A method for manufacturing a magnesium alloy battery case

Abstract

This invention relates to the field of battery casing production and processing technology for new energy vehicles, and provides a method for preparing a magnesium alloy battery casing, characterized by the following steps: (1) Slurry preparation: dried magnesium alloy particles are added to a semi-solid injection molding machine, the barrel temperature of the semi-solid injection molding machine is 540℃~550℃, and the screw shearing speed is 1800-2000rpm; (2) Vacuum injection: after mold closing, the vacuum pump is started and the pressure is drawn to 5-10KPa absolute pressure, and the slurry begins to be injected; a first-stage slow filling, injection The injection speed is 0.4-0.6 m / s until the screw advance stroke is 45-50%; the second stage is high-speed filling, the injection speed is increased to 4.0-4.5 m / s, during which air is continuously pumped out until the screw advance stroke is 85-90%, and the vacuum valve is closed; the third stage is pressurized filling, after the vacuum valve is closed, the injection pressure is increased to 130-150 MPa to complete the final filling; (3) the pressure holding stage, the built-in slider is driven to compress the reinforcing ribs on the bottom surface of the battery casing at 200-250 MPa and hold for 10-15s. This invention overcomes the shortcomings of the prior art, effectively reduces the porosity of the reinforcing ribs on the bottom surface of the battery casing, and improves the structural rigidity and explosion-proof capability.

Description

Technical Field

[0001] This invention relates to the field of battery casing production and processing technology for new energy vehicles, and specifically to a method for preparing a magnesium alloy battery casing. Background Technology

[0002] In existing technologies, when using semi-solid injection molding of magnesium alloys to form battery casings, especially for cases with a wall thickness of less than 1 mm, the distal ends, thin-walled flow ends, and particularly the reinforcing ribs of the battery casing are the areas where porosity and shrinkage are most likely to accumulate. The magnesium alloy containing highly reactive rare earth elements such as Sc and Sr developed by the applicant has a porosity as high as 0.8-1.2% in these areas due to its poor fluidity and tendency to solidify and segregate.

[0003] Therefore, we propose a method for preparing a magnesium alloy battery casing. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing a magnesium alloy battery casing, which effectively reduces the porosity of the reinforcing ribs on the bottom surface of the battery casing and improves structural rigidity and explosion-proof capability.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a magnesium alloy battery casing, characterized by comprising the following steps:

[0007] (1) Slurry preparation: The dried magnesium alloy particles are added to a semi-solid injection molding machine. The barrel temperature of the semi-solid injection molding machine is 540℃~550℃ and the screw shearing speed is 1800-2000rpm.

[0008] (2) Vacuum injection: After mold closing, start the vacuum pump and pump to an absolute pressure of 5-10 kPa. The slurry will then be injected. The first stage is slow filling with an injection speed of 0.4-0.6 m / s until the screw advances to 45-50% of its stroke. The second stage is high-speed filling with an injection speed of 4.0-4.5 m / s, during which air is continuously pumped out until the screw advances to 85-90% of its stroke. Then the vacuum valve is closed. The third stage is pressurized filling with the injection pressure increased to 130-150 MPa after the vacuum valve is closed. This completes the final filling.

[0009] (3) During the pressure holding stage, the built-in slider is driven to compress the reinforcing ribs on the bottom of the battery casing at 200-250 MPa for 10-15 seconds.

[0010] After using the above preparation method:

[0011] 1. The porosity and shrinkage cavity are greatly reduced, and the reliability of the rigid skeleton is greatly improved. The sliding block extrusion and refining process reduces the porosity and shrinkage cavity of the reinforcing rib to an extremely low level, transforming it from a porous thin layer into a continuous dense solid body. This eliminates internal voids, restores the effective moment of inertia of the cross section, and allows the reinforcing rib to truly play a physical support role, greatly improving the bending stiffness of the shell and suppressing vibration deformation.

[0012] The densification of the structure and the refinement of the grains result in a significant increase in shell strength and fatigue resistance. Strict control over the thermomechanical treatment caused by cooling and extrusion eliminates the shrinkage cavities that cause stress concentration and strengthens the material through grain refinement. The dense microstructure reduces crack initiation, and the reinforcing ribs are transformed into a high-strength mesh skeleton, which multiplies the yield strength and fatigue life of the shell, meeting high safety requirements.

[0013] Furthermore, in step (1) above, the magnesium alloy particles are dried in a vacuum oven under the conditions of 200℃, -98KPa, for 8-10 hours.

[0014] Furthermore, in step (2) above, after the mold is closed, the vacuum pump is started and the pressure is evacuated to 5 kPa absolute pressure, and the slurry begins to be injected; the first stage is slow filling with an injection speed of 0.6 m / s until the screw advance stroke is 45%; the second stage is high-speed filling with the injection speed increased to 4.0 m / s, during which air is continuously evacuated until the screw advance stroke is 85%, and the vacuum valve is closed; the third stage is pressurized filling with the injection pressure increased to 140 MPa after the vacuum valve is closed, and the final filling is completed.

[0015] Furthermore, in step (3) above, before the slider is pressed, the thickness of the cavity at the reinforcing rib is d1, and after the slider is pressed, the thickness of the cavity at the reinforcing rib is d2, and d1 is 1.1-1.15 times d2.

[0016] Furthermore, in step (3) above, a cooling circuit is provided inside the slider, the cooling circuit is 10-15mm away from the slider surface, the medium temperature is 60-80℃, the medium flow rate is 1.5-1.8m / s, and the medium pressure is 0.5-0.8MPa.

[0017] Furthermore, the magnesium alloy particles comprise the following components by mass percentage:

[0018] Al 7.25%;

[0019] Zn 1.2%;

[0020] Y 1.15%;

[0021] Ce 0.15%;

[0022] Sr 0.08%;

[0023] Mn 0.36%;

[0024] Ca 0.2%;

[0025] Sc 0.2%;

[0026] Unavoidable impurities ≤ 0.05%;

[0027] Mg balance.

[0028] Furthermore, the magnesium alloy particles are prepared by the following method:

[0029] S1. Raw material preparation: Weigh magnesium ingots, aluminum ingots, zinc ingots, magnesium-calcium master alloy, magnesium-yttrium master alloy, magnesium-cerium master alloy, magnesium-strontium master alloy, magnesium-manganese master alloy, and magnesium-scandium master alloy; and dry them.

[0030] S2. Melting: Place 90% of the magnesium ingots into a crucible and heat to 740°C until completely melted; maintain 740°C and add aluminum and zinc ingots until completely melted; raise the temperature to 785°C and add magnesium-scandium master alloy until completely melted, then add magnesium-yttrium master alloy until completely melted; lower the temperature to 750°C and add magnesium-calcium master alloy until completely melted, then add magnesium-cerium master alloy until completely melted; lower the temperature to 710°C and add magnesium-strontium master alloy and magnesium-manganese master alloy; finally, add the remaining 10% of the magnesium ingots.

[0031] S3. Refining: The alloy liquid is maintained at 710℃ and refined using rotary argon gas injection. The graphite rotor is inserted into the alloy liquid to 10 cm from the bottom of the crucible. The graphite rotor speed is 350 rpm and the argon gas flow rate is 5 L / min for 15 minutes. After refining, the alloy liquid is heated to 740℃ and left to stand for 20 minutes.

[0032] S4. Casting: Maintain the temperature of the refined alloy liquid at 690℃, preheat the mold to 250℃, and then cast.

[0033] S5. Annealing: After casting, the ingot is subjected to homogenization annealing treatment at 400℃ for 12 hours.

[0034] S6. Granulation: The annealed ingot is processed into particles with a diameter of 3-5mm. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] Raw material preparation:

[0038] Magnesium alloy particles, comprising the following components by mass percentage:

[0039] Al 7.25%;

[0040] Zn 1.2%;

[0041] Y 1.15%;

[0042] Ce 0.15%;

[0043] Sr 0.08%;

[0044] Mn 0.36%;

[0045] Ca 0.2%;

[0046] Sc 0.2%;

[0047] Unavoidable impurities ≤ 0.05%;

[0048] Mg balance.

[0049] The magnesium alloy particles were prepared by the following method:

[0050] S1. Raw material preparation: Weigh magnesium ingots, aluminum ingots, zinc ingots, magnesium-calcium master alloy, magnesium-yttrium master alloy, magnesium-cerium master alloy, magnesium-strontium master alloy, magnesium-manganese master alloy, and magnesium-scandium master alloy; and dry them.

[0051] S2. Melting: Place 90% of the magnesium ingots into a crucible and heat to 740°C until completely melted; maintain 740°C and add aluminum and zinc ingots until completely melted; raise the temperature to 785°C and add magnesium-scandium master alloy until completely melted, then add magnesium-yttrium master alloy until completely melted; lower the temperature to 750°C and add magnesium-calcium master alloy until completely melted, then add magnesium-cerium master alloy until completely melted; lower the temperature to 710°C and add magnesium-strontium master alloy and magnesium-manganese master alloy; finally, add the remaining 10% of the magnesium ingots.

[0052] S3. Refining: The alloy liquid is maintained at 710℃ and refined using rotary argon gas injection. The graphite rotor is inserted into the alloy liquid to 10 cm from the bottom of the crucible. The graphite rotor speed is 350 rpm and the argon gas flow rate is 5 L / min for 15 minutes. After refining, the alloy liquid is heated to 740℃ and left to stand for 20 minutes.

[0053] S4. Casting: Maintain the temperature of the refined alloy liquid at 690℃, preheat the mold to 250℃, and then cast.

[0054] S5. Annealing: After casting, the ingot is subjected to homogenization annealing treatment at 400℃ for 12 hours.

[0055] S6. Granulation: The annealed ingot is processed into particles with a diameter of 3-5mm.

[0056] Semi-solid injection molding of battery casing:

[0057] A method for preparing a magnesium alloy battery casing, characterized by comprising the following steps:

[0058] (1) Slurry preparation: The magnesium alloy particles were dried in a vacuum oven at 200℃ and -98KPa for 8 hours. The dried magnesium alloy particles were then added to a semi-solid injection molding machine at a barrel temperature of 540℃ and a screw shearing speed of 2000rpm.

[0059] (2) Vacuum injection: After the mold is closed, start the vacuum pump and pump to an absolute pressure of 5 kPa. The slurry will start to be injected. The first stage is slow filling with an injection speed of 0.6 m / s until the screw advances 45% of the stroke. The second stage is high-speed filling with an injection speed of 4.0 m / s. During this period, the air is continuously pumped out until the screw advances 85% of the stroke, and the vacuum valve is closed. The third stage is pressurized filling with the injection pressure increased to 140 MPa after the vacuum valve is closed to complete the final filling.

[0060] (3) During the pressure holding stage, the built-in slider is used to press the reinforcing ribs on the bottom surface of the battery casing with 200Pa and hold for 15s. Before the slider presses, the thickness of the cavity at the reinforcing rib is d1. After the slider presses, the thickness of the cavity at the reinforcing rib is d2. d1 is 1.1 times d2.

[0061] In step (3) above, a cooling circuit is provided inside the slider. The cooling circuit is 12mm away from the slider surface, the medium temperature is 60℃, the medium flow rate is 1.5m / s, and the medium pressure is 0.5MPa.

[0062] Comparative Example 1

[0063] Comparative Example 1 and Example 1 used the same magnesium alloy particle raw material.

[0064] A method for preparing a magnesium alloy battery casing, characterized by comprising the following steps:

[0065] (1) Slurry preparation: The magnesium alloy particles were dried in a vacuum oven at 200℃ and -98KPa for 8 hours. The dried magnesium alloy particles were then added to a semi-solid injection molding machine at a barrel temperature of 540℃ and a screw shearing speed of 2000rpm.

[0066] (2) Vacuum injection: After the mold is closed, start the vacuum pump and pump to an absolute pressure of 5 kPa. The slurry will start to be injected. The first stage is slow filling with an injection speed of 0.6 m / s until the screw advances 45% of the stroke. The second stage is high-speed filling with an injection speed of 4.0 m / s. During this period, the air is continuously pumped out until the screw advances 85% of the stroke, and the vacuum valve is closed. The third stage is pressurized filling with the injection pressure increased to 140 MPa after the vacuum valve is closed. The final filling is completed.

[0067] In step (2) above, a cooling circuit is provided inside the mold. The cooling circuit is 25mm away from the inner surface of the cavity. The medium temperature is 20℃, the medium flow rate is 1.5m / s, and the medium pressure is 0.5MPa.

[0068] Comparative Example 2

[0069] The differences between Comparative Example 2 and Comparative Example 1 are as follows:

[0070] In step (2), a cooling circuit is provided inside the mold. The cooling circuit is 25mm away from the inner surface of the cavity. The medium temperature is 60℃, the medium flow rate is 1.5m / s, and the medium pressure is 0.5MPa.

[0071] Comparative Example 3

[0072] The differences between Comparative Example 3 and Example 1 are as follows:

[0073] In step (3) above, a cooling circuit is provided inside the slider. The cooling circuit is 12mm away from the slider surface, the medium temperature is 20℃, the medium flow rate is 1.5m / s, and the medium pressure is 0.5MPa.

[0074] The thickness of the base plate and reinforcing ribs of the magnesium alloy battery casings prepared in Example 1 and Comparative Examples 1-3 above is 0.8 mm.

[0075] Porosity 0.03% 1.08% 3.23% ＜0.01% Shrinkage / Porosity Basic elimination Visible shrinkage cavities are prone to appear at the base of the reinforcing ribs. The reinforcing ligaments at the root are severely loose and contracted. It is prone to thermal stress cracks inside. Ease of demolding The surface of the slider is warm, providing a lubricating effect and resulting in good demolding performance. normal normal The low-temperature slider and the high-pressure, high-temperature material form a physical bond, making demolding impossible.

[0076] In Comparative Example 1, without the assistance of mechanical pressure from the slider, even with 20°C cold water, the heat could not be dissipated in time due to the excessive depth of the cooling circuit (which required ensuring mold strength). This resulted in severe internal shrinkage of the product, failing to resolve the fatal defect in the battery casing.

[0077] In Comparative Example 3, using 20°C cold water during pressurization would disrupt the balance between pressure and temperature. The low temperature would cause microscopic welding between the slider surface and the magnesium alloy, resulting in severe sticking to the mold, or even directly breaking the slider, making it unusable in practical applications.

[0078] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0079] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a magnesium alloy battery casing, characterized in that, Includes the following steps: (1) Slurry preparation: The dried magnesium alloy particles are added to a semi-solid injection molding machine. The barrel temperature of the semi-solid injection molding machine is 540℃~550℃ and the screw shearing speed is 1800-2000rpm. (2) Vacuum injection: After mold closing, start the vacuum pump and pump to an absolute pressure of 5-10 kPa. The slurry will then be injected. The first stage is slow filling with an injection speed of 0.4-0.6 m / s until the screw advances to 45-50% of its stroke. The second stage is high-speed filling with an injection speed of 4.0-4.5 m / s, during which air is continuously pumped out until the screw advances to 85-90% of its stroke. Then the vacuum valve is closed. The third stage is pressurized filling with the injection pressure increased to 130-150 MPa after the vacuum valve is closed. This completes the final filling. (3) During the pressure holding stage, the built-in slider is driven to compress the reinforcing ribs on the bottom of the battery casing at 200-250 MPa for 10-15 seconds.

2. The method for preparing a magnesium alloy battery casing according to claim 1, characterized in that, In step (1) above, the magnesium alloy particles are dried in a vacuum oven at 200℃ and -98KPa for 8-10 hours.

3. The method for preparing a magnesium alloy battery casing according to claim 1, characterized in that, In step (2) above, after the mold is closed, the vacuum pump is started and the pressure is evacuated to 5 kPa absolute pressure, and the slurry begins to be injected; the first stage is slow filling with an injection speed of 0.6 m / s until the screw advance stroke is 45%; the second stage is high-speed filling with the injection speed increased to 4.0 m / s, during which air is continuously evacuated until the screw advance stroke is 85%, and the vacuum valve is closed; the third stage is pressurized filling with the injection pressure increased to 140 MPa after the vacuum valve is closed, and the final filling is completed.

4. The method for preparing a magnesium alloy battery casing according to claim 1, characterized in that, In step (3) above, before the slider is pressed, the thickness of the cavity at the reinforcing rib is d1, and after the slider is pressed, the thickness of the cavity at the reinforcing rib is d2, and d1 is 1.1-1.15 times d2.

5. The method for preparing a magnesium alloy battery casing according to claim 4, characterized in that, In step (3) above, a cooling circuit is provided inside the slider. The cooling circuit is 10-15mm away from the slider surface. The medium temperature is 60-80℃, the medium flow rate is 1.5-1.8m / s, and the medium pressure is 0.5-0.8MPa.

6. The method for preparing a magnesium alloy battery casing according to claim 1, characterized in that, The magnesium alloy particles comprise the following components by mass percentage: Al 7.25%； Zn 1.2%; Y 1.15%； Ce 0.15%; Sr 0.08%； Mn 0.36%; Ca 0.2%; Sc 0.2%; Unavoidable impurities ≤ 0.05%; Mg balance.

7. The method for preparing a magnesium alloy battery casing according to claim 1, characterized in that, The magnesium alloy particles were prepared by the following method: S1. Raw material preparation: Weigh magnesium ingots, aluminum ingots, zinc ingots, magnesium-calcium master alloy, magnesium-yttrium master alloy, magnesium-cerium master alloy, magnesium-strontium master alloy, magnesium-manganese master alloy, and magnesium-scandium master alloy; and dry them. S2. Melting: Place 90% of the magnesium ingots into a crucible and heat to 740°C until completely melted; maintain 740°C and add aluminum and zinc ingots until completely melted; raise the temperature to 785°C and add magnesium-scandium master alloy until completely melted, then add magnesium-yttrium master alloy until completely melted; lower the temperature to 750°C and add magnesium-calcium master alloy until completely melted, then add magnesium-cerium master alloy until completely melted; lower the temperature to 710°C and add magnesium-strontium master alloy and magnesium-manganese master alloy; finally, add the remaining 10% of the magnesium ingots. S3. Refining: The alloy liquid is maintained at 710℃ and refined using rotary argon gas injection. The graphite rotor is inserted into the alloy liquid to 10 cm from the bottom of the crucible. The graphite rotor speed is 350 rpm and the argon gas flow rate is 5 L / min for 15 minutes. After refining, the alloy liquid is heated to 740℃ and left to stand for 20 minutes. S4. Casting: Maintain the temperature of the refined alloy liquid at 690℃, preheat the mold to 250℃, and then cast. S5. Annealing: After casting, the ingot is subjected to homogenization annealing treatment at 400℃ for 12 hours. S6. Granulation: The annealed ingot is processed into particles with a diameter of 3-5mm.