JPH0339765B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing aluminum alloy tubes for manufacturing wheels, and provides a preferred method for manufacturing aluminum alloy tubes that have excellent cold workability, high strength, and good corrosion resistance as materials for manufacturing vehicle wheels. This is what we are trying to provide. Manufacturing vehicle wheels from aluminum alloy materials is lightweight and has a unique luster, and is widely practiced as it is particularly suitable for energy saving purposes in recent years. The present applicant has also proposed production by the present applicant, for example, in JP-A-56-131033. By the way, the aluminum alloys used for such purposes are
JIS A5005, 5052, 5NO1, 5056, 5083, 5N02,
5454 and the like are known, but these have drawbacks in either or both of strength and moldability. For example, extruded pipe materials according to JIS A5005, 5052, and 5N01 may have good extrusion, rolling, or formability, but the Mg% is generally around 1 to 2%, and the maximum is as low as 2.8%, so the mechanical strength is poor in fatigue resistance. It is not necessarily favorable in terms of strength properties such as (δβ≒20Kg/mm ² or less), and in terms of structure, it has large recrystallized grains of 200 to 300μm, so it may cause wrinkles on the compressed surface when bending and forming. Defects are likely to occur, and these wrinkle-like defects deteriorate the fatigue properties of the product. On the other hand, those according to JISA5056, 5083, and 5N02 generally have a Mg content of about 4 to 5.5%, and at least 3.5%.
% or more, and therefore the mechanical strength and fatigue resistance as described above are high, but the extrusion, rolling and molding processability are significantly inferior. On the other hand, those of JIS A5454 have an intermediate Mg of 2.4 to 3.0, and are somewhat preferable in terms of strength, but
Since the Mn% is as high as 0.5 to 1.0%, a coarse grain layer with a thickness of approximately 300 μm occurs on the surface of the extruded tube, and the inside becomes a fiber structure, which causes cracks to occur in the axial direction when the tube is expanded and formed into a wheel. It will be easy. The present invention was devised after repeated detailed studies in view of the above-mentioned circumstances, and the
Mg: 2.8~3.5%, Mn: 0.2~0.5%, Cr: 0.05~
0.2%, Ti: 0.001~0.1%, B: 0.0001~0.01%, and the remainder consists of Al and unavoidable impurities.The size of the recrystallized grains in the axial cross section of the extruded raw tube is the average grain size. The present invention provides an aluminum alloy blank tube for wheel manufacturing, which is characterized by a diameter of 100 μm or less, and a preferable manufacturing method thereof is to homogenize an aluminum alloy ingot having the above composition at 500°C or higher for 3 to 24 hours. After chemical heat treatment, hot working rate (area reduction rate, where the billet cross-sectional area is B and the tube cross-sectional area is P, area reduction rate =
(expressed as (1-P/B)×100) is 95% or more extruded, and the temperature at the exit of the die during extrusion is 500° C. or higher. In other words, the product according to the present invention shows good results in extrusion, rolling and forming processability equivalent to JIS A5005 and 5052, and also has high values in mechanical properties and fatigue strength equivalent to JIS A5083 and 5056. Furthermore, even during tube expansion molding, no axial cracks occur. First, the reasons for limiting the composition range of the product according to the present invention will be explained as follows. be. As mentioned above, such Al-Mg alloys are solid solution hardening alloys, and the mechanical strength and fatigue strength improve as the amount of Mg in the solid solution increases. On the other hand, if the Mg content exceeds 3.5%, the degree of work hardening becomes significant, the elongation decreases, the formability deteriorates, and the material becomes more likely to break during the forming process. Therefore, it is set at 2.8 to 3.5%. Furthermore, this Mg
The amount should be specifically determined taking into account the contents of Mn and Cr.
Since all Cr tends to reduce moldability, when the amount added is relatively large, it is preferable to select a low amount within the above range. Mn is a reduction element along with Cr, which will be described later, and is added to prevent coarsening of recrystallized grains in Al-Mg alloys. Let the crystals come out,
During high-temperature extrusion processing, this crystallized material is further partially dissolved or finely dispersed to form Al-Mn, Al-Cr, Al-Mg.
- Fine compounds such as Mn-Cr, etc., which are in solid solution as mentioned above, become fine crystallized substances in the subsequent cooling process, and together with the internal strain caused by advanced processing, many recrystallization nuclei are generated and the crystallization occurs again. This brings about preferable refinement of the crystal structure and improves fatigue strength. However, Mg is a solid solution in the crystal grains in the ingot metal structure and is distributed as fine particles during heat treatment, and if it is less than 0.2%, the above effects cannot be obtained appropriately; % or more, the number of Mn particles increases and exhibits a type of precipitation hardening effect, impairing its formability.Also, hard and brittle giant Mn-based crystals are generated, reducing formability and increasing notch sensitivity, making it difficult to form. Since cracks would occur during processing, this was set as the upper limit of 0.2 to 0.5%. Cr acts in the same way as Mn for the purpose of preventing coarsening of recrystallized grains, but this Cr is dissolved in solid solution near the grain boundaries of crystals (surface layer of crystal grains) and must be included together with Mn. However, by heat treatment, it precipitates finely and improves fatigue strength.
If it is less than 0.05%, such an effect cannot be properly obtained, while if it is more than 0.20%, the crystallized compound tends to increase in size and become a starting point for cracking during rim processing, so the content is set at 0.05 to 0.2%. Ti and B prevent cracking of the ingot during casting by refining the crystal grains of the casting structure, and it is difficult to obtain this effect if the content is below the lower limit of each, and if the content is above the upper limit, it is difficult to obtain this effect. Then, Mn and Cr
Coarse intermetallic compounds are generated, which reduces mechanical properties such as elongation and toughness, and deteriorates fatigue strength. In principle, components other than the above are Al and unavoidable impurities, but Cu is within 0.1%, Ni
Even if Zn is contained within 0.1% and Zn is contained within 0.1%, the substance of the present invention will not be impaired. Similarly, Si may be contained as appropriate with an upper limit of 0.2% and Fe as an upper limit of 0.3%. Next, in the present invention, Mg, Mn,
An aluminum alloy raw tube containing Cr and Ti with the remainder being Al and unavoidable impurities, with an average grain size of recrystallized grains in the axial cross section of 100 μm or less, and is used for obtaining wheels. If the recrystallized grain size is larger than this, roughness and wrinkles are likely to occur on the bending surface during rim forming, and wrinkles and cracks are unavoidable, especially when the size exceeds 200 μm. be. In terms of fatigue resistance, it is possible to obtain a highly effective and highly durable product by setting the average grain size of recrystallized grains to 100 μm or less. Extrusion molding may be performed by either forward extrusion or backward extrusion. In addition, as a manufacturing method to accurately obtain the raw tube of the present invention as described above, homogenization heat treatment is carried out for a long time to sufficiently dissolve Mn and Cr as a solid solution, and the crystals and precipitates made of these are finely dispersed. It is necessary to do so. In other words, homogenization heat treatment itself has been conventionally carried out for such Al-Mg alloys, but conventionally it is about 500℃ x 2 hours, and although Mg homogenization can be achieved even at this level, According to the results of detailed study by the inventors,
The precipitation of Mn and Cr is still insufficient, and it is difficult to achieve sufficient precipitation of Mn and Cr to obtain the target properties in an alloy with the above-mentioned composition.
It is necessary to carry out homogenization heat treatment at a temperature of 500°C or higher for 3 hours or more, particularly at a temperature of 500°C or higher for 4 hours or more. Regarding the extrusion processing performed after this heat treatment, it is preferable to set the hot processing rate to 95% or more, and by performing processing with such a high processing rate, Mg, Mn, Cr, and Ti can be removed to the above-mentioned extent. In the containing aluminum alloy, a large number of recrystallization nuclei are generated and the structure can be refined. During this extrusion process, the temperature at the exit of the die is set to 500℃ or higher.
By keeping the temperature above ℃, recrystallization can be properly achieved after extrusion processing, and the fine crystals can become spherical, making it an accurate material that will not cause cracks during the subsequent molding process to form the rim part. can get.
If the die exit temperature does not reach 500℃, the structure obtained by extrusion will hardly recrystallize, resulting in a structure in which processed structure and recrystallized grains are mixed, so bending processes such as rim formation are not possible. Even if it is subsequently annealed, it does not become a uniform but fine recrystallized grain structure, but instead becomes a coarse recrystallized grain structure, and even if the bending workability is slightly improved, the In this case, rough skin defects are inevitable. Specific examples according to the present invention will be described below. Example 1 An Al alloy ingot (hollow billet) having the composition shown in Table 1 below was prepared.

[Table] All of these ingots were subjected to homogenization heat treatment at 540℃ for 6 hours, and then extruded using a large extruder to achieve a hot working rate of 98%.
A 290 mm (thickness: 5 mm) raw tube was manufactured. The temperature at the exit of the extrusion die is the same for any alloy ingot.
The temperature was 505 to 510°C, and the metal structure and other properties of the extrusion-molded pipe thus obtained are summarized in Table 2 below.

【table】

[Table] The structure of these extruded pipes is as shown in the attached drawing, Figure 1, of which (a) is that of JIS A5052, which is a comparative material, and (b) is that of comparative material.
The fiber structure inside JIS A5454, (c) shows the JIS A5154 material which is also a comparison material, and (d) shows the one according to the present invention. However, the results of tube expansion molding on the wheel rim section with the cross-sectional shape shown in Figure 3, which is a typical cross-sectional shape of a wheel, show that although the molding of (a) is easy, it has poor strength and fatigue resistance. It is clear from the results in Table 2 that it is inferior in properties such as bending properties and wrinkles occur in bending workability; cracks occur at the end of the expanded tube in the case of (b), and cracks occur in the case of (c). Although it was better than (a) in terms of strength, it was still insufficient, and it was confirmed that (d) according to the present invention was preferable in both strength and moldability. Example 2 An Al alloy ingot (hollow billet) having the composition shown in Table 3 below was used.

[Table] The ingot was soaked at 540°C for 6 hours, and then processed using a large extruder under the processing conditions shown in Table 4 below.
A hollow tube with a diameter of 300 mm and an inner diameter of 290 mm was manufactured. As for the comparative material, as shown in Table 4, the hollow tube was annealed for 350 x 2 hours.

[Table] The metal structures of these raw pipes are shown in Figure 2, where (a) is the one according to the present invention, (b) is the comparative material before annealing, and (c) is the annealed material. Show what comes after. However, the characteristics of these raw pipes are summarized as shown in Table 5 below.

[Table] In other words, the material according to the present invention has a fine and uniform recrystallized structure and has excellent bending workability, whereas the comparative material has significantly inferior bending workability, and even after annealing, it has a fine and uniform recrystallized structure. It has a structure in which recrystallized grains are mixed, and the surface becomes rough during bending. According to the present invention as explained above, it is possible to precisely manufacture an aluminum alloy base tube that has excellent cold workability, high strength, and does not cause surface roughness, and has industrial effects. This is a great invention.

[Brief explanation of drawings]

The drawings illustrate embodiments of the invention,
Fig. 1 is a micrograph at 15x magnification showing the metal structures of the comparative material and the inventive material in Example 1 of the present invention, and Fig. 2 shows the metal structures of the inventive material and the comparative material in Example 2. Fig. 3 is a sectional view of a vehicle wheel rim.

Claims (1)

[Claims] 1 Mg: 2.8-3.5%, Mn: 0.2-0.5%, Cr:
0.05~0.2%, Ti: 0.001~0.1%, B: 0.0001~
An aluminum alloy ingot containing 0.01% and the remainder consisting of Al and unavoidable impurities is heated at 500℃ or higher for 3
~Hot processing rate after 24 hours of homogenization heat treatment
1. A method for producing an aluminum alloy blank tube for wheel manufacturing, which comprises performing extrusion processing of 95% or more, and increasing the temperature at the exit of a die during the extrusion processing to exceed 500°C.