ALUMINUM ALLOY FORGED WHEEL AND METHOD FOR MANUFACTURING SAME

Abstract

A wheel forged from an aluminum alloy, comprising a hub part into which an axle is to be inserted, a disc part provided on a circumference of the hub part, and a rim part provided on the circumference of the disc part, wherein at least the disc part and / or the rim part are manufactured by forging an ingot obtained by casting an aluminum alloy containing 9.0 wt% to 12.5 wt% of Si, 0.5 wt% to 3.4 wt% of Cu, 0.2 wt% to 0.9 wt% of Mg, 0.7 wt% or less of Fe, 0.005 wt% to 0.15 wt% of Ti, one of Sr, Sb, Ca, and Na with 0.01 wt% to 0.15 wt% for Sr, 0.01 wt% to 0.20 wt% for Sb, 10 wt% to 200 wt% for Ca, and 10 to 200 wt. ppm for Na, wherein the aluminum alloy optionally further contains 0.3 wt.% or less of Mn, 0.2 wt.% or less of Cr, 0.2 wt.% or less of Ni and 0.4 wt.% or less of Zn and optionally further 0.0002 wt.% to 0.05 wt.-% B, the remainder being Al and unavoidable impurities, andthe metal structures of the disc part and / or the rim part have a band-like zone in which Si particles are present in a small amount, with a width of 20 µm or less and an average particle diameter of eutectic Si is 5 µm or less.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to an aluminum alloy forged wheel and a method for manufacturing the aluminum alloy forged wheel. 2. Description of the state of the art

[0002] Wheels made of aluminum alloy are commonly known as automotive wheels, where a hub portion, a disc portion, and a rim portion are formed integrally. Methods for manufacturing an aluminum alloy wheel include low-pressure casting, gravity casting, high-pressure casting, molten metal forging, and hot forging. Among these manufacturing methods, hot forging is considered the manufacturing method for producing aluminum alloy wheels with the best mechanical properties.

[0003] Japanese Patent Laid-Open No. 2007-210017 discloses a vehicle wheel including a hub portion to which an axle is to be attached, a disc portion disposed around the hub portion, and a rim portion integrally formed around the disc portion, the vehicle wheel being manufactured by forging an aluminum alloy containing, by weight, 0.95% to 1.35% Si, 0.8% to 1.2% Mg, 0.2% to 0.5% Cu, 0.4% to 0.7% Mn, 0.3% or less Fe, 0.05% to 0.25% Cr, and the balance being aluminum, the vehicle wheel having a metal structure in which crystal grains of a design surface of the disc portion and the rim portion have a particle diameter of 50 μm or less. Further descriptions of aluminum alloys can be found in JP H10 - 204 566 A, JP 2005 - 281 742 A, JP H05 - 287 427 A, DE 25 17 275 A1 and DE 38 23 476 A1. SUMMARY OF THE INVENTION

[0004] The above-described prior art can, as reported, provide a wheel forged from an aluminum alloy capable of achieving weight reduction while maintaining preferred mechanical properties.

[0005] Since a vehicle wheel is repeatedly subjected to stresses caused by uneven road surfaces and the like during extended travel, the vehicle wheel must be lightweight, yet strong and robust enough to withstand the repeated stresses exerted on the wheel during travel and not break. To achieve stable handling during extended travel, the vehicle wheel must also be virtually indeformable (very stiff) with respect to the stresses.

[0006] In addition, since heat is generated at an extremely high temperature when the vehicle is braking and the wheel is to be placed near a heat source, the wheel must also have sufficient heat resistance to maintain a high strength property even when exposed to high temperatures for a long time.

[0007] An object of the present invention is to meet such requirements for vehicle wheels and to provide a wheel forged from an aluminum alloy which is lightweight and has high fatigue strength against repeated loads, high rigidity, high heat resistance and the like.

[0008] In order to solve the above-described problem, the present invention is arranged as follows. A wheel forged from an aluminum alloy, comprising a hub part into which an axle is to be inserted, a disc part provided on a circumference of the hub part, and a rim part provided on a circumference of the disc part, wherein at least the disc part and / or the rim part are produced by forging an ingot obtained by casting an aluminum alloy containing 9.0 wt% to 12.5 wt% Si, 0.5 wt% to 3.4 wt% Cu, 0.2 wt% to 0.9 wt% Mg, 0.7 wt% or less Fe, 0.005 wt% to 0.15 wt% Ti, one of Sr, Sb, Ca and Na with 0.01 wt% to 0.15 wt% for Sr, 0.01 wt% to 0.20 wt% for Sb, 10 wt% to 200 wt% for Ca and 10 ppm by weight to 200 ppm by weight-ppm for Na, the remainder being Al and unavoidable impurities, and the metal structures of the disc part and / or the rim part have a band-like zone in which Si particles are present in a small amount, with a width of 20 µm or less and an average particle diameter of eutectic Si is 5 µm or less.

[0009] A wheel forged from an aluminum alloy with the properties described above is lightweight and has high fatigue strength, high rigidity, and high heat resistance. Therefore, a vehicle wheel with high strength and durability can be obtained, which is also capable of achieving preferred driving performance. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A and Fig. 1B are photographs illustrating a metal structure of an aluminum alloy forged wheel according to an embodiment of the present invention, wherein Fig. 1A illustrates a metal structure according to an example of the present invention and Fig. 1B illustrates a metal structure according to a comparative example; Fig. 2A to 2C are explanatory diagrams showing a shape example of an aluminum alloy forged wheel according to the embodiment of the present invention, wherein Fig. 2A represents an example (a one-piece example) formed exclusively by forging, Fig. 2B shows an example (a one-piece example) in which a rim part is spin-formed, and Fig. 2C illustrates an example (a two-part example) in which a rim part is bonded to a periphery of a disc part; Fig.3 is an explanatory diagram (an example of a type in which the disc part has a spoke shape) showing a shape example of the aluminum alloy forged wheel according to the embodiment of the present invention; Fig. 4 is an explanatory diagram showing a flow chart of the main manufacturing steps of a raw material block for forging; Fig. 5 is an explanatory diagram showing a flow chart of the machining steps of a wheel; Fig. 6 is an explanatory diagram showing a forging step; Fig. 7 is an explanatory diagram for comparing the specific fatigue strength and a specific elastic modulus of wheel materials; and Fig.8 is a graph showing a result (a variation in tensile strength relative to a temperature variation during 100 hours of heat exposure) of a heat resistance test of a disk part according to an example. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of the present invention will be described below. A wheel forged from an aluminum alloy according to the embodiment of the present invention contains a very high Si content, and after forging, an average particle diameter of eutectic Si in a metal structure becomes 5 µm or less.

[0011] Based on a new finding that an imbalance of eutectic Si particles in the metal structure significantly affects the fatigue strength against repeated loads, the aluminum alloy forged wheel according to the embodiment of the present invention focuses on “a width of a band-like zone in which Si particles are present in a small amount” serving as an index of fatigue strength and setting the width to 20 μm or less.

[0012] A machined article obtained by forging an ingot produced by casting a high-Si aluminum alloy exhibits "a band-like zone in which Si particles are present in a small amount," which is a trace of an α-phase from casting along a wrought metal flow. Fig.1A is a photograph showing an example of a metal structure of the aluminum alloy forged wheel according to the embodiment of the present invention, and Fig. Figure 1B is a photograph showing a metal structure of a comparative example that largely retains the previously described band-like zone. In the drawings, W denotes "a width of a band-like zone in which Si particles are present in a small amount."

[0013] With the comparison example, in which broad band-like zones, as in Fig. 1B, the band-like zones are fragile and promote crack propagation, leading to a decrease in tensile strength and fatigue strength. In particular, in a fatigue strength test (a rotating bending fatigue test with 10 7cycles), the band-like zones lead to premature abnormal fracture. In contrast, by limiting all Ws, where each W means “a width of the band-like zones in which Si particles are present in a small amount,” to 20 µm or less, as in Fig. 1A, the fatigue strength can be significantly increased. Fig. 1A and Fig. To obtain the metal structure shown in Figure 1B, it is important that, by miniaturizing an α-layer of a solidified forging structure and eutectic Si particles of a cast ingot to be used as a forging raw material and by performing a sufficient machining / forming process, the eutectic Si particles are crushed into fine particles by plastic flow deformation during forging, which should be uniformly dispersed, in order to miniaturize the ribbon-like zone and the previously described eutectic Si particles.

[0014] An aluminum alloy for forming the aluminum alloy forged wheel according to the embodiment of the present invention contains 9.0 wt% to 12.5 wt% of Si, 0.7 wt% or less of Fe, 0.5 wt% to 3.4 wt% of Cu, 0.2 wt% to 0.9 wt% of Mg, 0.005 wt% to 0.15 wt% of Ti, one of Sr, Sb, Ca and Na with 0.01 wt% to 0.15 wt% for Sr, 0.01 wt% to 0.20 wt% for Sb, 10 wt% to 200 wt% for Ca and 10 wt% to 200 wt% for Na, with the balance being Al and inevitable impurities.

[0015] Generally, Si contained in aluminum alloys is an alloying component effective in heat resistance, resulting in a reduction in the coefficient of thermal expansion in high temperatures. Si improves material strength through dispersion strengthening and precipitation strengthening, precipitates a Mg2Si phase, which is a compound of Si and Mg, through heat treatment to improve material strength, and enables robust material strength and heat resistance to be achieved through miniaturization and uniform dispersion of eutectic Si particles with an average particle diameter of 5 μm or less.

[0016] When the Si content is less than 9.0 wt%, since crystallization of eutectic Si particles hardly occurs, miniaturization and uniform dispersion of eutectic Si particles with an average particle diameter of 5 μm or less cannot be achieved, resulting in insufficient material strength. When the Si content exceeds 12.5 wt%, crystallization of coarse (for example, 100 μm or more) primary crystalline Si particles occurs and inhibits forging formability and spin formability, increasing the likelihood of abrasion and damage to cutting tool blades and deteriorating cutting ability. In addition, a crystallization point of the primary crystalline Si particles becomes a nucleus of fatigue fracture due to stress concentration and prevents an increase in fatigue strength.

[0017] The Cu contained in the aluminum alloy described above becomes a solid solution in a mother phase, precipitates as an Al2Cu phase through heat treatment, and improves both the material strength and heat resistance at 150 °C. When the Cu content is less than 0.5 wt%, a sufficient strength-improving effect through solid solution strengthening and dispersion strengthening is not achieved, and when the Cu content is more than 3.4 wt%, the crystallization of a coarse Al2Cu phase is more likely to occur, which reduces the forging formability and spin formability and deteriorates the corrosion resistance.

[0018] The Mg contained in the aluminum alloy described above improves material strength by precipitating a Mg2Si phase, as described above. When the Mg content is less than 0.2 wt%, the strength-enhancing effect is weak, and when the Mg content exceeds 0.9 wt%, the ductility decreases significantly, inhibiting forging formability and spin formability.

[0019] The Fe contained in the previously described aluminum alloy crystallizes as an acicular Al-Fe(-Si)-based intermetallic compound, increasing high-temperature strength. When the Fe content exceeds 0.7 wt%, giant acicular crystallized products are frequently formed, and these are likely to induce adverse effects, such as causing cracks during casting or spin forming, or the giant acicular crystallized products becoming nuclei of fatigue fractures.

[0020] The Ti contained in the aluminum alloy described above is added as a "heterogeneous nucleus," which is a crystal nucleus for miniaturizing a forged structure. Ti is added as an Al-Ti or Al-Ti-B based compound. When the Ti content is less than 0.005 wt%, the miniaturization effect of the forged structure is insufficient. When the Ti content exceeds 0.15 wt%, needle-like compounds crystallize, deteriorating forging formability and spin formability. These coarse needle-like compounds become nuclei of fatigue fracture and prevent the improvement of material strength.

[0021] A suitable content of B, added together with Ti as a miniaturizing agent, is 0.0002 wt% to 0.05 wt%. If a large amount of B is added, B couples with Ti and increases the likelihood of forming coarse needle-like compounds, which, as described above, can become nuclei of fatigue fracture.

[0022] A single element consisting of Sr, Sb, Ca, and Na is added to the aluminum alloy described above. These additives, when added in an appropriate amount, have the function of miniaturizing, granulating, and rounding the corners of the eutectic Si crystal products. If the amount of additives is too small, the miniaturization effect is weakened, but if the amount of additives is too large, coarse crystallized products are formed, which inhibits forging formability. Suitable amounts of each of the additives are 0.01 wt% to 0.15 wt% for Sr, 0.01 wt% to 0.20 wt% for Sb, 10 wt% to 200 wt% for Ca, and 10 wt% to 200 wt% for Na.

[0023] The aluminum alloy described above preferably further contains suitable amounts of Mn, Cr, Ni and Zn. Suitable contents thereof are 0.3 wt% or less for Mn, 0.2 wt% or less for Cr, 0.2 wt% or less for Ni and 0.4 wt% or less for Zn.

[0024] When Mn is present in 0.3 wt% or less, it causes crystallization of a fine Al-Mn-based or Al-Fe-Mn(-Si)-based intermetallic compound and suppresses the growth of recrystallized grains during hot forging or T6 heat treatment (a solution treatment). When the Mn content exceeds 0.3 wt%, crystallization of a coarse Al-Fe-Mn(-Si)-based intermetallic compound occurs, causing a decrease in material strength and ductility and adversely affecting the core of a fatigue fracture.

[0025] When Cr is present in 0.2 wt% or less, it causes crystallization of a fine Al-Cr-based or Al-Fe-Cr(-Si)-based intermetallic compound and suppresses the growth of recrystallized grains during hot forging or T6 heat treatment (a solution treatment). When the Cr content exceeds 0.2 wt%, crystallization of a coarse Al-Fe-Cr(-Si)-based intermetallic compound occurs, causing a decrease in machinability and leading to a decrease in ductility and material strength.

[0026] When Ni is contained in 0.2 wt% or less, Ni causes crystallization of a fine Al-Ni-based intermetallic compound and contributes to improving heat resistance. When the Ni content exceeds 0.2 wt%, crystallization of a coarse intermetallic compound containing Ni occurs, resulting in a decrease in machinability.

[0027] Zn is an impurity mixed from aluminum scrap or the like. Although Zn increases material strength when present together with Mg (precipitation of a MgZn2 phase), the Zn content is preferably low. If the Zn content exceeds 0.4 wt%, Zn may potentially impair corrosion resistance (resistance to stress corrosion cracking, etc.).

[0028] The aluminum alloy forged wheel according to the embodiment of the present invention can be applied to various shapes such as those used in Fig. 2A to 2C and 3. A wheel 1, which refers to all the form examples described here, includes a hub part 2 into which an axle is to be inserted, a disc part 3 provided on a circumference of the hub part 2, and a rim part 4 provided on a circumference of the disc part 3. The wheel 1 shown in Fig.The example shown in Figure 2A represents an example in which the wheel 1 is formed exclusively by forging, while the example shown in Fig. 2B shows an example in which the rim part 4 of the wheel 1 is spin-formed. In both Fig. 2A and Fig. In the examples shown in Figure 2B, the hub part 2, the disc part 3 and the rim part 4 are cast in one piece (in a one-piece mold).

[0029] The Fig. The example shown in Fig. 2C represents an example in which the hub part 2 and the disc part 3 are integrally molded and the rim part 4, which has been separately formed, is bonded to a periphery of the disc part 3 with an adhesive point C. The example shown in Fig. The example shown in Figure 2C represents an example of bonding two element parts. In addition, the Fig. The example shown in Figure 3 represents an example in which the disc part 3 is manufactured in a spoke shape 30.

[0030] An aluminum alloy forged wheel according to the embodiment of the present invention includes all the previously described shape examples, and at least the disc part 3 and / or the rim part 4 are manufactured by forging a block, which is obtained by casting an aluminum alloy containing 9.0 wt% to 12.5 wt% Si, 0.5 wt% to 3.4 wt% Cu, 0.2 wt% to 0.9 wt% Mg, 0.7 wt% or less Fe, 0.005 wt% to 0.15 wt% Ti, one of Sr, Sb, Ca and Na with 0.01 wt% to 0.15 wt% for Sr, 0.01 wt% to 0.20 wt% for Sb, 10 wt-ppm to 200 wt-ppm for Ca and 10 wt-ppm to 200 wt-ppm for Na, the remainder being Al and unavoidable impurities, and the metal structures of the disc part and / or the rim part have a band-like zone in which Si particles are present in a small amount, with a width of 20 µm or less and an average particle diameter of eutectic Si is 5 µm or less.

[0031] In the Fig. 2C, for example, a forging material of the above-described metal structure is formed by forging a raw material block for forging formed from the above-described aluminum alloy, the forging material is spin-formed to form the rim part 4, the rim part 4 is separated from the forging material, and the separated rim part 4 is bonded to a periphery of the disc part 3 in a separately formed integral article formed by the hub part 2 and the disc part 3.

[0032] An example of a method for manufacturing the aluminum alloy forged wheel according to the embodiment of the present invention will now be described with reference to Fig. 4 to 6. In this case, the manufacturing steps of the Fig. 2B shown wheel 1 is described as an example.

[0033] In the production of the Fig. 2B, a starting material block is first formed for forging the previously described aluminum alloy. Fig. Figure 4 shows a flow chart of the main manufacturing steps of the raw material block for forging.

[0034] As in Fig.4, the raw material block for forging is formed through a melting step (S01) of melting a raw material such as bare aluminum metal, a chemical component adjusting step (S02) of adjusting chemical components of a produced molten metal, a refining step (S03) of performing a purification treatment of the molten metal, a casting step (S04), a homogenization treatment step (S05), a peeling step (S06), a cutting step (S07), and the like.

[0035] In the melting step (S01), molten metal is produced by heating the starting material to a temperature of, for example, 700 °C or higher. Additional elements are added to the produced molten metal to customize the molten metal with preferred chemical components (S02). The additional elements to be added to a main metal Al are the above-described Si, Cu, Mg, Fe, Ti, Sr, and the like, and component analysis is performed by emission spectroscopic analysis to adjust the components so that a content of Si is 9.0 wt% to 12.5 wt%, a content of Cu is 0.5 wt% to 3.4 wt%, a content of Mg is 0.2 wt% to 0.9 wt%, a content of Fe is 0.7 wt% or less, a content of Ti is 0.005 wt% to 0.15 wt%, a content of Sr is 0.01 wt% to 0.15 wt%, and the balance is Al and inevitable impurities (SO2).

[0036] In the refining step (S03), for example, degassing is performed to adjust the hydrogen gas content to 0.35 cc / 100 g-Al or less. In addition, treatment to remove non-metallic inclusions and the like is performed as needed in this step.

[0037] In the casting step (S04), an ingot is cast in continuous and semi-continuous casting using the molten metal whose components have been adjusted.

[0038] The homogenization treatment step (S05) is a step for heating the cast ingot obtained in the casting step (S04) and stabilizing its metal structure. In the homogenization treatment step (S05), by heating the cast ingot for a prescribed time (1.5 to 12 hours) at a prescribed temperature, solidification deformation of the casting is prevented and the metal structure is homogenized.

[0039] The treatment temperature in the homogenization treatment step (S05) is preferably 470 °C to 520 °C. If the treatment temperature is lower than 470 °C compared to a treatment temperature within the above-described range, the homogenization of the metal structure and the dissolution of solute atoms remain insufficient, and if the treatment temperature exceeds 520 °C, partial melting (burning) may possibly occur.

[0040] In the cast ingot subjected to the homogenization treatment, imperfect portions of a cast surface of the cast ingot are peeled and removed in the peeling step (S06), and the cast ingot is cut to a prescribed forging raw material weight in the cutting step (S07). Accordingly, the raw material ingot for forging is formed.

[0041] Fig.Figure 5 shows a flow chart of the wheel processing steps for forging the raw material block for forging. In a hot forging step (S11), the formed raw material block for forging is formed into a prescribed wheel shape by forging. In this case, as shown in Fig. As shown in Figure 6, a forging material T1 is obtained by placing a heated columnar forging stock block W between an upper die F1 and a lower die F2 and press forging it under a heating condition. The heating condition in this step is set so that a temperature of the forging stock block W reaches 400°C to 520°C, and more preferably 450°C to 490°C.

[0042] In a hot spin forming step (S12), the rim part 4 of the wheel 1 is formed by spin forming the forging material T1 in a state where the forging material T1 is heated to 100°C to 400°C. For spin forming, a rotary compression roller is provided that compresses a side surface while rotating the forging material T1, and a spreading process of the forging material T1 is performed while the compression roller is moved parallel to a rotation axis of the material. During spreading, plastic working with a forging effect occurs, and since the metal structure is miniaturized, the material strength is improved. The hot spin forming step (S12) prevents recrystallization of the rim part 4. After the hot spin forming step (S12), a heat treatment step (S13) is performed to prevent internal deformation.

[0043] In the heat treatment step (S13), solution treatment, quenching, and aging are performed. In solution treatment, the material is heated to a temperature just below the melting point, and the solute atoms (Si, Mg, and Cu) are dissolved as a solid solution in a mother phase. In this case, a machined body obtained by hot spin forming the forging material T1 is heated to 480°C to 540°C for 0.5 to 5 hours.

[0044] Quenching necessarily involves water cooling of the machined body, which undergoes solution treatment. Warm water quenching using quenching water at a temperature of 60°C or less is preferred. Quenching the machined body brings the dissolved atoms of Si, Mg, and Cu into a solid solution state down to room temperature. Aging treatment involves aging the quenched machined body for 2 to 10 hours at 160°C to 210°C. Due to these heat treatments, a fine Mg2Si phase and a fine Al2Cu phase are uniformly dispersed and precipitated, and the metallic structure of the machined body is strengthened.

[0045] In a mechanical process step (S14), a mechanical process is performed on the machined body that has undergone the heat treatment to form the hub part 2, the disc part 3, and the rim part 4. In the mechanical process step (S14), a turning process is performed by a lathe and a milling process is performed by a machining center. In the turning process, as in the Fig.3, a finishing process is performed with a lathe or the like, in which approximately the entire wheel 1 consisting of the disc-shaped hub part 2, the disc part 3 provided on the circumference of the hub part 2, and the rim part 4 provided on the circumference of the disc part 3 is rotated to form an outer shape of the wheel 1. In the milling process, a finishing process is performed with a turning tool such as an end mill, in which the hub part 2 and the spoke shape 30 of the disc part 3 extending radially from the hub part 2 are rotated to form the hub part 2 and the disc part 3 into a prescribed shape. In the mechanical process step (S14), a pattern such as notches may be further formed on a surface to improve the design quality, or hollow profiles may be provided in the wheel 1 to achieve further weight reduction.

[0046] In a surface treatment step (S15), with respect to the machined body subjected to the mechanical process, level differences of indentations left by the cutting tool, burrs generated by the cutting process, and the like are removed over the entire surface, and round chamfers are performed at the corners, and then chemical surface treatment, plating, painting, and the like are performed as required. [Examples]

[0047] Examples of a forged aluminum alloy wheel according to the present invention are described below. Table 1 shows chemical components of aluminum alloys used in the respective examples and a comparative example. In the table, numerical values ​​represent wt%, and among the chemical components, “Al” includes both Al and unavoidable impurities (“balance” denotes a wt% of the balance). Examples 1 to 8 represent examples in which a raw material ingot for forging, produced by casting the aluminum alloys having the chemical components listed in Table 1, is subjected to a forging process to produce a metal structure as shown in Fig.1A, in which a width of a band-like zone in which Si particles are present in a small amount is 20 μm or less, and an average particle diameter of eutectic Si is 5 μm or less. Furthermore, while the comparative example is manufactured by forging a raw material ingot for forging, which is produced by casting the aluminum alloy having the chemical component shown in Table 1, an average Si particle diameter is 6.4 μm, and a band-like zone in which Si particles are present in a small amount is as wide as in Fig. 1B shown. [Table 1] Chemical components Si Fe Cu Mn Mg Cr Ni Zn Ti Sr Al Example 1 10,1 0,17 0,89 0,00 0,48 0,00 0,01 0,01 0,03 0,03 rest Example 2 10,7 0,21 2,43 0,00 0,37 0,00 0,01 0,01 0,03 0,03 rest Example 3 11,6 0,54 3,22 0,00 0,56 0,00 0,01 0,01 0,02 0,03 rest Example 4 10,6 0,24 2,45 0,00 0,36 0,00 0,01 0,01 0,03 0,03 rest Example 5 9,9 0,22 1,87 0,00 0,15 0,00 0,01 0,01 0,03 0,03 rest Example 6 11,3 0,57 1,18 0,00 0,72 0,00 0,01 0,01 0,03 0,03 rest Example 7 10,2 0,23 0,87 0,00 0,50 0,00 0,01 0,01 0,03 0,03 rest Example 8 9,3 0,20 0,63 0,00 0,30 0,00 0,01 0,01 0,04 0,03 rest Comparison example 10,1 0,14 0,86 0,03 0,50 0,01 0,01 0,01 0,02 0,03 rest

[0048] Table 2 shows the fatigue strength, elastic modulus, and average particle diameter of eutectic Si of the respective examples and the comparative example shown in Table 1. The fatigue strength in this case is the finite life strength at a repetition rate of 107 cycles, based on "JIS Z 2274 Method of Rotating Bending Fatigue Testing of Metals." The elastic modulus in this case is a measured value of the elastic modulus at room temperature, which is measured using an ultrasonic pulse method.

[0049] In Example 1, Example 2 and the comparative example shown in Table 2, fatigue strength, elastic modulus and an average particle diameter of eutectic Si are measured in the disc part 3 of the wheel 1 of the mold (the wheel is formed solely by forging) which are in Fig.2A. Furthermore, in Examples 3 to 8 in Table 2, the fatigue strength, the elastic modulus and an average particle diameter of eutectic Si in the disk part 3 and the rim part 4 of the spoke shape 30 in the wheel 1 of the invention shown in Fig. 3 shown shape. [Table 2] Disc part (spoke part) Rim part Fatigue strength [Mpa] 10 7 Zyklen Elastic modulus [GPa] Si average particle diameter [µm] Fatigue strength [Mpa] 10 7 Zyklen Elastic modulus [GPa] Si average particle diameter [µm] Example 1 172 77,3 4, 3 - - Example 2 1 8 7 78,4 4,3 - - - Example 3 227 80,1 2,5 218 79,9 2,6 Example 4 208 78,1 2,5 206 78,7 2,4 Example 5 180 77,3 2,3 180 77,5 2,2 Example 6 186 78,6 2,7 188 78,5 2,8 Example 7 173 77,4 2,5 171 77,4 2,4 Example 8 165 76,7 2,5 160 76,3 2,3 Comparison example * 130 77,4 6,4 - - - * Denotes premature fracture

[0050] As can be seen from Table 2, in Examples 1 to 8, which have a metal structure in which a width of a ribbon-like zone in which Si particles are present in a small amount is 20 μm or less and an average particle diameter of eutectic Si is 5 μm or less, in the disc part or the rim part, the fatigue strength is 155 MPa or more and the elastic modulus is 76 GPa or more. It is concluded that the disc parts and the rim parts in Examples 1 to 8 have higher strength and durability than those of the comparative example in which premature fracture occurs at about 130 MPa in a fatigue strength test. In particular, it is shown that in Examples 3 to 8, high strength and durability as well as high rigidity are obtained in the wheel 1 having the spoke shape 30.

[0051] Fig.Figure 7 is a graph comparing the fatigue strength and elastic modulus in Examples 1 to 8 with those of the comparative example and general materials for a forged wheel. In this case, to compare the fatigue strength and elastic modulus per equal weight, the values ​​of the respective materials are plotted on coordinates representing the specific fatigue strength (= fatigue strength / density) on an ordinate and the specific elastic modulus (= elastic modulus / density) on an abscissa. AC4CH and A6061 are shown as examples of general aluminum alloy materials for a forged wheel.

[0052] On the Fig.From the coordinates shown in Figure 7, by comparing the values ​​converted to the same weight unit, it is found that the further to the right a material is placed, the higher the rigidity of the material (in other words, the material is less deformable and hard), and the further up a material is placed, the stronger the material (in other words, the material is less fragile with respect to repetitive loads). It is concluded that the wheels according to Examples 1 to 8 have significantly higher rigidity and are stronger and more robust than the forged wheels according to Comparative Example, AC4CH, and A6061. As described above, the wheels according to Examples of the present invention are lightweight, yet strong and robust, and have a strength property including high rigidity.

[0053] In addition, Fig.8 shows a result (a variation in tensile strength with respect to a temperature variation during a 100-hour heat exposure) of a heat resistance test of the disc part according to Example 2. Similarly to this example, it was observed that the wheels according to Examples 1 to 8 allow a decrease rate of tensile strength to be maintained at about 20% even when the wheels are exposed to a high temperature of 150°C for 100 hours in a heat resistance test. Therefore, the wheels according to Examples 1 to 8 have high heat resistance. [List of reference symbols] 1 wheel 2 Hub part 3 disc part 4 rim part 30 spoke shape C Adhesive point F1 upper form F2 lower form T1 forging material W Starting material block for forging

Claims

[1] A wheel forged from an aluminum alloy, comprising a hub part into which an axle is to be inserted, a disc part provided on a circumference of the hub part, and a rim part provided on the circumference of the disc part, wherein at least the disc part and / or the rim part are produced by forging an ingot obtained by casting an aluminum alloy containing 9.0 wt% to 12.5 wt% Si, 0.5 wt% to 3.4 wt% Cu, 0.2 wt% to 0.9 wt% Mg, 0.7 wt% or less Fe, 0.005 wt% to 0.15 wt% Ti, one of Sr, Sb, Ca and Na with 0.01 wt% to 0.15 wt% for Sr, 0.01 wt% to 0.20 wt% for Sb, 10 wt-ppm to 200 wt-ppm for Ca and 10 to 200 wt-ppm for Na, wherein the aluminum alloy optionally further contains 0.3 wt% or less Mn, 0.2 wt% or less Cr, 0.2 wt% or less Ni and 0.4 wt% or less Zn and optionally further contains 0.0002 wt% to 0.05 wt% B, the remainder being Al and unavoidable impurities, and the metal structures of the disc part and / or the rim part have a band-like zone in which Si particles are present in a small amount, with a width of 20 µm or less and an average particle diameter of eutectic Si is 5 µm or less. [2] An aluminum alloy forged wheel according to claim 1, wherein the disc member and / or the rim member have a strength property including a 10 7 -Fatigue bending strength of 155 MPa or more and a modulus of elasticity of 76 GPa or more. [3] An aluminum alloy forged wheel according to claim 1 or 2, wherein the rim part is spin-formed from a forged material in one piece with the disc part, the metal structures of the disc part and the rim part each have a band-like zone in which Si particles are present in a small amount, with a width of 20 µm or less and an average particle diameter of eutectic Si is 5 µm or less, and a strength property of the disc part and the rim part a 10 7 -Fatigue bending strength of 155 MPa or more and a modulus of elasticity of 76 GPa or more. [4] An aluminum alloy forged wheel according to any one of claims 1 to 3, wherein the rim member is bonded to the disc member. [5] A method of manufacturing a wheel forged from an aluminum alloy, comprising a hub part into which an axle is to be inserted, a disc part provided on a circumference of the hub part, and a rim part provided on a circumference of the disc part, the method comprising: Forming a starting material block for forging by casting an aluminum alloy containing 9.0 wt% to 12.5 wt% of Si, 0.7 wt% or less of Fe, 0.5 wt% to 3.4 wt% of Cu, 0.2 wt% to 0.9 wt% of Mg, 0.005 wt% to 0.15 wt% of Ti, one of Sr, Sb, Ca and Na with 0.01 wt% to 0.15 wt% for Sr, 0.01 wt% to 0.20 wt% for Sb, 10 wt% to 200 wt% for Ca and 10 wt% to 200 wt% for Na, the balance being Al and unavoidable impurities; Forming at least the disc part and / or the rim part from a forging material obtained by forging the starting material block for forging; and Forming the metal structures of the disc part and / or the rim part to have a ribbon-like zone in which Si particles are present in a small amount, with a width of 20 µm or less and an average particle diameter of eutectic Si is 5 µm or less. [6] A method of manufacturing an aluminum alloy forged wheel according to claim 5, wherein the rim part is formed by spin forming the forging material. [7] A method of manufacturing an aluminum alloy forged wheel according to claim 5, wherein the rim part is formed from the forging material and the rim part is bonded to a separately formed disc part.

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