JPS6314059B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum alloy for processing that has high strength, high impact resistance, and high fatigue strength, and a method for producing the same.
This article relates to JIS2000 series aluminum alloy materials and their manufacturing methods. As is well known, forged aluminum alloy materials have high strength per unit weight, that is, specific strength, high impact resistance, and high fatigue strength, so they are widely used in automobile parts, aircraft parts, and various other mechanical devices. It's getting old. Forging methods for obtaining this type of forged material are broadly classified into free forging and die forging, but in the case of free forging, which is mainly used to obtain large forged materials, continuous casting or semi-continuous casting is usually used. The resulting billet with a diameter of about 150 mm to 300 mm is used. In this way, conventional large-diameter billets used as free forging materials for large forgings have a casting structure that varies widely within the cross section, and in particular, there is a large variation in the position near the outer skin of the billet and near the center. Therefore, the mechanical properties may vary depending on the cross-sectional area, and there is a risk that defects such as pinholes, segregation, micro-syringes, and micro-cracks may exist. In order to obtain a good product, it is of course necessary to thoroughly inspect the billet of the forged material to select good products, and during forging, it is necessary to forge many times to eliminate the defects and non-uniform casting structure. There was a problem in that the forging process required a considerable amount of time and labor because it had to be repeated. On the other hand, die forging is normally used to obtain small forged products, but the small diameter material used for this is about 5 mmφ to 70 mmφ. It is usually obtained by casting a billet, subjecting the billet to homogenization heat treatment at a temperature of about 450°C to 600°C for about 2 to 20 hours, and then extruding it at a temperature of about 350 to 500°C. It was hot. As described above, since conventional small diameter forged materials require extrusion processing, they not only have high manufacturing costs but also have various problems as described below. In other words, (1) JIS2000 series Al-Cu-based alloys generally have high deformation resistance and low deformability during extrusion;
It is difficult to set extrusion conditions such as extrusion speed, and if the extrusion conditions are inappropriate, coarse recrystallized grains may occur near the surface of the extruded material, and microcracks may occur from the recrystallized grain boundaries. If such an extruded material is forged, there is a risk that breakage may occur due to the coarse recrystallized grains or their intergranular cracks. (2) As mentioned above, since the deformation resistance during extrusion is large, the processing heat generated by the die and material during extrusion causes
The later in the extrusion process, the extrusion process is performed at a higher temperature, and as a result, the properties of the extruded material change in the longitudinal direction, and the properties after forging also vary, resulting in non-uniform product properties. (3) In extrusion processing, the amount of deformation of the material is different between the outer skin and the center, so the processed structure formed by extrusion is different between the two parts,
In particular, with JIS 2000 series Al-Cu-based alloys, the amount of deformation is large near the outer skin of the extruded material, resulting in a fine processed structure, whereas the amount of deformation is small near the center of the extruded material, resulting in a coarse processed structure. If forging is performed against such a non-uniform working structure, the fiber structure produced during forging may be fragmented, leading to deterioration of dynamic properties such as fatigue strength and impact value. (4) In extrusion processing, crystallized substances and crystal grains such as intermetallic compounds in the billet are elongated in the extrusion direction, so the extruded material has a texture with a specific direction, and therefore is suitable for use as a forging material. Since it is not isotropic and homogeneous, the extrusion direction must be considered during forging, but depending on the shape of the product, it may not be necessary to forge in the optimal direction for all parts. In many cases, it is difficult to do so, and in that case, there is a risk that cracks may occur or the mechanical strength may locally decrease, leading to a decrease in fatigue strength. As mentioned above, small-diameter forged materials obtained by extrusion have unavoidable problems due to extrusion, especially anisotropy and inhomogeneity, which makes it difficult to have satisfactory mechanical properties, especially The reality is that fatigue strength and impact strength cannot always be obtained. It is also possible to use a small diameter rod obtained by continuous casting or semi-continuous casting as the small diameter forged material, but in that case, there are the same problems of heterogeneity and defects in the casting structure as with the large diameter billet mentioned above. Of course, before these problems were actually solved on an industrial scale,
The reality is that it is difficult to continuously cast small diameter rods of approximately 100 mmφ or less. Due to the above circumstances, the inventors of the present invention, as mentioned above, did not perform secondary plastic processing such as hot extrusion processing, which may adversely affect the properties.
Development of processing alloys that are homogeneous, have few defects, and have excellent mechanical properties, so that they can be subjected to processing such as forging with the continuous casting ingot itself or only after heat treatment. After extensive research into the development of aluminum alloys, we have found that the above requirements can be met by appropriately combining the composition and microstructure factors, and that by casting under appropriate conditions, aluminum alloys can have the appropriate microstructure factors. They discovered that it was possible to produce an alloy and came up with this invention. In other words, the first invention of this application is based on a specific component composition, specific structural conditions in an ingot, especially secondary dendrite arm spacing (hereinafter abbreviated as DAS), crystal grain size, and a second phase consisting of an intermetallic compound. It is characterized by the combination of particle size and various conditions, specifically Cu2.0-9.0%, Mg0.2-1.2%,
Si0.2-1.2%, Mn0.2-0.8%Ti, or Ti and B in total amount 0.005-0.15%, the remainder substantially consisting of Al and unavoidable impurities, and DAS is 15μm
An aluminum alloy for processing that has high strength, high impact properties, and high fatigue strength, and has a crystal grain size of 80 μm or less, and a second phase particle consisting of an intermetallic compound of 10 μm or less. be. Further, the second invention of this application is characterized by a combination of a specific component composition and specific structural conditions, particularly conditions regarding the uniformity of distribution of solute components (solid solution components) at grain boundaries and within grains. Specifically, it has the same component composition as the component composition of the first invention, and the ratio a/ This is an aluminum alloy for processing, characterized in that b is 0.70 or more. Further, the third invention of this application is characterized by the conditions for producing the aluminum alloy of the first invention. Specifically, a molten alloy having the above composition is melted, and the molten metal is Continuously cast at a solidification rate of 25℃/sec or higher, with a crystal grain size of 80μm or less and a secondary dendrite arm spacing of 15μm.
The present invention provides a method for producing an aluminum alloy for processing having high strength, high impact properties, and high fatigue strength, in which the second phase particles made of intermetallic compounds are 10 μm or less. Note that "processing" herein does not necessarily mean forging, but also includes other plastic working such as rolling, drawing/wire drawing, and extrusion, and further includes machining such as cutting. Therefore, the aluminum alloy for processing according to the present invention can be used in various plastic working and machining processes. It goes without saying that "continuous casting" here includes not only so-called completely continuous casting, but also so-called semi-continuous casting, in which a certain length is continuously cast. Each invention of this application will be explained in more detail below. First, to explain the reason for limiting the composition common to each invention, if Cu is less than 2.0%, sufficient mechanical strength cannot be obtained, and if it exceeds 9.0%, Cu is insufficient even if the ingot is subjected to solution treatment. As a result, mechanical properties such as strength, elongation, and impact value deteriorate, causing casting cracks and the like, making it difficult to manufacture the material. Conventionally, it was thought that if Cu content exceeds 6.0%, continuous casting would be difficult due to casting cracks, but at any position in the cross-sectional direction of the ingot, 25°C/sec
By continuous casting at the above solidification rate, it became possible to cast materials with a Cu content of up to 9.0%. The reason why the upper limit of the Cu content that can be continuously cast has been expanded is that by solidifying at a uniform high solidification rate within the cross section of the ingot, segregation within the cross section is reduced, making it possible to achieve an ideal internal Cu content. This is thought to be due to the fact that it is now cast in a state close to solidification. Furthermore, if Mg is less than 0.2%, sufficiently high strength cannot be obtained, while if Mg exceeds 1.2%, it forms an intermetallic compound with Si, reducing elongation and toughness. High fatigue strength and high impact strength cannot be obtained. Furthermore, if Si is less than 0.2%, no heat treatment effect will be obtained, and if it exceeds 1.2%, toughness will decrease and high impact strength will not be obtained. And also Mn
If it is less than 0.2%, the effect of obtaining high strength and high impact value will not be achieved, and if it exceeds 0.8%, coarse grains will be formed, which will not be able to satisfy the microstructure conditions described below and will also be a cause of a decrease in strength. In addition, the above-mentioned Cu, Mg, Si,
In addition to Mn, the total amount of Ti or Ti and B
Add 0.005% to 0.15%. Like this Ti or
By adding Ti/B, the crystal grains can be further refined and better mechanical properties can be obtained. The aluminum alloy for processing according to the first invention of this application has the above-mentioned composition, and also has the above-mentioned structural conditions, particularly the microstructure conditions,
That is, it is necessary that the crystal grain size as a cast structure is 80 μm or less, the DAS is 15 μm or less, and the second phase particles consisting of an intermetallic compound are 10 μm or less. Here, the second phase particles consisting of intermetallic compounds include Al-Cu, Mg-Si, Al-Mn-
Fe, Al-Fe-Si, etc. can be considered. The reason for specifying the microstructure conditions as described above is that if the crystal grain size, DAS, and second phase particle size exceed the above ranges,
Even if the alloy composition is within the above-mentioned composition range, the desired high strength, high fatigue strength, and high impact strength cannot be obtained, and if the above-mentioned sizes exceed the above-mentioned ranges, the isotropy of the structure may be affected. This is because it tends to become inhomogeneous as it loses its properties, and as a result, the workability of forging, machining, etc. is impaired, making it impossible to achieve the basic purpose of the present invention. In order to obtain the working aluminum alloy ingot of the first invention having the above-mentioned structural conditions by continuous casting, the solidification rate is 25°C/sec at any position within the cross section of the ingot. Continuous casting can be carried out by setting the cooling conditions as follows. That is, such a manufacturing method is the third invention of this application. In the above manufacturing method, the solidification rate was set at 25℃/sec.
The reason for the above stipulation is that if the solidification rate is gradually increased from a rate sufficiently lower than 25℃/sec, the grain size will suddenly change around 25℃/sec.
DAS and second phase particles are refined to meet the above conditions, in other words, at 25℃/
This is because, assuming that sec is the critical solidification rate, the various properties aimed at in the first invention are satisfied. The solidification rate here means the rate of temperature decrease at the solid-liquid interface in a continuous casting mold, and its value has been determined experimentally by inserting a thermocouple into the liquid phase from above the mold. It is detected by measuring the temperature change at the position where the solid phase contacts the solid phase. Furthermore, as a specific casting method for continuous casting as mentioned above, the commonly used float continuous casting method may be adopted, but especially for castings of 5 mmφ to 70 mm.
In order to cast materials with a diameter as small as φ, we first developed the
It is desirable to adopt the gas pressurized hot top continuous casting method proposed in No. 53-15222 and JP 54-128431, and to apply the gas pressurized hot top continuous casting method to the manufacturing method of the present invention. This allows the effects of the present invention to be best exhibited. The continuous casting ingot obtained as described above may be directly used as a working material for plastic working or machining, or may be subjected to homogenization heat treatment and then subjected to various processing, or It may be subjected to various processing after being subjected to heat treatment such as T ₆ treatment. Here, as mentioned above, the casting structure rapidly becomes finer when the solidification rate is around 25℃/sec. To explain this, based on the attached metal cross-sectional photograph, Figure 1 shows continuous casting at a solidification rate of 25℃/sec. Cu4.5%−
Mg0.6% - Si0.6% - Mn0.4% - Ti0.01% - balance Al
Fig. 2 shows the structure of an aluminum alloy having the same composition as above, which was continuously cast at a solidification rate of 0.5°C/sec. At first, uniform granular crystals appear on the entire surface, and the DAS is 15 μm.
It is clear that the second phase particles consisting of intermetallic compounds are all 10 μm or less, whereas in the case of the material shown in Figure 2, the DAS exceeds 15 μm. Moreover, it is clear that the second phase particles made of intermetallic compounds also have become considerably coarse. Next, to explain the aluminum alloy for processing according to the second invention of this application, in addition to the above-mentioned composition range conditions, this alloy has microstructural conditions such as Cu, Mg, Si, Mn, etc. in the crystal grains of the ingot. The concentration a of the solute component and Cu at the grain boundary,
Ratio a/ to concentration b of solute components such as Mg, Si, Mn, etc.
b is specified to be 0.70 or more. By making the solute concentration distribution within the grains and at the grain boundaries uniform in this way, properties close to those of the alloy of the first invention can be obtained. That is, when obtaining a continuous casting ingot (billet) with a relatively large diameter of about 100 mmφ or more, the solidification rate should be as specified in the third invention.
Even if the temperature is set at 25°C/sec or more, it may be difficult to make the crystal grain size of the ingot structure, DAS, and second phase particle sizes as fine as specified in the first invention. , by applying appropriate homogenization heat treatment to the ingot obtained at a solidification rate of 25 ° C / sec or more and adjusting the solute concentration distribution so that the ratio a / b is 0.70 or more as described above, Effects similar to those obtained when the structure is made finer as in the first invention can be obtained. This homogenization heat treatment finally changes the ratio a/b to
0.5 at a temperature of 450℃ to 530℃ so that it is 0.70 or higher.
Heat treatment may be performed for ~20 hours. In addition, in the above-mentioned aluminum alloy for processing of the first invention, it is ideal not only to set the crystal grain size, DAS, and second phase particle size as described above, but also to set the ratio a/b to 0.70 or more. It is desirable to set it to , and by doing so, various characteristics are further improved. Next, Examples and Comparative Examples of the invention of this application will be described, and their characteristic improvement effects will be explained in detail with reference to the attached graphs. Example 1 4.7%Cu-0.7%Si-0.6%Mn-0.5%Mg-0.012
A molten aluminum alloy consisting of %Ti-0.003%B with the balance Al was produced and cast into a 53 mm diameter round bar by gas pressure hot-top continuous casting at a solidification rate of 25°C/sec. Comparative Example 1 Casting was carried out in the same manner as in Example 1 except that the solidification rate was 0.15° C./sec. Comparative Example 2 Casting was carried out in the same manner as in Example 1 except that the solidification rate was 3° C./sec. Test pieces along the axial direction were cut from the round bars obtained in Example 1 and Comparative Examples 1 and 2 at different distances from the outer periphery, and each test piece was heated at 505°C for 6 hours. hot water cooling
Thereafter, it was subjected to an aging treatment at 170°C for 8 hours to obtain a so-called _T6 material, and its tensile strength and push strength were measured at room temperature. The results are shown in FIG. In Fig. 3, the x mark indicates the test piece obtained in Example 1 (25℃/sec), and the ● mark indicates the test piece obtained in Comparative Example 1 (0.15℃/sec).
sec), the ○ mark is the test piece obtained by Comparative Example 2 (
℃/sec) are shown. As is clear from Figure 3, when the solidification rate is 0.15°C/sec and 3°C/sec, there is a considerable difference in tensile strength and elongation at the outer periphery and center, whereas Speed is 25℃/
sec, it can be seen that there is almost no variation in both tensile strength and elongation, and that they are almost uniform from the outer periphery to the center. In addition, the DAS of the ingot round bars obtained in Example 1 and Comparative Examples 1 and 2,
Table 1 shows the results of measuring the size of the phase particles and the solute concentration ratio a/b within the grains and at the grain boundaries.

[Table] As is clear from Table 1, the solidification rate is 25℃/
In the case of sec, both DAS and second phase particles are fine and the solute concentration ratio a/b is large, but the solidification rate is 0.15℃/
sec, 3℃/sec, the DAS and second phase particles become much coarser and the solute concentration ratio a/b also decreases.If you refer to these results and the test results in Figure 3, these It is clear that the microstructural factors have a large influence on tensile strength and elongation. Example 2 4.5%Cu-0.6%Si-0.6%Mg-0.8%Mn-0.015
A molten alloy with a composition of %Ti and balance Al is produced and cast into a 78mmφ round bar using a gas pressure hot-top continuous casting method, varying the solidification rate from 5℃/sec to 80℃/sec. did. The obtained round bar ingot
A test material was prepared by homogenizing at 505°C for 8 hours. Wedge test pieces as shown in Fig. 4 were cut out from the test materials of each solidification rate, and the wedge test pieces were hot forged at temperatures of 300°C, 400°C, and 450°C. The critical machining rate at which cracking occurred was measured. The results are shown in FIG. In FIG. 5, the shaded area above each broken line represents the area where cracks occur. As is clear from FIG. 5, as the forging temperature increases, the critical working rate for forging crack occurrence increases. In addition, as the solidification rate increases at any forging temperature, the critical machining rate for forging cracking increases, making it difficult for cracks to occur, and the critical machining rate for cracking increases markedly especially when the solidification rate is around 25°C/sec. It is clear that This fact corresponds to the fact that the structure changes significantly at a solidification rate of around 25° C./sec as described above. Furthermore, the test materials of each of the above-mentioned solidification rates were tested for general hot workability by the hot torsion method (for example, described in "Light Metal" Vol. 20, No. 5, Horiuchi et al.), and were tested for deformation resistance and deformability. was measured. The results are shown in FIG.
As is clear from Figure 6, the deformation resistance is the solidification rate of 25
It clearly decreases when the solidification rate is around 25°C/sec, and the deformability also increases markedly when the solidification rate is around 25°C/sec. From these results, it is clear that the alloy according to the present invention has extremely good workability. Example 3 2.3%Au-0.3%Mg-0.3%Si-0.2%Mn-0.02
Alloy with a composition of %Ti-balance Al (denoted as A alloy)
and 4.5%Cu−0.6%Mg−0.7%Si−0.6%Mn−
An alloy with a composition of 0.01% Ti - balance Al (referred to as B alloy) and 8.7% Cu - 1.0% Mg - 1.0% Si - 0.7% Mn.
- 0.012% Ti - 0.003% B - The balance is Al (referred to as C alloy).
These are made using gas pressurized hot-top continuous casting method.
The solidification rate was varied from around 6°C/sec to around 80°C/sec and cast into a round bar with a diameter of 62 mm. Furthermore, C
The addition of Ti and B in the alloy is Al-5%Ti-
A master alloy with a composition of 0.7% B was used. For each round bar ingot obtained in Example 3 above
When DAS was measured, the results shown in FIG. 7 were obtained. As is clear from Figure 7, the DAS is A, B,
C For each alloy, the solidification rate decreases rapidly as the solidification rate increases until it reaches about 25°C/sec.
It was confirmed that the critical solidification rate is set at 25°C/sec, and that the solidification rate remains approximately constant at about 6 μm at higher solidification rates. From this, it is clear that in the aluminum alloy having the composition of the present invention, the solidification rate of 25°C/sec has an important meaning in terms of structure, that is, it is the critical solidification rate for microstructural refinement.
Furthermore, FIG. 8 shows the results of measuring the tensile strength and elongation of round bar ingots of alloy B at various solidification rates as representative of the above-mentioned alloys. As is clear from FIG. 8, it was confirmed that both the tensile strength and elongation increased in accordance with the DAS measurement results shown in FIG. In particular, it can be seen that the improvement in elongation is remarkable.
Furthermore, FIG. 9 shows the results of an impact test and a drawing test performed on round bar ingots of alloy B at various solidification speeds. In these cases as well, the solidification rate is 25
It was confirmed that the impact value and reduction rate (reduction rate of area) were significantly improved at °C/sec. From the test results of the above examples, the alloy material of the present invention has a DAS of 15 μm or less at a solidification rate of 25°C/sec, and the strength, elongation, impact value, and reduction rate are all remarkable at the solidification rate and DAS. No significant change was observed even if the solidification rate was further increased, and it is therefore clear that the solidification rate of 25°C/sec is the critical point. Example 4 4.0%Cu-0.2%Si-0.6%Mg-0.6%Mn-0.01
A molten aluminum alloy having a composition of %Ti and balance Al was produced and cast into a round bar of 35 mmφ at a solidification rate of 30° C./sec using a gas-pressure hot-top continuous casting method. The round bar ingot was forged into a conrod using normal hot forging, heat treated at 505℃ for 2 hours, water cooled and solution treated, and aged at room temperature for 2 days (T ₄ treatment). A fatigue test was conducted with the above-mentioned conrod shape. Comparative Example 3 A molten alloy having the same composition as in Example 4 was cast by ordinary direct chill casting, and hot extrusion was performed at an extrusion ratio of 40 to obtain an extruded rod of 35 mmφ. This extruded rod was subjected to hot forging, solution treatment, and _T4 treatment under the same conditions as in Example 4, and a fatigue test was conducted. The fatigue test results of Example 4 and Comparative Example 3 are shown in FIG. In addition, since the stress value of the connecting rod changes within its plane, the vertical axis in FIG. 10 is indicated by the test load. As is clear from FIG. 10, it was confirmed that the fatigue strength of the forged material obtained in Example 4 was significantly superior to that obtained in Comparative Example 3. This is because in Comparative Example 3, the extruded material is used as the forging material, so the fibrous texture generated during extrusion is divided during forging, and a normal fibrous structure is not formed by forging, whereas in Example 4, the internal structure This is thought to be because the forging material is an ingot with uniform and isotropic properties, so a normal fibrous structure is obtained regardless of the forging direction. As is clear from the above description and each example, the aluminum alloy for processing of the present invention is homogeneous and isotropic from the center to the surface, and has high strength, high impact properties, and high fatigue strength. Moreover, because it has excellent workability, it can be directly subjected to plastic working such as forging and machining such as cutting without performing preliminary processing such as extrusion. The manufacturing cost of the parts is low, and excellent properties can be exhibited through various processing such as forging without being adversely affected by preliminary processing such as extrusion. Furthermore, according to the method for producing an aluminum alloy for processing according to the present invention, effects such as being able to simply and easily obtain an alloy having excellent properties as described above can be obtained.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional photograph of the metallographic structure of the alloy of this invention.
Fig. 2 is a cross-sectional photograph of the metallographic structure of the comparative material, Fig. 3 is a graph showing the tensile strength and elongation of the test pieces according to Example 1 and Comparative Examples 1 and 2, and Fig. 4 is a perspective view showing the shape of the wedge test piece. Figure 5 is a graph showing the results of measuring the critical machining rate for forging crack occurrence using a wedge test piece using the sample material of Example 2. A graph showing the results of measuring resistance and deformability, Fig. 7 is a graph showing the DAS measurement results of each alloy ingot according to Example 3, and Fig. 8 is a graph showing the results of measuring DAS of each alloy ingot according to Example 3. Figure 9 is a graph showing the tensile strength and elongation of the specimen, and Figure 10 is a graph showing the impact value and reduction ratio of the specimen obtained from the B alloy ingot.
The figure is a graph showing the fatigue strength characteristics of the forged materials obtained in Example 4 and Comparative Example 3.

Claims (1)

[Claims] 1 Cu2.0-9.0% (weight%, the same applies hereinafter), Mg0.2
~1.2%, Si0.2~1.2%, Mn0.2~0.8%, Ti or Ti and B in a total amount of 0.005~0.15%, the remainder substantially consisting of Al and unavoidable impurities, and crystal grains The diameter is 80 μm or less, and the secondary dentrite arm interval is 15 μm or less,
In addition, the second phase particles consisting of intermetallic compounds are 10 μm thick.
An aluminum alloy for processing having high strength, high impact properties and high fatigue strength, characterized by: 2 Cu2.0~9.0%, Mg0.2~1.2%, Si0.2~1.2%,
Mn0.2-0.8%, Ti or Ti and B in total amount
0.005 to 0.15%, the remainder substantially consisting of Al and unavoidable impurities, and the ratio a/b of the solute concentration a within the grain to the solute concentration b at the grain boundary is
An aluminum alloy for processing having high strength, high impact properties, and high fatigue strength, characterized by a coefficient of 0.70 or more. 3 Cu2.0~9.0%, Mg0.2~1.2%, Si0.2~1.2%,
Mn0.2-0.8%, Ti or Ti and B in total amount
A molten aluminum alloy with a composition of 0.005 to 0.15%, the balance substantially consisting of Al and unavoidable impurities is produced, and the molten metal is continuously cast at a solidification rate of 25°C/sec or more to produce a crystal grain size of 80 μm or less. In addition, the secondary dentrite arm spacing is 15 μm or less, and the second phase particles consisting of intermetallic compounds are
A method for producing an aluminum alloy for processing having high strength, high impact properties, and high fatigue strength, characterized by obtaining an aluminum alloy having a diameter of 10 μm or less.