A magnesium-rare earth alloy wheel hub capable of being rapidly high-temperature solid-solution treated and a preparation method thereof

Abstract

A magnesium rare earth alloy wheel hub capable of rapid high-temperature solid solution treatment and its preparation method are disclosed. The magnesium alloy composition by weight percentage is: Nd: 1.4–2.0%, Gd: 2.0–3.0%, Zn: 0.04–0.20%, La: 0.1–0.4%, Zr: 0.3–0.7%, total impurity elements ≤0.2%, with the remainder being Mg. La, Nd, and Gd elements are compositely added to the magnesium alloy. La enhances the strengthening effect of the Mg-Nd precipitate phase, combined with the dispersion strengthening effect of the introduced Mg-La phase. Simultaneously, the Mg generated by La in the alloy is utilized... 12 The pinning grain boundaries of the La phase effectively suppress grain coarsening in magnesium alloys, thus avoiding the reduction in mechanical properties caused by increased solution treatment temperature. This ensures that the mechanical properties of magnesium alloy wheels prepared using high-temperature solution treatment meet the requirements for automotive wheels. It also significantly shortens the high-temperature solution treatment time in the manufacturing process of magnesium alloy automotive wheels, resulting in a marked improvement in production efficiency and a substantial reduction in manufacturing costs, thus meeting the requirements for mass production of magnesium alloy automotive wheels.

Description

Technical Field

[0001] This invention relates to the field of metal structural materials technology, and in particular to a magnesium rare earth alloy wheel hub that can be rapidly and at high temperatures for solid solution treatment, and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, possess advantages such as high specific strength, high specific stiffness, and good vibration damping, and are widely used in aerospace, transportation, and 3C industries. To save energy, reduce emissions, improve driving comfort, and enhance vehicle dynamics, modern transportation is moving towards lightweight design. In ordinary passenger cars, replacing aluminum alloy wheels with magnesium alloy wheels can achieve a weight reduction of approximately 10%, demonstrating significant lightweighting effects.

[0003] However, in actual production, while magnesium alloy automotive wheel forming technology has evolved from early low-pressure casting to the currently mainstream one-time extrusion molding and forging techniques, neither has achieved large-scale application. One of the main reasons is the lack of low-cost magnesium alloy wheel manufacturing technology. Existing magnesium alloy automotive wheel manufacturing primarily utilizes the following two methods:

[0004] The first type uses conventional commercial magnesium alloy AZ91D and produces magnesium alloy car wheels using low-pressure casting technology. However, the resulting car wheels are prone to casting defects such as shrinkage porosity and hot cracking, resulting in poor wheel performance and obvious safety hazards.

[0005] The second method uses conventional commercial magnesium alloy AZ80 and obtains magnesium alloy car wheels through one-time extrusion molding. Although there are no manufacturing defects and the performance can meet the requirements, the material utilization rate is low (about 35%), and the equipment depreciation and machining costs are high, resulting in high manufacturing costs for magnesium alloy car wheels, which is unacceptable to ordinary car manufacturers.

[0006] Magnesium alloy automotive wheels are mostly manufactured using casting processes. High-temperature solution treatment followed by low-temperature aging is a typical heat treatment process for high-strength cast magnesium alloys, often referred to as T6 treatment. T6 treatment is also a standard procedure for aluminum alloy automotive wheels; for example, low-pressure cast A356.2 aluminum alloy wheels and forged 6061 aluminum alloy wheels both require T6 heat treatment. In the T6 heat treatment process, the high-temperature solution treatment places high demands on the equipment's temperature control accuracy and temperature field uniformity, resulting in higher equipment manufacturing and maintenance costs.

[0007] Chinese patent CN200510030457.8 discloses "Rare Earth-Containing High-Strength Cast Magnesium Alloy and Its Preparation Method". The weight percentage of the rare earth components of the cast magnesium alloy is: Nd: 2.5~3.6%, Zr: 0.35-0.8%, Zn≤0.4%, Ca≤0.5%, and the total amount of impurity elements Si, Fe, Cu and Ni is less than 0.02%, with the balance being Mg. By adding Nd, Zr, Zn and Ca alloys, a high-strength magnesium alloy is obtained by smelting and heat treatment. The conventional heat treatment process is: (525~540)°C×(4~12)h solution treatment + 200°C×(12~20)h aging treatment.

[0008] Chinese patent CN201710204140.4 discloses a "sand casting magnesium rare earth alloy and its preparation method". The disclosed high-strength magnesium rare earth alloy has the following composition by weight percentage: Gd: 8.0~14.0%, Zn: 0.01~0.85%, Zr: 0.3~0.7%, with the balance being magnesium and unavoidable impurities. The total weight percentage of the impurities does not exceed 0.2%. Its conventional heat treatment process is: solution treatment at (480~530)°C for (8~16) hours + aging treatment at (200~225)°C for (12~128) hours.

[0009] The standard heat treatment process for conventional commercial high-strength magnesium rare earth alloy WE43 (typical composition: Mg-4wt.%Y-2wt.%Nd-1wt.%RE) is: solution treatment at 525°C for 8 hours + aging treatment at 250°C for 16 hours.

[0010] The standard heat treatment process for commercial magnesium rare earth alloy ZM6 (Mg-Nd-Zn-Zr) is: solution treatment at (525~535)°C for (12~16) hours + aging treatment at 200°C for (12~16) hours.

[0011] The standard heat treatment process for the commercial high-strength magnesium rare earth alloy EV31 (Mg-Nd-Gd-Zn-Zr, Elektron 21) developed by Magnesium Elektron is: solution treatment at 520°C for 8 hours + aging treatment at 200°C for 16 hours.

[0012] Therefore, the heat treatment time used for magnesium rare earth alloys is relatively long. In order to improve production efficiency, manufacturers usually need to equip multiple high-temperature solution treatment furnaces for products with large batches, which significantly increases the costs of site, equipment maintenance, and equipment calibration.

[0013] To improve the production efficiency and reduce manufacturing costs of magnesium alloy automotive wheels, higher solution treatment temperatures and shorter solution treatment times can be employed. However, while higher solution treatment temperatures shorten the solution treatment time, they also lead to overall coarsening of the alloy grains and abnormal growth of local grains, significantly reducing the mechanical properties of the alloy and the stability of the casting's mechanical properties, failing to meet the requirements for automotive wheel applications. Therefore, there is an urgent need to conduct technical research on the design of novel magnesium rare earth alloy compositions to enable shorter solution treatment times, thereby reducing the manufacturing cost of magnesium alloy wheels and meeting the requirements for mass production of magnesium alloy automotive wheels. Summary of the Invention

[0014] The purpose of this invention is to provide a magnesium rare earth alloy wheel hub that can be rapidly subjected to high-temperature solution treatment and its preparation method, avoiding the reduction in the mechanical properties of the alloy due to the increase in solution treatment temperature, so that the mechanical properties of the prepared magnesium alloy wheel hub can meet the requirements of automobile wheel hubs; moreover, it significantly shortens the high-temperature solution treatment time in the preparation process of magnesium alloy automobile wheel hubs, significantly improves the production efficiency of magnesium alloy automobile wheel hubs, greatly reduces the manufacturing cost of magnesium alloy automobile wheel hubs, and meets the requirements of mass production of magnesium alloy automobile wheel hubs.

[0015] To achieve the above objectives, the technical solution of the present invention is as follows:

[0016] A magnesium rare earth alloy wheel hub capable of rapid high-temperature solution treatment, characterized in that the magnesium alloy composition by weight percentage is: Nd: 1.4~2.0%, Gd: 2.0~3.0%, Zn: 0.04~0.20%, La: 0.1~0.4%, Zr: 0.3~0.7%, total impurity elements ≤0.2%, and the remainder is Mg.

[0017] Preferably, the impurity element includes at least one of silicon, iron, copper, and nickel, and Si≤0.01%, Fe≤0.01%, Cu≤0.03%, and Ni≤0.005%.

[0018] The mechanical properties of the magnesium rare earth alloy wheel hub spokes of this invention are: yield strength ≥165MPa, tensile strength ≥270MPa, and elongation ≥5.8%; the mechanical properties of the lower wheel rim are: yield strength ≥177MPa, tensile strength ≥276MPa, and elongation ≥6.9%.

[0019] In the component design of this invention:

[0020] Nd (Neodymium): Existing research shows that the solid solubility of Nd in Mg solid solution is almost zero at 200°C, while it is 3.6 wt% at the eutectic temperature of 552°C. Adding only a small amount of Nd results in good age-hardening precipitation strengthening and solid solution strengthening effects in alloys. This study shows that when the Nd content is >2.0 wt.%, the Mg generated during casting under high-temperature solution treatment... 12 The Nd phase is difficult to completely dissolve in a short time; when the Nd content is <1.4 wt.%, the alloy strengthening effect is low during subsequent aging treatment, and the mechanical properties of the casting are difficult to guarantee. Therefore, in this invention, the Nd content is controlled at 1.4~2.0 wt.%.

[0021] Gd (gadolinium): This study shows that when the Nd content is reduced to below 2.0 wt.%, the mechanical properties of the casting decrease. To further improve the mechanical properties of the alloy, this invention introduces a small amount of Gd to enhance the solid solution strengthening effect. However, when the Gd content is >3 wt.%, the tendency for oxide scale formation during alloy casting increases significantly. Therefore, in this invention, the Gd content is controlled at 2.0~3.0 wt.%.

[0022] Zn (zinc): Existing research shows that when trace amounts of Zn are added to Mg-Nd and Mg-Gd alloy systems, Zn exists in the magnesium matrix and precipitates in the form of solid-solution atoms. This can promote the activation of non-basal plane slip systems during room temperature plastic deformation of magnesium alloys, significantly improving the room temperature plasticity of the alloys. This invention has found that when the Zn content is >0.2 wt.%, during the solution treatment process, Zn reacts with Zr to form needle-like Zn₂Z. r3 While this phase offers some strengthening effect, it negatively impacts the alloy's plasticity. Therefore, in this invention, the Zn element content is controlled at 0.04~0.20 wt.%.

[0023] La (lanthanum): La has almost no solid solubility in magnesium alloys, but La reacts with Mg at 610°C to form Mg. 12 La eutectic phase; this study shows that Mg 12 The La phase effectively pins grain boundaries during high-temperature solution treatment at 545–555°C, thus inhibiting grain coarsening in magnesium alloys. Simultaneously, trace amounts of La dissolved into the magnesium matrix increase the number density of Mg-Nd precipitates, enhancing the strengthening effect of age-hardening precipitates. When the La content is >0.4 wt.%, the Mg content in the alloy... 12 La phase grains coarsen, significantly reducing alloy plasticity. Therefore, in this invention, the La element content is controlled at 0.10~0.40 wt.%.

[0024] Zr (zirconium): Similar to conventional Zr-containing magnesium alloys, the main role of Zr in the alloy of this invention is grain refinement, and the content of Zr element is 0.3~0.7 wt.%.

[0025] This invention employs lower Nd and Gd content, and incorporates La to enhance the strengthening effect of the Mg-Nd precipitate. Combined with the dispersion strengthening effect of the introduced Mg-La phase, this ensures the magnesium alloy possesses high mechanical properties. Simultaneously, the La element generates Mg in the alloy. 12 The La phase exhibits excellent grain boundary pinning during solution treatment at 545–555°C, effectively suppressing grain coarsening and thus preventing a decrease in mechanical properties due to increased solution treatment temperature. This ensures that the mechanical properties of the prepared magnesium alloy wheel hub meet the requirements for automotive wheels. Therefore, using the magnesium alloy composition described in this invention to prepare automotive wheels allows for a solution treatment temperature increase to the range of 550 ± 5°C and a solution treatment time reduction to 30–60 minutes, improving the production efficiency and reducing the manufacturing cost of magnesium alloy automotive wheels.

[0026] The method for preparing the magnesium rare earth alloy wheel hub of the present invention includes the following steps:

[0027] 1) Batching and smelting

[0028] Prepare the ingredients as described, and then melt them to obtain a magnesium alloy melt;

[0029] 2) Casting

[0030] The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. The temperature of the melt in the ladle is 700~740°C, the temperature of the mold is 300~550°C, and the tilting time of the ladle is 10~30s from 0° to 90°.

[0031] 3) Hot spinning

[0032] According to the size requirements of the spinning blank, the wheel hub casting blank is surface-processed to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 400~450°C for a time of >1h. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank.

[0033] 4) Heat treatment

[0034] The wheel hub blank undergoes high-temperature solution treatment at a temperature of 545~550°C for 30~60 minutes; then it is quenched and subjected to single-stage aging treatment to obtain a high-strength magnesium alloy wheel hub blank.

[0035] 5) Surface coating

[0036] The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, painting and other coating processes to obtain the finished magnesium alloy wheel.

[0037] Preferably, in step 1), pure magnesium, pure zinc, Mg-Nd, Mg-Gd, Mg-Zr, and Mg-La master alloys are used as raw materials. The raw materials are preheated at 150~250°C for more than 3 hours. Pure magnesium is placed in a crucible resistance furnace with a protective atmosphere and completely melted. Then, the temperature is raised to 700~720°C, and pure zinc, Mg-Nd, Mg-Gd, and Mg-La master alloys are added to the magnesium melt. After all the above alloys have melted, the melt temperature is raised to 760~780°C, and Mg-Zr master alloy is added to the melt. After the Mg-Zr master alloy melts, the surface dross is skimmed off, and the mixture is stirred for 2~3 minutes. The melt temperature is lowered to 750~760°C for continuous refining. After refining, the temperature is raised to 780~790°C and allowed to stand for 15~30 minutes. Finally, the temperature is cooled to 690~740°C, and the surface dross is skimmed off to obtain magnesium alloy melt for later use.

[0038] Preferably, the protective atmosphere is a mixture of SF6 and CO2.

[0039] Preferably, in step 4), the transfer time from the end of the high-temperature solution treatment of the wheel hub blank to quenching is <20s.

[0040] Preferably, in step 4), the quenching is water quenching at a water temperature of 25~80℃.

[0041] Preferably, in step 4), the temperature of the single-stage aging treatment is 200~225°C, and the time of the single-stage aging treatment is 8~16h.

[0042] Preferably, in step 4), the cavity and ladle are filled with inert gas during the tilt casting process, and preferably, the inert gas is nitrogen.

[0043] Preferably, in step 3), during hot spinning, the core mold temperature is 300~400°C, the spinning wheel speed is 300~900 r / min, and the feed rate is 0.25~1.5 mm / r.

[0044] In this invention, the high-temperature solution treatment temperature is set at 545~555°C, and the added La element reacts with Mg at 610°C to form Mg. 12 La eutectic phase, forming Mg 12 The La phase has excellent grain boundary pinning properties, which effectively suppresses the coarsening of magnesium alloy grains, resulting in materials with high mechanical properties.

[0045] Since the solution treatment temperature of this invention can be increased to 545~555°C, the solution treatment time can be shortened to 30~60 minutes, while traditional magnesium rare earth alloys require at least 4 hours of solution treatment time when using solution treatment process to produce automobile wheels.

[0046] The production of automobile wheel hubs using the magnesium alloy composition and high-temperature solution treatment process described in this invention not only improves the mechanical properties of the resulting automobile wheel hubs to meet the usage requirements of existing automobile wheel hubs by increasing the solution treatment temperature, but also significantly reduces the production time of automobile wheel hubs, improves the production efficiency of magnesium alloy automobile wheel hubs, and reduces the manufacturing cost of magnesium alloy automobile wheel hubs.

[0047] The beneficial effects of this invention are:

[0048] 1. The magnesium rare earth alloy of this invention incorporates La and small amounts of Nd and Gd elements. La enhances the strengthening effect of the Mg-Nd precipitate, and combined with the dispersion strengthening effect of the introduced Mg-La phase, ensures the magnesium alloy possesses high mechanical properties. Simultaneously, the Mg generated in the alloy by La... 12 The La phase effectively pins grain boundaries during solution treatment at 545–555°C, thus suppressing grain coarsening in magnesium alloys. This prevents a decrease in the alloy's mechanical properties due to increased solution treatment temperature, ensuring that the prepared magnesium alloy wheel hub meets the requirements for automotive wheels. The mechanical properties of the obtained magnesium alloy wheel hub spokes are: yield strength ≥ 165 MPa, tensile strength ≥ 270 MPa, and elongation ≥ 5.8%; the mechanical properties of the lower rim are: yield strength ≥ 177 MPa, tensile strength ≥ 276 MPa, and elongation ≥ 6.9%.

[0049] 2. Because this invention employs a relatively high solution treatment temperature of 545~555°C, the solution treatment time can be reduced to 30~60 minutes. Compared to the at least 4 hours required for solution treatment using traditional magnesium rare earth alloys, the solution treatment time is significantly shortened. Therefore, while ensuring the obtained automotive wheel hub has high mechanical properties, the production efficiency of magnesium alloy automotive wheel hubs is significantly improved, greatly reducing the manufacturing cost of magnesium alloy automotive wheel hubs and meeting the requirements for mass production of magnesium alloy automotive wheel hubs. Attached Figure Description

[0050] Figure 1 The image shows the microstructure of the magnesium alloy wheel hub spokes before solution treatment in Example 2 of this invention.

[0051] Figure 2 This is a microstructure image of the magnesium alloy wheel hub spokes after solution treatment in Example 2 of the present invention. Detailed Implementation

[0052] The technical solution of the present invention will be described in detail below through embodiments. These embodiments are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0053] The magnesium rare earth alloy composition of this invention is shown in Table 1, with the remainder being Mg and unavoidable impurities.

[0054] Example 1

[0055] 1) Batching and smelting

[0056] Pure magnesium, pure zinc, Mg-Nd, Mg-Gd, and Mg-Zr master alloys are preheated at 200°C for at least 3 hours. The dried pure magnesium is then completely melted in a crucible resistance furnace under a protective atmosphere of SF6 and CO2. The temperature is then raised to 720°C, and pure zinc, Mg-Nd, and Mg-Gd master alloys are directly added to the molten magnesium. After all the alloys have melted, the melt temperature is raised to 760-780°C, and Mg-Zr master alloy is added. Once the Mg-Zr master alloy melts, surface dross is skimmed off, and the mixture is stirred for 2-3 minutes. The melt temperature is then lowered to 750-760°C for continuous refining. After refining, the temperature is raised to 780°C and allowed to stand for 15-30 minutes. Finally, the melt is cooled to 690-740°C, and surface dross is skimmed off to obtain the magnesium alloy melt for later use.

[0057] 2) Casting

[0058] The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. During the tilting casting process, the mold cavity and ladle are filled with nitrogen gas, and the temperature of the melt in the ladle is 720°C; the temperature of the bottom mold is 300°C, and a water-cooling channel is provided on the outer ring of the bottom mold; the temperature of the side mold is 300°C, and a feeding riser is provided on the upper part of the side mold, with a riser mold temperature of 550°C; the temperature of the upper mold is 400°C; a feeding riser is provided at the center of the upper mold, with a riser mold temperature of 550°C; the tilting time of the ladle from 0° to 90° is 15s;

[0059] 3) Hot spinning

[0060] According to the size requirements of the spinning blank, the surface of the wheel hub casting blank is machined using a CNC lathe to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 450°C for 2 hours. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank. During hot spinning, the mandrel temperature is 350°C, the spinning wheel speed is 600 r / min, and the feed rate is 0.4 mm / r.

[0061] 4) Heat treatment

[0062] The wheel hub blank undergoes a high-temperature solution treatment at a temperature of 550°C for 55 minutes, followed by quenching in water at 80°C, and finally a single-stage aging treatment at a temperature of 217°C for 13 hours to obtain a high-strength magnesium alloy wheel hub blank.

[0063] 5) Surface coating

[0064] The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, painting and other coating processes to obtain the finished magnesium alloy wheel.

[0065] The performance of the obtained magnesium alloy automotive wheel hubs is shown in Table 2.

[0066] Example 2

[0067] 1) Batching and smelting

[0068] Pure magnesium, pure zinc, Mg-Nd, Mg-Gd, and Mg-Zr master alloys are preheated at 200°C for at least 3 hours. The dried pure magnesium is then completely melted in a crucible resistance furnace under a protective atmosphere of SF6 and CO2. The temperature is then raised to 700°C, and pure zinc, Mg-Nd, and Mg-Gd master alloys are directly added to the molten magnesium. After all the alloys have melted, the melt temperature is raised to 760-780°C, and Mg-Zr master alloy is added. Once the Mg-Zr master alloy melts, surface dross is skimmed off, and the mixture is stirred for 2-3 minutes. The melt temperature is then lowered to 750-760°C for continuous refining. After refining, the temperature is raised to 780°C and allowed to stand for 15-30 minutes. Finally, the melt is cooled to 690-740°C, and surface dross is skimmed off to obtain the magnesium alloy melt for later use.

[0069] 2) Casting

[0070] The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. During the tilting casting process, the mold cavity and ladle are filled with nitrogen gas, and the temperature of the melt in the ladle is 720°C; the temperature of the bottom mold is 300°C, and a water-cooling channel is provided on the outer ring of the bottom mold; the temperature of the side mold is 300°C, and a feeding riser is provided on the upper part of the side mold, with a riser mold temperature of 550°C; the temperature of the upper mold is 400°C; a feeding riser is provided at the center of the upper mold, with a riser mold temperature of 550°C; the tilting time of the ladle from 0° to 90° is 20s;

[0071] 3) Hot spinning

[0072] According to the size requirements of the spinning blank, the surface of the wheel hub casting blank is machined using a CNC lathe to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 410°C for 2 hours. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank. During hot spinning, the mandrel temperature is 300°C, the spinning wheel speed is 400 r / min, and the feed rate is 0.9 mm / r.

[0073] 4) Heat treatment

[0074] The wheel hub blank undergoes a high-temperature solution treatment at a temperature of 545°C for 60 minutes, followed by quenching in water at 60°C, and finally a single-stage aging treatment at a temperature of 215°C for 9 hours to obtain a high-strength magnesium alloy wheel hub blank.

[0075] 5) Surface coating

[0076] The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, painting and other coating processes to obtain the finished magnesium alloy wheel.

[0077] The performance of the obtained magnesium alloy automotive wheel hubs is shown in Table 2.

[0078] Figure 1 and Figure 2 The images show the microstructure of the magnesium alloy wheel hub spokes before and after solution treatment in Example 2 of this invention. It can be seen from the images that the average grain size of the magnesium alloy wheel hub before solution treatment is 54±6μm, and the average grain size of the magnesium alloy wheel hub after solution treatment is 58±8μm. There is no obvious coarsening of the grain size before and after solution treatment.

[0079] Example 3

[0080] 1) Batching and smelting

[0081] Pure magnesium, pure zinc, Mg-Nd, Mg-Gd, and Mg-Zr master alloys are preheated at 200°C for at least 3 hours. The dried pure magnesium is then completely melted in a crucible resistance furnace under a protective atmosphere of SF6 and CO2. The temperature is then raised to 740°C, and pure zinc, Mg-Nd, and Mg-Gd master alloys are directly added to the molten magnesium. After all the alloys have melted, the melt temperature is raised to 760-780°C, and Mg-Zr master alloy is added. Once the Mg-Zr master alloy melts, surface dross is skimmed off, and the mixture is stirred for 2-3 minutes. The melt temperature is then lowered to 750-760°C for continuous refining. After refining, the temperature is raised to 780°C and allowed to stand for 15-30 minutes. Finally, the melt is cooled to 690-740°C, and surface dross is skimmed off to obtain the magnesium alloy melt for later use.

[0082] 2) Casting

[0083] The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. During the tilting casting process, the mold cavity and ladle are filled with nitrogen gas, and the temperature of the melt in the ladle is 720°C; the temperature of the bottom mold is 300°C, and a water-cooling channel is provided on the outer ring of the bottom mold; the temperature of the side mold is 300°C, and a feeding riser is provided on the upper part of the side mold, with a riser mold temperature of 550°C; the temperature of the upper mold is 400°C; a feeding riser is provided at the center of the upper mold, with a riser mold temperature of 550°C; the tilting time of the ladle from 0° to 90° is 10s;

[0084] 3) Hot spinning

[0085] According to the size requirements of the spinning blank, the surface of the wheel hub casting blank is machined using a CNC lathe to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 500°C for 1 hour. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank. During hot spinning, the mandrel temperature is 400°C, the spinning wheel speed is 700 r / min, and the feed rate is 1.5 mm / r.

[0086] 4) Heat treatment

[0087] The wheel hub blank undergoes a high-temperature solution treatment at a temperature of 555°C for 30 minutes, followed by quenching in water at 25°C, and finally a single-stage aging treatment at a temperature of 2208°C for 15 hours to obtain a high-strength magnesium alloy wheel hub blank.

[0088] 5) Surface coating

[0089] The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, painting and other coating processes to obtain the finished magnesium alloy wheel.

[0090] The performance of the obtained magnesium alloy automotive wheel hubs is shown in Table 2.

[0091] Example 4

[0092] 1) Batching and smelting

[0093] Pure magnesium, pure zinc, Mg-Nd, Mg-Gd, and Mg-Zr master alloys are preheated at 200°C for at least 3 hours. The dried pure magnesium is then completely melted in a crucible resistance furnace under a protective atmosphere of SF6 and CO2. The temperature is then raised to 730°C, and pure zinc, Mg-Nd, and Mg-Gd master alloys are directly added to the molten magnesium. After all the alloys have melted, the melt temperature is raised to 760-780°C, and Mg-Zr master alloy is added. Once the Mg-Zr master alloy melts, surface dross is skimmed off, and the mixture is stirred for 2-3 minutes. The melt temperature is then lowered to 750-760°C for continuous refining. After refining, the temperature is raised to 780°C and allowed to stand for 15-30 minutes. Finally, the melt is cooled to 690-740°C, and surface dross is skimmed off to obtain the magnesium alloy melt for later use.

[0094] 2) Casting

[0095] The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. During the tilting casting process, the mold cavity and ladle are filled with nitrogen gas, and the temperature of the melt in the ladle is 720°C; the temperature of the bottom mold is 300°C, and a water-cooling channel is provided on the outer ring of the bottom mold; the temperature of the side mold is 300°C, and a feeding riser is provided on the upper part of the side mold, with a riser mold temperature of 550°C; the temperature of the upper mold is 400°C; a feeding riser is provided at the center of the upper mold, with a riser mold temperature of 550°C; the tilting time of the ladle from 0° to 90° is 30s;

[0096] 3) Hot spinning

[0097] According to the size requirements of the spinning blank, the surface of the wheel hub casting blank is machined using a CNC lathe to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 460°C for 2.5 hours. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank. During hot spinning, the mandrel temperature is 370°C, the spinning wheel speed is 500 r / min, and the feed rate is 0.25 mm / r.

[0098] 4) Heat treatment

[0099] The wheel hub blank undergoes a high-temperature solution treatment at a temperature of 552°C for 40 minutes, followed by quenching in water at 40°C, and finally a single-stage aging treatment at a temperature of 220°C for 12 hours to obtain a high-strength magnesium alloy wheel hub blank.

[0100] 5) Surface coating

[0101] The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, painting and other coating processes to obtain the finished magnesium alloy wheel.

[0102] The performance of the obtained magnesium alloy automotive wheel hubs is shown in Table 2.

[0103] Example 5

[0104] 1) Batching and smelting

[0105] Pure magnesium, pure zinc, Mg-Nd, Mg-Gd, and Mg-Zr master alloys are preheated at 200°C for at least 3 hours. The dried pure magnesium is then completely melted in a crucible resistance furnace under a protective atmosphere of SF6 and CO2. The temperature is then raised to 735°C, and pure zinc, Mg-Nd, and Mg-Gd master alloys are directly added to the molten magnesium. After all the alloys have melted, the melt temperature is raised to 760-780°C, and Mg-Zr master alloy is added. Once the Mg-Zr master alloy melts, surface dross is skimmed off, and the mixture is stirred for 2-3 minutes. The melt temperature is then lowered to 750-760°C for continuous refining. After refining, the temperature is raised to 780°C and allowed to stand for 15-30 minutes. Finally, the melt is cooled to 690-740°C, and surface dross is skimmed off to obtain the magnesium alloy melt for later use.

[0106] 2) Casting

[0107] The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. During the tilting casting process, the mold cavity and ladle are filled with nitrogen gas, and the temperature of the melt in the ladle is 720°C; the temperature of the bottom mold is 300°C, and a water-cooling channel is provided on the outer ring of the bottom mold; the temperature of the side mold is 300°C, and a feeding riser is provided on the upper part of the side mold, with a riser mold temperature of 550°C; the temperature of the upper mold is 400°C; a feeding riser is provided at the center of the upper mold, with a riser mold temperature of 550°C; the tilting time of the ladle from 0° to 90° is 25s;

[0108] 3) Hot spinning

[0109] According to the size requirements of the spinning blank, the surface of the wheel hub casting blank is machined using a CNC lathe to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 450°C for 2 hours. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank. During hot spinning, the mandrel temperature is 320°C, the spinning wheel speed is 900 r / min, and the feed rate is 1.2 mm / r.

[0110] 4) Heat treatment

[0111] The wheel hub blank undergoes a high-temperature solution treatment at a temperature of 547°C for 50 minutes, followed by quenching in water at 35°C, and finally a single-stage aging treatment at a temperature of 225°C for 8 hours to obtain a high-strength magnesium alloy wheel hub blank.

[0112] 5) Surface coating

[0113] The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, painting and other coating processes to obtain the finished magnesium alloy wheel.

[0114] The performance of the obtained magnesium alloy automotive wheel hubs is shown in Table 2.

[0115] Example 6

[0116] 1) Batching and smelting

[0117] Pure magnesium, pure zinc, Mg-Nd, Mg-Gd, and Mg-Zr master alloys are preheated at 200°C for at least 3 hours. The dried pure magnesium is then completely melted in a crucible resistance furnace under a protective atmosphere of SF6 and CO2. The temperature is then raised to 725°C, and pure zinc, Mg-Nd, and Mg-Gd master alloys are directly added to the molten magnesium. After all the alloys have melted, the melt temperature is raised to 760-780°C, and Mg-Zr master alloy is added. Once the Mg-Zr master alloy melts, surface dross is skimmed off, and the mixture is stirred for 2-3 minutes. The melt temperature is then lowered to 750-760°C for continuous refining. After refining, the temperature is raised to 780°C and allowed to stand for 15-30 minutes. Finally, the melt is cooled to 690-740°C, and surface dross is skimmed off to obtain the magnesium alloy melt for later use.

[0118] 2) Casting

[0119] The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. During the tilting casting process, the mold cavity and ladle are filled with nitrogen gas, and the temperature of the melt in the ladle is 720°C; the temperature of the bottom mold is 300°C, and a water-cooling channel is provided on the outer ring of the bottom mold; the temperature of the side mold is 300°C, and a feeding riser is provided on the upper part of the side mold, with a riser mold temperature of 550°C; the temperature of the upper mold is 400°C; a feeding riser is provided at the center of the upper mold, with a riser mold temperature of 550°C; the tilting time of the ladle from 0° to 90° is 18s;

[0120] 3) Hot spinning

[0121] According to the size requirements of the spinning blank, the surface of the wheel hub casting blank is machined using a CNC lathe to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 430°C for 1.2 hours. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank. During hot spinning, the mandrel temperature is 330°C, the spinning wheel speed is 80,000 r / min, and the feed rate is 0.6 mm / r.

[0122] 4) Heat treatment

[0123] The wheel hub blank undergoes a high-temperature solution treatment at a temperature of 549°C for 60 minutes, followed by quenching in water at 55°C, and finally a single-stage aging treatment at a temperature of 205°C for 10 hours to obtain a high-strength magnesium alloy wheel hub blank.

[0124] 5) Surface coating

[0125] The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, painting and other coating processes to obtain the finished magnesium alloy wheel.

[0126] The performance of the obtained magnesium alloy automotive wheel hubs is shown in Table 2.

[0127] Example 7

[0128] 1) Batching and smelting

[0129] Pure magnesium, pure zinc, Mg-Nd, Mg-Gd, and Mg-Zr master alloys are preheated at 200°C for at least 3 hours. The dried pure magnesium is then completely melted in a crucible resistance furnace under a protective atmosphere of SF6 and CO2. The temperature is then raised to 720°C, and pure zinc, Mg-Nd, and Mg-Gd master alloys are directly added to the molten magnesium. After all the alloys have melted, the melt temperature is raised to 760-780°C, and Mg-Zr master alloy is added. Once the Mg-Zr master alloy melts, surface dross is skimmed off, and the mixture is stirred for 2-3 minutes. The melt temperature is then lowered to 750-760°C for continuous refining. After refining, the temperature is raised to 780°C and allowed to stand for 15-30 minutes. Finally, the melt is cooled to 690-740°C, and surface dross is skimmed off to obtain the magnesium alloy melt for later use.

[0130] 2) Casting

[0131] The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. During the tilting casting process, the mold cavity and ladle are filled with nitrogen gas, and the temperature of the melt in the ladle is 720°C; the temperature of the bottom mold is 300°C, and a water-cooling channel is provided on the outer ring of the bottom mold; the temperature of the side mold is 300°C, and a feeding riser is provided on the upper part of the side mold, with a riser mold temperature of 550°C; the temperature of the upper mold is 400°C; a feeding riser is provided at the center of the upper mold, with a riser mold temperature of 550°C; the tilting time of the ladle from 0° to 90° is 22s.

[0132] 3) Hot spinning

[0133] According to the size requirements of the spinning blank, the surface of the wheel hub casting blank is machined using a CNC lathe to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 470°C for 3 hours. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank. During hot spinning, the mandrel temperature is 355°C, the spinning wheel speed is 650 r / min, and the feed rate is 1.3 mm / r.

[0134] 4) Heat treatment

[0135] The wheel hub blank undergoes a high-temperature solution treatment at a temperature of 552°C for 45 minutes, followed by quenching in water at 70°C, and finally a single-stage aging treatment at a temperature of 212°C for 16 hours to obtain a high-strength magnesium alloy wheel hub blank.

[0136] 5) Surface coating

[0137] The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, painting and other coating processes to obtain the finished magnesium alloy wheel.

[0138] The performance of the obtained magnesium alloy automotive wheel hubs is shown in Table 2.

[0139] Comparative Example 1

[0140] Magnesium alloy automotive wheel hubs were prepared using the same process as in Example 2. The only difference was that La was not added in this comparative example. The mechanical properties of the obtained automotive wheel hubs are shown in Table 2.

[0141] As can be seen from Table 2, without the addition of La, the room temperature mechanical properties of the car wheel hub spokes and rims are significantly reduced, especially the room temperature yield strength and tensile strength.

[0142] Comparative Example 2

[0143] Magnesium alloy automotive wheel hubs were prepared using the same process as in Example 2. The only difference was that Gd was not added in this comparative example. The mechanical properties of the obtained automotive wheel hubs are shown in Table 2.

[0144] As can be seen from Table 2, without the addition of Gd, the room temperature mechanical properties of the car wheel hub spokes and rims are significantly reduced, especially the room temperature yield strength and tensile strength.

[0145] Comparative Example 3

[0146] Magnesium alloy automotive wheel hubs were prepared using the same process as in Example 2. The only difference was that the La content in this comparative example was 0.6 wt%, exceeding the upper limit of 0.4 wt% specified in this invention.

[0147] As can be seen from Table 2, adding too much La significantly reduces the room temperature mechanical properties of the wheel hub spokes and rims, especially the room temperature plasticity of the wheel hub spokes and rims.

[0148] Comparative Example 4

[0149] Automobile wheel hubs are manufactured using AZ91D magnesium alloy and low-pressure casting technology.

[0150] The high-temperature solution treatment temperature during the process was 420℃, and the treatment time was 12h. Compared with Comparative Example 4, the solution treatment time in the present invention was reduced by 91.67%. The mechanical properties of the obtained automobile wheel hub are shown in Table 2.

[0151] As shown in Table 2, the magnesium alloy automobile wheel hub obtained by the present invention has higher strength and plasticity. The yield strength at the spokes is increased by 70%, the tensile strength by 18%, and the elongation by 207%; the yield strength at the lower edge is increased by 53%, the tensile strength by 21%, and the elongation by 165%.

[0152] Comparative Example 5

[0153] Magnesium alloy automotive wheel hubs were manufactured using AZ80 magnesium alloy through a one-time extrusion molding process. The mechanical properties of the resulting automotive wheel hubs are shown in Table 2.

[0154] Compared with Comparative Example 5, the magnesium alloy automobile wheel hub prepared using the alloy and process described in this invention has a higher material utilization rate. The material utilization rate in Comparative Example 5 is 30-40%, while the material utilization rate of the technical solution of this invention is 70-80%, which is about 100% higher.

[0155] As shown in Table 2, the magnesium alloy wheel hub for automobiles obtained by this invention has higher strength, with the yield strength at the lower edge of the wheel increased by 56%, while the mechanical properties of other parts are comparable.

[0156] Comparative Example 6

[0157] Automobile wheel hubs were prepared using the alloy and method described in Chinese Patent ZL201210556668.5, wherein the solution treatment temperature was 400℃ and the solution treatment time was 8 hours. The solution treatment solution of this invention saves more than 87.5% of the solution treatment time. The mechanical properties of the obtained automobile wheel hubs are shown in Table 2.

[0158] As shown in Table 2, the magnesium alloy car wheel hub obtained by this invention has higher strength and plasticity. The yield strength at the spokes is increased by 11%, the tensile strength by 18%, and the elongation by 53%; the yield strength at the lower edge is increased by 15%, the tensile strength by 21%, and the elongation by 33%.

[0159] Compared to the car wheel hub obtained in Comparative Example 6, the magnesium alloy car wheel hub obtained by this invention has higher resistance to hot cracking and is easier to cast. Poor hot cracking resistance is one of the main reasons why Mg-Zn-Al-Mn magnesium alloy wheels have not been able to be mass-produced.

[0160] Furthermore, compared with the gravity and low-pressure casting methods used in Comparative Example 6 to manufacture the spinning blank, the tilt casting method used in the present invention to prepare the spinning blank is more conducive to controlling internal shrinkage / cavity defects in the casting and improving the internal quality of the casting.

[0161] Figure 1 and Figure 2 The images show the microstructure of the magnesium alloy wheel hub spokes before and after solution treatment in Example 2 of this invention. As can be seen from the images, the average grain size in the microstructure before solution treatment is 54±6 μm; the average grain size in the microstructure after solution treatment is 58±8 μm. There is almost no grain coarsening before and after solution treatment. This indicates that using the composition described in this invention for high-temperature solution treatment can effectively suppress grain coarsening in the magnesium alloy, thereby avoiding the reduction in the mechanical properties of the alloy due to the increase in solution treatment temperature, and ensuring that the mechanical properties of the prepared magnesium alloy wheel hub meet the requirements of automotive wheels.

[0162] In summary, through the above embodiments and comparative examples, it can be seen that the present invention can use rapid high-temperature solid solution treatment of magnesium rare earth alloys to prepare automobile wheel hubs with mechanical properties that meet the requirements, significantly shortening the high-temperature solid solution time in the preparation process of magnesium alloy wheel hubs and reducing the manufacturing cost of magnesium alloy wheel hubs.

[0163]

[0164]

Claims

1. A magnesium rare earth alloy wheel hub capable of rapid high-temperature solution treatment, characterized in that, The magnesium rare earth alloy composition by weight percentage is: Nd: 1.4~2.0%, Gd: 2.0~3.0%, Zn: 0.04~0.20%, La: 0.1~0.4%, Zr: 0.3~0.7%, total impurity elements ≤0.2%, the remainder being Mg; The high-temperature solution treatment temperature is 545~555°C, and the high-temperature solution treatment time is 30~60min.

2. The magnesium rare earth alloy wheel hub as described in claim 1, characterized in that, The impurity element includes at least one of silicon, iron, copper, and nickel, and Si≤0.01%, Fe≤0.01%, Cu≤0.03%, and Ni≤0.005%.

3. The magnesium rare earth alloy wheel hub as described in claim 1 or 2, characterized in that, The mechanical properties of the magnesium rare earth alloy wheel hub spokes are: yield strength ≥165MPa, tensile strength ≥270MPa, elongation ≥5.8%; the mechanical properties of the lower wheel rim are: yield strength ≥177MPa, tensile strength ≥276MPa, elongation ≥6.9%.

4. The method for preparing a magnesium rare earth alloy wheel hub as described in any one of claims 1 to 3, characterized in that, Includes the following steps: 1) Batching and smelting The magnesium rare earth alloy is prepared by mixing the raw materials according to its composition and then smelting to obtain a magnesium alloy melt. 2) Casting The magnesium alloy melt is used to obtain a wheel hub casting blank through a tilting casting process. The melt temperature in the ladle is 700~740°C, the mold temperature is 300~550°C, and the tilting time of the ladle tilting angle is 10~30s from 0° to 90°. 3) Hot spinning According to the size requirements of the spinning blank, the wheel hub casting blank is surface-processed to obtain the wheel hub spinning blank. Then, the wheel hub spinning blank is preheated at a temperature of 400~450°C for a time of >1h. After preheating, the rim part of the wheel hub spinning blank is hot-spinned using a hot spinning process to produce the wheel hub blank. 4) Heat treatment The wheel hub blank undergoes a high-temperature solution treatment at a temperature of 545~555°C for 30~60 minutes; then it is quenched and subjected to a single-stage aging treatment to obtain a high-strength magnesium alloy wheel hub blank. 5) Surface coating The high-strength cast magnesium alloy wheel blank is subjected to surface machining to obtain a semi-finished wheel. Then, it undergoes surface pickling, alkali washing, chemical passivation, and painting processes to obtain the finished magnesium alloy wheel.

5. The method for preparing the magnesium rare earth alloy wheel hub as described in claim 4, characterized in that, In step 1), pure magnesium, pure zinc, Mg-Nd, Mg-Gd, Mg-Zr, and Mg-La master alloys are used as raw materials. The raw materials are preheated at 150~250°C for more than 3 hours. Pure magnesium is placed in a crucible resistance furnace with a protective atmosphere and completely melted. Then the temperature is raised to 700~720°C, and pure zinc, Mg-Nd, Mg-Gd, and Mg-La master alloys are added to the magnesium melt. After all the above alloys have melted, the melt temperature is raised to 760~780°C, and Mg-Zr master alloy is added to the melt. After the Mg-Zr master alloy melts, the surface dross is skimmed off, and the mixture is stirred for 2~3 minutes. The melt temperature is lowered to 750~760°C for continuous refining. After refining, the temperature is raised to 780~790°C and allowed to stand for 15~30 minutes. Finally, the temperature is cooled to 690~740°C, and the surface dross is skimmed off to obtain magnesium alloy melt for later use.

6. The method for preparing the magnesium rare earth alloy wheel hub as described in claim 5, characterized in that, The protective atmosphere is a mixture of SF6 and CO2.

7. The method for preparing the magnesium rare earth alloy wheel hub as described in claim 4, characterized in that, In step 4), the transfer time from the end of the high-temperature solution treatment of the wheel hub blank to quenching is <20s.

8. The method for preparing a magnesium rare earth alloy wheel hub as described in claim 4, characterized in that, In step 4), the quenching is water quenching at a water temperature of 25~80℃.

9. The method for preparing a magnesium rare earth alloy wheel hub as described in claim 4, characterized in that, In step 4), the temperature of the single-stage aging treatment is 200~225°C, and the time of the single-stage aging treatment is 8~16h.

10. The method for preparing a magnesium rare earth alloy wheel hub as described in claim 4, characterized in that, In step 4), the cavity and ladle are filled with inert gas during the tilt casting process.

11. The method for preparing a magnesium rare earth alloy wheel hub as described in claim 10, characterized in that, In step 4), the inert gas is nitrogen.

12. The method for preparing a magnesium rare earth alloy wheel hub as described in claim 4, characterized in that, In step 3), during hot spinning, the core mold temperature is 300~400°C, the spinning wheel speed is 300~900r / min, and the feed rate is 0.25~1.5mm / r.

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