Thixotropic injection casting forming and heat treatment combined strengthening method for complex ultrathin lightweight magnesium alloy material

Abstract

The invention discloses a thixotropic injection casting forming and heat treatment combined strengthening method for a complex ultrathin lightweight magnesium alloy material, and relates to a forming and heat treatment combined method for a magnesium alloy material. The invention aims to solve the technical problem that the mechanical property of the existing complex ultrathin light-weight magnesium alloy material is poor. According to the method, AZ91D magnesium alloy particles serve as raw materials, the density is improved through semi-solid thixotropic injection casting parameter regulation and heat treatment strengthening, defects are strictly controlled, the technology of low-temperature short-time solid solution + room-temperature water cooling + short-time aging + air cooling is adopted, and the tensile strength, the yield strength and the ductility after the heat treatment technology are obviously improved; the heat treatment process is an important guiding direction for thixotropic injection casting heat dissipation pieces, supporting pieces and structural pieces in the future. The thixotropic injection casting technology and the special heat treatment technology are excellent combinations for forming the complex ultrathin lightweight magnesium alloy shell, the combination can further improve the mechanical property of a structural part, and the application potential of the alloy is broken through.

Description

Technical Field

[0001] This invention relates to a forming and heat treatment method for magnesium alloy materials. Background Technology

[0002] Traditional magnesium alloy forming methods include gravity casting and die casting. However, with advancements in technology, thixotropic injection casting technology is increasingly used in automotive structural parts, 3C products, aerospace, defense, industrial equipment, and green manufacturing. In thixotropic injection casting, the rotation of a screw within a barrel, combined with external heating, heats and shears the particles, achieving densification within the barrel. Upon reaching the storage section, a semi-solid slurry with excellent flowability and shape-filling properties is formed. This slurry is then injected at high speed into a mold through a nozzle, where it rapidly cools and solidifies under high speed and pressure, forming parts with specific shapes and dimensions. Thixotropic injection casting, due to its low porosity, high density, and strong ability to form complex structures, is playing an increasingly important role in complex ultra-thin applications. These characteristics also ensure that the mechanical properties of related magnesium alloy products can be further enhanced through appropriate heat treatment processes. Simultaneously, the mechanical potential of traditional industrial magnesium alloys can be further improved. Complex, ultra-thin, lightweight magnesium alloy materials, such as those used in laptop casings, have the following characteristics: a length of 360mm, a width of 251mm, a minimum thickness of 0.6mm, and a weight of 192g. These dimensional characteristics place higher demands on the formability of the laptop casing: firstly, the outer surface of the laptop casing must be smooth and have a clear outline; secondly, the inner surface of the laptop has a large number of bosses (3mm), control panels (1.5mm), ribs (1mm), etc., with strict dimensional requirements. Summary of the Invention

[0003] The present invention aims to solve the technical problem of poor mechanical properties of complex, ultra-thin, lightweight magnesium alloy materials, and provides a thixotropic injection casting method combined with heat treatment to strengthen complex, ultra-thin, lightweight magnesium alloy materials.

[0004] The thixotropic injection casting combined with heat treatment strengthening method for complex ultrathin lightweight magnesium alloy materials of the present invention is carried out according to the following steps:

[0005] 1. AZ91D magnesium alloy particles are dried in a vacuum drying oven. The dried AZ91D magnesium alloy particles are then transferred to a thixotropic injection casting machine. The thixotropic injection casting machine includes a feeding unit, a conveying unit, a heating and stirring unit, an injection unit, a forming unit, a cooling unit, an ejection unit, and a control unit. In the thixotropic injection casting machine, a step-by-step heating method is used from feeding to discharging to prepare the semi-solid slurry. The thixotropic injection casting temperature is 560℃~620℃. The complex ultra-thin lightweight magnesium alloy material is formed under the following conditions: injection pressure of 10MPa~20MPa, thixotropic injection speed of 1m / s~3m / s, thixotropic holding time of 5s~15s, and mold temperature of 200℃~250℃. After holding the pressure, the complex ultra-thin lightweight magnesium alloy material is cooled to room temperature in the cooling unit and then ejected by the ejector pin. The dimensions of the formed complex ultra-thin lightweight magnesium alloy material are: length 360mm, width 251mm, minimum thickness 0.6mm, and weight 192g.

[0006] 2. The complex ultrathin lightweight magnesium alloy material prepared in step 1 is subjected to heat treatment. The heat treatment adopts a process of low temperature short-time solution treatment + room temperature water cooling + short-time aging + air cooling. The low temperature short-time solution treatment process is: holding at 360℃~420℃ for 0.5h~6h. The short-time aging process is: holding at 150℃~210℃ for 0.5h~6h.

[0007] In step one of this invention, the process of casting the complex, ultra-thin, lightweight magnesium alloy material, from the start of thixotropic injection casting to the end of material ejection, takes approximately 50-55 seconds. The entire thixotropic injection casting process involves continuous heating without interruption, and the entire process can be completed by only one person, significantly reducing labor costs and energy consumption for heating. Simultaneously, the product yield reaches over 98%, further reducing costs.

[0008] This invention enables thixotropic injection casting of complex, ultra-thin, and lightweight magnesium alloy materials. The formed products have stable dimensions, complete filling, high mechanical properties, and dense microstructure. This has strong guiding significance for the development of the field of thixotropic injection casting and magnesium alloy products.

[0009] The heat treatment process proposed in step two of this invention is specifically designed for complex, ultra-thin, lightweight magnesium alloy materials (such as laptop shells). The solidus temperature of AZ91D magnesium alloy is approximately 470°C, while the traditional solution temperature is 440°C with a holding time of 8-20 hours. For ultra-thin laptop shells of 0.6mm, this invention creatively proposes a solution temperature below 440°C while simultaneously reducing the solution time (less than 8 hours) to achieve rapid solution treatment and lower heat treatment energy consumption. This reduces heat treatment defects caused by excessively high solution temperatures and long solution times, while ensuring effective dissolution of alloying elements. After low-temperature, short-time solution treatment, the tensile strength of the product increases, the yield strength decreases slightly, but the elongation increases significantly, demonstrating the effectiveness of the solution treatment. This solution treatment process is closely related to the particle size of AZ91D material, thixotropic injection casting technology, the basic parameters of complex laptop shell structural components, and the densification of the microstructure. It is an innovative method for further strengthening the heat treatment process for forming complex thin-walled parts using thixotropic injection casting. The precipitation temperature of the aging precipitates is 150℃~210℃. This invention uses short-time artificial aging (less than 8 hours). Short-time aging not only ensures the effective precipitation of the precipitates but also effectively suppresses the growth of phases and defects, resulting in increased tensile strength and yield strength, and a slight decrease in elongation. This is because the supersaturated solid solution formed after solution treatment disperses and precipitates fine-sized nanoscale precipitates after aging. After the heat treatment process, the tensile strength, yield strength, and elongation are significantly improved compared to those after thixotropic injection casting, further proving the effectiveness of this heat treatment process. This heat treatment process is an important guiding direction for the future development of thixotropic injection casting heat sinks, supports, and structural components.

[0010] This invention achieves phase control and regulation through process control: after thixotropic injection casting, the Mg matrix contains Mg atoms with larger sizes. 17 Al 12 The Al8Mn5 phase and Al8Mn5 phase precipitate; after low-temperature short-time solid solution treatment, Mg 17 Al 12 The Al8Mn5 phase and the Al8Mn5 phase are fully dissolved in the Mg matrix; after short-time aging treatment, the nanoscale Mg phase precipitates out. 17 Al 12 Phase, Mg 16 Al 12The dispersed distribution of Zn and Al8Mn5 phases effectively enhances the tensile strength of the material. Fine-grain strengthening, dislocation strengthening, solid solution strengthening, and texture strengthening effectively ensure the material's room-temperature mechanical properties: tensile strength reaches 351 MPa, yield strength reaches 201 MPa, and elongation reaches 7.2%, exceeding the performance limits of AZ91D magnesium alloy and demonstrating strong application potential. Thixotropic injection casting technology combined with special heat treatment processes is an excellent combination for forming complex, ultra-thin, lightweight magnesium alloy shells. This combination can further improve the mechanical properties of structural components, pushing the alloy's application potential to new heights. Attached Figure Description

[0011] Figure 1 XRD pattern;

[0012] Figure 2 The mechanical properties of the product from step one of Experiment 1 (thixotropic injection casting), the product from step two of Experiment 1 (solution treatment), and the product from step three of Experiment 1 (aging treatment) are shown in the diagram.

[0013] Figure 3 It shows the changes in microstructure before and after heat treatment. Detailed Implementation

[0014] Specific Implementation Method 1: This implementation method is a thixotropic injection casting forming combined with heat treatment strengthening method for complex ultrathin lightweight magnesium alloy materials, specifically carried out according to the following steps:

[0015] 1. AZ91D magnesium alloy particles are dried in a vacuum drying oven. The dried AZ91D magnesium alloy particles are then transferred to a thixotropic injection casting machine. The thixotropic injection casting machine includes a feeding unit, a conveying unit, a heating and stirring unit, an injection unit, a forming unit, a cooling unit, an ejection unit, and a control unit. In the thixotropic injection casting machine, a step-by-step heating method is used from feeding to discharging to prepare the semi-solid slurry. The thixotropic injection casting temperature is 560℃~620℃. The complex ultra-thin lightweight magnesium alloy material is formed under the following conditions: injection pressure of 10MPa~20MPa, thixotropic injection speed of 1m / s~3m / s, thixotropic holding time of 5s~15s, and mold temperature of 200℃~250℃. After holding the pressure, the complex ultra-thin lightweight magnesium alloy material is cooled to room temperature in the cooling unit and then ejected by the ejector pin. The dimensions of the formed complex ultra-thin lightweight magnesium alloy material are: length 360mm, width 251mm, minimum thickness 0.6mm, and weight 192g.

[0016] 2. The complex ultrathin lightweight magnesium alloy material prepared in step 1 is subjected to heat treatment. The heat treatment adopts a process of low temperature short-time solution treatment + room temperature water cooling + short-time aging + air cooling. The low temperature short-time solution treatment process is: holding at 360℃~420℃ for 0.5h~6h. The short-time aging process is: holding at 150℃~210℃ for 0.5h~6h.

[0017] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the particle size of the AZ91D magnesium alloy particles mentioned in step one is 3mm~8mm. Everything else is the same as in Specific Implementation Method One.

[0018] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the drying temperature in step one is 180℃~200℃, and the drying time is 2 hours. Everything else is the same as in Specific Implementation Method One or Two.

[0019] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the step-by-step heating method described in Step One involves temperatures successively increasing to 400℃, 475℃, 550℃, and the thixotropic injection casting temperature. Everything else is the same as in Specific Implementation Methods One to Three.

[0020] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that step one is performed under the following conditions: thixotropic injection casting temperature of 580℃, thixotropic injection casting pressure of 15MPa, thixotropic injection casting speed of 2.5m / s, thixotropic holding time of 10s, and mold temperature of 210℃. Everything else is the same as in Specific Implementation Method Four.

[0021] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Three in that the drying temperature in step one is 200℃ and the drying time is 2 hours. Everything else is the same as in Specific Implementation Method Three.

[0022] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the temperature for the low-temperature short-time solid solution described in step two is 380°C. Everything else is the same as in Specific Implementation Method Six.

[0023] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the low-temperature short-time solidification time described in step two is 0.5 hours. Everything else is the same as in Specific Implementation Method Seven.

[0024] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the short-term aging temperature described in step two is 180°C. Everything else is the same as in Specific Implementation Method Eight.

[0025] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the short-term effect time mentioned in step two is 4 hours. Everything else is the same as in Specific Implementation Method Nine.

[0026] The invention was verified using the following experiments:

[0027] Experiment 1: This experiment demonstrates a thixotropic injection casting method combined with heat treatment to strengthen complex, ultrathin, lightweight magnesium alloy materials. The specific steps are as follows:

[0028] 1. AZ91D magnesium alloy particles are dried in a vacuum drying oven at 200℃ for 2 hours. The dried AZ91D magnesium alloy particles are then transferred to a thixotropic injection casting machine, which includes a feeding unit, a conveying unit, a heating and stirring unit, an injection unit, a forming unit, a cooling unit, an ejection unit, and a control unit. In the thixotropic injection casting machine, a step-by-step heating method is used from feeding to discharging to prepare the semi-solid slurry. The step-by-step heating temperatures are 400℃, 475℃, 550℃, and the thixotropic injection casting temperature. The complex ultrathin lightweight magnesium alloy material was formed under the following conditions: temperature 580℃, thixotropic injection casting pressure 15MPa, thixotropic injection casting speed 2.5m / s, thixotropic holding time 10s, and mold temperature 210℃. After holding the pressure, the complex ultrathin lightweight magnesium alloy material was cooled to room temperature in a cooling unit and then ejected by an ejector pin. The dimensions of the formed complex ultrathin lightweight magnesium alloy material were: length 360mm, width 251mm, minimum thickness 0.6mm, and weight 192g. The tensile strength, yield strength, and elongation of the complex ultrathin lightweight magnesium alloy material were measured to be 289MPa, 196MPa, and 2.8%.

[0029] The particle size of the AZ91D magnesium alloy particles is 3mm~8mm;

[0030] 2. The complex ultrathin lightweight magnesium alloy material prepared in step one was subjected to low-temperature short-time solution treatment followed by room-temperature water cooling; the low-temperature short-time solution treatment process was as follows: holding at 380℃ for 0.5h; the tensile strength of the product was measured to be 316MPa, the yield strength to be 165MPa, and the elongation to be 18.1%;

[0031] Third, the product from step two is subjected to short-time aging and air cooling. The short-time aging process is as follows: heat treatment at 180℃ for 4 hours. The tensile strength of the product is measured to be 351MPa, the yield strength is 201MPa, and the elongation is 7.2%.

[0032] Experiment 2: This experiment differs from Experiment 1 in that the low-temperature short-time solution treatment process described in step 2 is as follows: the product is kept at 360℃ for 0.5 hours; the tensile strength of the product is measured to be 236 MPa, the yield strength to be 146 MPa, and the elongation to be 7%. This experiment does not involve aging.

[0033] Experiment 3: This experiment differs from Experiment 1 in that the low-temperature short-time solution treatment process described in step 2 is: holding at 400℃ for 0.5h; the tensile strength of the product was measured to be 313MPa, the yield strength to be 154MPa, and the elongation to be 6.6%. This experiment does not involve aging.

[0034] Figure 1 The XRD patterns show the product of step one in Experiment 1 (black curve), the product of step two in Experiment 1 (red curve), and the product of step three in Experiment 1 (blue curve). It can be seen that the main phases in the thixotropic injection casting are the Mg matrix and Mg2+. 17 Al 12 Phase (black curve); after short-term solid solution at low temperature, Mg 17 Al 12 The phase completely dissolves into the Mg matrix, forming a supersaturated solid solution (red curve); after a short-time aging treatment, Mg... 17 Al 12 The phase is diffusely precipitated in large quantities within the body (blue curve).

[0035] Figure 2 The mechanical property diagrams for the products from Step 1 (thixotropic injection casting), Step 2 (solution treatment), and Step 3 (aging treatment) of Experiment 1 show that thixotropic injection casting is suitable for producing complex, ultra-thin, and lightweight AZ91D magnesium alloy laptop shells. The tensile strength is 289 MPa, the yield strength is 196 MPa, and the elongation is 2.8%, ensuring the basic mechanical properties of AZ91D. Its density ensures it can undergo subsequent heat treatment. After low-temperature short-time solution treatment, the tensile strength is 316 MPa, the yield strength is 165 MPa, and the elongation is 18.1%, showing a significant increase in elongation and a slight decrease in yield strength. After short-time aging treatment, the tensile strength is 351 MPa, the yield strength is 201 MPa, and the elongation is 7.2%, completely expanding the application limits of AZ91D. This proves that thixotropic injection casting combined with special heat treatment is a very practical performance enhancement combination.

[0036] Figure 3 These are diagrams showing the changes in microstructure before and after heat treatment. Figure 3 (a) is the product of step one of experiment one. It can be seen that after thixotropic injection casting, Mg 17 Al 12 The phase is widely distributed at the grain boundaries, forming a network that effectively protects the mechanical properties of the material. Figure 3 (b) is the product of step three in Experiment 1. It can be seen that after heat treatment, Mg 17 Al 12 The phase dissolves into the matrix and precipitates in the form of nano-precipitates. The different bright-colored regions are still Mg phases, but with different preferred orientations.

Claims

1. A method for strengthening complex, ultrathin, lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment, characterized in that... The method is performed according to the following steps:

1. AZ91D magnesium alloy particles are dried in a vacuum drying oven. The dried AZ91D magnesium alloy particles are then transferred to a thixotropic injection casting machine. The thixotropic injection casting machine includes a feeding unit, a conveying unit, a heating and stirring unit, an injection unit, a forming unit, a cooling unit, an ejection unit, and a control unit. In the thixotropic injection casting machine, a step-by-step heating method is used from feeding to discharging to prepare the semi-solid slurry. The thixotropic injection casting temperature is 560℃~620℃. The complex ultra-thin lightweight magnesium alloy material is formed under the following conditions: injection pressure of 10MPa~20MPa, thixotropic injection speed of 1m / s~3m / s, thixotropic holding time of 5s~15s, and mold temperature of 200℃~250℃. After holding the pressure, the complex ultra-thin lightweight magnesium alloy material is cooled to room temperature in the cooling unit and then ejected by the ejector pin. The dimensions of the formed complex ultra-thin lightweight magnesium alloy material are: length 360mm, width 251mm, minimum thickness 0.6mm, and weight 192g.

2. The complex ultrathin lightweight magnesium alloy material prepared in step 1 is subjected to heat treatment. The heat treatment adopts a process of low temperature short-time solution treatment + room temperature water cooling + short-time aging + air cooling. The low temperature short-time solution treatment process is: holding at 360℃~420℃ for 0.5h~6h. The short-time aging process is: holding at 150℃~210℃ for 0.5h~6h.

2. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that... The particle size of the AZ91D magnesium alloy particles mentioned in step one is 3mm~8mm.

3. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that... The drying temperature in step one is 180℃~200℃, and the drying time is 2 hours.

4. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that... The step-by-step heating method described in step one involves temperatures of 400℃, 475℃, 550℃, and thixotropic injection casting temperature.

5. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that... In step one, the molding process is carried out under the following conditions: thixotropic injection casting temperature of 580℃, thixotropic injection casting pressure of 15MPa, thixotropic injection casting speed of 2.5m / s, thixotropic holding time of 10s, and mold temperature of 210℃.

6. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that... The drying temperature in step one is 200℃, and the drying time is 2 hours.

7. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that... The temperature for the low-temperature short-time solid solution described in step two is 380℃.

8. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that: The time for low-temperature short-time solidification mentioned in step two is 0.5 hours.

9. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that... The temperature for short-term aging mentioned in step two is 180℃.

10. The method for strengthening complex ultrathin lightweight magnesium alloy materials by thixotropic injection casting combined with heat treatment according to claim 1, characterized in that... The short-term timeframe mentioned in step two is 4 hours.

Images