2 ≦ X ≦ 1.5, 5X ≦ Y ≦ 7X, And Y are atomic%.
In a composition expressed by mass%, a rare earth element is not added (100-ab) Mg-aAl-bZn alloy. The ranges are 3 ≦ a ≦ 15 and 6 ≦ b ≦ 12, and 2 ≦ a ≦ 15 and 12 <b ≦ 35, and a and b are mass %.
And about moderate dispersion | distribution and disperse | distributing a quasicrystal phase or its approximate crystal phase can be performed by the method similar to the said patent documents 1-4.
And when forging a magnesium alloy in which the quasicrystalline phase or the approximate crystalline phase thus obtained is dispersed, in the case of an Mg—Zn—RE alloy using rare earth elements, 450 ° C., preferably 400 ° C., More preferably, the temperature is 300 ° C. or less, and in the case of an Mg—Zn—Al alloy that does not use rare earth elements, it is desirable that the temperature be 350 ° C., preferably 300 ° C., more preferably 250 ° C. or less.
When this heating temperature is excessive, the quasicrystalline phase or its approximate crystalline phase disappears during forging. The shape of the forged part is not limited to a simple shape such as a shaft, a sphere, or a plate, but may be an uneven shape such as a gear, a screw, a cam, or a saw tooth as shown in the embodiment, or a shaft, a sphere, or a plate. It may be a complicated shape with irregularities formed on the part.
This is because the quasicrystalline phase becomes the nucleus of dynamic recrystallization during forging, and a fine and equiaxed grain structure is obtained. In addition, since the quasicrystalline phase shows good matching with the crystal lattice of magnesium, even if it exists at a high volume ratio, it does not easily become a nucleus of fracture, and does not lead to deterioration of characteristics, particularly ductility. Therefore, as a result of the effective use of the function, it seems that the crystal of the forged product is maintained equiaxed. As a result, a forged molded product having uniform, equiaxed, and fine crystal grains can be produced by warm forging regardless of the microstructure structure before forging. In addition, the mechanical properties are characterized by the uniform hardness distribution without the yield anisotropy seen in wrought magnesium alloys.

7.5% by mass zinc and 1.7% by mass yttrium were melt-cast in commercial pure magnesium (purity 99.95%) to produce a master alloy. First, the mother alloy was heat treated in the atmosphere at 400 ° C. for 24 hours, and then an extruded billet having a diameter of 90 mm was prepared by machining. The extrusion billet was put into an extrusion container heated to 300 ° C., held for about 30 minutes, and then extruded at an extrusion ratio of 5: 1 to obtain an extruded material having a diameter of 40 mm. Thereafter, in order to prepare a forging sample, it was again put into an extrusion container heated to 370 ° C., held for about 30 minutes, and then a rod-shaped forging sample having a diameter of 20 mm was obtained at an extrusion ratio of 4: 1. . FIG. 1 shows an example of microstructure observation of a forging sample by an optical microscope. The crystal grain size of the magnesium matrix of the forging sample is 15.3 μm, and it can be confirmed that it is equiaxed. (However, the crystal grain size is determined by the intercept method.) An internal gear having an inner diameter of 58 mm, an outer diameter of 60 mm, and a gear shape of 60 teeth is used, temperature: 300 ° C., initial strain rate: 1.1. Warm closed forging was performed at × 10 ⁻³ s ⁻¹ to obtain a forged molded material. FIG. 2 shows a photograph of the appearance after forging. It can be confirmed that the molded product, particularly the gear part, is free from cracks and defects, and the material is uniformly filled in the entire internal gear and the entire logo.
FIGS. 3 and 4 show examples of observing the microstructure of the forged material by an optical microscope and an electron beam backscatter diffraction method. The average crystal grain size of the magnesium matrix in the vicinity of the gear portion ((A) in FIG. 2, the same applies hereinafter) (FIG. 3) and the forging center ((B) in FIG. 2, the same applies hereinafter) (FIG. 4) They were 12.5 and 11.0 μm, respectively, and the aspect ratio was 2.5 or less. It can be confirmed that crystal grain refinement occurs by closed forging and that the equiaxed state is maintained.
Further, the hardness in the vicinity of the region observed in the fine structure is 61.4 and 65.2 Hv, and the hardness in the gear portion and the central portion is almost the same value, so that the hardness is uniform as a whole. I think.
From the above results, it can be seen that the molded product has a uniform structure and hardness over the entire closed forging material.
A tensile test piece having a parallel part diameter of 2.5 mm and a length of 10 mm, and a compression test piece having a diameter of 4 mm and a height of 8 mm were collected from the forged molded material, and an initial tensile / compression strain rate: 1 × 10 ⁻³ s ^−1. The room temperature tensile / compression test was conducted. FIG. 5 shows a nominal stress-nominal strain curve obtained by a room temperature tensile / compression test. The tensile and compressive yield stresses of the forging material are 120 and 124 MPa, respectively. Further, the ratio of compressive / tensile yield stress is 1 or more, suggesting that there is no yield anisotropy observed in the wrought magnesium alloy and that it can be deformed isotropically.
FIG. 6 shows an X-ray diffraction result of the forged member. The white circles in the figure are diffraction peaks of the quasicrystalline phase (Mg ₃ Zn ₆ Y ₁ ) composed of Mg—Zn—Y, and the presence of the quasicrystalline phase can be confirmed in the forged molded member produced in Example 1.

8% by mass zinc and 4% by mass aluminum were melt cast in commercial pure magnesium (purity 99.95%) to produce a master alloy. First, the mother alloy was heat-treated at 325 ° C. for 48 hours in the air, and then an extruded billet having a diameter of 40 mm was prepared by machining. This extruded billet was put into an extrusion container heated to 265 ° C., held for about 30 minutes, and then subjected to warm extrusion at an extrusion ratio of 4: 1 to obtain a rod-shaped forging sample having a diameter of 20 mm. FIG. 7 shows an example of microstructural observation of a forging sample using an optical microscope. Since the crystal grains of the forging sample have a small amount of warm strain imparted, the crystal grain size of the magnesium matrix in the major axis and minor axis direction is about 250, 50 μm (average aspect ratio 5). 3: 1) can be confirmed.
Using an internal gear having the same shape as in Example 1, warm closed forging was performed at a temperature of 250 ° C. and an initial compression strain rate of 4.5 × 10 ⁻³ s ⁻¹ to obtain a forged material. 8 and 9 show examples of microstructure observation after forging by an optical microscope and electron beam backscatter diffraction method.
The average crystal grain size of the magnesium matrix in the vicinity of the gear part (FIG. 8) and the forging center part (FIG. 9) is 5.8 and 5.9 μm, respectively. it can. 7-9, the structure which shows an equiaxed fine crystal grain was obtained by warm forging irrespective of the form of the magnesium mother phase before forging. Further, the hardness in the vicinity of the region observed with the fine structure was 83.1 and 83.3 Hv. From the above results, it can be seen that, as in Example 1, the formed product has a uniform structure and hardness over the entire area of the closed forging material.
A tensile test piece having a parallel part diameter of 2.5 mm and a length of 10 mm, and a compression test piece having a diameter of 4 mm and a height of 8 mm were collected from the forged molded material, and an initial tensile / compression strain rate: 1 × 10 ⁻³ s ^−1. The room temperature tensile / compression test was conducted. The tensile and compressive yield stresses of the forged molded material are 197 and 198 MPa, respectively, and the ratio of the compressive / tensile yield stress is 1 or more as in Example 1, there is no yield anisotropy, and isotropic It suggests that it can be deformed.
Further, from the analysis results of FIG. 6 and the like, the black portions in FIGS. 8 and 9 are considered to be quasicrystalline phases.

JP 2002-309332 A JP 2005-113234 A JP 2005-113235 A WO2008 / 016150 JP 2003-277899 A JP 2004-176180 A

Claims (6)

A magnesium alloy forged product obtained by forging a magnesium alloy in which a quasicrystalline phase or an approximate crystalline phase thereof is dispersed in a magnesium matrix into a predetermined shape,
The chemical composition of the magnesium alloy is such that a rare earth element is added (100-XY) at. % Mg-Xat. % RE-Yat. % Zn alloy (RE = Y, Gd, Dy, Ho, Er, Tb), and the composition range formed by the quasicrystalline phase consisting of Mg—Zn—RE or its approximate crystalline phase in the magnesium matrix is 0. .2 ≦ X ≦ 1.5, 5X ≦ Y ≦ 7X, X and Y are atomic%,
The quasi-crystalline phase or a magnesium alloy forging its approximate crystal phase and wherein the magnesium mother phase dispersed is equiaxed. A magnesium alloy forged product obtained by forging a magnesium alloy in which a quasicrystalline phase or an approximate crystalline phase thereof is dispersed in a magnesium matrix into a predetermined shape,
The chemical composition of the magnesium alloy is (100-ab) Mg-aAl-bZn alloy not containing a rare earth element, expressed in mass%, and a quasicrystalline phase composed of Mg-Zn-Al, or an approximation thereof. The compositional regions that the crystal phase forms in the magnesium matrix are 3 ≦ a ≦ 15 and 6 ≦ b ≦ 12, and 2 ≦ a ≦ 15 and 12 <b ≦ 35, where a and b are mass%,
The quasi-crystalline phase or a magnesium alloy forging its approximate crystal phase and wherein the magnesium mother phase dispersed is equiaxed. The magnesium alloy forged product according to claim 1 or 2 , wherein the aspect ratio of the magnesium matrix phase is 2.5 or less. The magnesium alloy forged product according to any one of claims 1 to 3 , wherein the concavo-convex portion has a complicated shape formed at least in part, and the magnesium matrix phase is also equiaxed in the concavo-convex portion. Magnesium alloy forgings characterized by that. It is a manufacturing method of the magnesium alloy forgings according to claim 1 ,
A method for producing a magnesium alloy forged product, wherein the magnesium alloy is forged by a press die having a predetermined shape as an inner die by warm forging performed by heating the magnesium alloy at 450 ° C. or lower . It is a manufacturing method of the magnesium alloy forgings according to claim 2 ,
A method for producing a magnesium alloy forged product, characterized in that the magnesium alloy is forged by a press die having a predetermined shape as an inner die by warm forging performed by heating the magnesium alloy at 350 ° C. or lower .