Magnesium alloy wheel hub spinning blank gravity casting forming method

Abstract

This invention provides a gravity casting method for magnesium alloy wheel hub spun blanks, comprising the following steps: S1, preparing a magnesium alloy wheel hub spun blank mold; S2, mold installation and heating: installing the magnesium alloy wheel hub spun blank mold on a gravity casting machine, and heating the mold with resistance heating elements to obtain a non-uniform mold temperature field suitable for forming the magnesium alloy wheel hub spun blank; S3, injecting magnesium alloy melt into a ladle; S4, gravity casting; S5, low-pressure extrusion: performing low-pressure extrusion using the gravity casting machine; S6, opening the mold and removing the part. This invention, by employing low-pressure extrusion and feeding measures and obtaining a non-uniform temperature field through in-situ heating, can effectively improve the material utilization rate of the wheel hub, effectively solving the industry-wide problems of casting defects such as shrinkage cavities / thermal cracks at the rim-spoke junction and shrinkage porosity / shrinkage cavities at the mounting plate in the forming of magnesium alloy wheel hub spun blanks, thus achieving the production of qualified castings of magnesium alloy wheel hub spun blanks.

Description

Technical Field

[0001] This invention relates to the field of metal casting technology, specifically to a gravity casting method for a magnesium alloy wheel hub spinning blank. Background Technology

[0002] As the lightest metallic structural material, magnesium alloys possess advantages such as high specific strength and stiffness, and excellent vibration damping, making them widely used in aerospace, transportation, and 3C (computer, communication, and consumer electronics) fields. To save energy, reduce emissions, improve driving comfort, and enhance vehicle dynamics, modern transportation is trending towards lightweight design. Replacing aluminum alloy wheels with magnesium alloy wheels in ordinary passenger cars can achieve a weight reduction of approximately 10%, demonstrating significant lightweighting effects. However, in actual production, while magnesium alloy wheel forming technology has evolved from early low-pressure casting to the more mainstream one-time extrusion molding (Linzhou Dingxin DX & Henan Dewei DW) and forging-turning technology (General Motors), large-scale application has not yet been achieved. One major reason for this is the lack of low-cost magnesium alloy wheel manufacturing technology. On the one hand, magnesium alloy automotive wheels produced using conventional commercial magnesium alloy AZ91D and low-pressure casting technology are highly susceptible to casting defects such as shrinkage porosity and hot cracking, resulting in poor wheel performance and significant safety hazards. On the other hand, while magnesium alloy automotive wheels produced using conventional commercial magnesium alloy AZ80 and one-time extrusion molding are free of manufacturing defects and meet performance requirements, their low material utilization rate (~35%) and high equipment depreciation and machining costs keep manufacturing costs high, making them unacceptable to most automakers. Therefore, designing and developing low-cost magnesium alloy wheel manufacturing technologies has become a key factor in enabling the large-scale application of magnesium alloy automotive wheels.

[0003] Compared with conventional wheel forming methods, casting + spinning composite forming technology (referred to as casting-spinning technology) has significant advantages in the manufacturing of magnesium alloy automotive wheels:

[0004] Compared with gravity casting and low-pressure casting, the casting-spinning technology significantly increases the thickness of the wheel rim, significantly reduces the difficulty of overall wheel rim casting, significantly improves the wheel rim casting yield, and significantly reduces the overall manufacturing cost of the wheel rim. At the same time, because the wheel rim is formed by spinning, the mechanical properties of the wheel rim are also significantly better than those of gravity casting and low-pressure casting, reaching, approaching or even exceeding the level of single extrusion and forging-spinning.

[0005] Compared with single-stage extrusion and forging-spinning technology, casting-spinning technology significantly improves material utilization and reduces the overall manufacturing cost of magnesium alloy automotive wheels, which is more conducive to promoting the application of magnesium alloy wheels in ordinary automobiles.

[0006] Although the casting-spinning technology has significant advantages in manufacturing magnesium alloy wheels, it is not yet widely used. The main reasons are as follows: (1) When preparing magnesium alloy wheel spinning blanks using conventional gravity casting or low-pressure casting, casting defects such as shrinkage porosity / shrinkage cavity and hot cracks are easily generated at the junction of the wheel rim and spokes; (2) The solidification rate at the center mounting plate of the wheel hub is low, which easily leads to casting defects such as shrinkage porosity / shrinkage cavity, and the microstructure at the center mounting plate is coarse and the mechanical properties are low; (3) When spinning the rim of the magnesium alloy wheel spinning blank, the rim is prone to cracking, and the yield of the spinning process is low; (4) When the magnesium alloy wheel hub is spun and then heat-treated, the rim deformation is large during quenching, and it is difficult to ensure that the rim size meets the requirements using conventional straightening methods; (5) When the magnesium alloy wheel hub is spun and then heat-treated, the grain size coarsens significantly, and the strength and plasticity of the wheel hub decrease significantly.

[0007] Therefore, there is a need to provide a gravity casting method for magnesium alloy wheel hub spinning blanks to solve industry-wide problems such as hot cracking and shrinkage at the junction of the rim and spokes during the forming of magnesium alloy wheel hub spinning blanks, and to achieve the production of qualified castings of magnesium alloy wheel hub spinning blanks. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this invention is to provide a gravity casting method for magnesium alloy wheel hub spinning blanks, thereby solving industry-wide problems such as hot cracking and shrinkage cavities at the junction of the rim and spokes during the forming of magnesium alloy wheel hub spinning blanks, and realizing the production of qualified castings of magnesium alloy wheel hub spinning blanks.

[0009] The present invention provides a gravity casting method for a magnesium alloy wheel hub spinning blank, comprising the following steps:

[0010] S1. Prepare the magnesium alloy wheel hub spinning blank mold;

[0011] S2. Mold installation and heating: The magnesium alloy wheel hub spinning blank mold is installed on the gravity casting machine, and the magnesium alloy wheel hub spinning blank mold is heated by resistance heating element to obtain a non-uniform mold temperature field suitable for the forming of magnesium alloy wheel hub spinning blank.

[0012] S3, Magnesium alloy melt injection into the ladle;

[0013] S4. Gravity casting: The magnesium alloy melt fills the magnesium alloy wheel hub spinning blank mold under the action of gravity;

[0014] S5. Low-pressure extrusion: After the magnesium alloy melt is filled, it is extruded under low pressure through the gravity casting machine. After extrusion, pressure is maintained and the magnesium alloy melt solidifies under the low-pressure extrusion pressure.

[0015] S6. Mold opening and part removal: After the magnesium alloy wheel hub spinning blank casting has completely solidified, open the mold and remove the casting.

[0016] Preferably, in step S1, the magnesium alloy wheel hub spinning blank mold includes a bottom mold, a side mold, an upper mold, and a central extrusion rod of the upper mold. The bottom mold, side mold, upper mold, and central extrusion rod of the upper mold cooperate to form a mold cavity. The ladle is located above the side mold and the upper mold. The ladle is connected to the mold cavity. A ladle plug is provided at the connection between the ladle and the mold cavity.

[0017] Preferably, in step S2, the upper die center extrusion rod is connected to the upper die cylinder of the gravity casting machine.

[0018] Preferably, in step S2, the resistance heating element includes an upper heating element for the side mold, a middle heating element for the bottom mold, an outer heating element for the upper mold, an inner heating element for the upper mold, and a ladle heating element.

[0019] Preferably, in step S2, the non-uniform mold temperature field includes: 350-450°C at the upper part of the side mold, 350-450°C at the middle part of the bottom mold, 400-500°C at the outer side of the upper mold, and 450-550°C at the inner side of the upper mold.

[0020] Preferably, in step S2, the heating temperature of the ladle is 640-680℃.

[0021] Preferably, in step S3, a protective gas is used for protection during the casting process, and the protective gas is a mixture of 0.1-1% SF6 and 99-99.9% CO2.

[0022] Preferably, in step S4, the ladle plug is opened, and the magnesium alloy melt fills the mold cavity under the action of gravity.

[0023] Preferably, in step S5, the upper die cylinder of the gravity casting machine pushes the upper die center extrusion rod to perform low-pressure extrusion on the wheel hub center mounting plate, and the extrusion pressure of the low-pressure extrusion is 0.2-4.5MPa.

[0024] Preferably, in step S5, after the magnesium alloy melt is filled and before the upper die center extrusion rod extrudes, an extrusion waiting time is set, which is 10-30 seconds.

[0025] Preferably, in step S1, air-cooling channels are provided inside the center extrusion rod of the upper die and at the lower part of the side die; in step S5, the center extrusion rod of the upper die and the lower part of the side die are cooled by turning on the air-cooling system.

[0026] Compared with the prior art, the present invention has the following technical features:

[0027] (1) The present invention uses in-situ heating of the mold to obtain a non-uniform mold temperature field;

[0028] This invention is the first to employ an in-situ heating method for the mold, which involves localized heating only of the upper part of the side mold, the middle part of the bottom mold, the outer side of the upper mold, and the inner side of the upper mold. This method achieves a non-uniform mold temperature field suitable for the spinning of magnesium alloy wheel hub blanks. Within this non-uniform mold temperature field, the temperature is lowest at the junction of the wheel rim and spokes. This ensures that the molten alloy at the junction solidifies first after pouring, thus helping to eliminate casting defects such as shrinkage cavities and hot cracks at the junction.

[0029] (2) The present invention employs low-pressure extrusion and shrinkage compensation measures;

[0030] In existing methods for spinning aluminum alloy wheel hub blanks using tilt casting, a riser is used at the center of the hub for feeding. This invention proposes for the first time to use low-pressure extrusion at the center of the hub to perform pressure feeding at the spokes, center mounting plate, and rim-spoke junction, thereby helping to eliminate shrinkage casting defects at the center mounting plate, spokes, and rim-spoke junction.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention obtains a non-uniform temperature field by in-situ heating, which makes the junction of the wheel hub, wheel rim and spoke a low temperature zone, ensuring that the magnesium alloy in this area solidifies first during the casting process, thereby solving the industry problem of casting defects such as shrinkage cavities and hot cracks that are prone to occur at the junction of the wheel rim and spoke.

[0033] (2) The present invention adopts low-pressure extrusion and feeding measures, which can effectively compress the pressure at the junction of the center mounting plate, spokes, and rim spokes, reducing shrinkage defects at the junction of the center mounting plate, spokes, and rim spokes, and can also effectively avoid chemical component segregation caused by excessive local extrusion pressure. In addition, removing the riser of the center mounting plate can also improve the material utilization rate of the hub.

[0034] (3) This invention effectively solves the industry-wide problems such as shrinkage and porosity at the junction of the wheel rim and spokes and shrinkage / porosity at the mounting plate when the magnesium alloy wheel hub spun blank is formed. The casting qualification rate can reach 95%, realizing the production of qualified castings of magnesium alloy wheel hub spun blank. Attached Figure Description

[0035] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0036] Figure 1 This is a schematic diagram illustrating the magnesium alloy wheel hub spinning blank mold, which is the main feature of this invention.

[0037] Figure 2 This is a schematic diagram illustrating the main feature of the invention: magnesium alloy melt is poured into a ladle.

[0038] Figure 3 This is a schematic diagram illustrating the main features of the invention: opening the ladle plug;

[0039] Figure 4 This is a schematic diagram illustrating how molten magnesium alloy completes the filling of the mold cavity for spinning blanks under the action of gravity.

[0040] Figure 5 This is a schematic diagram illustrating how the central extrusion rod of the wheel hub completes low-pressure extrusion under the action of the upper die cylinder.

[0041] Figure 6 This invention mainly embodies the morphological image of the junction of the rim and spoke of the AZ91D magnesium alloy wheel hub spinning blank prepared in Example 2;

[0042] Figure 7 This invention primarily demonstrates the microstructure of the spokes of the AZ91D magnesium alloy wheel hub spinning blank in Example 2.

[0043] Figure 8 This invention mainly embodies the morphology of the junction between the rim and spoke of the AZ91D magnesium alloy wheel hub spinning blank prepared in Comparative Example 1;

[0044] Figure 9 The microstructure diagram of the AZ91D magnesium alloy wheel hub spinning blank in Comparative Example 2, which is the main embodiment of this invention, shows the presence of macroscopic segregation at the spokes.

[0045] As shown in the figure:

[0046] Side mold 1, bottom mold 2, upper mold 3

[0047] 4. Ladle; 5. Mold cavity; 6. Upper rim riser

[0048] 7. Center riser; 8. Center extrusion rod of upper die; 9. Upper heating plate of side die.

[0049] Bottom mold middle heating element 10; Upper mold outer heating element 11; Upper mold inner heating element 12

[0050] 13. Ladle heating element; 14. Hub center mounting plate; 15. Hub spokes.

[0051] 16 Wheel hub and rim; 17 Wheel rim and spoke junction; 18 Ladle plug Detailed Implementation

[0052] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0053] Example 1

[0054] like Figure 1 As shown, a gravity casting method for a magnesium alloy wheel hub spinning blank according to the present invention includes the following steps:

[0055] S1. Prepare the magnesium alloy wheel hub spinning blank mold;

[0056] S2. Mold Installation and Heating: Install the magnesium alloy wheel hub spinning blank mold on the gravity casting machine, and heat the magnesium alloy wheel hub spinning blank mold with resistance heating elements to obtain a non-uniform mold temperature field suitable for the forming of magnesium alloy wheel hub spinning blank, ensuring that the mold temperature is lowest at the junction of the wheel rim and spokes.

[0057] S3, Magnesium alloy melt injection ladle 4;

[0058] S4. Gravity casting: Magnesium alloy melt fills the magnesium alloy wheel hub spinning blank mold under the action of gravity.

[0059] S5. Low-pressure extrusion: After the magnesium alloy melt is filled, it is subjected to low-pressure extrusion through a gravity casting machine. After extrusion, the pressure is held and the magnesium alloy melt solidifies under the low-pressure extrusion pressure.

[0060] S6. Mold opening and part removal: After the magnesium alloy wheel hub spinning blank casting has completely solidified, open the mold and remove the casting.

[0061] This application provides a gravity casting method for magnesium alloy wheel hub spun blanks, including steps such as preparing a magnesium alloy wheel hub spun blank mold, mold installation and heating, magnesium alloy molten material injection into a ladle, gravity casting, low-pressure extrusion, and mold opening and part removal. This application can achieve high-quality preparation of magnesium alloy wheel hub spun blanks, effectively achieving the compensation of shrinkage at the wheel hub center mounting plate 14, wheel hub spokes 15, and wheel hub-rim junction 17, effectively eliminating shrinkage and crack defects at the wheel rim-spoke junction, avoiding chemical composition segregation caused by excessive local extrusion pressure, and improving the material utilization rate of the wheel hub.

[0062] In S1, the magnesium alloy wheel hub spinning blank mold includes a side mold 1, a bottom mold 2, an upper mold 3, and a central extrusion rod 8 of the upper mold. The ladle 4 is located above both the side mold 1 and the upper mold 3, and the ladle 4 is connected to the mold cavity 5. A ladle plug 18 is provided at the connection between the ladle 4 and the mold cavity 5. Air cooling channels are provided in the center of the central extrusion rod 8 of the upper mold and the lower part of the side mold 1.

[0063] In S2, the upper die center extrusion rod 8 is connected to the upper die cylinder of the gravity casting machine.

[0064] In S2, the resistance heating elements include an upper heating element 9 for the side mold, a middle heating element 10 for the bottom mold, an outer heating element 11 for the upper mold, an inner heating element 12 for the upper mold, and a ladle heating element 13. No heating devices are provided at other locations on the mold. This application employs an in-situ mold heating method that heats only the upper part of the side mold 1, the middle part of the bottom mold 2, the outer side of the upper mold 3, and the inner side of the upper mold 3. This method can obtain a non-uniform mold temperature field suitable for the spinning of magnesium alloy wheel hub blanks.

[0065] In S2, the non-uniform mold temperature field includes: the temperature of the upper part of the side mold 1 is 350-450℃, the temperature of the middle part of the bottom mold 2 is 350-450℃, the temperature of the outer side of the upper mold 3 is 400-500℃, the temperature of the inner side of the upper mold 3 is 450-550℃, and the temperature of the ladle 4 is 640-680℃.

[0066] like Figure 2 As shown, in S3, the magnesium alloy melt is injected into ladle 4; during the casting process, a protective gas is used for protection, which is a mixture of 0.1-1% SF6 and 99-99.9% CO2.

[0067] like Figure 3 and 4 As shown in S4, when the ladle plug 18 is opened, the magnesium alloy melt fills the mold cavity 5 of the magnesium alloy wheel hub spinning blank mold under the action of gravity.

[0068] like Figure 5 As shown in S5, the upper die cylinder of the gravity casting machine pushes the upper die center extrusion rod 8 to perform low-pressure extrusion on the hub center mounting plate 14. The extrusion pressure of the low-pressure extrusion is 0.2-4.5 MPa. The upper die 3 is provided with a center riser 7, and the upper part of the side die 1 is provided with an upper wheel rim riser 6. The center riser 7 provides alloy melt for feeding during low-pressure extrusion, and the upper wheel rim riser 6 is used to feed the solidification shrinkage at the rim.

[0069] In S5, after the magnesium alloy melt is filled and before the upper die center extrusion rod 8 extrudes, an extrusion waiting time is set, preferably between 10 and 30 seconds. After gravity filling, after a certain waiting time, the upper die center extrusion rod 8 completes low-pressure extrusion under the action of the upper die cylinder, and performs pressure compensation on the hub center mounting plate 14, hub spokes 15, and hub rim junction 17.

[0070] The lower extrusion pressure not only effectively compensates for the pressure loss of the hub center mounting plate 14, hub spokes 15, and hub-rim junction 17, but also avoids chemical segregation caused by excessive local extrusion pressure. Conventional extrusion casting pressure is typically ≥40MPa. Excessive extrusion pressure leads to solid / liquid phase separation in the alloy during extrusion, causing macroscopic segregation at the hub center mounting plate 14 and hub spokes 15, significantly reducing the service performance of the hub and increasing its service risk.

[0071] In S1, the core of the central extrusion rod and the lower part of the side die are provided with air-cooling channels; in S5, the central extrusion rod 8 of the upper die and the lower part of the side die 1 are cooled by turning on the air-cooling.

[0072] In S6, after the magnesium alloy wheel hub spinning blank casting has completely solidified, the mold is opened and the casting is taken out.

[0073] The non-uniform temperature field obtained by in-situ heating in this application makes the junction 17 of the wheel hub and wheel rim a low-temperature zone, which can ensure that the magnesium alloy in this area solidifies first during the casting process, thereby solving the industry problem that casting defects such as shrinkage cavities and hot cracks are prone to occur at the junction of wheel rim and wheel spokes.

[0074] This application employs a low-pressure extrusion feeding method, which can effectively provide pressure feeding for the hub center mounting plate 14, hub spokes 15, and the hub-rim junction 17, reducing shrinkage defects at the junction, and avoiding chemical segregation caused by excessive local extrusion pressure. Furthermore, it changes the existing gravity casting method for aluminum alloy hub blanks, which uses risers for feeding at the hub center, effectively improving the material utilization rate of the hub.

[0075] This application effectively solves the industry-wide problem of casting defects such as shrinkage cavities / hot cracks at the junction of the rim and spokes and shrinkage porosity / shrinkage cavities at the mounting plate during the forming of magnesium alloy wheel hub spinning blanks, and realizes the production of qualified castings of magnesium alloy wheel hub spinning blanks.

[0076] Example 2

[0077] Based on Example 1, this example describes the preparation of a 20-inch AZ91D magnesium alloy wheel hub spinning blank using a gravity casting method.

[0078] The molding method includes the following steps:

[0079] S1, Prepare a magnesium alloy wheel hub spinning blank mold: The mold consists of four side molds 1, one bottom mold 2, one upper mold 3, one ladle 4, and one upper mold center extrusion rod 8, wherein the ladle 4 is located above the side molds 1 and the upper mold 3, and a ladle plug 18 is provided at the bottom of the ladle 4.

[0080] S2, Mold Installation and Heating: The magnesium alloy wheel hub spinning blank mold is installed on the gravity casting machine. The central extrusion rod 8 of the upper mold is connected to the upper mold cylinder of the gravity casting machine. Resistance heating elements are installed on the upper part of the side mold 1, the middle part of the bottom mold 2, the outer side of the upper mold 3, the inner side of the upper mold 3, and the outer side of the ladle 4. The mold temperature field is non-uniform by heating the mold in situ through the resistance heating elements. After heating, the temperature of the upper part of the side mold 1 is 400±10℃, the temperature of the middle part of the bottom mold 2 is 400±10℃, the temperature of the outer side of the upper mold 3 is 450±10℃, the temperature of the inner side of the upper mold 3 is 480±10℃, and the temperature of the ladle 4 is 660±10℃.

[0081] S3, Magnesium alloy melt injection ladle 4: AZ91D magnesium alloy melt at 720±10℃ is injected manually into ladle 4, which is covered with a protective gas. The protective gas is a mixture of 0.5% SF6 and 99.5% CO2.

[0082] S4 Gravity Casting: With the ladle plug 18 opened, the molten magnesium alloy fills the spin-forming mold cavity 5 under the influence of gravity. The ladle plug 18 has a cross-sectional area of ​​400 cm². 2 .

[0083] S5 Low-Pressure Extrusion: After the magnesium alloy melt is poured, wait 20 seconds, and then the upper die cylinder pushes the upper die center extrusion rod 8 to perform low-pressure extrusion on the hub center mounting plate 14 at a speed of 0.2 m / s and a pressure of 1.0 MPa. After extrusion, hold the pressure for 240 seconds. The dimensions of the center riser are 160 mm in diameter and 50 mm in height.

[0084] S6 Mold Opening and Part Removal: After the casting has completely solidified, open the mold and remove the casting.

[0085] like Figure 6 and 7 As shown, the AZ91D magnesium alloy wheel hub spinning blank obtained by this method contains Mg 17 Al 12 The phases are fine and dispersed, and the internal quality is good. The structure of the hub center mounting plate 14, hub spokes 15, and hub-rim junction 17 is dense, with no obvious casting defects such as shrinkage porosity, shrinkage cavities, or hot cracks.

[0086] Example 3

[0087] Based on Example 1, this example describes the preparation of a 20-inch Mg-1.7Nd-2.5Gd-0.12Zn-0.1La-0.4Zr magnesium alloy wheel hub spinning blank using a gravity casting method. This alloy is a high-strength and high-toughness cast magnesium rare earth alloy disclosed in patent application CN202210242706.3.

[0088] The molding method described is basically the same as that in Example 2, except that:

[0089] S2, Mold Installation and Heating: The temperature of different parts of the mold in the non-uniform mold temperature field is different. Specifically, the temperature of the upper part of the side mold 1 is 440±10℃, the temperature of the middle part of the bottom mold 2 is 440±10℃, the temperature of the outer side of the upper mold 3 is 490±10℃, the temperature of the inner side of the upper mold 3 is 500±10℃, and the temperature of the ladle 4 is 670±10℃.

[0090] S5, Low-pressure extrusion: After waiting for 10 seconds, the upper die cylinder pushes the upper die center extrusion rod 8 to perform low-pressure extrusion on the wheel hub center mounting plate 14 at a speed of 0.4 m / s and a pressure of 2.0 MPa. After extrusion, the pressure is held for 180 seconds.

[0091] The Mg-1.7Nd-2.5Gd-0.12Zn-0.1La-0.4Zr magnesium alloy wheel hub spinning blank obtained by this method has good internal quality. The hub center mounting plate 14, hub spokes 15, and hub-rim junction 17 have dense structure and no obvious casting defects such as shrinkage porosity, shrinkage cavities, or hot cracks.

[0092] Comparative Example 1

[0093] This comparative example demonstrates the preparation of an AZ91D magnesium alloy wheel hub spinning blank using the existing gravity casting method for aluminum alloy wheel hub spinning blanks. The forming method includes the following steps:

[0094] S1. Prepare the magnesium alloy wheel hub spinning blank mold: The mold consists of a bottom mold, four side molds, an upper mold and a ladle. The ladle is located above the side molds and the upper mold. A ladle plug is set at the bottom of the ladle. A hidden riser is set at the center of the upper mold. Gravity feeding is performed on the central mounting plate through the hidden riser.

[0095] S2, Mold Installation and Heating: After placing the magnesium alloy wheel hub spinning blank mold in an oven and heating it to 450℃, remove the mold from the oven and install it on the gravity casting machine. After installation, the mold temperature is still relatively uniform, at about 420℃.

[0096] S3, Magnesium alloy melt injection ladle 4: AZ91D magnesium alloy melt at 720±10℃ is injected manually into a ladle covered with a protective gas, which is a mixture of 0.5% SF6 and 99.5% CO2.

[0097] S4, Gravity Casting: Open the ladle plug, and the magnesium alloy melt fills the mold cavity under the action of gravity.

[0098] S5, Mold Opening and Part Removal: After the casting has completely solidified, open the mold and remove the casting.

[0099] The main differences between this comparative example and Example 2 are: (1) The casting mold is different. The existing aluminum alloy wheel hub spinning blank mold has a hidden riser instead of an extrusion rod at the center mounting plate. The hidden riser is used to gravity feed the center mounting plate; (2) The mold temperature field is different. The mold is heated to 450°C in an oven and then installed on a gravity casting machine. After installation, the mold temperature is about 420°C. At this time, the mold has a relatively uniform mold temperature field, while the non-uniform mold temperature field used in Example 2.

[0100] like Figure 8 As shown, the AZ91D magnesium alloy wheel hub spinning blank obtained by the method of Example 2 has obvious shrinkage cavities and cracks at the junction of the rim and spokes, and the casting quality is unqualified. This wheel hub spinning blank cannot be used for subsequent wheel hub production.

[0101] Comparative Example 2

[0102] This comparative example describes the preparation of a 20-inch AZ91D magnesium alloy wheel hub spinning blank. The forming method of this comparative example is basically the same as that of Example 2, except that the extrusion pressure in the S5 low-pressure extrusion is increased to 5.0 MPa.

[0103] like Figure 9 As shown, the AZ91D magnesium alloy wheel hub spinning blank obtained by this method exhibits large-area macrosegregation in the center of the spokes, with Mg in the macrosegregated microstructure. 17 Al 12 The phase content is significantly increased compared to conventional tissues, Mg 17 Al 12 The phase is a brittle phase. Brittle phases connected in a network are prone to brittle fracture under external force, leading to substandard casting quality. The microstructure of Example 2 at the same location is as follows: Figure 7 As shown, compared with conventional microstructures, significant solid-liquid phase separation occurred during the solidification process of magnesium alloys when the extrusion pressure increased, leading to a sharp increase in the content of the second phase in local areas and the formation of macroscopic segregation. For AZ91D magnesium alloys, the macroscopic segregation manifested as Mg... 17 Al 12 The phase content increased significantly; macrosegregation significantly reduced the service performance of the wheel hub and increased the service risk of the wheel hub.

[0104] Comparative Example 3

[0105] This comparative example describes the preparation of a 20-inch AZ91D magnesium alloy wheel hub spinning blank. The forming method of this comparative example is basically the same as that of Example 2, except that the extrusion pressure in the S5 low-pressure extrusion is reduced to 0.1 MPa.

[0106] The AZ91D magnesium alloy wheel hub spinning blank obtained by this method exhibits significant shrinkage porosity at the center mounting plate. This indicates that due to insufficient extrusion pressure, the shrinkage at the center mounting plate was not effectively compensated. Therefore, this wheel hub spinning blank cannot be used for subsequent wheel hub production.

[0107] In summary, compared with the prior art, the gravity casting method for magnesium alloy wheel hub spinning blanks provided in this application can achieve high-quality preparation of magnesium alloy wheel hub spinning blanks: it effectively realizes the feeding of the wheel hub center mounting plate 14, wheel hub spokes 15, and wheel hub rim junction 17, effectively eliminates shrinkage and crack defects at the wheel rim spoke junction, casting defects such as shrinkage porosity / shrinkage cavity at the mounting plate, avoids chemical composition segregation caused by excessive local extrusion pressure, and improves the material utilization rate of the wheel hub.

[0108] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0109] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A magnesium alloy wheel hub spinning blank gravity casting forming method characterized by, Includes the following steps: S1. Prepare a magnesium alloy wheel hub spinning blank mold. The magnesium alloy wheel hub spinning blank mold includes a side mold (1), a bottom mold (2), an upper mold (3), and an upper mold center extrusion rod (8). The side mold (1), bottom mold (2), upper mold (3), and upper mold center extrusion rod (8) cooperate to form a mold cavity (5). The ladle (4) is located above the side mold (1) and the upper mold (3). The ladle (4) is connected to the mold cavity (5). A ladle plug (18) is provided at the connection between the ladle (4) and the mold cavity (5). S2. Mold installation and heating: The magnesium alloy wheel hub spinning blank mold is installed on the gravity casting machine. The upper mold center extrusion rod (8) is connected to the upper mold cylinder of the gravity casting machine. The magnesium alloy wheel hub spinning blank mold is heated by resistance heating elements to obtain a non-uniform mold temperature field suitable for the forming of magnesium alloy wheel hub spinning blank. The resistance heating elements include the upper side mold heating element (9), the middle bottom mold heating element (10), the outer side upper mold heating element (11), the inner side upper mold heating element (12), and the ladle heating element (13). S3, Magnesium alloy melt is injected into the ladle (4); S4. Gravity casting: The magnesium alloy melt fills the magnesium alloy wheel hub spinning blank mold under the action of gravity; S5. Low-pressure extrusion: After the magnesium alloy melt is filled, the upper mold center extrusion rod (8) is pushed by the upper mold cylinder of the gravity casting machine to perform low-pressure extrusion on the hub center mounting plate (14). The extrusion pressure of the low-pressure extrusion is 0.2-4.5MPa. After extrusion, pressure is maintained and the magnesium alloy melt solidifies under the low-pressure extrusion pressure. S6. Mold opening and part removal: After the magnesium alloy wheel hub spinning blank casting has completely solidified, open the mold and remove the casting.

2. The magnesium alloy wheel-hub spinning blank gravity casting forming method according to claim 1, characterized by, In S2, the non-uniform mold temperature field includes: 350-450°C at the upper part of the side mold (1), 350-450°C at the middle part of the bottom mold (2), 400-500°C at the outer side of the upper mold (3), and 450-550°C at the inner side of the upper mold (3).

3. The magnesium alloy wheel hub spinning blank gravity casting forming method according to claim 1, characterized by, In S2, the heating temperature of the ladle (4) is 640-680°C.

4. The gravity casting method for magnesium alloy wheel hub spin forming blanks as described in claim 1, characterized in that, In step S3, a protective gas is used for protection during the casting process. The protective gas is a mixture of 0.1-1% SF6 and 99-99.9% CO2.

5. The gravity casting method for magnesium alloy wheel hub spin forming blanks as described in claim 1, characterized in that, In step S4, the ladle plug (18) is opened, and the magnesium alloy melt fills the mold cavity (5) under the action of gravity.

6. The gravity casting method for magnesium alloy wheel hub spin forming blanks as described in claim 1, characterized in that, In S5, after the magnesium alloy melt is filled and before the upper die center extrusion rod (8) extrudes, an extrusion waiting time is set, which is 10-30 seconds.

7. The gravity casting method for magnesium alloy wheel hub spin forming blanks as described in claim 1, characterized in that, In S1, air-cooling channels are provided inside the center extrusion rod (8) of the upper die and at the lower part of the side die (1); In step S5, the upper die center extrusion rod (8) and the lower part of the side die (1) are cooled by turning on the air cooling system.

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