A method for preparing a high-strength automobile wheel hub

Abstract

The invention provides a method for preparing a high-strength automobile wheel hub, comprising the following steps: providing a container with a discharge port at the bottom and sealing the discharge port, weighing various pure metals according to the composition of the alloy and placing them in the container, heating to obtain a melt 10-20° C. above the liquidus, extending a porous graphite rod into the melt for bubbling, the gas flow rate is 1-5 L / min, the rotation speed of the porous graphite rod is 100-500 rpm, when the solid content of the melt is 40-50%, and the average particle size of the grains of the melt with a depth of 1-2 cm is 40-50 μm, removing the porous graphite rod, removing the seal so that the melt flows out from the discharge port and enters a pressure chamber of a vertical extrusion casting machine, and then performing die casting, the injection speed is 0.04-0.1 m / s, the melt in the pressure chamber is injected into the mounting disk of the hub mold from the ingate of the hub mold and passes through the mounting disk, the spoke, the outer rim, the rim and the inner rim in sequence.

Description

Technical Field

[0001] The invention relates to the field of semi-solid alloy manufacturing, and in particular to a method for preparing a high-strength automobile wheel hub. Background Art

[0002] With the increasing demand for lightweight automobiles, aluminum alloy wheels are increasingly used. Aluminum alloys have good casting properties and specific strength, and a wide solid-liquid phase range. The preparation methods of aluminum alloy wheels mainly include solid forging, low-pressure casting, gravity casting, liquid die forging and semi-solid die casting, among which semi-solid die casting has received extensive attention from researchers. Semi-solid die casting is to cool the semi-solid slurry to a solid content of 10-50% and then perform die casting to obtain the desired finished parts close to the required size. Semi-solid die casting requires strict control of various parameters in the casting process. The pouring temperature of the slurry, the temperature of the mold, the extrusion speed and the mold runner will have a significant impact on the final casting, especially for more complex castings such as wheels, which have a large thickness area inside, such as the spokes. When cooling, this area cools slowly, and it is easy for a large amount of solid phase to surround the liquid phase, resulting in shrinkage holes. By using water cooling to apply a stronger refrigeration effect to the area, the cooling rate of the area can be increased to avoid shrinkage holes. However, the spokes are directly connected to the rim, and there may be a large area with a small amount of liquid phase surrounded by a large amount of solid phase during the solidification process of the rim. If the spokes solidify too quickly, especially the area where the spokes are connected to the rim, the liquid phase in some areas of the rim will not be replenished, and shrinkage holes may occur in the rim. The shrinkage holes caused by uneven cooling can be reduced by lowering the slurry temperature, but this may lead to insufficient filling. The problem of insufficient filling can be avoided by increasing the injection speed, but at this time the slurry is prone to air entrainment, resulting in shrinkage holes. It is difficult to solve the above problems through conventional parameter adjustments, and the above defects will significantly affect the performance of the automobile wheel hub.

[0003] Therefore, it is necessary to propose a method for preparing a high-strength automobile wheel hub. Summary of the invention

[0004] A first aspect of the present invention provides a method for preparing a high-strength automobile wheel hub, characterized in that it comprises the following steps:

[0005] A container with a discharge port at the bottom is provided and the discharge port is sealed. Various pure metals are weighed according to the composition of the alloy and placed in the container. The melt is heated to obtain a melt 10-20° C. above the liquidus line. A porous graphite rod is inserted into the melt for bubbling. The gas flow rate is 1-5 L / min and the rotation speed of the porous graphite rod is 100-500 rpm. When the solid content of the melt is 40-50% and the average particle size of the grains with a depth of 1-2 cm in the melt is 40-50 μm, the porous graphite rod is removed, and the seal is removed so that the melt flows out of the discharge port and enters the pressure chamber of a vertical extrusion casting machine. Then, die casting is performed. The injection speed is 0.04-0.1 m / s. The melt in the pressure chamber is injected into the mounting plate of the hub mold through the ingate of the hub mold and passes through the mounting plate, the spoke, the outer rim, the rim and the inner rim in sequence.

[0006] This scheme obtains a high-solid content melt by combining the bubble method with weak stirring. Under this parameter, the bubble method and weak stirring method can avoid introducing bubbles into the semi-solid melt. The newly generated small-particle grains are distributed at the top of the melt, and the large-particle grains generated by further growth of the grains are distributed at the bottom of the melt. Therefore, the average particle size of the grains at the bottom of the melt is greater than the average particle size of the grains at the top of the melt. When the solid content of the melt reaches 40-50% and the average particle size of the grains at a melt depth of 1-2 cm is 40-50μm, the discharge port at the bottom of the container is opened at this time, so that the large-particle grains at the bottom of the container are first transferred to the bottom of the pressure chamber. The melt at the bottom of the pressure chamber has large-particle grains while the top The melt has small grains. During the filling process of die casting, the melt flows out of the pressure chamber and passes through the ingate, mounting plate, spokes, outer rim, rim and inner rim in sequence. The top melt first enters the mounting plate from the ingate. The top melt with higher fluidity can reach the positions of the rim and inner rim farther away at a lower injection speed, thereby avoiding the problem of air entrainment caused by too fast an injection speed. When the bottom melt enters the mounting plate from the ingate, because the rim and inner and outer rim areas have been fully filled with the top melt, the bottom melt with lower fluidity can complete the filling of thicker areas such as the mounting plate and spokes at a lower injection speed, thereby completing the full filling of the hub at a lower injection speed. During the cooling process after filling, the bottom melt distributed in the thicker area has larger grains and thus has a better heat transfer rate, thereby reducing the generation of hot spots and further resulting in defects such as shrinkage and shrinkage cavities, improving the mechanical strength of the hub, and the fine grains are not easy to produce a large amount of solid phase surrounding a small amount of liquid phase in the thinner rim area, thereby further reducing the shrinkage cavities in the above-mentioned area and improving the strength of the hub. This solution obtains a melt with different particle size distributions by controlling the preparation parameters of GISS (gas induced semi-solid processing technology), and combines it with the extrusion casting process of the hub, solving the problem of insufficient filling and shrinkage cavities when the semi-solid melt is used in hub casting, and can obtain a high-strength automobile hub.

[0007] Furthermore, the alloy is one of magnesium alloy, aluminum alloy and titanium alloy. The above method is applicable to various alloy materials that can prepare semi-solid slurry.

[0008] Furthermore, the alloy is an aluminum alloy. Aluminum alloys are widely used in the field of automobile manufacturing. Furthermore, the aluminum alloy is A356.2. Further, in terms of weight fraction, the composition of the A356.2 aluminum alloy includes 6.5-7.5% silicon, 0.3-0.45% magnesium, 0-0.12% iron, 0-0.05% manganese, 0-0.1% copper, 0-0.05% zinc, 0-0.2% titanium and the balance aluminum. The automobile wheel hub prepared from the above materials has better strength.

[0009] Further, the gas flow rate is 3-5 L / min. Using a higher gas flow rate provides a faster cooling rate and a higher shearing effect, which is conducive to forming a large number of crystal nuclei, thereby producing refined grains.

[0010] Furthermore, the rotation speed of the porous graphite rod is 100-300 rpm. If the rotation speed of the porous graphite rod is too fast, the bubble content in the melt will increase; if the rotation speed of the porous graphite rod is too low, the shear force provided is too low, and refined small grains cannot be formed.

[0011] Furthermore, when the solid content of the melt is 50%, the porous graphite rod is removed. Using a melt with a higher solid content provides a longer growth time for the grains at the bottom of the melt to increase the particle size of the grains at the bottom of the melt. If the solid content is further increased, the crystal nucleus growth in the melt is dominant, which will lead to excessive coarsening of the grains.

[0012] Furthermore, the distance between the porous graphite rod and the bottom of the container is 5-10 mm. Controlling the distance between the porous graphite rod and the bottom of the container can avoid air flow turbulence and improve the uniformity of bubble distribution.

[0013] A second aspect of the present invention provides a high-strength automobile wheel hub, which is prepared by the above-mentioned preparation method.

[0014] The high-strength automobile wheel hub has high mechanical strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a product schematic diagram of the automobile wheel hub of Example 3.

[0016] Figure 2 This is a product schematic diagram of the automobile wheel hub of Comparative Example 1.

[0017] Figure 3 The figure is a schematic diagram of an automobile wheel hub mold according to an embodiment.

[0018] Figure 4 A schematic diagram of a container according to an embodiment. DETAILED DESCRIPTION

[0019] For ease of understanding of the application, the application will be described more fully below. The application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the application more thorough and comprehensive.

[0020] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of the present application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0022] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0023] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0024] The percentage contents involved in this application, unless otherwise specified, refer to mass percentage for solid-liquid mixing and solid-solid mixing, and refer to volume percentage for liquid-liquid mixing.

[0025] The percentage concentrations mentioned in this application, unless otherwise specified, refer to the final concentration, which refers to the percentage of the added component in the system after the addition of the component.

[0026] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range of instrument control.

[0027] The "particles" mentioned in this application, or materials with a defined particle size distribution, are not necessarily spherical in shape, but may be irregular, primary particles or secondary particles. The particle size of irregular particles is the average of their maximum diameter and minimum diameter.

[0028] like Figure 3 As shown, an automobile wheel hub mold 100 of an embodiment includes an ingate 1, the ingate 1 is connected to the mounting plate 2, and the mounting plate 2, the spoke 3, the outer wheel rim 4, the rim 5 and the inner wheel rim 6 are connected in sequence. During die casting, the pressure chamber of the vertical extrusion casting machine is connected to the ingate 1, and the slurry enters the ingate 1 from the pressure chamber and passes through the mounting plate 2, the spoke 3, the outer wheel rim 4, the rim 5 and the inner wheel rim 6 in sequence. In other embodiments, other general automobile wheel hub molds can also be used, as long as the slurry passes through the mounting plate 2, the spoke 3, the outer wheel rim 4, the rim 5 and the inner wheel rim 6 in sequence.

[0029] like Figure 4 As shown, a schematic diagram of a container 200 of an embodiment is shown, and the container is a soup spoon, and a discharge port 7 is provided at the bottom of the container, and the discharge port 7 is closed. At this time, metal material can be added into the container and heated to obtain a melt. After the melt is prepared, the seal of the discharge port 7 can be removed so that the melt can flow out from the discharge port 7.

[0030] Example 1: Various pure metals are weighed according to the composition of A356.2 aluminum alloy and transferred to a spoon. The pure metals include (mass fraction, the same below) silicon: 6.91%, nickel: 0.009%, magnesium: 0.320%, copper: 0.004%, iron: 0.109%, zinc: 0.014%, titanium: 0.104%, manganese: 0.003%, strontium: 0.0001%, and the rest is aluminum.

[0031] After the metal raw materials are mixed, they are heated to 10° C. above the liquidus to form a melt.

[0032] The melt is subjected to GISS treatment to obtain a semi-solid melt. Specifically, a porous graphite rod is inserted into the melt for bubbling, the distance between the graphite rod and the bottom of the spoon is 5 mm, the gas flow rate is 3 L / min, the rotation speed of the porous graphite rod is 100 rpm, and when the solid content of the melt is 40%, the porous graphite rod is removed, and the bottom (1-2 cm away from the bottom of the melt) and the surface (1-2 cm deep in the melt) of the melt are sampled and the particle size is detected, the spoon is transferred to the top of the pressure chamber of the vertical extrusion casting machine, the discharge port at the bottom of the spoon is opened so that the melt in the spoon flows out from the bottom first and enters the pressure chamber, the pressure chamber is connected to the inner gate of the hub mold and injected into the mounting plate of the hub mold for casting, the mold temperature is 350 ° C, the injection speed is 0.1 m / s, the pressure is 50 MPa, the holding time is 15 s, and after T6 heat treatment, the automobile wheel hub is obtained.

[0033] Example 2: Various pure metals are weighed according to the composition of A356.2 aluminum alloy and transferred to a spoon. The pure metals include silicon: 6.91%, nickel: 0.009%, magnesium: 0.320%, copper: 0.004%, iron: 0.109%, zinc: 0.014%, titanium: 0.104%, manganese: 0.003%, strontium: 0.0001%, and the rest is aluminum.

[0034] After the metal raw materials are mixed, they are heated to 10° C. above the liquidus to form a melt.

[0035] The melt is subjected to GISS treatment to obtain a semi-solid melt. Specifically, a porous graphite rod is inserted into the melt for bubbling, the distance between the graphite rod and the bottom of the spoon is 5 mm, the gas flow rate is 1 L / min, the rotation speed of the porous graphite rod is 500 rpm, and when the solid content of the melt is 40%, the porous graphite rod is removed, and the bottom (1-2 cm away from the bottom of the melt) and the surface (1-2 cm deep in the melt) of the melt are sampled and the particle size is detected, the spoon is transferred to the top of the pressure chamber of the vertical extrusion casting machine, the discharge port at the bottom of the spoon is opened so that the melt in the spoon flows out from the bottom first and enters the pressure chamber, the pressure chamber is connected to the inner gate of the hub mold and injected into the mounting plate of the hub mold for casting, the mold temperature is 350 ° C, the injection speed is 0.1 m / s, the pressure is 50 MPa, the holding time is 15 s, and after T6 heat treatment, the automobile wheel hub is obtained.

[0036] Example 3: Various pure metals are weighed according to the composition of A356.2 aluminum alloy and transferred to a spoon. The pure metals include silicon: 6.91%, nickel: 0.009%, magnesium: 0.320%, copper: 0.004%, iron: 0.109%, zinc: 0.014%, titanium: 0.104%, manganese: 0.003%, strontium: 0.0001%, and the rest is aluminum.

[0037] After the metal raw materials are mixed, they are heated to 20° C. above the liquidus to form a melt.

[0038] The melt is subjected to GISS treatment to obtain a semi-solid melt. Specifically, a porous graphite rod is inserted into the melt for bubbling, the distance between the graphite rod and the bottom of the spoon is 5 mm, the gas flow rate is 3 L / min, the rotation speed of the porous graphite rod is 300 rpm, and when the solid content of the melt is 50%, the porous graphite rod is removed, and the bottom (1-2 cm away from the bottom of the melt) and the surface (1-2 cm deep in the melt) of the melt are sampled and the particle size is detected, the spoon is transferred to the top of the pressure chamber of the vertical extrusion casting machine, the discharge port at the bottom of the spoon is opened so that the melt in the spoon flows out from the bottom first and enters the pressure chamber, the pressure chamber is connected to the inner gate of the wheel hub mold and injected into the mounting plate of the wheel hub mold for casting, the mold temperature is 350 ° C, the injection speed is 0.1 m / s, the pressure is 50 MPa, the holding time is 15 s, and after T6 heat treatment, the automobile wheel hub is obtained.

[0039] Example 4: Various pure metals are weighed according to the composition of A356.2 aluminum alloy and transferred to a spoon. The pure metals include silicon: 6.91%, nickel: 0.009%, magnesium: 0.320%, copper: 0.004%, iron: 0.109%, zinc: 0.014%, titanium: 0.104%, manganese: 0.003%, strontium: 0.0001%, and the rest is aluminum.

[0040] After the metal raw materials are mixed, they are heated to 10° C. above the liquidus to form a melt.

[0041] The melt is subjected to GISS treatment to obtain a semi-solid melt. Specifically, a porous graphite rod is inserted into the melt for bubbling, the distance between the graphite rod and the bottom of the spoon is 5 mm, the gas flow rate is 3 L / min, the rotation speed of the porous graphite rod is 100 rpm, and when the solid content of the melt is 40%, the porous graphite rod is removed, and the bottom (1-2 cm away from the bottom of the melt) and the surface (1-2 cm deep in the melt) of the melt are sampled and the particle size is detected, the spoon is transferred to the top of the pressure chamber of the vertical extrusion casting machine, the discharge port at the bottom of the spoon is opened so that the melt in the spoon flows out from the bottom first and enters the pressure chamber, the pressure chamber is connected to the inner gate of the wheel hub mold and injected into the mounting plate of the wheel hub mold for casting, the mold temperature is 350 ° C, the injection speed is 0.04 m / s, the pressure is 50 MPa, the holding time is 15 s, and after T6 heat treatment, the automobile wheel hub is obtained.

[0042] Comparative Example 1: Various pure metals were weighed according to the composition of A356.2 aluminum alloy and transferred to a spoon. The pure metals included silicon: 6.91%, nickel: 0.009%, magnesium: 0.320%, copper: 0.004%, iron: 0.109%, zinc: 0.014%, titanium: 0.104%, manganese: 0.003%, strontium: 0.0001%, and the rest was aluminum.

[0043] After the metal raw materials are mixed, they are heated to 10° C. above the liquidus to form a melt.

[0044] The melt is subjected to GISS treatment to obtain a semi-solid melt. Specifically, a porous graphite rod is inserted into the melt for bubbling, the distance between the graphite rod and the bottom of the spoon is 5 mm, the gas flow rate is 3 L / min, the rotation speed of the porous graphite rod is 100 rpm, and when the solid content of the melt is 40%, the porous graphite rod is removed, and the bottom (1-2 cm away from the bottom of the melt) and the surface (1-2 cm deep in the melt) of the melt are sampled and the particle size is detected, the spoon is transferred to the top of the pressure chamber of the vertical extrusion casting machine, the spoon is tilted so that the melt in the spoon flows out from the top first and enters the pressure chamber, the pressure chamber is connected to the inner gate of the wheel hub mold and injected into the mounting plate of the wheel hub mold for casting, the mold temperature is 350 ° C, the injection speed is 0.1 m / s, the pressure is 50 MPa, the holding time is 15 s, and after T6 heat treatment, the automobile wheel hub is obtained.

[0045] Comparative Example 2: Various pure metals were weighed according to the composition of A356.2 aluminum alloy and transferred to a spoon. The pure metals included silicon: 6.91%, nickel: 0.009%, magnesium: 0.320%, copper: 0.004%, iron: 0.109%, zinc: 0.014%, titanium: 0.104%, manganese: 0.003%, strontium: 0.0001%, and the rest was aluminum.

[0046] After the metal raw materials are mixed, they are heated to 10° C. above the liquidus to form a melt.

[0047] The melt is subjected to GISS treatment to obtain a semi-solid melt. Specifically, a porous graphite rod is inserted into the melt for bubbling, the distance between the graphite rod and the bottom of the spoon is 5 mm, the gas flow rate is 8 L / min, the rotation speed of the porous graphite rod is 1000 rpm, and when the solid content of the melt is 40%, the porous graphite rod is removed, and the bottom (1-2 cm away from the bottom of the melt) and the surface (1-2 cm deep in the melt) of the melt are sampled and the particle size is detected, the spoon is transferred to the top of the pressure chamber of the vertical extrusion casting machine, the discharge port at the bottom of the spoon is opened so that the melt in the spoon flows out from the bottom first and enters the pressure chamber, the pressure chamber is connected to the inner gate of the wheel hub mold and injected into the mounting plate of the wheel hub mold for casting, the mold temperature is 350 ° C, the injection speed is 0.1 m / s, the pressure is 50 MPa, the holding time is 15 s, and after T6 heat treatment, the automobile wheel hub is obtained.

[0048] Comparative Example 3: Various pure metals were weighed according to the composition of A356.2 aluminum alloy and transferred to a spoon. The pure metals included silicon: 6.91%, nickel: 0.009%, magnesium: 0.320%, copper: 0.004%, iron: 0.109%, zinc: 0.014%, titanium: 0.104%, manganese: 0.003%, strontium: 0.0001%, and the rest was aluminum.

[0049] After the metal raw materials are mixed, they are heated to 10° C. above the liquidus to form a melt.

[0050] The melt is subjected to GISS treatment to obtain a semi-solid melt. Specifically, a porous graphite rod is inserted into the melt for bubbling, the distance between the graphite rod and the bottom of the spoon is 5 mm, the gas flow rate is 3 L / min, the rotation speed of the porous graphite rod is 100 rpm, and when the solid content of the melt is 40%, the porous graphite rod is removed, and the bottom (1-2 cm away from the bottom of the melt) and the surface (1-2 cm deep in the melt) of the melt are sampled and the particle size is detected, the spoon is transferred to the top of the pressure chamber of the vertical extrusion casting machine, the discharge port at the bottom of the spoon is opened so that the melt in the spoon flows out from the bottom first and enters the pressure chamber, the pressure chamber is connected to the inner gate of the wheel hub mold and injected into the mounting plate of the wheel hub mold for casting, the mold temperature is 350 ° C, the injection speed is 0.25 m / s, the pressure is 50 MPa, the holding time is 15 s, and after T6 heat treatment, the automobile wheel hub is obtained.

[0051] Comparative Example 4: Various pure metals were weighed according to the composition of A356.2 aluminum alloy and transferred to a spoon. The pure metals included silicon: 6.91%, nickel: 0.009%, magnesium: 0.320%, copper: 0.004%, iron: 0.109%, zinc: 0.014%, titanium: 0.104%, manganese: 0.003%, strontium: 0.0001%, and the rest was aluminum.

[0052] After the metal raw materials are mixed, they are heated to 10° C. above the liquidus to form a melt.

[0053] The melt is subjected to electromagnetic stirring treatment to obtain a semi-solid melt. Specifically, the parameters of electromagnetic stirring are: 30 Hz, 1 kW. When the solid content of the melt is 40%, the bottom (1-2 cm away from the bottom of the melt) and the surface (1-2 cm deep into the melt) of the melt are sampled and the particle size is detected. The spoon is transferred to the top of the pressure chamber of the vertical extrusion casting machine, and the discharge port at the bottom of the spoon is opened so that the melt in the spoon flows out from the bottom first and enters the pressure chamber. The pressure chamber is connected to the inner gate of the hub mold and injected into the mounting plate of the hub mold for casting. The mold temperature is 350 ° C, the injection speed is 0.1 m / s, the pressure is 50 MPa, and the holding time is 15 s. After T6 heat treatment, the automobile wheel hub is obtained.

[0054] Tensile strength test method: Test the rim and spoke areas in accordance with the national standard GB / T228.1-2010 “Tensile test of metallic materials Part 1: Room temperature test method” and record the data in Table 1.

[0055] Table 1 Test results of tensile strength and grain size of Examples 1-4 and Comparative Examples 1-4.

[0056]

[0057] According to the data in Table 1 and Figure 1-Figure 2 It can be seen that the tensile strength of the rim of the wheel hub of Examples 1-4 is higher than that of Comparative Examples 1-4. This is because the present solution obtains a high-solid content melt by combining a bubble method with weak stirring. Under this parameter, the bubble method and weak stirring method can avoid introducing bubbles into the semi-solid melt. Newly generated small-particle grains are distributed at the top of the melt, and large-particle grains generated by further growth of the grains are distributed at the bottom of the melt. Therefore, the average particle size of the grains at the bottom of the melt is greater than the average particle size of the grains at the top of the melt. When the solid content of the melt reaches 40-50% and the average particle size of the grains at a melt depth of 1-2 cm is 40-50 μm, the discharge port at the bottom of the container is opened at this time, so that the large-particle grains at the bottom of the container are first transferred to the bottom of the pressure chamber. The bottom melt in the pressure chamber has large grains and the top melt has small grains. During the filling process of die casting, the melt flows out of the pressure chamber and passes through the ingate, mounting plate, spokes, outer rim, rim and inner rim in sequence. The top melt first enters the mounting plate from the ingate. The top melt with higher fluidity can reach the positions of the rim and inner rim farther away at a lower injection speed, thereby avoiding the problem of air entrainment caused by too fast an injection speed. When the bottom melt enters the mounting plate from the ingate, because the rim and inner and outer rim areas have been fully filled with the top melt, the bottom melt with lower fluidity can complete the filling of thicker areas such as the mounting plate and spokes at a lower injection speed, thereby completing the full filling of the hub at a lower injection speed. During the cooling process after filling, the bottom melt distributed in the thicker area has larger grains and thus has a better heat transfer rate, thereby reducing the generation of hot spots and further resulting in defects such as shrinkage and shrinkage holes, improving the mechanical strength of the hub, and the fine grains are not likely to produce a large amount of solid phase surrounding a small amount of liquid phase in the thinner rim area, thereby further reducing shrinkage holes in the above area and improving the strength of the hub. Figure 1 and Figure 2The results show that the wheel hub of Example 3 has no obvious shrinkage and shrinkage defects, while the wheel hub of Comparative Example 1 has obvious shrinkage and shrinkage defects. The tensile strength of the rim and spoke of Comparative Example 1 is lower than that of Example 3. This is because the melt is poured out by tilting the spoon, and the small particles on the top of the melt first enter the pressure chamber and mix with the large particles that enter the pressure chamber later, forming a melt with large and small crystal nuclei evenly distributed. When entering the mold from the pressure chamber, the melt on the top of the pressure chamber enters the mold first, and its fluidity is worse than that of Example 3. Therefore, it is difficult to fill the remote area such as the rim at this injection speed, and a large number of shrinkage and shrinkage holes are generated after solidification, which leads to a significant reduction in the tensile strength of the rim. The tensile strength of the spokes of Comparative Examples 2 and 4 is slightly improved compared with that of Example 1, because their grains are finer, but the compressive strength of their rims is significantly reduced compared with that of Example 1, because at this solid content and grain size, the fluidity of the melt is poor, and at a lower injection speed, it is difficult for the melt to fill the far-end areas such as the rim, which significantly reduces the tensile strength of the rim. The tensile strength of the rim of Comparative Example 3 is significantly reduced compared with that of Example 1, because it uses an overly high injection speed, resulting in air entrainment during the melt filling process, which significantly reduces the tensile strength of the rim area.

[0058] Example 2 uses a lower gas flow rate and a higher rotation speed, which results in an increase in the particle size of the surface grains. The fluidity of the melt that enters the mold first is poor, which affects the filling of the melt into the rim. Example 3 uses a preferred gas flow rate and a rotation speed of the graphite rod to provide a suitable shear force to reduce the particle size of the surface grains, and controls the solid content of the melt to 50% to reduce shrinkage holes caused by melt shrinkage during solidification. The hub obtained in this way has the best tensile strength. Example 4 uses a lower injection speed and can still obtain a hub that meets the requirements.

[0059] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a high-strength automobile wheel hub, characterized in that: The following steps are included: A container with a discharge port at the bottom is provided and the discharge port is sealed. Various pure metals are weighed according to the composition of the alloy and placed in the container. The melt is heated to obtain a melt 10-20° C. above the liquidus line. A porous graphite rod is inserted into the melt for bubbling. The distance between the porous graphite rod and the bottom of the container is 5-10 mm. The gas flow rate is 1-5 L / min. The rotation speed of the porous graphite rod is 100-500 rpm. When the solid content of the melt is 40-50% and the average particle size of the grains at the bottom of the melt is larger than that of the grains at the top of the melt, the melt is heated to 100-20° C., and the melt is heated to 100-20 ... When the average particle size is 40-50 μm and the average particle size of the grains at a depth of 1-2 cm of the melt is 40-50 μm, the porous graphite rod is removed, and the seal is removed so that the melt flows out from the discharge port and enters the pressure chamber of the vertical extrusion casting machine, so that the bottom melt in the pressure chamber has large-particle grains and the top melt has small-particle grains, and then die casting is performed with an injection speed of 0.04-0.1 m / s. The melt in the pressure chamber is injected into the mounting disk of the hub mold through the inner gate of the hub mold and passes through the mounting disk, spokes, outer rim, rim and inner rim in sequence.

2. The preparation method according to claim 1, characterized in that: The alloy is one of a magnesium alloy, an aluminum alloy and a titanium alloy.

3. The preparation method according to claim 1, characterized in that: The gas flow rate is 3-5 L / min.

4. The preparation method according to claim 1, characterized in that: The rotation speed of the porous graphite rod is 100-300 rpm.

5. The preparation method according to claim 1, characterized in that: When the solid content of the melt is 50%, the porous graphite rod is removed.

6. The preparation method according to claim 1, characterized in that: The alloy is an aluminum alloy.

7. The preparation method according to claim 6, characterized in that: The aluminum alloy is A356.

2.

8. The preparation method according to claim 7, characterized in that: In terms of weight fraction, the composition of the A356.2 aluminum alloy includes 6.5-7.5% silicon, 0.3-0.45% magnesium, 0-0.12% iron, 0-0.05% manganese, 0-0.1% copper, 0-0.05% zinc, 0-0.2% titanium and the balance aluminum.

9. A high-strength automobile wheel hub, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 8.

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