Die-casting process for magnesium alloy porous structural part

Abstract

The invention discloses a die-casting process for a magnesium alloy porous structural part, and relates to the field of die-casting processes and the technical field of magnesium alloy casting processing, raw materials are dried after being soaked in a weakly alkaline cleaning solution, the temperature is increased in two stages during smelting, and eccentric refining stirring with the eccentric distance being 1 / 5-1 / 3 of the diameter of a stirring head is adopted. The mold is preheated through three-stage gradient heating, finally, the temperature is controlled in a zoning mode, the temperature of a sprue area is 220-250 DEG C, the temperature of a cavity body area is 180-200 DEG C, and the temperature of an exhaust area is 150-170 DEG C. Four-section injection cooperating with mold swing is adopted for injection molding, and the speed of each section is accurately matched with the swing speed. And after forming, a casting is subjected to high-temperature heat preservation for 1-2 hours at the temperature of 200-220 DEG C and then transferred to a low-temperature environment of 120-140 DEG C to be cooled. According to the technology, through collaborative optimization of all links, compared with a traditional technology, the filling efficiency can be improved by 30% or above, internal defects are reduced by 40%, and good quality improvement and economic benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the field of die-casting processes, and particularly to a die-casting process for magnesium alloy porous structural parts. Background Art

[0002] In the field of modern industrial manufacturing, magnesium alloys are widely used in industries such as aerospace, automotive manufacturing, and electronic equipment due to their excellent properties such as low density, high specific strength, and corrosion resistance. They have unique advantages especially in the production of porous structural parts. Porous structural magnesium alloy parts can achieve specific mechanical properties, heat dissipation properties, or acoustic properties while reducing weight, meeting the usage requirements under complex working conditions. However, traditional magnesium alloy die-casting processes face many technical bottlenecks in the production of porous structural parts and are difficult to meet the increasingly stringent product quality requirements.

[0003] From the perspective of mold preheating, traditional die-casting processes usually adopt an overall uniform preheating method without considering the difference in heat load in different regions of the mold during the filling process. As the inlet of the molten metal, the gate area requires a higher temperature to maintain the fluidity of the alloy liquid, while too high a temperature in the exhaust area may cause ineffective gas discharge, and improper temperature control in the main cavity area will affect the filling speed and solidification quality. This rough preheating method is likely to cause defects such as gate cold shut, internal pores, and shrinkage porosity in the casting, reducing the product qualification rate.

[0004] In the injection molding stage, most of the existing technologies adopt a fixed injection speed or simple segmented control, which cannot adapt to the complex filling requirements of porous structures. The pore distribution and shape of porous structural parts increase the flow resistance of the molten metal. A fixed injection speed is likely to cause turbulence of the molten metal in the cavity, entrain gas to form pores, or cause short shot due to insufficient pressure at the end of filling. At the same time, the traditional process lacks coordinated control of mold movement and injection process, making it difficult to achieve uniform filling of the molten metal in complex pore structures, restricting the forming accuracy and mechanical properties of the product.

[0005] There are also limitations in raw material treatment and subsequent aging processes. In the traditional melting process, the effect of central stirring on the breaking and removal of slag and gas is limited, resulting in insufficient purity of the alloy liquid and affecting the mechanical properties of the casting. And single-temperature aging treatment cannot fully refine the microstructure of magnesium alloys and is difficult to meet the performance requirements of both high strength and high toughness at the same time. In addition, with the continuous increase in the demand for lightweight and high-performance magnesium alloy porous structural parts in industries such as new energy vehicles and high-end equipment, the disadvantages of traditional processes in terms of production efficiency and product consistency have become more obvious. There is an urgent need for innovative processes to break through technical bottlenecks and meet the development needs of modern manufacturing.

[0006] In summary, developing a die-casting process that can effectively solve the above problems and achieve the production of high-quality magnesium alloy porous structural parts is of great significance for enhancing the core competitiveness of China's high-end equipment manufacturing industry and promoting the application of magnesium alloy materials in key fields. Summary of the Invention

[0007] The purpose of the present invention is to provide a die-casting process for magnesium alloy porous structural parts. Through the cleaning, melting and eccentric refining pretreatment of magnesium alloy raw materials, the mold is preheated by three-stage gradient heating and zone temperature control. With the assistance of the four-stage injection speed control coordinated by the mold swing, the molten metal is accurately filled into the porous mold cavity. Finally, the structure is refined by differential temperature aging treatment, and the high-quality magnesium alloy porous structural parts are die-cast through the coordinated action of each link.

[0008] To achieve the above purpose, the present invention provides the following technical solutions: A die-casting process for magnesium alloy porous structural parts, characterized in that different regions of the mold are preheated in zones, specifically divided into the gate region, the main cavity region and the exhaust region. After the magnesium alloy raw materials are pretreated and melted, they are injected into the preheated mold. The injection process is through four-stage injection coordinated by the mold swing; the die-cast magnesium alloy castings are subjected to differential temperature aging treatment.

[0009] The different regions of the mold are preheated in zones, specifically, the gate region is preheated to 220 - 250 °C, the main cavity region is preheated to 180 - 200 °C, and the exhaust region is preheated to 150 - 170 °C. The higher temperature in the gate region ensures smooth flow of the alloy liquid, the moderate temperature in the main cavity region balances the filling and solidification speeds, and the lower temperature in the exhaust region is conducive to gas discharge while preventing the overflow of the molten metal.

[0010] The mold preheating process is divided into three stages. In the first stage, at a fixed heating rate, the overall temperature of the mold is raised to 100 - 120 °C and maintained for 15 minutes; in the second stage, the mold temperature is continued to be raised to 160 - 180 °C at the same fixed heating rate and kept warm for 10 minutes; in the third stage, based on the heat load characteristics of different regions of the mold, the mold is divided into the gate region, the main cavity region and the exhaust region for zone temperature control. The gate region is preheated to 220 - 250 °C in the third stage, the main cavity region is preheated to 180 - 200 °C, and the exhaust region is preheated to 150 - 170 °C. The three-stage preheating reduces thermal stress through gradient heating. The first stage eliminates water vapor, the second stage equalizes the matrix temperature, and the third stage of zone temperature control meets the functional requirements of different regions. For example, a higher temperature is required in the gate to maintain fluidity.

[0011] The fixed heating rate is 5 - 8 °C / minute. This can avoid thermal cracks in the mold due to rapid heating and ensure production efficiency. Through experiments, it is verified that the thermal stress in the mold is the smallest within this range.

[0012] The specific steps for controlling the four-stage injection speed with the mold swing coordination are as follows: During the injection process, the injection speed is divided into four stages for precise control. In the first stage of low-speed injection, the speed is set at 0.5 - 1 m / s, and at the same time, the mold starts to swing in the predetermined direction at a swing rate of 1 - 3° / s. In the second stage of medium-speed injection, the speed is increased to 1.5 - 2 m / s, and the mold swing rate is adjusted to 3 - 5° / s. In the third stage of high-speed injection, the speed reaches 3 - 4 m / s, and the mold swings to the set maximum angle and then remains stationary. In the fourth stage of deceleration injection, when approaching the completion of filling, the speed is reduced to 0.5 - 1 m / s, and the mold starts to swing in the reverse direction to return to the original position. Swinging the mold in the low-speed stage can guide the smooth filling of the molten metal; accelerating and increasing the swing speed in the medium-speed stage can break the initial solidified layer; keeping the mold stationary in the high-speed stage ensures complete filling; swinging in the reverse direction in the deceleration stage can eliminate the last air holes.

[0013] The maximum angle range of the mold swing is 5 - 15°, and the ratio of the reverse reset swing rate of the mold to the forward swing rate is 1:1 - 1:1.5. The swing angle of 5 - 15° can both prevent the overflow of the molten metal and generate sufficient centrifugal force to promote filling. The slightly faster reverse reset rate of 1:1.5 can reduce the backflow of the molten metal to form cold laps.

[0014] For the differential temperature aging treatment, the die-cast magnesium alloy castings are first placed in a high-temperature environment of 200 - 220°C and kept warm for 1 - 2 hours, and then quickly transferred to a low-temperature environment of 120 - 140°C for cooling. High-temperature aging promotes the precipitation of strengthening phases, low-temperature aging inhibits the formation of coarse grains, and the temperature gradient generated by rapid transfer can refine the microstructure and improve the strength and toughness of the castings.

[0015] The pretreatment of the magnesium alloy raw materials is specifically as follows: The qualified raw materials are immersed in a weakly alkaline cleaning solution for 15 - 20 minutes. The cleaning solution contains 5% sodium carbonate and 3% surfactant, and then placed in a hot air drying oven at 80 - 100°C for drying for 30 minutes.

[0016] When melting the magnesium alloy raw materials, the magnesium alloy raw materials are put into the melting equipment, first heated to 400 - 450°C and kept at this temperature for 10 - 15 minutes, and then quickly heated to 680 - 720°C to complete the complete melting process of the magnesium alloy. Keeping warm for 10 - 15 minutes in the low-temperature stage can make the alloying elements diffuse evenly, and quickly heating to 680 - 720°C can reduce gas absorption and oxidation and ensure the purity of the alloy liquid.

[0017] When melting the magnesium alloy raw materials, eccentric refining stirring is carried out, and the eccentricity of the eccentric stirring head is 1 / 5 - 1 / 3 of the diameter of the stirring head.

[0018] First, the magnesium alloy raw materials are pretreated. They are immersed in a weakly alkaline cleaning solution containing a specific proportion of sodium carbonate and surfactant to remove surface impurities, and then dried to prepare for subsequent melting. The melting process is divided into two stages. First, it is maintained at a low temperature of 400 - 450 °C for a period of time to allow the alloying elements to diffuse uniformly, and then rapidly heated to 680 - 720 °C to complete full melting. During this period, eccentric refining stirring with an eccentricity of 1 / 5 - 1 / 3 of the diameter of the stirring head is used to effectively break up the slag and gas, improving the refining effect.

[0019] The mold preheating is divided into three stages. First, the overall temperature of the mold is raised to 100 - 120 °C at a fixed heating rate and maintained. Then it is further heated to 160 - 180 °C for heat preservation. Finally, based on the heat load characteristics of different regions, the gate area is preheated to 220 - 250 °C, the main cavity area is preheated to 180 - 200 °C, and the exhaust area is preheated to 150 - 170 °C. Such zonal preheating can reduce the concentration of thermal stress and meet the functional requirements of different regions.

[0020] In the injection molding stage, the mold cavity is filled through four-stage injection speed control coordinated with mold swing. In the first stage of low-speed injection, the speed is set at 0.5 - 1 m / s, and at the same time, the mold starts to swing in the predetermined direction at a swing rate of 1 - 3 ° / s to guide the smooth filling of the molten metal. In the second stage of medium-speed injection, the speed is increased to 1.5 - 2 m / s, and the mold swing rate is adjusted to 3 - 5 ° / s to break through the initial solidified layer. In the third stage of high-speed injection, the speed reaches 3 - 4 m / s, and the mold swings to the set maximum angle of 5 - 15 ° and then remains stationary to ensure complete filling. In the fourth stage of decelerated injection, when approaching the end of filling, the speed is reduced to 0.5 - 1 m / s, and the mold starts to swing in the reverse direction to reset, eliminating the last air holes. Moreover, the ratio of the reverse reset swing rate of the mold to the forward swing rate is 1:1 - 1:1.5 to avoid the molten metal from falling back to form cold laps.

[0021] After die-casting, the magnesium alloy castings are subjected to differential temperature aging treatment. First, they are placed in a high-temperature environment of 200 - 220 °C for heat preservation for 1 - 2 hours to promote the precipitation of strengthening phases. Subsequently, they are rapidly transferred to a low-temperature environment of 120 - 140 °C for cooling to inhibit the formation of coarse grains, using the temperature gradient to refine the microstructure and improve the strength and toughness of the castings. Through the synergistic effect of these steps in the whole process, the die-casting production of high-quality magnesium alloy porous structural parts is realized.

[0022] Compared with the prior art, the beneficial effects of the present invention are: Through three-stage gradient heating and zone temperature control, compared with traditional overall uniform preheating, it can more accurately match the heat load characteristics of different regions of the mold. High-temperature preheating in the gate area can ensure good fluidity of the magnesium alloy liquid during filling, reducing cold shuts and blockages at the gate; a moderate temperature in the main cavity area achieves a balance between filling and solidification; a low temperature setting in the exhaust area is conducive to gas discharge, effectively reducing the porosity of the casting and improving the forming quality.

[0023] In the injection molding process, the four-stage injection speed control coordinated with mold swing is the core breakthrough. Most of the existing technologies use a fixed injection speed or simple segmentation, which is difficult to meet the complex filling requirements of porous structures. In the present invention, low-speed swing guides the molten metal to fill smoothly, avoiding turbulence caused by impact; medium-speed swing with increased amplitude breaks the solidified layer to ensure filling depth; the mold remains stationary at high speed to ensure complete filling; reverse swing at the deceleration stage eliminates pores. Compared with traditional processes, the filling efficiency is increased by more than 30%, and internal defects are reduced by 40%. At the same time, the precise setting of the swing angle and rate of the mold makes the distribution of the molten metal in the cavity more uniform, significantly improving the forming accuracy of complex porous structures.

[0024] Raw material treatment and aging treatment also have advantages. Eccentric refining stirring can generate stronger eddy currents during melting compared with traditional central stirring, effectively breaking slag and gas, improving the purity of the alloy liquid and enhancing its mechanical properties.

[0025] Thermal cycling aging treatment can refine the microstructure through rapid conversion between high and low temperatures. Compared with single-temperature aging, it can increase the strength of the casting by 20%-25% and the toughness by 15%-20%, significantly improving the comprehensive performance of the product.

[0026] The collaborative optimization of each link not only ensures product quality but also shortens the production cycle, reduces the scrap rate, and has good economic benefits and industrial application value. Description of the Drawings

[0027] Figure 1 It is a process flow diagram of a die-casting process for a magnesium alloy porous structure part of the present invention. Detailed Embodiments

[0028] Next, the technical solutions in the embodiments of the present invention will be fully described in conjunction with the drawings in the embodiments of the present invention.

[0029] As Figure 1 shown, a die-casting process for a magnesium alloy porous structure part is characterized in that different regions of the mold are preheated in zones, specifically divided into the gate area, the main cavity area, and the exhaust area. The magnesium alloy raw materials are pretreated and melted and then injected into the preheated mold. The injection process is through four-stage injection coordinated with mold swing; the magnesium alloy casting after die-casting is subjected to thermal cycling aging treatment.

[0030] The different regions of the mold are preheated in zones. Specifically, the gate area is preheated to 220 - 250 °C, the main cavity area is preheated to 180 - 200 °C, and the exhaust area is preheated to 150 - 170 °C.

[0031] The preheating process of the mold is divided into three stages. In the first stage, at a fixed heating rate, the overall temperature of the mold is raised to 100 - 120 °C and maintained for 15 minutes. In the second stage, the mold temperature is continued to be raised to 160 - 180 °C at the same fixed heating rate and kept warm for 10 minutes. In the third stage, based on the heat load characteristics of different regions of the mold, the mold is divided into the gate area, the main cavity area, and the exhaust area for zone temperature control. The gate area is preheated to 220 - 250 °C in the third stage, the main cavity area is preheated to 180 - 200 °C, and the exhaust area is preheated to 150 - 170 °C.

[0032] The fixed heating rate is 5 - 8 °C per minute.

[0033] The specific steps for controlling the four-stage injection speed in coordination with the mold swing are as follows: During the injection process, the injection speed is divided into four stages for precise control. In the first stage, low-speed injection is carried out, with the speed set at 0.5 - 1 m / s, and at the same time, the mold starts to swing in a predetermined direction at a swing rate of 1 - 3 ° / s. In the second stage, medium-speed injection is carried out, with the speed increased to 1.5 - 2 m / s, and the mold swing rate is adjusted to 3 - 5 ° / s. In the third stage, high-speed injection is carried out, with the speed reaching 3 - 4 m / s, and the mold swings to the set maximum angle and then remains stationary. In the fourth stage, deceleration injection is carried out, and the speed is reduced to 0.5 - 1 m / s when approaching the completion of filling, and the mold starts to swing in the reverse direction to reset.

[0034] The maximum angle range of the mold swing is 5 - 15 °, and the ratio of the reverse reset swing rate of the mold to the forward swing rate is 1:1 - 1:1.5.

[0035] For the differential temperature aging treatment, the die-cast magnesium alloy casting is first placed in a high-temperature environment of 200 - 220 °C and kept warm for 1 - 2 hours, and then quickly transferred to a low-temperature environment of 120 - 140 °C for cooling.

[0036] The pretreatment of the magnesium alloy raw material is specifically as follows: The qualified raw material is immersed in a weakly alkaline cleaning solution for 15 - 20 minutes. The cleaning solution contains 5% sodium carbonate and 3% surfactant, and then it is placed in a hot air drying oven at 80 - 100 °C and dried for 30 minutes.

[0037] When melting the magnesium alloy raw material, the magnesium alloy raw material is put into the melting equipment, first heated to 400 - 450 °C and maintained at this temperature for 10 - 15 minutes, and then quickly heated to 680 - 720 °C to complete the complete melting process of the magnesium alloy.

[0038] When melting the magnesium alloy raw materials, eccentric refining stirring is carried out, and the eccentricity of the eccentric stirring head is 1 / 5 - 1 / 3 of the diameter of the stirring head.

[0039] In the specific implementation process, first, the magnesium alloy raw materials are pretreated. Qualified raw materials are selected and immersed in a weakly alkaline cleaning solution prepared from 5% sodium carbonate and 3% surfactant, and soaked for 15 - 20 minutes to remove impurities such as oil stains and oxide films, and then placed in a hot air drying oven at 80 - 100 °C for 30 minutes for drying. Then, melting is carried out. The pretreated raw materials are put into the melting equipment. First, the temperature is raised to 400 - 450 °C and maintained for 10 - 15 minutes to allow the alloying elements to diffuse preliminarily, and then the temperature is rapidly raised to 680 - 720 °C. At the same time, the eccentric refining stirring device is started, and the eccentricity of the eccentric stirring head is set to 1 / 5 - 1 / 3 of the diameter of the stirring head to break up the molten slag and gas to improve the purity of the molten alloy. The mold preheating is divided into three stages. In the first stage, the whole mold is heated to 100 - 120 °C at a rate of 5 - 8 °C per minute and maintained for 15 minutes; in the second stage, the temperature is continuously raised to 160 - 180 °C and kept warm for 10 minutes; in the third stage, temperature control is carried out in zones based on the heat load characteristics. The gate area is preheated to 220 - 250 °C, the main cavity area is preheated to 180 - 200 °C, and the exhaust area is preheated to 150 - 170 °C. During injection molding, four-stage injection with mold swing coordination is adopted. In the first stage, the low-speed injection speed is 0.5 - 1 m / s, and the mold swing rate is 1 - 3 ° / s; in the second stage, the medium-speed injection speed is 1.5 - 2 m / s, and the swing rate is 3 - 5 ° / s; in the third stage, the high-speed injection speed is 3 - 4 m / s, and the mold swings to 5 - 15 ° and then stops; in the fourth stage, the deceleration injection speed is reduced to 0.5 - 1 m / s, and the mold resets at a reverse swing rate of 1 - 3 ° / s. Finally, the castings formed by die casting are first placed in a high-temperature environment at 200 - 220 °C for heat preservation for 1 - 2 hours, and then quickly transferred to a low-temperature environment at 120 - 140 °C for cooling to refine the microstructure and improve the strength and toughness. Through practical verification, this process can effectively improve the forming quality and comprehensive performance of magnesium alloy porous structural parts and reduce the scrap rate by precisely controlling the parameters of each link and their coordinated cooperation.

Claims

1. A die-casting process for a magnesium alloy porous structural member, characterized in that, The mold is preheated in different areas, specifically the gate area, the cavity main area and the exhaust area. The magnesium alloy raw materials are pretreated and melted and then injected into the preheated mold. The injection process is a four-stage injection process coordinated by the mold swing. The magnesium alloy castings after die casting are subjected to temperature difference aging treatment.

2. The die-casting process for a magnesium alloy porous structure according to claim 1, characterized in that: The mold is preheated in different areas, specifically, the gate area is preheated to 220-250°C, the cavity main area is preheated to 180-200°C, and the exhaust area is preheated to 150-170°C.

3. The die-casting process of a magnesium alloy porous structural part according to claim 2, characterized in that, The mold preheating process is divided into three stages. In the first stage, the mold temperature is raised to 100-120°C at a fixed heating rate and maintained for 15 minutes. In the second stage, the mold temperature is raised to 160-180°C at the same fixed heating rate and maintained for 10 minutes. In the third stage, based on the heat load characteristics of different areas of the mold, the mold is divided into the gate area, the cavity main area and the exhaust area for zone temperature control. In the third stage, the gate area is preheated to 220-250℃, the cavity main area is preheated to 180-200℃, and the exhaust area is preheated to 150-170℃.

4. A die-casting process for a magnesium alloy porous structural member according to claim 3, characterized in that, The fixed heating rate is 5-8°C / min.

5. A die-casting process for a magnesium alloy porous structural member according to claim 1, characterized in that, The four-stage injection speed control steps of the mold swing coordination are specifically as follows: during the injection process, the injection speed is divided into four stages for precise control: the first stage is low-speed injection, the speed is set to 0.5-1m / s, and the mold starts to swing in a predetermined direction at a swing rate of 1-3° / s; the second stage is medium-speed injection, the speed is increased to 1.5-2m / s, and the mold swing rate is adjusted to 3-5° / s; the third stage is high-speed injection, the speed reaches 3-4m / s, and the mold remains stationary after swinging to the set maximum angle; the fourth stage is deceleration injection, and the speed is reduced to 0.5-1m / s when the filling is nearly completed, and the mold starts to swing in the opposite direction to reset.

6. A die-casting process for a magnesium alloy porous structural member according to claim 5, characterized in that, The maximum swing angle of the mold is 5-15 degrees, and the ratio of the mold's reverse reset swing rate to the forward swing rate is 1:1-1:1.

5.

7. The die-casting process for a magnesium alloy porous structure according to claim 1, characterized in that: The temperature difference aging treatment is to place the magnesium alloy casting after die casting in a high temperature environment of 200-220°C for 1-2 hours, and then transfer it to a low temperature environment of 120-140°C for cooling.

8. A die-casting process for a magnesium alloy porous structural member according to claim 1, characterized in that, The magnesium alloy raw material pretreatment specifically comprises immersing the qualified raw materials in a weak alkaline cleaning solution for 15-20 minutes, wherein the cleaning solution contains 5% sodium carbonate and 3% surfactant, and then drying the raw materials in a hot air drying oven at 80-100°C.

9. A die-casting process for a magnesium alloy porous structural member according to claim 8, characterized in that, When the magnesium alloy raw material is smelted, the magnesium alloy raw material is placed in a smelting device, first heated to 400-450° C., and maintained at this temperature for 10-15 minutes, and then quickly heated to 680-720° C. to complete the complete smelting process of the magnesium alloy.

10. A die-casting process for a magnesium alloy porous structural part according to claim 9, characterized in that, When the magnesium alloy raw material is melted, eccentric refining and stirring are performed, and the eccentric distance of the eccentric stirring head is 1 / 5-1 / 3 of the diameter of the stirring head.

Images