Aluminum alloy die-casting process for improving the composition uniformity of die-casting parts

Abstract

An aluminum alloy die-casting process for improving the uniformity of the composition of die-castings relates to the technical field of aluminum alloy casting processing. A low-pressure die-casting process is used to inject an aluminum-based melt with uniform composition into a cavity, and the melt in the die-casting cavity is heated and heated to ensure that the precipitated phase Mg2Si is dissolved into the aluminum-based melt. After that, the melt is kept warm to ensure that the melt is filled densely. Subsequently, a water-cooled active cooling technology is used to accelerate the solidification speed, shorten the time between the precipitation of the Mg2Si dispersed phase and the solidification of the aluminum alloy, inhibit the floating of the Mg2Si dispersed phase, and improve the uniformity of the composition of the aluminum alloy die-casting. In addition, a short insulation is performed near the solidification temperature line, and then water-cooling is performed to slowly cool, thereby ensuring the density of the aluminum alloy die-casting. The present invention can greatly improve the uniformity of the composition of the aluminum alloy die-casting while ensuring the aluminum alloy die-casting, thereby achieving the improvement of the performance of the aluminum alloy die-casting and ensuring the efficient and stable production of the aluminum alloy die-casting.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy casting processing, and in particular to an aluminum alloy die-casting process for improving the uniformity of die-casting components. Background Art

[0002] Aluminum alloy has the advantages of high specific strength, corrosion resistance, and easy processing and forming. It is widely used to produce frames, structural components, etc. The replacement application of aluminum alloy parts in new energy vehicles is an important way to achieve lightweight vehicles and improve driving range. There are many ways to form aluminum alloys, including casting, forging, die-casting and other processes. Among them, the die-casting process has the characteristics of high production efficiency, high density of aluminum alloy parts, and high precision of parts. It has broad application prospects in the field of new energy vehicle parts. Die-casting is a precision casting method that uses high pressure to force the aluminum alloy melt into the mold cavity. The main steps are as follows: first, the aluminum alloy melt of the target composition is melted, and then the evenly mixed aluminum alloy melt is injected into the mold cavity under high pressure. Then, it is kept warm for a long time to ensure that the mold cavity is filled densely, and then air-cooled to solidify and form to obtain aluminum alloy die-cast parts.

[0003] However, the main problem of this conventional production process is the contradiction between the density of parts and the uniformity of composition. Long-term heat preservation can ensure that the mold cavity is fully filled and improve the density of parts. However, long-term heat preservation will cause uneven distribution of composition. Mg formed in aluminum alloy 2 The Si precipitate phase has a lower density than the aluminum-based melt, so long-term heat preservation above the solidification temperature will cause Mg 2 The floating of Si precipitates causes the formation of Si-deficient areas at the bottom of aluminum alloy die-cast parts and Si-rich areas at the top. The uniformity of component distribution in aluminum alloy die-cast parts is related to their mechanical properties and plays a vital role in the large-scale application of die-cast parts in the field of new energy vehicles. Therefore, it is necessary to improve the die-casting process to avoid the phenomenon of uneven distribution of elemental components in die-cast parts. Summary of the invention

[0004] The invention provides an aluminum alloy die-casting process for improving the uniformity of the composition of a die-casting, which improves the uniformity of the distribution of elemental composition while improving the density of the die-casting.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] An aluminum alloy die-casting process for improving the uniformity of die-casting composition, wherein the melt injected into the die-casting mold cavity is heated to Mg 2 Si eutectic temperature point, and short-term heat preservation and filling are performed to ensure the precipitation of Mg phase 2Si is fully dissolved into the aluminum-based melt; then it is quickly cooled to the solidification point of the aluminum alloy, shortening the time from Mg 2 The time between the precipitation of Si phase and the solidification of aluminum alloy melt inhibits the Mg 2 The floating of Si precipitated phase promotes the composition uniformity of aluminum alloy die castings; after a short insulation at the solidification point temperature, it is slowly cooled to the demolding temperature of the aluminum alloy die casting to ensure the density of the die casting and improve the shrinkage defects caused by rapid cooling in the early stage.

[0007] As a preferred technical solution, the heating of the aluminum-based melt in the die-casting mold is achieved by a mold-built-in heater, and the cooling of the aluminum-based melt is achieved by a mold-built-in coolant circulation pipeline, and the cooling rate is regulated by controlling the coolant flow rate.

[0008] As a preferred technical solution, the specific process steps are as follows:

[0009] ① Aluminum alloy smelting: The ingot is heated to a molten state by a regenerative crucible furnace, and then a certain amount of slag removal agent is added to remove the slag, and the aluminum alloy melt is kept warm for a long time to ensure the uniform distribution of elements in the melt;

[0010] ② Degassing and refining: Degassing and refining are carried out on the above-mentioned aluminum alloy melt. The temperature of the aluminum alloy melt is set to a specific range of the molten state. Then, the degassing rotor is inserted into the aluminum-based melt and an inert gas is introduced. The inert gas is evenly distributed in the aluminum alloy melt as the rotor rotates, so that harmful gases in the aluminum alloy melt are removed. Then, a certain amount of refining agent is added to further remove slag and purify the aluminum-based melt;

[0011] ③ Low-pressure casting: First, heat the die-casting mold to prevent the product from being scrapped or even stuck due to low temperature, then close the mold, and then inject the refined aluminum-based melt into the mold cavity under a certain pressure to fill the mold;

[0012] ④ Homogenization of aluminum alloy die castings: The mold is then heated to raise the temperature of the aluminum alloy melt inside the mold cavity to Mg 2 The die casting is heated to above the Si eutectic temperature point, and is kept warm and further filled; then the mold is quickly cooled to the solidification point of the aluminum alloy by using a coolant, and is kept warm for a short time; finally, the coolant flow rate is reduced to allow the aluminum alloy die casting to slowly cool to the demolding temperature point for demolding, and quenching is performed to obtain the aluminum alloy die casting blank;

[0013] ⑤ Heat treatment of aluminum alloy die-castings: Place the aluminum alloy die-casting blank into a heat treatment furnace for solution treatment, take it out and quench it, and finally perform aging treatment to obtain the finished aluminum alloy die-casting.

[0014] As a further preferred technical solution, in the aluminum alloy die casting process:

[0015] During the aluminum alloy smelting process, the temperature of the aluminum alloy melt is maintained at 690-760°C, the holding time is maintained at 10-30 minutes, and the amount of slag cleaning agent added is maintained at 0.01-0.05%.

[0016] During the degassing refining process, the temperature of the aluminum alloy melt is set at 700-730°C, the rotation speed of the rotor is 400-800rpm, the flow rate of the inert gas is 25-60L / min; and the amount of the refining agent added is maintained at 0.01-0.05%.

[0017] During the low-pressure casting process, the mold temperature is controlled at 300-450°C before the aluminum-based melt is injected into the die-casting mold cavity, and the filling pressure is maintained at 200-350 mbar.

[0018] During the homogenization process of aluminum alloy die castings, the melt injected into the die casting mold cavity is heated to 920-1000℃, and then kept warm for 50-120s. After the aluminum-based melt is kept warm for filling, it is cooled to 535-630℃ within 30-100s, and then kept warm for 10-30s. After a short heat preservation at the solidification point temperature, it is cooled to 300-450℃ within 80-150s before demolding.

[0019] During the heat treatment of aluminum alloy die castings, the solution temperature range is selected to be 520-560℃, the holding time is 5-15h, the quenching cooling water temperature is 30-70℃, the quenching time is maintained at 150-250s, the aging temperature is controlled at 140-170℃, and the holding time is maintained at 4-10h.

[0020] Compared with the prior art, the aluminum alloy die-casting process for improving the uniformity of the composition of die-casting parts proposed in the present invention has the following beneficial effects:

[0021] 1. The present invention combines the phase diagram and heats the aluminum alloy melt injected into the mold cavity to raise the temperature so that the aluminum alloy melt reaches Mg 2 Above the Si eutectic temperature, Mg in the melt 2 The Si precipitated phase dissolves back into the aluminum alloy melt, thereby avoiding the floating of the precipitated phase and effectively avoiding the compositional inhomogeneity of the aluminum alloy die casting.

[0022] 2. The present invention proposes a temperature-adjustable die-casting mold, in which the temperature in the die-casting cavity can be increased by non-contact heating; and then the time between the precipitation of the precipitated phase and the solidification of the melt can be shortened by active cooling with cooling water, thereby improving the composition uniformity of the die-casting. In addition, compared with directly heating a large amount of aluminum-based melt in a crucible during the smelting stage, the energy consumption of directly heating the melt in the die-casting mold cavity is significantly lower.

[0023] 3. The present invention can improve the temperature of the aluminum alloy in the mold cavity to promote the fluidity of the aluminum alloy melt, and the heat preservation can fully ensure the uniform distribution of elements in the aluminum alloy melt and the complete filling of the cavity. In addition, the short-term heat preservation at the solidification point temperature can improve the density deterioration caused by the rapid cooling in the early stage, and the increase in the viscosity of the melt near the solidification point can slow down the Mg 2 The floating of Si precipitated phase improves the density and the uniformity of elemental composition distribution.

[0024] 4. The present invention can solve the contradiction between the density and element distribution uniformity of aluminum alloy die castings in conventional die casting processes by changing the temperature process flow of the aluminum alloy melt in the mold cavity and adjusting the insulation temperature point and insulation time, thereby improving the mechanical service performance of aluminum alloy die castings.

[0025] In addition, the present invention also proposes an aluminum alloy die-casting mold, including a mold body and a mold cavity. A coolant circulation pipeline is arranged in the mold body, which is used to cool the heated mold, and the cooling rate is reasonably regulated by controlling the coolant flow rate; an electric heating pipeline and a thermocouple hole are also arranged in the mold body, which are used to install a heater and a temperature sensor respectively, and both are electrically connected to a controller; the temperature sensor is used to monitor the temperature of the mold surface in real time; the heater heats the mold according to the output signal of the controller; the controller controls the working state of the heater and the coolant flow rate in the coolant circulation pipeline according to a preset program according to the output signal of the temperature sensor.

[0026] Compared with the prior art, the aluminum alloy die-casting mold proposed in the present invention has the following beneficial effects:

[0027] 1. The non-contact heating method is adopted to avoid the safety hazards of the traditional resistance wire heating method.

[0028] 2. The temperature sensor is used to monitor the temperature of the mold surface in real time, so that the heater can heat accurately according to actual needs, avoiding the high energy consumption problem of traditional resistance wire heating.

[0029] 3. The working time and working state of the heater are controlled by the controller, which realizes the automation of the heating process and reduces the complexity of manual operation.

[0030] 4. Setting up a heat insulation layer reduces heat loss and improves energy utilization.

[0031] 5. The cooling system cools the heated mold, effectively extending the service life of the mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the Mg-Si binary phase diagram.

[0033] Figure 2 It is a die-casting temperature variation curve (comparison between conventional die-casting process and the die-casting process of the present invention).

[0034] Figure 3 It is a schematic diagram of the structure of aluminum alloy die-casting mold. DETAILED DESCRIPTION

[0035] The preferred embodiments and comparative embodiments of the present invention are described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0036] Example 1

[0037] In this embodiment, the aluminum alloy die-casting process for improving the uniformity of the composition of the die-casting part proposed in the present invention is adopted, and the aluminum alloy melt injected into the die-casting mold cavity is heated to achieve Mg 2 The Si dispersed phase is dissolved back and kept at high temperature for a specific time to ensure full filling. Then active water cooling is used to achieve rapid cooling of the aluminum alloy melt and shorten the Mg 2 The time between the precipitation of Si dispersed phase and the solidification of aluminum alloy can avoid Mg 2 The Si dispersed phase floats to improve the composition uniformity of aluminum alloy die castings. The specific process steps are as follows:

[0038] ① Aluminum alloy smelting: A356 ingot (50kg) is heated to a molten state by a regenerative crucible furnace. The Si content in the A356 aluminum alloy melt is 6.5-7.5%, the Mg content is 0.3-0.5%, the Ti content is 0.08-0.2%, and the content of other impurity elements should be controlled within the required range of the A356 alloy. The temperature of the aluminum alloy melt is maintained at 700°C, and the holding time is maintained at 15 minutes to ensure the uniform distribution of elements in the melt. Subsequently, a certain amount of slag cleaning agent is added for slag cleaning, and the amount of slag cleaning agent added is 0.03%.

[0039] ② Degassing and refining: Degassing and refining are carried out on the above aluminum alloy melt. The temperature of the aluminum alloy melt is set at 710℃, and then the degassing rotor is inserted into the aluminum-based melt and inert gas is introduced. The flow rate of the inert gas is 35L / min. The inert gas is evenly distributed in the aluminum alloy melt as the rotor rotates. The rotor speed during the degassing and refining process is 500rpm. The H 2 After the harmful gases are removed, 0.03% of refining agent is added to further remove the slag and purify the aluminum-based melt.

[0040] ③ Low-pressure casting: First, heat the mold to 350℃ and keep it warm for 10 minutes to prevent the product from being scrapped or even the mold from locking due to low temperature. Then, close the mold and inject the refined aluminum-based melt into the mold cavity at a pressure of 300mbar to fill the mold.

[0041] ④Homogeneous treatment of aluminum alloy die castings: according to Figure 1 The Mg-Si binary phase diagram is used to determine the heating point of the mold. The mold is heated to 950°C, and the aluminum alloy melt inside the mold cavity is heated to Mg 2 Si eutectic temperature point, and then keep warm and further fill the mold. The filling time is 80s. At this time, Mg 2 The Si precipitated phase will be redissolved into the aluminum melt. Then, the mold is quickly cooled down using cooling water at 25°C, and the coolant flow rate is adjusted so that the temperature of the die casting is reduced to 580°C within 50 seconds, which is lower than the solidification point of the aluminum alloy. The die casting is then kept warm for a short time of 20 seconds, thereby ensuring rapid cooling and solidification of the aluminum alloy die casting while improving the density of the die casting. Subsequently, the cooling rate of the die casting is reduced by reducing the water cooling rate. After 100 seconds, the temperature is reduced to 400°C and the mold is further demolded, and the aluminum alloy die casting blank is obtained by quenching. The temperature change curve of the homogenization treatment of the aluminum alloy die casting is shown in the figure. Figure 2 shown.

[0042] ⑤ Heat treatment of aluminum alloy die castings: The aluminum alloy die casting blank is placed in a heat treatment furnace for solution treatment, the solution temperature is selected to be 530°C, the holding time is 10h, then taken out and placed in cooling water at 40°C for quenching, and kept for 200s, and finally aged, the aging temperature is 150°C and kept for 5h, and finally the finished aluminum alloy die casting is obtained. After analysis and detection, the density of the aluminum alloy die casting prepared by the process of the present invention is 99.2%, and the upper and lower parts are sampled and tested respectively. The test results are shown in Table 1 below, and the composition distribution is uniform.

[0043] Table 1 Element composition of the upper and lower parts of the aluminum alloy die casting prepared by the present invention

[0044] Si Mg Ti Al upper part 6.34 0.312 0.124 92.68 lower part 6.25 0.304 0.140 92.85

[0045] Comparative Example 1

[0046] In this embodiment, a conventional process for preparing the composition uniformity of die-cast aluminum alloy parts is adopted, by filling and insulating the aluminum alloy melt injected into the die-casting mold cavity, and then using active water cooling to achieve solidification of the aluminum alloy melt, and finally obtaining an aluminum alloy die-casting part.

[0047] Steps ① and ② are the same as those in Example 1.

[0048] ③ Low-pressure casting: First, heat the mold to 350°C to prevent the product from being scrapped or even stuck due to low temperature. Then close the mold and inject the refined aluminum-based melt into the mold cavity at a pressure of 300mbar for 80s.

[0049] ④ Solidification of aluminum alloy die castings: Use 25°C cooling water to quickly cool the mold, adjust the cooling water flow rate to ensure that the aluminum alloy die casting temperature drops to 400°C within 30s, and then further demold it, and quench it to obtain the aluminum alloy die casting blank.

[0050] Step ⑤ The heat treatment of the aluminum alloy die casting is the same as that of Example 1. After analysis and detection, the density of the aluminum alloy die casting prepared in Comparative Example 1 is 98.3%, and the detection results of the upper and lower parts are shown in Table 2 below. The Si element and Mg element are enriched in the upper area, and the component distribution is uneven, which will affect the mechanical properties of the aluminum alloy die casting.

[0051] Table 2 Element composition of the upper and lower parts of aluminum alloy die castings prepared according to conventional process

[0052] Si Mg Ti Al upper part 6.84 0.335 0.116 92.54 lower part 5.97 0.299 0.145 93.43

[0053] Combination Figure 2 As can be seen from the results in Tables 1 and 2, the die-casting process proposed in the present invention can solve the contradiction between the density and the uniformity of element distribution of aluminum alloy die-castings in the conventional die-casting process, improve the uniformity of element distribution while improving the density, and improve the mechanical service performance of aluminum alloy die-castings.

[0054] Example 2

[0055] The aluminum alloy die-casting mold designed by the present invention is as follows Figure 3 As shown, its structure mainly includes a mold body 1 and a mold cavity 2. A coolant circulation pipeline 5 is set in the mold body 1 to cool the heated mold. At the same time, by controlling the coolant flow rate, the reasonable regulation of the cooling rate is achieved. In addition, an electric heating pipeline 4 and a thermocouple hole 3 are also set in the mold body 1, which are used to install a heater and a temperature sensor respectively, and both are electrically connected to a controller (not shown in the figure).

[0056] The temperature sensor is used to monitor the temperature of the mold surface in real time. The heater heats the mold according to the output signal of the controller. The controller controls the working state of the heater and the flow rate of the coolant in the coolant circulation pipeline according to the output signal of the temperature sensor according to the preset program.

[0057] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. An aluminum alloy die-casting process for improving the uniformity of die-casting composition, characterized in that: The melt injected into the die-casting mold cavity is heated to above the Mg2Si eutectic temperature point, and is briefly kept warm for filling to ensure that the precipitated phase Mg2Si is fully dissolved in the aluminum-based melt; then it is quickly cooled to the solidification point temperature of the aluminum alloy to shorten the time from the precipitation of the Mg2Si precipitate phase to the solidification of the aluminum alloy melt, inhibit the floating of the Mg2Si precipitate phase, and promote the composition uniformity of the aluminum alloy die-casting; after a short insulation at the solidification point temperature, it is slowly cooled to the demolding temperature of the aluminum alloy die-casting to ensure the density of the die-casting and improve the shrinkage defects caused by the rapid cooling in the early stage.

2. The aluminum alloy die-casting process according to claim 1, characterized in that: Before the aluminum-based melt is injected into the die-casting mold cavity, the mold temperature is controlled at 300-450 °C and the filling pressure is maintained at 200-350 mbar.

3. The aluminum alloy die-casting process according to claim 2, characterized in that: After the melt injected into the die casting mold cavity is heated to 920-1000 ℃, it is kept warm and filled for 50-120 s.

4. The aluminum alloy die-casting process according to claim 3, characterized in that: After the aluminum-based melt is kept warm and filled, it is cooled to 535-630°C within 30-100 seconds and then kept warm for 10-30 seconds.

5. The aluminum alloy die-casting process according to claim 4, characterized in that: After a short heat preservation at the solidification point temperature, it is cooled to 300-450℃ within 80-150s and then demoulded.

6. The aluminum alloy die-casting process according to any one of claims 1 to 5, characterized in that: The heating of the aluminum-based melt in the die-casting mold is achieved by a mold-built-in heater, and the cooling of the aluminum-based melt is achieved by a mold-built-in coolant circulation pipeline, and the cooling rate is regulated by controlling the coolant flow rate.

7. The aluminum alloy die-casting process according to claim 6, characterized in that: The specific process steps are as follows: ① Aluminum alloy smelting: The ingot is heated to a molten state by a regenerative crucible furnace, and then a certain amount of slag removal agent is added to remove the slag, and the aluminum alloy melt is kept warm for a long time to ensure the uniform distribution of elements in the melt; ② Degassing and refining: Degassing and refining are carried out on the above-mentioned aluminum alloy melt. The temperature of the aluminum alloy melt is set to a specific range of the molten state. Then, the degassing rotor is inserted into the aluminum-based melt and an inert gas is introduced. The inert gas is evenly distributed in the aluminum alloy melt as the rotor rotates, so that harmful gases in the aluminum alloy melt are removed. Then, a certain amount of refining agent is added to further remove slag and purify the aluminum-based melt; ③ Low-pressure casting: First, heat the die-casting mold to prevent the product from being scrapped or even stuck due to low temperature, then close the mold, and then inject the refined aluminum-based melt into the mold cavity under a certain pressure to fill the mold; ④ Homogenization treatment of aluminum alloy die castings: Then heat the mold to raise the temperature of the aluminum alloy melt inside the mold cavity to above the Mg2Si eutectic temperature, and keep it warm and further fill the mold; then use the coolant to quickly cool the mold to the solidification point of the aluminum alloy, and keep it warm for a short time; finally, reduce the coolant flow rate so that the aluminum alloy die casting is slowly cooled to the demolding temperature point for demolding treatment, and quench to obtain the aluminum alloy die casting blank; ⑤ Heat treatment of aluminum alloy die-castings: Place the aluminum alloy die-casting blank into a heat treatment furnace for solution treatment, take it out and quench it, and finally perform aging treatment to obtain the finished aluminum alloy die-casting.

8. The aluminum alloy die-casting process according to claim 7, characterized in that: During the aluminum alloy smelting process, the temperature of the aluminum alloy melt is maintained at 690-760 ℃, the holding time is maintained at 10-30 min, and the amount of slag cleaning agent added is maintained at 0.01-0.05%; during the degassing refining process, the temperature of the aluminum alloy melt is set at 700-730 ℃, the rotor speed is 400-800rpm, and the flow rate of inert gas is 25-60 L / min; the amount of refining agent added is maintained at 0.01-0.05%.

9. The aluminum alloy die-casting process according to claim 7, characterized in that: During the heat treatment of aluminum alloy die castings, the solution temperature range is selected to be 520-560 ℃, the holding time is 5-15 h, the temperature of the quenching cooling water is 30-70 ℃, the quenching time is maintained at 150-250 s, the aging temperature is controlled at 140-170 ℃, and the holding time is maintained at 4-10 h.

10. The aluminum alloy die-casting process according to claim 6, characterized in that: The die-casting mold includes a mold body and a mold cavity. A coolant circulation pipeline is arranged in the mold body for cooling the heated mold. The cooling rate is reasonably regulated by controlling the coolant flow rate. An electric heating pipeline and a thermocouple hole are also arranged in the mold body for installing a heater and a temperature sensor, respectively, and both are electrically connected to a controller. The temperature sensor is used to monitor the temperature of the mold surface in real time. The heater heats the mold according to the output signal of the controller. The controller controls the working state of the heater and the coolant flow rate in the coolant circulation pipeline according to a preset program according to the output signal of the temperature sensor.

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