Aluminum alloy for automobile main structural beam and preparation method of aluminum alloy

Abstract

The invention discloses an aluminum alloy for an automobile main structural beam and a preparation method of the aluminum alloy. The preparation method comprises the following steps: S01, respectively preparing a cross beam and a towing beam in the automobile torsion beam; s02, the two ends of the cross beam and the position, connected with the cross beam, in the towing beam are subjected to laser hot melting treatment, and the hot melting temperature is controlled to range from 350 DEG C to 400 DEG C; s03, the cross beam and the towing beam in the step S02 are placed in a directional magnetic field and a directional water curtain, and hot melting connection of the cross beam and the towing beam is achieved for 0.2-0.5 h under the action of moving and cooling of the external magnetic field and the directional water curtain; and S04, the directional water curtain in the step S03 is removed, the temperature is controlled to be 80-100 DEG C, and a chromic acid solution is directionally and rotationally sprayed to the connecting position of the cross beam and the towing beam to form a passivation layer. The automobile torsion beam obtained through the preparation method has high strength and high corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of automobile body structures, and in particular relates to an aluminum alloy for an automobile main structure beam and a preparation method thereof. Background Art

[0002] As an important component of the vehicle chassis, the automobile torsion beam is connected to the left and right wheels at both ends. It is mainly used to bear the weight of the vehicle and absorb road unevenness. This type of beam has torsional elasticity and can absorb and disperse the impact and vibration of the vehicle during driving to a certain extent.

[0003] The existing main structural beams of automobiles, such as torsion beams, are made of aluminum alloy materials as raw materials. The raw materials contain Mg-Al-Cu or Mg-Al-Zn-Cu alloy clusters, which enhance the strength of aluminum materials while maintaining the light weight of aluminum alloy materials, so as to prepare automobile chassis that are beneficial to improving economic benefits. However, the corrosion resistance of existing aluminum alloy materials is poor, and the prepared automobile torsion beams are easily corroded when exposed to various environments for a long time. In particular, the cross arm and the trailing arm of the torsion beam are fixedly connected by bolts. When corroded, the strength of the torsion beam will be reduced, and in severe cases, the beam will be broken. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide an aluminum alloy for automobile main structural beams and a preparation method thereof, aiming to solve the technical problem of existing torsion beams breaking due to reduced strength caused by corrosion.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides the following technical solution: a method for preparing an aluminum alloy for a main structural beam of an automobile, comprising the following steps:

[0007] S01: Prepare the cross beam and the drag beam in the automobile torsion beam respectively;

[0008] S02: The two ends of the crossbeam and the position where the towing beam is connected to the crossbeam are treated by laser heat melting, and the heat melting temperature is controlled at 350-400°C;

[0009] S03: placing the crossbeam and the towing beam in step S02 in a directional magnetic field and a directional water curtain, so that the crossbeam and the towing beam are hot-melt-connected for 0.2-0.5h under the action of the external magnetic field and the moving cooling of the directional water curtain;

[0010] S04: removing the directional water curtain in step S03, controlling the temperature at 80-100° C., and directionally spraying a chromic acid solution at the connection position between the cross beam and the towing beam to form a passivation layer.

[0011] Further, the crossbeam in step S01 includes a rigid section and plastic and tough sections arranged on both sides of the rigid section, the rigid section includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 0.08%-0.09% titanium, and 2.5%-3% magnesium, and the rigid section is prepared by the following process:

[0012] A. Place the rigid section processing material in a trough induction furnace for smelting at a temperature of 700-750°C for 1-1.5 hours, using fluoride as the smelting solvent;

[0013] B. Quench the processed product obtained in step A with water, and then naturally age it for 10-12 hours.

[0014] Furthermore, the step B comprises:

[0015] B01: quenching the processed product obtained in step A with water, and after quenching, the temperature is controlled at 80-100° C.;

[0016] B02: Directional rotary spraying of chromic acid solution onto the surface of the object processed in step B01, reacting at a temperature of 80-100°C for 1-1.5 hours, and natural aging for 10-12 hours.

[0017] Further, the plastic-tough segment includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 2.5%-3% magnesium, and 0.1%-0.35% rare earth elements, and the plastic-tough segment includes the following process for preparation:

[0018] M. Place the processed material of the plastic-tough section in a trough induction furnace for smelting at a smelting temperature of 500-570°C for 30 minutes, and then smelt at a smelting temperature of 700-750°C for 30-45 minutes;

[0019] N. The processed product obtained in step M is first oil-cooled for 4-5 hours, then water-cooled for 2-3 hours, and finally air-cooled to room temperature.

[0020] Further, the step N comprises:

[0021] N01: The processed product obtained in step M is first oil-cooled for 4.5 hours and then water-cooled for 2.5 hours;

[0022] N02: Directional spin spraying of chromic acid solution onto the surface of the workpiece in step N01, reacting at 90°C for 1.5h, and finally air cooling to room temperature.

[0023] Furthermore, the method further comprises the following steps:

[0024] O: Use a ruler to measure the position 1 of the rigid section 5-8 cm away from the end surface, and the position 2 of the plastic section 5-8 cm away from the end surface, and perform laser heat melting treatment on the positions 1 and 2 respectively;

[0025] P: After reaching the hot-melt state, place it in a directional magnetic field, hot-melt connection for 0.5 hours, and then air-cool to room temperature.

[0026] Further, the towing beam in step S01 includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 0.1%-0.2% phosphorus, 2.5%-3% magnesium, and 0.1%-0.35% rare earth elements; the towing beam is prepared by the following process:

[0027] The processed material of the tow beam is placed in a trough induction furnace for smelting at a temperature of 700-750° C. for 1-1.5 hours, and the smelting solvent is fluoride; the processed material obtained in step A is quenched with water, and after quenching, it is naturally aged for 10-12 hours.

[0028] A main structural beam of an automobile is manufactured by the manufacturing method as described above, comprising a crossbeam, a pair of drag beams arranged at opposite ends of the crossbeam, and a shock absorbing spring installed on the drag beam, wherein the drag beam is provided with a brake disc connected to the tire.

[0029] Furthermore, a reinforcing plate is provided at the connection between the cross beam and the towing beam.

[0030] The beneficial effects of the present invention are as follows: compared with the prior art, a method for preparing an aluminum alloy for an automobile main structural beam in the present invention uses laser hot-melt treatment on the two end positions of the crossbeam and the connection position between the towing beam and the crossbeam, and places them in a directional magnetic field and a directional water curtain for hot-melt connection. The directional magnetic field can guide the crystals at the connection to grow into columnar crystals, and the movement of the directional water curtain can further promote the crystals to grow into columnar crystals along the specified direction on the one hand, and on the other hand, the directional water curtain is water-cooled to obtain columnar crystals with fine grains, so that the obtained components have the advantages of less segregation, dense structure, high plasticity and toughness, and high strength; a passivation layer is formed at the connection position between the crossbeam and the towing beam by directional rotary spraying of chromic acid solution and under the action of the directional magnetic field, thereby enhancing the corrosion resistance of the connection.

[0031] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art may be taught from the practice of the present invention. The objectives and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0033] Figure 1 A flow chart of a method for preparing an automobile torsion beam according to an embodiment of the present invention;

[0034] Figure 2 A schematic structural diagram of an automobile torsion beam is provided for one embodiment of the present invention;

[0035] Figure 3 This is a schematic structural diagram of a crossbeam proposed in one embodiment of the present invention.

[0036] Figure Number:

[0037] 100-torsion beam;

[0038] 1- beam;

[0039] 2-Drag beam;

[0040] 3- shock-absorbing spring;

[0041] 4-Brake disc;

[0042] 5-Reinforcement plate. DETAILED DESCRIPTION

[0043] like Figure 1 As shown, this embodiment proposes a method for preparing an aluminum alloy for a main structural beam of an automobile, comprising the following steps:

[0044] S01: Prepare the cross beam and the drag beam in the automobile torsion beam respectively;

[0045] S02: The two ends of the crossbeam and the position where the towing beam is connected to the crossbeam are treated by laser heat melting, and the heat melting temperature is controlled at 350-400°C;

[0046] S03: placing the crossbeam and the towing beam in step S02 in a directional magnetic field and a directional water curtain, so that the crossbeam and the towing beam are hot-melt-connected for 0.2-0.5h under the action of the external magnetic field and the moving cooling of the directional water curtain;

[0047] S04: removing the directional water curtain in step S03, controlling the temperature at 80-100° C., and directionally spraying a chromic acid solution at the connection position between the cross beam and the towing beam to form a passivation layer.

[0048] In the present application, the two end positions of the crossbeam and the connection position between the towing beam and the crossbeam are treated with laser heat melting, and are placed in a directional magnetic field and a directional water curtain for heat melting connection. The directional magnetic field can guide the crystals at the connection to grow into columnar crystals, and the movement of the directional water curtain can further promote the growth of the crystals into columnar crystals along the specified direction. On the other hand, the directional water curtain is water-cooled to obtain columnar crystals with fine grains. The generated columnar crystal structure can eliminate the transverse grain boundaries in the structural parts, thereby reducing the number of grain boundaries in the structural parts, thereby obtaining the advantages of less component segregation, dense structure, high plasticity and toughness, and high strength. By directional rotary spraying of chromic acid solution and under the action of the directional magnetic field, a passivation layer is formed at the connection position between the crossbeam and the towing beam, thereby enhancing the corrosion resistance of the connection.

[0049] Preferably, the moving speed of the directional water curtain is 5-20 mm / s, and the pressure of the directional water curtain is 30-40 MPa. Specifically, the moving speed of the directional water curtain can be 5 mm / s, 6 mm / s, 7 mm / s, 8 mm / s, 9 mm / s, 10 mm / s, 12 mm / s, 14 mm / s, 16 mm / s, 18 mm / s, 20 mm / s; the pressure of the directional water curtain is 30 MPa, 32 MPa, 34 MPa, 36 MPa, 38 MPa, 40 MPa, etc. Of course, according to actual conditions and specific needs, the moving speed and pressure of the directional water curtain can also be set to other values, which are not limited here.

[0050] In the present application, by controlling the hot melt temperature at the end of the crossbeam and the tow beam and placing them in an external magnetic field and a directional water curtain for rapid cooling, without adding any refinement agent, the microstructure at the end of the crossbeam and the tow beam can be refined, and the grains can be promoted to grow into slender columnar crystals along the directional magnetic field and the water curtain, thereby improving the mechanical properties. The crossbeam produced according to this method can significantly improve its tensile strength, reduce its porosity, and increase the service life of the crossbeam.

[0051] The chromic acid in the present application is a trivalent chromium compound, specifically a trivalent chromium salt. There is no hexavalent chromium in this compound (or in the worst case, its amount is a negligible minimum amount). A wide range of anions can be used, and more than one trivalent chromium compound can be used. The preferred chromium compound is chromium fluoride. Chromium nitrate can also be used, either together with chromium fluoride or as a separate trivalent chromium compound. The preferred chromium compound can be added to the solution in the form of chromium fluoride tetrahydrate and chromium nitrate nonahydrate. By spraying chromic acid on the connection position of the crossbeam and the towing beam, a dense oxide layer can be formed, which better prevents oxidation from occurring at the connection and enhances the service life of the crossbeam and the towing beam.

[0052] In the present application, specifically, the hot melt temperature may be 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, etc.

[0053] In the present application, specifically, the duration of the hot melt connection can be 0.2h, 0.3h, 0.4h, 0.45h, 0.5h, etc.

[0054] For further information, see Figure 3 As shown, the crossbeam in step S01 includes a rigid section and plastic and tough sections arranged on both sides of the rigid section, the rigid section includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 0.08%-0.09% titanium, and 2.5%-3% magnesium, and the rigid section is prepared by the following process:

[0055] A. Place the rigid section processing material in a trough induction furnace for smelting at a temperature of 700-750°C for 1-1.5 hours, using fluoride as the smelting solvent;

[0056] B. Quench the processed product obtained in step A with water, and then naturally age it for 10-12 hours.

[0057] In the present application, the crossbeam is configured as a rigid section and plastic sections on both sides, that is, the rigid section can ensure the overall rigidity; the plastic section can be compressed to absorb energy and induce deformation. By ensuring the overall rigidity, absorbing energy and inducing deformation, the crossbeam has a higher torsional resistance.

[0058] In the present application, when the torsion beam is in use, the rigid section of the beam plays a supporting role, and the plastic-tough sections on both sides of the rigid section are subjected to a large torsion. By improving the plastic toughness of the plastic-tough sections on both sides of the rigid section, when subjected to a large torsion, the plastic-tough sections can better absorb energy and simultaneously undergo torsional deformation to adapt to different road conditions such as potholes. After passing through potholes, the plastic-tough sections have good elasticity and can be restored to their original state, making them durable and making it less likely for the connection between the beam and the towing beam to break.

[0059] Specifically, by providing the material composition of the rigid section with a higher mass percentage of chromium and a small amount of titanium, when calcined at a high temperature of 700-750°C, a chromium oxide layer and a titanium oxide layer can be formed, thereby improving the corrosion resistance of the structure; through high-temperature quenching, the strength and hardness of the rigid section can be enhanced.

[0060] In the present application, since the chromium oxide in the rigid segment can form a dense oxide film, it can effectively isolate the metal from the contact with the external corrosive medium, thereby providing corrosion protection, and the chemical inertness of chromium oxide enables it to remain stable in a variety of environments and is not prone to chemical reactions, thereby greatly improving the corrosion resistance of the rigid segment; at the same time, under the action of ultraviolet rays, the titanium oxide in the rigid segment can produce highly oxidizing hydroxyl radicals that can resist external corrosive substances and improve the product's aging resistance.

[0061] Preferably, the aluminum content may be 78%, 78.5%, 79%, 79.5%, 80%, etc.; the silicon content may be 0.1%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, etc.; the iron content may be 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, etc.; the copper content may be 0.09%, 0.095%, 0.1%, etc. ; The manganese content may be 0.08%, 0.1%, 0.14%, 0.18%, 0.2%, etc.; the chromium content is 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc.; the titanium content is 0.08%, 0.085%, 0.086%, 0.088%, 0.09%, etc.; the magnesium content is 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc.

[0062] Table 1 is a comparison table of the properties of the rigid segment with different chromium contents and the same other contents.

[0063]

[0064]

[0065] It can be seen from Table 1 that with the increase of chromium content, the resistivity of the rigid segment gradually increases, and the corrosion resistance of the rigid segment is better.

[0066] Further, the step B comprises:

[0067] B01: quenching the processed product obtained in step A with water, and after quenching, the temperature is controlled at 80-100° C.;

[0068] B02: Directional rotary spraying of chromic acid solution onto the surface of the object processed in step B01, reacting at a temperature of 80-100°C for 1-1.5 hours, and natural aging for 10-12 hours.

[0069] In the present application, a higher strength can be obtained by quenching the rigid section; a passivation layer can be formed on the surface by directionally spraying a chromic acid solution on the surface, thereby further improving the corrosion resistance of the rigid section; and the moisture on the surface of the passivation layer can be completely evaporated by reacting at a temperature of 80-100°C.

[0070] Further, the plastic-tough segment includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 2.5%-3% magnesium, and 0.1%-0.35% rare earth elements, and the plastic-tough segment includes the following process for preparation:

[0071] The processed material of the plastic-tough section is placed in a trough induction furnace for melting at a melting temperature of 500-570°C for 30 minutes, and then melted at a melting temperature of 700-750°C for 30-45 minutes;

[0072] The processed product obtained in step M is first oil-cooled for 4-5 hours, then water-cooled for 2-3 hours, and finally air-cooled to room temperature.

[0073] In the present application, by adding 0.1%-0.35% of rare earth elements to the components of the plastic-tough section, the grains can be strengthened and the mechanical strength of the plastic-tough section can be further improved; by melting at different high temperatures for a short time, high-temperature casting can be achieved to improve the uniformity of the crystal phase; by first oil-cooling the processed object and then water-cooling it, the crystallization stress can be reduced and the torsional resistance of the plastic-tough section can be enhanced.

[0074] Specifically, in the present application, rare earth elements such as lanthanum and cerium are added to promote the formation of columnar β crystals and form ultrafine microstructures. In addition, after adding rare earth elements lanthanum and cerium, the effects of fine grain strengthening, dispersion strengthening and solid solution strengthening in the deposit are enhanced, so that the plastic-tough section obtains excellent mechanical properties.

[0075] In the present application, by adopting different preparation processes for the rigid section and the plastic-tough section, the entire beam is able to ensure overall rigidity, absorb energy and induce deformation, that is, the connection between the plastic-tough section and the towing beam has higher torsion resistance.

[0076] Preferably, the aluminum content may be 78%, 78.5%, 79%, 79.5%, 80%, etc.; the silicon content may be 0.1%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, etc.; the iron content may be 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, etc.; the copper content may be 0.09%, 0.095%, 0.1 % etc.; the manganese content may be 0.08%, 0.1%, 0.14%, 0.18%, 0.2% etc.; the chromium content is 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2% etc.; the rare earth element content is 0.1%, 0.15%, 0.2%, 0.3%, 0.35% etc.; the magnesium content is 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3% etc.

[0077] Further, the step N comprises:

[0078] N01: The processed product obtained in step M is first oil-cooled for 4.5 hours and then water-cooled for 2.5 hours;

[0079] N02: Directional spin spraying of chromic acid solution onto the surface of the workpiece in step N01, reacting at 90°C for 1.5h, and finally air cooling to room temperature.

[0080] In the present application, by achieving different cooling speeds, that is, by pre-oil cooling, the alloy material is prevented from being easily broken during the quenching process due to high-temperature stress generated by too low a cooling temperature. At the same time, a large number of stress defects at the grain boundaries are also avoided. Oil cooling further provides growth opportunities for columnar crystals. Subsequently, through water cooling treatment, on the one hand, it is prevented that the columnar crystals are too large and cause the structural performance of the parts to deteriorate. On the other hand, a high-strength stress layer can be formed on the surface of the structure, thereby offsetting the external stress, greatly improving the performance of the product and extending the service life of the product.

[0081] By directional rotary spraying of chromic acid solution on its surface, a passivation layer can be formed on its surface, further improving the corrosion resistance of the plastic-tough section; by reacting at a temperature of 90°C, the moisture on the surface of the passivation layer is completely evaporated.

[0082] In this application, the following steps are also included:

[0083] O: Use a ruler to measure the position 1 of the rigid section 5-8 cm away from the end surface, and the position 2 of the plastic section 5-8 cm away from the end surface, and perform laser heat melting treatment on the positions 1 and 2 respectively;

[0084] P: After reaching the hot-melt state, place it in a directional magnetic field, hot-melt connection for 0.5 hours, and then air-cool to room temperature.

[0085] After the rigid segment and the plastic-tough segment are prepared by the above method, position 1 of the rigid segment 5-8 cm away from its end face and position 2 of the plastic-tough segment 5-8 cm away from its end face are measured by a ruler, and positions 1 and 2 are treated by laser hot melting, and then placed in a directional magnetic field. Under the action of the external magnetic field, columnar crystals are formed along the specified direction, so that the combination position has the advantages of dense structure, high plasticity and toughness, and high strength.

[0086] Preferably, the length of position 1 can be 5cm, 6cm, 7cm, 8cm, etc.; the length of position 2 can be 5cm, 6cm, 7cm, 8cm, etc. Of course, according to actual conditions and specific needs, the length of position 1 or position 2 can also be set to other values, which is not limited here.

[0087] Further, the supporting beam in step S01 includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 0.1%-0.2% phosphorus, 2.5%-3% magnesium, and 0.1%-0.35% rare earth elements; the plastic-tough segment is prepared by the following process:

[0088] The processed material of the plastic-tough section is placed in a trough induction furnace for melting at a temperature of 700-750° C. for 1-1.5 hours, and the melting solvent is fluoride; the processed material obtained in step A is quenched with water, and after quenching, naturally aged for 10-12 hours.

[0089] In the present application, phosphorus is added to the tow beam to enhance the fluidity of the liquid, which is beneficial to enhance the subsequent crystallization forming; by adding rare earth elements, the grains can be strengthened and the mechanical strength of the plastic-tough section can be further improved; by quenching the tow beam, the strength of the tow beam can be further enhanced.

[0090] Preferably, the aluminum content may be 78%, 78.5%, 79%, 79.5%, 80%, etc.; the silicon content may be 0.1%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, etc.; the iron content may be 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, etc.; the copper content may be 0.09%, 0.095%, 0.1 % etc.; the manganese content can be 0.08%, 0.1%, 0.14%, 0.18%, 0.2%, etc.; the chromium content is 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc.; the rare earth element content is 0.1%, 0.15%, 0.2%, 0.3%, 0.35%, etc.; the magnesium content is 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc.

[0091] The present application also provides a main structural beam for an automobile, which is prepared by the above-mentioned method for preparing the aluminum alloy for the main structural beam for an automobile, which will not be described in detail here. Figure 2 and Figure 3 As shown, the main structural beam 100 of the automobile includes a cross beam 1 and a pair of towing beams 2, the pair of towing beams 2 are arranged at opposite ends of the cross beam 1, a shock absorbing spring 3 is installed on the towing beam 2, a brake disc 4 is arranged on the towing beam 2, and the brake disc 4 is connected with the tire. In addition, a reinforcing plate 5 is also arranged at the connection between the cross beam 1 and the towing beam 2, and the reinforcing plate 5 can be welded to the cross beam 1 and the towing beam 2. By arranging the reinforcing plate 5, the bonding force between the cross beam 1 and the towing beam 2 can be enhanced, and the inch breakage at the connection can be effectively avoided.

[0092] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing an aluminum alloy for an automobile main structural beam, characterized in that: The steps include: S01: Prepare the cross beam and the drag beam in the automobile torsion beam respectively; S02: The two ends of the crossbeam and the position where the towing beam is connected to the crossbeam are treated by laser heat melting, and the heat melting temperature is controlled at 350-400°C; S03: placing the crossbeam and the towing beam in step S02 in a directional magnetic field and a directional water curtain, so that the crossbeam and the towing beam are hot-melt-connected for 0.2-0.5h under the action of the external magnetic field and the moving cooling of the directional water curtain; S04: removing the directional water curtain in step S03, controlling the temperature at 80-100° C., and directionally spraying a chromic acid solution at the connection position between the cross beam and the towing beam to form a passivation layer.

2. The method for preparing an aluminum alloy for an automobile main structural beam according to claim 1, characterized in that: The crossbeam in step S01 includes a rigid section and plastic sections disposed on both sides of the rigid section, wherein the rigid section includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 0.08%-0.09% titanium, and 2.5%-3% magnesium, and the rigid section is prepared by the following process: A. Place the rigid section processing material in a trough induction furnace for smelting at a temperature of 700-750°C for 1-1.5 hours, using fluoride as the smelting solvent; B. Quench the processed product obtained in step A with water, and then naturally age it for 10-12 hours.

3. The method for preparing an aluminum alloy for an automobile main structural beam according to claim 2, characterized in that: The step B comprises: B01: quenching the processed product obtained in step A with water, and after quenching, the temperature is controlled at 80-100° C.; B02: Directional rotary spraying of chromic acid solution onto the surface of the object processed in step B01, reacting at a temperature of 80-100°C for 1-1.5 hours, and natural aging for 10-12 hours.

4. The method for preparing an aluminum alloy for an automobile main structural beam according to claim 2, characterized in that: The plastic-tough segment includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 2.5%-3% magnesium, and 0.1%-0.35% rare earth elements. The plastic-tough segment is prepared by the following process: M. Place the processed material of the plastic-tough section in a trough induction furnace for smelting at a smelting temperature of 500-570°C for 30 minutes, and then smelt at a smelting temperature of 700-750°C for 30-45 minutes; N. The processed product obtained in step M is first oil-cooled for 4-5 hours, then water-cooled for 2-3 hours, and finally air-cooled to room temperature.

5. The method for preparing an aluminum alloy for automobile main structural beam according to claim 4, characterized in that: The step N comprises: N01: The processed product obtained in step M is first oil-cooled for 4.5 hours and then water-cooled for 2.5 hours; N02: Directional spin spraying of chromic acid solution onto the surface of the workpiece in step N01, reacting at 90°C for 1.5h, and finally air cooling to room temperature.

6. The method for preparing an aluminum alloy for an automobile main structural beam according to claim 4, characterized in that: The following steps are also included: O: Use a ruler to measure the position 1 of the rigid section 5-8 cm away from its end surface, and the position 2 of the plastic section 5-8 cm away from its end surface, and perform laser heat melting treatment on the positions 1 and 2 respectively; P: After reaching the hot-melt state, place it in a directional magnetic field, hot-melt connection for 0.5 hours, and then air-cool to room temperature.

7. The method for preparing an aluminum alloy for automobile main structural beam according to claim 1, characterized in that: The towing beam in step S01 includes 78%-80% aluminum, 0.1%-0.2% silicon, 0.4%-0.6% iron, 0.09%-0.1% copper, 0.08%-0.2% manganese, 1%-2% chromium, 0.1%-0.2% phosphorus, 2.5%-3% magnesium, and 0.1%-0.35% rare earth elements; the towing beam is prepared by the following process: The processed material of the tow beam is placed in a trough induction furnace for smelting at a temperature of 700-750° C. for 1-1.5 hours, and the smelting solvent is fluoride; the processed material obtained in step A is quenched with water, and after quenching, it is naturally aged for 10-12 hours.

8. A main structural beam of an automobile, characterized in that: It is manufactured by the preparation method according to any one of claims 1 to 7, comprising a crossbeam, a pair of towing beams arranged at opposite ends of the crossbeam, and a shock-absorbing spring installed on the towing beam, wherein the towing beam is provided with a brake disc connected to the tire.

9. The main structural beam of an automobile according to claim 8, characterized in that: A reinforcing plate is also provided at the connection between the cross beam and the towing beam.

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