A method for preparing lightweight semi-solid aluminum alloy die castings for new energy vehicles

Abstract

The invention discloses a method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles, and relates to the technical field of semi-solid die castings. The invention adopts a reasonable ratio of elements such as aluminum, magnesium, and silicon, and adopts pulsed airflow to assist stirring to enhance the smelting effect, which can effectively refine the grains and make the crystal phase uniform, which is beneficial to improving the mechanical properties of the die casting. At the same time, there are no bubbles in the melt formed, and the mold cavity can be completely filled; then, metal aluminum, metal nickel, and rare earth lanthanum are used as raw materials to obtain a metal modifier, which is used as a nucleation particle to improve the nucleation rate and purify the interface, and a semi-solid state is initially formed to enhance the mechanical properties of the die casting. Then, a vertical spiral pipe is used as a cooling pipe for secondary cooling. During the cooling process, the spiral blade surface is driven to rotate by the flow of the molten liquid, so as to effectively control the solid phase fraction of the semi-solid slurry, thereby improving the mechanical properties of the die casting.

Description

Technical Field

[0001] The present invention relates to the technical field of semi-solid die castings, and in particular to a method for preparing lightweight semi-solid aluminum alloy die castings for new energy vehicles. Background Art

[0002] Aluminum alloy has low density, good corrosion resistance and excellent plasticity. It has incomparable advantages over other lightweight materials in terms of production cost, part quality, material utilization, manufacturing technology, mechanical properties, and sustainable development. Therefore, aluminum alloy will become the preferred lightweight material in the new energy vehicle industry.

[0003] Semi-solid forming technology of aluminum alloy has the advantages of cost close to traditional die-casting process and performance close to forging. It is suitable for manufacturing complex automotive parts and various thin-walled parts. Therefore, it has the potential to replace some automotive aluminum alloy liquid die-casting and forgings. In the preparation of semi-solid alloy by electromagnetic stirring, a relatively high-power electromagnetic stirring must be performed. Only then can a semi-solid alloy material or billet with fine and spherical primary crystals be obtained. However, once the shear rate is less than 500S -1 , the grain morphology deteriorates and it is difficult to form. However, the high shear rate will cause irreversible effects on the interior of the alloy, ultimately reducing the internal quality of the die casting. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles, so as to solve the problems existing in the prior art.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles, comprising the following preparation steps:

[0006] (1) Pure aluminum, aluminum silicon alloy, aluminum titanium alloy, pure magnesium, aluminum zinc alloy, electrolytic copper, aluminum zirconium alloy, and aluminum iron alloy are mixed and placed in a vertical melting furnace, evacuated to 0.1-1.0 kPa, heated to 730-740° C., and kept warm for 30-60 minutes. Then, the stirrer and the air inlet solenoid valve at the upper end of the vertical melting furnace are turned on, and the temperature is raised to 780-800° C., and kept warm until the melt is completely melted;

[0007] (2) The melt temperature is reduced to 720-750°C, a refining agent is added, and after refining for 10-30 minutes, the agitator and the solenoid valve are turned off, and after standing for 15 minutes, the slag is removed, and the agitator and the solenoid valve are turned on to add a metal modifier. After processing for 60 minutes, the stirring speed is increased to 200-400 r / min, and the temperature is reduced to 600-615°C to obtain a semi-solid slurry;

[0008] (3) Open the valve at the bottom of the vertical melting furnace to allow the semi-solid slurry to be cast into a semi-solid die-casting machine along the vertical cooling pipe to obtain lightweight semi-solid aluminum alloy die-casting parts for new energy vehicles; the mold temperature is 240-320° C., the injection force is 280 KN, and the injection speed is 0.3-0.9 m / s.

[0009] Furthermore, the semi-solid aluminum alloy die casting includes the following raw material components in weight percentage: 0.5-2.5% magnesium, 3.0-5.2% silicon, 0.02-0.05% titanium, 1.2-2.4% copper, 2.5-4.8% zinc, 0.03-0.06% zirconium, 1-1.5% iron, 0.01-0.03% lanthanum, 0.8-1.5% nickel, other metal and non-metal impurity elements are 0.05%, and the rest is aluminum.

[0010] Furthermore, the stirring speed of the stirrer in steps (1) and (2) is 10 to 40 r / min.

[0011] Furthermore, the pulse frequency of the solenoid valve in steps (1) and (2) is 0.5 Hz. After the solenoid valve is opened, the argon mixed gas is filled to a pressure of 3 to 15 kPa, maintained for 8 to 20 seconds, and then evacuated to 0.1 to 1.0 kPa, and then the argon mixed gas is filled to a pressure of 3 to 15 kPa, maintained for 8 to 20 seconds, and this cycle is repeated.

[0012] Furthermore, the argon mixed gas is a mixture of argon and nitrogen in a volume ratio of 5:1.

[0013] Furthermore, the amount of the refining agent added in step (2) is 1 to 4 kg per ton of melt.

[0014] Furthermore, the refining agent in step (2) is prepared by mixing potassium chloride, sodium chloride and sodium hexafluoroaluminate in a mass ratio of 40-50:25-35:18-25.

[0015] Furthermore, the amount of the metal modifier added in step (2) is 1 to 4 kg per ton of melt.

[0016] Furthermore, the preparation method of the metal modifier in step (2) is as follows: aluminum powder, nickel powder and lanthanum powder are mixed at an atomic fraction of 40-50:10-15:0.1-0.5 to obtain metal powder, sodium stearate is added at a mass ratio of 0.02 times the mass of the metal powder, the ball-to-material ratio is 15-20:1, ball milling is performed at 400-500 rpm for 8-12 hours, cold pressing is performed at 1000 MPa, sintering is performed at 1250° C. for 4 hours under argon protection, and grinding is performed through a 100 mesh sieve to obtain alloy powder; the alloy powder, potassium chloride and sodium chloride are mixed at a mass ratio of 10:5:5 and ground through a 400 mesh sieve.

[0017] Furthermore, in step (3), a spiral rod is used in the middle of the vertical cooling pipe, and the outer layer is wrapped with a cooling water jacket, and the cooling water is natural water at 20 to 40°C.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0019] The present invention forms an alloy phase with uniform grain structure through reasonable proportion of elements such as aluminum, magnesium, silicon, etc. The present invention places each alloy in a vertical melting furnace, first performs preliminary heating and melting, and melts the low-melting-point metal. At this time, the stirrer is turned on to diffuse the molten liquid. As the temperature rises, it is melted and combined with other metals to reduce the existence of low-melting-point eutectics. The side of the vertical melting furnace is connected with an electromagnetic valve to control the incoming gas to generate a pulsed airflow. Through stirring, the pulsed airflow is prompted to fully mix with the molten liquid, and the smelting effect is accelerated. The pulsed airflow can form a larger vortex structure, increase the instability of the flow field, thereby enhancing the mixing effect of the fluid, and prevent the particles with higher density from being affected by the stirring force during the stirring process and moving to the outer surface to form an unstable gradient structure. At the same time, during the stirring process, the microbubbles formed by the pulsed airflow can be discharged, so that the semi-solid slurry in the later stage can completely fill the mold cavity in the die casting, and the mechanical properties of the die casting are improved. The present invention adopts pulsed airflow to assist stirring, strengthen the crushing effect, avoid the generation of plate-like structures, form an alloy structure with fine and uniform grains, and strengthen the melting effect to achieve rapid melting.

[0020] The present invention adopts metal aluminum, metal nickel and rare earth lanthanum as raw materials, realizes alloying through mechanical grinding, and mixes with potassium chloride and sodium chloride to form a metal modifier, which is sprayed into the melt in the furnace, and takes it as a nucleation particle to reduce the surface tension on the phase boundary of the liquid metal, and the energy fluctuation required for generating the crystal nucleus is small, and the nucleation rate of uniform nucleation is improved, and compounds are generated with impurity elements, impurity atoms are removed, and the interface is purified. It can also absorb the heat of the liquid metal and then melt, so that the liquid metal raw material is cooled and a large number of crystal nuclei are generated, and a semi-solid state is initially formed. In addition, during the spraying process, continuous pulse airflow assists stirring, accelerates mixing and cooling, and then utilizes the vertical spiral pipe connected to the bottom, and the semi-solid slurry flows down along the spiral surface with the action of gravity, and tap water is passed through the outer side of the pipe to cool the liquid, and the spiral blade surface is driven to rotate during the downstream process, and then the slurry is stirred, and the cooling of the semi-solid slurry is effectively controlled to form a suitable solid phase fraction, which is conducive to better die-casting of the semi-solid slurry and improves the mechanical properties of the die-casting. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] In order to more clearly illustrate the method provided by the present invention, the following examples are used to describe in detail the various index testing methods of the semi-solid aluminum alloy die castings produced in the following examples.

[0023] Mechanical properties: The tensile strength and yield strength of the embodiment and the comparative example of the same size were measured using an Instron 8801 tensile testing machine.

[0024] Example 1; (1) Pure aluminum, aluminum silicon alloy, aluminum titanium alloy, pure magnesium, aluminum zinc alloy, electrolytic copper, aluminum zirconium alloy, and aluminum iron alloy are mixed and placed in a vertical melting furnace, evacuated to 0.1 kPa, heated to 730°C, and kept warm for 30 minutes. Then, a stirrer with a stirring speed of 10 r / min and an air inlet solenoid valve with a pulse frequency of 0.5 Hz at the upper end of the vertical melting furnace are turned on. After opening the solenoid valve, argon mixed gas is filled in until the pressure is 3 kPa, maintained for 8 seconds, evacuated to 0.1 kPa, and then argon mixed gas is filled in until the pressure is 3 kPa, maintained for 8 seconds, and this process is repeated. The volume ratio of argon to nitrogen in the argon mixed gas is 5:1. The temperature is raised to 780°C and kept warm until the melt is completely melted to obtain a melt.

[0025] (2) Aluminum powder, nickel powder, and lanthanum powder were mixed at an atomic fraction of 40:10:0.1 to obtain metal powder, sodium stearate was added at a mass ratio of 0.02 times the mass of the metal powder, the ball-to-material ratio was 15:1, ball milling was performed at 400 rpm for 8 hours, cold pressing was performed at 1000 MPa, sintering was performed at 1250° C. for 4 hours under argon protection, and then grinding was passed through a 100 mesh sieve to obtain alloy powder; the alloy powder, potassium chloride, and sodium chloride were mixed at a mass ratio of 10:5:5 and ground through a 400 mesh sieve to obtain a metal modifier;

[0026] (3) The melt was cooled to 720°C, and a refining agent was added. The mass ratio of potassium chloride, sodium chloride, and sodium hexafluoroaluminate in the refining agent was 40:25:18, and the amount added was 1 kg / ton of the melt. After refining for 10 minutes, the agitator and the solenoid valve were turned off. After standing for 15 minutes, the slag was removed, and the agitator and the solenoid valve were turned on to add a metal modifier. The amount added was 1 kg / ton of the melt. After processing for 60 minutes, the stirring speed was increased to 200 r / min, and the temperature was reduced to 600°C to obtain a semi-solid slurry;

[0027] (4) Open the valve at the bottom of the vertical melting furnace to cast the semi-solid slurry into the semi-solid die-casting machine along the vertical cooling pipe. The vertical cooling pipe adopts a spiral rod in the middle and is wrapped with a cooling water jacket on the outside. The cooling water is natural water at 20°C, thereby obtaining a lightweight semi-solid aluminum alloy die-casting for new energy vehicles; the mold temperature is 240°C, the injection force is 280KN, and the injection speed is 0.3m / s; the semi-solid aluminum alloy die-casting comprises the following raw material components in weight percentage: 0.5% magnesium, 3.0% silicon, 0.02% titanium, 1.2% copper, 2.5% zinc, 0.03% zirconium, 1% iron, 0.01% lanthanum, 1.0% nickel, 0.05% other metal and non-metal impurity elements, and the rest is aluminum.

[0028] Example 2; (1) Pure aluminum, aluminum silicon alloy, aluminum titanium alloy, pure magnesium, aluminum zinc alloy, electrolytic copper, aluminum zirconium alloy, and aluminum iron alloy are mixed and placed in a vertical melting furnace, evacuated to 0.65 kPa, heated to 735°C, and kept warm for 45 minutes. Then, a stirrer with a stirring speed of 25 r / min and an air inlet solenoid valve with a pulse frequency of 0.5 Hz at the upper end of the vertical melting furnace are turned on. After opening the solenoid valve, argon mixed gas is filled to a pressure of 9 kPa, maintained for 14 seconds, evacuated to 0.65 kPa, and then filled with argon mixed gas to a pressure of 9 kPa, maintained for 14 seconds, and repeated in this manner. The volume ratio of argon to nitrogen in the argon mixed gas is 5:1. The temperature is raised to 790°C and kept warm until it is completely melted to obtain a molten liquid.

[0029] (2) Aluminum powder, nickel powder, and lanthanum powder were mixed at an atomic fraction of 45:12.5:0.3 to obtain metal powder, sodium stearate was added at a mass ratio of 0.02 times the mass of the metal powder, the ball-to-material ratio was 20:1, ball milling was performed at 450 rpm for 10 hours, cold pressing was performed at 1000 MPa, sintering was performed at 1250° C. for 4 hours under argon protection, and then grinding was passed through a 100 mesh sieve to obtain alloy powder; the alloy powder, potassium chloride, and sodium chloride were mixed at a mass ratio of 10:5:5 and ground through a 400 mesh sieve to obtain a metal modifier;

[0030] (3) The melt temperature was lowered to 735° C., and a refining agent was added. The mass ratio of potassium chloride, sodium chloride, and sodium hexafluoroaluminate in the refining agent was 45:30:21.5, and the amount added was 2.5 kg / ton of melt. After refining for 20 minutes, the agitator and the solenoid valve were turned off. After standing for 15 minutes, the slag was removed, and the agitator and the solenoid valve were turned on to add a metal modifier. The amount added was 2.5 kg / ton of melt. After processing for 60 minutes, the stirring speed was increased to 300 r / min, and the temperature was lowered to 608° C. to obtain a semi-solid slurry;

[0031] (4) Open the valve at the bottom of the vertical melting furnace to cast the semi-solid slurry into a semi-solid die-casting machine along a vertical cooling pipe. A spiral rod is used in the middle of the vertical cooling pipe, and a cooling water jacket is wrapped on the outer layer. The cooling water is natural water at 30°C, thereby obtaining a lightweight semi-solid aluminum alloy die-casting for new energy vehicles; the mold temperature is 280°C, the injection force is 280KN, and the injection speed is 0.6m / s; the semi-solid aluminum alloy die-casting comprises the following raw material components in weight percentage: 2% magnesium, 4.1% silicon, 0.035% titanium, 1.8% copper, 3.6% zinc, 0.045% zirconium, 1.25% iron, 0.02% lanthanum, 0.8% nickel, 0.05% other metal and non-metal impurity elements, and the rest is aluminum.

[0032] Example 3; (1) Pure aluminum, aluminum silicon alloy, aluminum titanium alloy, pure magnesium, aluminum zinc alloy, electrolytic copper, aluminum zirconium alloy, and aluminum iron alloy are mixed and placed in a vertical melting furnace, evacuated to 1.0 kPa, heated to 740°C, and kept warm for 60 minutes. Then, a stirrer with a stirring speed of 40 r / min and an air inlet solenoid valve with a pulse frequency of 0.5 Hz at the upper end of the vertical melting furnace are turned on. After opening the solenoid valve, argon mixed gas is filled in until the pressure reaches 15 kPa, and maintained for 20 seconds. Then, the mixture is evacuated to 1.0 kPa, and then argon mixed gas is filled in until the pressure reaches 15 kPa, and maintained for 20 seconds. This process is repeated, and the volume ratio of argon to nitrogen in the argon mixed gas is 5:1. The mixture is heated to 800°C and kept warm until it is completely melted to obtain a molten liquid.

[0033] (2) Aluminum powder, nickel powder, and lanthanum powder were mixed at an atomic fraction of 50:15:0.5 to obtain metal powder, sodium stearate was added at a mass ratio of 0.02 times the mass of the metal powder, the ball-to-material ratio was 20:1, and the mixture was ball-milled at 500 rpm for 12 hours, and then cold-pressed at 1000 MPa. Under argon protection, the mixture was sintered at 1250° C. for 4 hours, and then ground through a 100-mesh sieve to obtain alloy powder; the alloy powder, potassium chloride, and sodium chloride were mixed at a mass ratio of 10:5:5 and ground through a 400-mesh sieve to obtain a metal modifier;

[0034] (3) The melt was cooled to 750° C., and a refining agent was added. The mass ratio of potassium chloride, sodium chloride, and sodium hexafluoroaluminate in the refining agent was 50:35:25, and the amount added was 4 kg / ton of the melt. After refining for 30 minutes, the agitator and the solenoid valve were turned off. After standing for 15 minutes, the slag was removed, and the agitator and the solenoid valve were turned on to add a metal modifier. The amount added was 4 kg / ton of the melt. After processing for 60 minutes, the stirring speed was increased to 400 r / min, and the temperature was reduced to 615° C. to obtain a semi-solid slurry;

[0035] (4) Open the valve at the bottom of the vertical melting furnace to cast the semi-solid slurry into the semi-solid die-casting machine along the vertical cooling pipe. The vertical cooling pipe adopts a spiral rod in the middle and is wrapped with a cooling water jacket on the outside. The cooling water is natural water at 40°C, thereby obtaining a lightweight semi-solid aluminum alloy die-casting for new energy vehicles; the mold temperature is 320°C, the injection force is 280KN, and the injection speed is 0.9m / s; the semi-solid aluminum alloy die-casting comprises the following raw material components in weight percentage: 2.5% magnesium, 5.2% silicon, 0.05% titanium, 2.4% copper, 4.8% zinc, 0.06% zirconium, 1.5% iron, 0.03% lanthanum, 0.9% nickel, 0.05% other metal and non-metal impurity elements, and the rest is aluminum.

[0036] Comparative Example 1; (1) Pure aluminum, aluminum-silicon alloy, aluminum-titanium alloy, pure magnesium, aluminum-zinc alloy, electrolytic copper, aluminum-zirconium alloy, and aluminum-iron alloy were mixed and placed in a vertical melting furnace, evacuated to 0.65 kPa, heated to 735° C., kept warm for 45 min, and then turned on a stirrer with a stirring speed of 25 r / min, heated to 790° C., and kept warm until completely melted to obtain a molten liquid;

[0037] (2) Aluminum powder, nickel powder, and lanthanum powder were mixed at an atomic fraction of 45:12.5:0.3 to obtain metal powder, sodium stearate was added at a mass ratio of 0.02 times the mass of the metal powder, the ball-to-material ratio was 20:1, ball milling was performed at 450 rpm for 10 hours, cold pressing was performed at 1000 MPa, sintering was performed at 1250° C. for 4 hours under argon protection, and then grinding was passed through a 100 mesh sieve to obtain alloy powder; the alloy powder, potassium chloride, and sodium chloride were mixed at a mass ratio of 10:5:5 and ground through a 400 mesh sieve to obtain a metal modifier;

[0038] (3) The melt temperature was lowered to 735° C., and a refining agent was added. The mass ratio of potassium chloride, sodium chloride, and sodium hexafluoroaluminate in the refining agent was 45:30:21.5, and the amount added was 2.5 kg / ton of melt. Argon was sprayed, and the argon flow rate was 15 mL / min and the argon pressure was 0.35 MPa. After refining for 20 minutes, the agitator was turned off, and after standing for 15 minutes, degassing, slag removal, and the agitator was turned on. The amount added was 2.5 kg / ton of melt. After processing for 60 minutes, the stirring speed was increased to 800 r / min, and the temperature was lowered to 608° C. to obtain a semi-solid slurry;

[0039] (4) Open the valve at the bottom of the vertical melting furnace to cast the semi-solid slurry into a semi-solid die-casting machine along a vertical cooling pipe. A spiral rod is used in the middle of the vertical cooling pipe, and a cooling water jacket is wrapped on the outer layer. The cooling water is natural water at 30°C, thereby obtaining a lightweight semi-solid aluminum alloy die-casting for new energy vehicles; the mold temperature is 280°C, the injection force is 280KN, and the injection speed is 0.6m / s; the semi-solid aluminum alloy die-casting comprises the following raw material components in weight percentage: 2% magnesium, 4.1% silicon, 0.035% titanium, 1.8% copper, 3.6% zinc, 0.045% zirconium, 1.25% iron, 0.02% lanthanum, 0.8% nickel, 0.05% other metal and non-metal impurity elements, and the rest is aluminum.

[0040] Comparative Example 2; (1) Pure aluminum, aluminum silicon alloy, aluminum titanium alloy, pure magnesium, aluminum zinc alloy, electrolytic copper, aluminum zirconium alloy, and aluminum iron alloy were mixed and placed in a vertical melting furnace, evacuated to 0.65 kPa, heated to 735°C, and kept warm for 45 minutes. Then, a stirrer with a stirring speed of 25 r / min and an air inlet solenoid valve with a pulse frequency of 0.5 Hz at the upper end of the vertical melting furnace were turned on. After opening the solenoid valve, argon mixed gas was filled to a pressure of 9 kPa, maintained for 14 seconds, evacuated to 0.65 kPa, and then argon mixed gas was filled to a pressure of 9 kPa, maintained for 14 seconds, and this process was repeated. The volume ratio of argon to nitrogen in the argon mixed gas was 5:1. The temperature was raised to 790°C and kept warm until the melt was completely melted to obtain a molten liquid.

[0041] (2) The melt was cooled to 735° C., and a refining agent was added. The mass ratio of potassium chloride, sodium chloride, and sodium hexafluoroaluminate in the refining agent was 45:30:21.5, and the amount added was 2.5 kg / ton of melt. After refining for 20 minutes, the agitator and the solenoid valve were turned off. After standing for 15 minutes, the slag was removed, and the agitator and the solenoid valve were turned on. The stirring speed was increased to 550 r / min, and the temperature was reduced to 608° C. to obtain a semi-solid slurry;

[0042] (3) Open the valve at the bottom of the vertical smelting furnace to cast the semi-solid slurry into a semi-solid die-casting machine along a vertical cooling pipe. A spiral rod is used in the middle of the vertical cooling pipe, and a cooling water jacket is wrapped on the outer layer. The cooling water is natural water at 30°C, thereby obtaining a lightweight semi-solid aluminum alloy die-casting for new energy vehicles; the mold temperature is 280°C, the injection force is 280KN, and the injection speed is 0.6m / s; the semi-solid aluminum alloy die-casting comprises the following raw material components in weight percentage: 2% magnesium, 4.1% silicon, 0.035% titanium, 1.8% copper, 3.6% zinc, 0.045% zirconium, 1.25% iron, 0.02% lanthanum, 0.8% nickel, 0.05% other metal and non-metal impurity elements, and the rest is aluminum.

[0043] Comparative Example 3; (1) Pure aluminum, aluminum silicon alloy, aluminum titanium alloy, pure magnesium, aluminum zinc alloy, electrolytic copper, aluminum zirconium alloy, and aluminum iron alloy were mixed and placed in a vertical melting furnace, evacuated to 0.65 kPa, heated to 735°C, and kept warm for 45 minutes. Then, a stirrer with a stirring speed of 25 r / min and an air inlet solenoid valve with a pulse frequency of 0.5 Hz at the upper end of the vertical melting furnace were turned on. After opening the solenoid valve, argon mixed gas was filled to a pressure of 9 kPa, maintained for 14 seconds, evacuated to 0.65 kPa, and then filled with argon mixed gas to a pressure of 9 kPa, maintained for 14 seconds, and repeated in this manner. The volume ratio of argon to nitrogen in the argon mixed gas was 5:1. The temperature was raised to 790°C and kept warm until the melt was completely melted to obtain a molten liquid.

[0044] (2) Aluminum powder, nickel powder, and lanthanum powder were mixed at an atomic fraction of 45:12.5:0.3 to obtain metal powder, sodium stearate was added at a mass ratio of 0.02 times the mass of the metal powder, the ball-to-material ratio was 20:1, ball milling was performed at 450 rpm for 10 hours, cold pressing was performed at 1000 MPa, sintering was performed at 1250° C. for 4 hours under argon protection, and then grinding was passed through a 100 mesh sieve to obtain alloy powder; the alloy powder, potassium chloride, and sodium chloride were mixed at a mass ratio of 10:5:5 and ground through a 400 mesh sieve to obtain a metal modifier;

[0045] (3) The melt was cooled to 735°C, and a refining agent was added. The mass ratio of potassium chloride, sodium chloride, and sodium hexafluoroaluminate in the refining agent was 45:30:21.5, and the amount added was 2.5 kg / ton of melt. After refining for 20 minutes, the agitator and the solenoid valve were turned off. After standing for 15 minutes, the slag was removed, and the agitator and the solenoid valve were turned on to add a metal modifier. The amount added was 2.5 kg / ton of melt. After processing for 60 minutes, the stirring speed was increased to 550 r / min, and the temperature was reduced to 608°C to obtain a semi-solid slurry. The slurry was cast. Casting into a semi-solid die-casting machine, a lightweight semi-solid aluminum alloy die-casting for new energy vehicles is obtained; the mold temperature is 280°C, the injection force is 280KN, and the injection speed is 0.6m / s; the semi-solid aluminum alloy die-casting includes the following raw material components in weight percentage: 2% magnesium, 4.1% silicon, 0.035% titanium, 1.8% copper, 3.6% zinc, 0.045% zirconium, 1.25% iron, 0.02% lanthanum, 0.8% nickel, other metal and non-metal impurity elements are 0.05%, and the rest is aluminum.

[0046] Effect example

[0047] Table 1 below shows the performance analysis results of the semi-solid aluminum alloy die castings using Examples 1 to 3 of the present invention and Comparative Examples 1 to 3.

[0048] Table 1

[0049]

[0050]

[0051] From the comparison of the experimental data of the embodiment and the comparative example, it can be found that the present invention adopts pulsed airflow to assist stirring during the smelting process, which can effectively refine the grains and make the crystal phase uniform, which is beneficial to improving the mechanical properties of the die-casting, and at the same time forms a bubble-free melt. The added metal modifier effectively generates crystal nuclei, improves the nucleation rate of uniform nucleation, removes impurity atoms, purifies the interface, and improves the mechanical properties. The present invention also uses a vertical spiral pipe as a cooling pipe, and uses the flow of semi-solid slurry to drive the rotation of the spiral blade, effectively controlling the solid phase fraction of the semi-solid slurry, and indirectly improving the mechanical properties.

[0052] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations within the meaning and scope of the equivalent elements of the claims be included in the invention. Any marking in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for preparing lightweight semi-solid aluminum alloy die castings for new energy vehicles, characterized in that: The method comprises the following preparation steps: (1) Pure aluminum, aluminum silicon alloy, aluminum titanium alloy, pure magnesium, aluminum zinc alloy, electrolytic copper, aluminum zirconium alloy, and aluminum iron alloy are mixed and placed in a vertical melting furnace, evacuated to 0.1~1.0 kPa, heated to 730~740°C, and kept warm for 30~60 minutes. Then, the agitator and the air inlet solenoid valve at the upper end of the vertical melting furnace are turned on, and the temperature is raised to 780~800°C, and kept warm until the melt is completely melted; the pulse frequency of the solenoid valve is 0.5 Hz. After opening the solenoid valve, argon mixed gas is filled to a pressure of 3~15 kPa, and maintained for 8~20 seconds, and then evacuated to 0.1~1.0 kPa, and then argon mixed gas is filled to a pressure of 3~15 kPa, and maintained for 8~20 seconds, and this process is repeated; (2) Aluminum powder, nickel powder and lanthanum powder are mixed at an atomic fraction of 40-50:10-15:0.1-0.5 to obtain metal powder, and sodium stearate is added at a mass ratio of 0.02 times the mass of the metal powder. The ball-to-material ratio is 15-20:1, and the ball milling is carried out at 400-500 rpm for 8-12 hours. The mixture is cold pressed at 1000 MPa, sintered at 1250°C for 4 hours under argon protection, and then ground through a 100-mesh sieve to obtain alloy powder; the alloy powder, potassium chloride and sodium chloride are mixed at a mass ratio of 10:5:5, and ground through a 400-mesh sieve to obtain a metal modifier; the melt is cooled to 720-750°C, and a refining agent is added. After refining for 10-30 minutes, turn off the agitator and the solenoid valve, let it stand for 15 minutes, remove the slag, open the agitator and the solenoid valve to add the metal modifier, and after processing for 60 minutes, increase the stirring speed to 200-400r / min, cool to 600-615℃, and obtain a semi-solid slurry; the pulse frequency of the solenoid valve is 0.5Hz, and after opening the solenoid valve, fill it with argon mixed gas to a pressure of 3-15kPa, keep it for 8-20s, evacuate it to 0.1-1.0kPa, and then fill it with argon mixed gas to a pressure of 3-15kPa, keep it for 8-20s, and repeat this process; (3) Open the valve at the bottom of the vertical melting furnace to allow the semi-solid slurry to be cast into the semi-solid die-casting machine along the vertical cooling pipe to obtain lightweight semi-solid aluminum alloy die-casting parts for new energy vehicles; the mold temperature is 240~320℃, the injection force is 280KN, and the injection speed is 0.3~0.9m / s; The semi-solid aluminum alloy die casting comprises the following raw material components in weight percentage: 0.5-2.5% magnesium, 3.0-5.2% silicon, 0.02-0.05% titanium, 1.2-2.4% copper, 2.5-4.8% zinc, 0.03-0.06% zirconium, 1-1.5% iron, 0.01-0.03% lanthanum, 0.8-1.5% nickel, 0.05% other metal and non-metal impurity elements, and the rest is aluminum.

2. The method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles according to claim 1, characterized in that: The stirring speed of the stirrer in steps (1) and (2) is 10-40 r / min.

3. The method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles according to claim 1, characterized in that: The argon mixed gas in steps (1) and (2) is a mixture of argon and nitrogen in a volume ratio of 5:

1.

4. The method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles according to claim 1, characterized in that: The amount of refining agent added in step (2) is 1-4 kg / ton of melt.

5. The method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles according to claim 1, characterized in that: The refining agent in step (2) is prepared by mixing potassium chloride, sodium chloride and sodium hexafluoroaluminate in a mass ratio of 40-50:25-35:18-25.

6. The method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles according to claim 1, characterized in that: The amount of the metal modifier added in step (2) is 1-4 kg / ton of melt.

7. The method for preparing a lightweight semi-solid aluminum alloy die casting for new energy vehicles according to claim 1, characterized in that: The vertical cooling tube in step (3) has a spiral rod in the middle and a cooling water jacket on the outside. The cooling water is natural water at 20-40°C.

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