Liquid-lifting low-pressure casting method for aluminum alloy chassis

Abstract

The present invention relates to the field of low-pressure casting, and more specifically, to a method for casting an aluminum alloy chassis using liquid riser low-pressure casting. The method comprises connecting a riser tube and an ingrown runner, wherein the liquid outlet of the riser tube is connected to the inlet of the ingrown runner, the inner diameter of the riser tube gradually decreases from an end remote from the ingrown runner to an end near the ingrown runner, and the inner diameter of the ingrown runner gradually increases from an end near the riser tube to an end remote from the riser tube, and the diameter of the liquid outlet is larger than the diameter of the inlet. By directly connecting the riser tube and the ingrown runner, the configuration of the sprue and runner is reduced, the flow path of the molten aluminum is shortened, and thus the loss of pressure transmitted to the main mold is reduced, which is conducive to improving the shrinkage feeding capacity and reducing the adhesion of the molten aluminum to the sprue and runner, that is, reducing the loss of the molten aluminum.

Description

Technical Field

[0001] The present invention relates to the field of low-pressure casting, and in particular to a liquid-lifting low-pressure casting method for an aluminum alloy chassis. Background Art

[0002] Compared to traditional gravity casting, low-pressure casting offers controllable filling speeds, smoother molten aluminum flow, and fewer secondary inclusions. Compared to sand casting, metal mold casting offers faster cooling, more easily achieving a fine, dense structure and high mechanical properties, and easier automation and clean production. Therefore, metal mold low-pressure casting is widely used in the production of automotive parts such as aluminum alloy wheels, chassis components, and engine components, as well as in military applications such as aerospace. Low-pressure casting typically involves the following process stages: liquid filling, mold building, pressurization, pressure maintenance, and pressure relief.

[0003] However, the low-pressure casting method provided by the related art has limited shrinkage compensation capability and causes large loss of aluminum liquid. Summary of the Invention

[0004] The objectives of the present invention include, for example, providing a low-pressure casting method for an aluminum alloy chassis with liquid lifting, which can improve the shrinkage feeding capacity and reduce the loss of aluminum liquid, thereby achieving the purpose of improving the qualified rate and saving costs.

[0005] The embodiments of the present invention can be implemented as follows:

[0006] The present invention provides a low-pressure casting method for an aluminum alloy chassis using liquid riser, comprising: connecting a liquid riser pipe and an ingrown runner, wherein the liquid outlet of the liquid riser pipe is connected to the inlet of the ingrown runner, the inner diameter of the liquid riser pipe gradually decreases from an end away from the ingrown runner to an end close to the ingrown runner, the inner diameter of the ingrown runner gradually increases from an end close to the liquid riser pipe to an end away from the liquid riser pipe, and the diameter of the liquid outlet is larger than the diameter of the inlet;

[0007] The low-pressure casting method for aluminum alloy chassis includes: liquid raising, mold filling, pressurization, pressure holding and air cooling; among them,

[0008] The rate of liquid rise is 12.7-21 mbar / s, and the pressure of the liquid rise is 200±10 mbar;

[0009] The filling process includes the first stage and the second stage in sequence. The rate of the first stage is 2-20 mbar / s and the pressure of the first stage is 240±10 mbar. The rate of the second stage is 5-30 mbar / s and the pressure of the second stage is 310±10 mbar.

[0010] The boost rate is 8 to 66.7 mbar / s, and the boost pressure is 450 ± 50 mbar;

[0011] The pressure holding process includes a pressure reduction and holding stage and a stable pressure holding stage. The pressure in the stable pressure holding stage is 350±50mbar, and the time of the pressure reduction and holding stage is 35-45s.

[0012] Air cooling starts at the stable pressure holding stage, and the air cooling flow rate is 30~80m 3 / h conditions, and last for at least 200s.

[0013] In an alternative embodiment, the rate of the first stage is less than the rate of the second stage.

[0014] In an optional embodiment, the pressure reduction rate in the pressure reduction and pressure maintenance stage is 4.4-11.4 mbar / s.

[0015] In an optional embodiment, the rate of pressurization is greater than the rate of filling.

[0016] In an optional embodiment, the angle between the inner wall of the riser tube and its axis is 2-4°; and the diameter of the liquid outlet is 55-65 mm.

[0017] In an optional embodiment, the angle between the inner wall of the ingrown channel and its axis is 5-7°.

[0018] In an optional embodiment, the axial height of the riser is greater than the axial height of the ingrown channel; and the diameter of the liquid outlet is 3-5 mm larger than the diameter of the inlet.

[0019] In an optional embodiment, a step surface is provided at the junction of the riser tube and the ingrown channel, and the step surface is distributed around the circumference of the inlet.

[0020] In an optional embodiment, the riser tube includes a riser tube body and a base connected to the outer periphery of the riser tube body, the base is provided with an annular groove, the annular grooves are distributed around the outer periphery of the riser tube body, and the annular grooves are provided adjacent to the ingrown channel; the riser tube body is provided with a liquid outlet;

[0021] An air cooling pipe is provided in the annular groove, which includes an annular tube and multiple air outlet nozzles connected to the annular tube. The multiple air outlet nozzles are distributed in sequence along the circumference of the annular tube, and all the air outlet nozzles blow air toward the bottom of the annular groove.

[0022] In an optional embodiment, the air cooling step includes a first air cooling stage and a second air cooling stage performed sequentially, and the flow rate of the first air cooling stage is 30-40m 3 / h, the flow rate of the second air cooling stage is 40~80m 3 / h; wherein, the flow rate of the first air cooling stage is less than the flow rate of the second air cooling stage, and the time of the first air cooling stage is less than 15s and greater than 0s.

[0023] The beneficial effects of the low-pressure casting method for the aluminum alloy chassis with liquid rising in an embodiment of the present invention include, for example: by directly connecting the rising pipe and the ingrowth, the configuration of the sprue and the runner is reduced, the flow path of the molten aluminum is shortened, thereby reducing the loss of pressure transmitted to the main mold, which is beneficial to improving the shrinkage compensation capability and reducing the adhesion of the molten aluminum to the sprue and the runner, that is, reducing the loss of molten aluminum.

[0024] At the same time, the inner diameter of the riser tube gradually decreases from the end away from the ingrown to the end near the ingrown. This allows the riser tube to convey molten aluminum to the ingrown in a reduced diameter, increasing the pressure of the molten aluminum during delivery and reducing bubbles in the molten aluminum. Meanwhile, the inner diameter of the ingrown gradually increases from the end near the riser tube to the end away from the riser tube. The diameter of the liquid outlet is larger than the diameter of the inlet, allowing the ingrown diameter to be expanded. This allows the molten aluminum entering the ingrown to rise smoothly after degassing. This ensures that the molten aluminum can rise smoothly and fill up smoothly after degassing the molten aluminum, fully enhancing the shrinkage feeding capacity.

[0025] The low-pressure casting method for an aluminum alloy chassis with liquid lifting provided in an embodiment of the present invention, after liquid lifting, also adopts a segmented method for filling the mold and performs pressure maintenance at a relatively low pressure. At the same time, air cooling is started after the pressure maintenance is performed for a period of time. On the one hand, it can fully reduce the formation of defects such as shrinkage cavities and shrinkage porosity, and improve the density and mechanical properties of low-pressure casting. On the other hand, it can also promote the formation of fine needle-shaped martensitic structure, so that the low-pressure cast aluminum alloy chassis has both good hardness and strength and good toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 A cross-sectional view of a riser pipe, an ingrown channel, and an air-cooling pipe in an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the structure of the liquid riser body and the air cooling tube in an embodiment of the present invention.

[0029] Icons: 100-liquid lifting pipe; 101-step surface; 110-liquid lifting pipe body; 120-base; 121-annular groove; 200-inner gate; 300-air cooling pipe; 310-annular pipe; 320-air outlet nozzle. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0032] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0033] In the description of the present invention, it should be noted that the terms "inner" and "outer" and the like, when used to indicate orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is typically placed when in use. These terms are intended solely to facilitate the description of the present invention and simplify the description, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" and the like are used solely for distinction and should not be construed as indicating or implying relative importance.

[0034] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0035] Please refer to Figure 1 The present embodiment provides a method for low-pressure casting of an aluminum alloy chassis by liquid lifting, comprising: connecting a riser tube 100 and an ingrown runner 200, wherein the liquid outlet of the riser tube 100 is connected to the inlet of the ingrown runner 200, the inner diameter of the riser tube 100 gradually decreases from an end away from the ingrown runner 200 to an end close to the ingrown runner 200, and the inner diameter of the ingrown runner 200 gradually increases from an end close to the riser tube 100 to an end away from the riser tube 100, and the diameter of the liquid outlet is larger than the diameter of the inlet.

[0036] By directly connecting the riser tube 100 and the ingrow 200—that is, directly connecting the riser tube 100, the ingrow 200, and the cast chassis body, and then connecting to the riser—the number of sprues and runners is reduced. The ceramic body between the riser tube 100 and the chassis body mold is also eliminated, shortening the aluminum liquid flow path and reducing pressure losses transmitted to the chassis body mold. This improves shrinkage feeding capacity and reduces aluminum liquid adhesion to the sprue and runners, thereby reducing aluminum liquid loss. Furthermore, eliminating the sprue and runners also reduces the need for coating on the sprue and runners, which helps improve production efficiency and reduce costs.

[0037] At the same time, the inner diameter of the riser tube 100 gradually decreases from the end away from the ingrow 200 to the end closer to the ingrow 200. This allows the riser tube 100 to convey molten aluminum to the ingrow 200 in a reduced diameter manner. This increases the pressure of the molten aluminum as it is conveyed to the ingrow 200, expelling gas from the molten aluminum and reducing bubbles in the molten aluminum. The inner diameter of the ingrow 200 gradually increases from the end closer to the riser tube 100 to the end farther from the riser tube 100. The diameter of the liquid outlet is larger than the diameter of the inlet, allowing the ingrow 200 to convey the liquid in an expanding diameter. This allows the molten aluminum entering the ingrow 200 to rise smoothly after the gas is reduced. This ensures that the molten aluminum can rise smoothly and fill up after the gas in the molten aluminum is reduced, thereby fully improving the shrinkage feeding capacity.

[0038] It should be noted that by directly connecting the riser pipe 100 and the ingrowth 200, the runner and the sprue are reduced, and the overall size of the mold can be reduced, that is, the projected area of ​​the casting system can be reduced, and the mold clamping force required by the casting machine is reduced.

[0039] Optionally, the angle α between the inner wall of the riser tube 100 and its axis is 2-4°, for example, 2°, 3°, 4°, etc., which are not specifically limited herein. The diameter of the liquid outlet is 55-65 mm, for example, 55 mm, 58 mm, 60 mm, 63 mm, 65 mm, etc., which are not specifically limited herein. This configuration, on the one hand, increases the pressure of the molten aluminum when the riser tube 100 transports the molten aluminum to the ingrown channel 200, thereby expelling gas from the molten aluminum and reducing bubbles entrained in the molten aluminum, thereby reducing the formation of defects such as shrinkage cavities and porosity, and improving shrinkage feeding capacity. On the other hand, it also ensures that the transportation of the molten aluminum is not adversely affected, thereby ensuring production efficiency.

[0040] Optionally, the angle β between the inner wall of the ingrow 200 and its axis is 5-7°, for example, 5°, 6°, 7°, etc., which is not specifically limited here. This configuration ensures that the molten aluminum entering the ingrow 200 rises smoothly without rising too quickly, which helps to fully reduce the formation of defects such as shrinkage cavities and porosity, and improves shrinkage feeding capacity.

[0041] Optionally, the axial height of the riser tube 100 is greater than the axial height of the ingrown 200. Setting the axial height of the riser tube 100 higher can more effectively ensure that the gas in the riser tube 100 is fully squeezed out when the riser tube 100 transports the molten aluminum, thereby reducing the formation of defects such as shrinkage cavities and shrinkage porosity and improving shrinkage feeding capacity.

[0042] Optionally, the diameter of the outlet is 3-5 mm larger than the inlet, for example, 3 mm, 4 mm, or 5 mm. This allows the molten aluminum to flow slowly from the larger outlet to the smaller inlet, preventing the molten aluminum from gushing into the ingrowth 200 and causing holes during casting. This further reduces the formation of defects such as shrinkage cavities and porosity, and improves shrinkage feeding capabilities.

[0043] Optionally, a stepped surface 101 is provided at the junction of the riser tube 100 and the ingrown runner 200. The stepped surfaces 101 are distributed circumferentially around the inlet. The provision of the stepped surfaces 101 ensures a slow flow of molten aluminum as it flows from the outlet to the inlet. Specifically, the stepped surfaces 101 provide a certain degree of obstruction and buffering for the molten aluminum flowing from the outlet to the inlet. Furthermore, the molten aluminum in the riser tube 100 can be guided by the stepped surfaces 101 to flow from the inlet into the ingrown runner 200. This alleviates the problem of molten aluminum entering the ingrown runner 200 in a gushing direction, which can lead to the formation of holes in the casting. This further reduces the formation of defects such as shrinkage cavities and porosity, and improves shrinkage feeding capability.

[0044] Alternatively, see Figure 1 and Figure 2 The riser pipe 100 includes a riser pipe body 110 and a base 120 connected to the outer circumference of the riser pipe body 110, the base 120 is provided with an annular groove 121, the annular groove 121 is distributed around the outer circumference of the riser pipe body 110, and the annular groove 121 is arranged adjacent to the inner runner 200; the riser pipe body 110 is provided with a liquid outlet and a step surface 101; an air-cooling pipe 300 is arranged in the annular groove 121, the air-cooling pipe 300 includes an annular pipe 310 and a plurality of air outlet nozzles 320 connected to the annular pipe 310, the annular pipe 310 is embedded in the annular groove 121, and is distributed around the outer circumference of the riser pipe 100, the plurality of air outlet nozzles 320 are distributed in sequence along the circumference of the annular pipe 310, and the air outlet nozzles 320 all blow air toward the bottom of the annular groove 121. Such an arrangement, on the one hand, can make the wind blow toward the ingrown channel 200 and the mold connected to the ingrown channel 200, which is beneficial to improving the efficiency of air cooling; on the other hand, it can increase the formation of fine needle-shaped martensitic structure, so that the low-pressure cast aluminum alloy chassis has both good hardness and strength and good toughness.

[0045] The low-pressure casting method for the aluminum alloy chassis of this embodiment includes: liquid raising, mold filling, pressurization, pressure holding and air cooling; wherein,

[0046] The rate of liquid lifting is 12.7 to 21 mbar / s (for example, 12.7 mbar / s, 13 mbar / s, 15 mbar / s, 17 mbar / s, 19 mbar / s, 21 mbar / s, etc., not specifically limited herein), and the pressure of the liquid lifting is 200 ± 10 mbar (for example, 190 mbar, 195 mbar, 200 mbar, 205 mbar, 210 mbar, etc., not specifically limited herein);

[0047] The filling process includes the first and second stages in sequence. The rate of the first stage is 2 to 20 mbar / s (for example, 2 mbar / s, 5 mbar / s, 8 mbar / s, 10 mbar / s, 13 mbar / s, 16 mbar / s, 18 mbar / s, 20 mbar / s, etc., which are not specifically limited herein), and the pressure of the first stage is 240 ± 10 mbar (for example, 230 mbar, 235 mbar, 240 mbar, 245 mbar, 250 mbar, etc., which are not specifically limited herein). The rate of the second stage is 2 to 20 mbar / s (for example, 2 mbar / s, 5 mbar / s, 8 mbar / s, 10 mbar / s, 13 mbar / s, 16 mbar / s, 18 mbar / s, 20 mbar / s, etc., which are not specifically limited herein). The rate is 5-30 mbar / s (for example, 5 mbar / s, 8 mbar / s, 10 mbar / s, 13 mbar / s, 15 mbar / s, 18 mbar / s, 20 mbar / s, 23 mbar / s, 25 mbar / s, 27 mbar / s, 30 mbar / s, etc., not specifically limited herein), and the pressure in the second stage is 310±10 mbar (for example, 300 mbar, 305 mbar, 310 mbar, 315 mbar, 320 mbar, etc., not specifically limited herein);

[0048] The boost rate is 8 to 66.7 mbar / s (for example, 8 mbar / s, 10 mbar / s, 15 mbar / s, 20 mbar / s, 25 mbar / s, 30 mbar / s, 35 mbar / s, 40 mbar / s, 45 mbar / s, 50 mbar / s, 55 mbar / s, 60 mbar / s, 63 mbar / s, 66.7 mbar / s, etc., not specifically limited herein), and the boost pressure is 450 ± 50 mbar (for example, 400 mbar, 430 mbar, 450 mbar, 480 mbar, 500 mbar, etc., not specifically limited herein);

[0049] The pressure holding stage includes a pressure reduction and holding stage and a pressure stabilization stage. The duration of the pressure reduction and holding stage is 35-45 seconds (for example, 35 seconds, 37 seconds, 40 seconds, 43 seconds, 45 seconds, etc., not specifically limited here). The pressure in the pressure stabilization stage is 350±50 mbar (for example, 300 mbar, 330 mbar, 350 mbar, 380 mbar, 400 mbar, etc., not specifically limited here).

[0050] Air cooling starts 35 to 45 seconds (for example, 35 seconds, 38 seconds, 40 seconds, 43 seconds, 45 seconds, etc., not specifically limited here) after the start of pressure maintenance, that is, air cooling starts in the stable pressure maintenance stage, and the air cooling flow rate is 30 to 80m 3 / h(for example: 30m 3 / h、40m 3 / h、50m 3 / h、60m 3 / h、70m 3 / h、80m 3 / h, etc., not specifically limited here), and the duration is at least 200s.

[0051] After the liquid is raised, the mold is filled in sections and the pressure is maintained at a relatively low pressure. At the same time, air cooling begins after a period of pressure maintenance. On the one hand, it can fully reduce the formation of defects such as shrinkage cavities and shrinkage, and improve the density and mechanical properties of low-pressure casting. On the other hand, it can also promote the formation of fine needle-shaped martensite structure, so that the low-pressure cast aluminum alloy chassis has good hardness and strength, as well as good toughness.

[0052] Optionally, during the filling process, the rate in the first stage is lower than the rate in the second stage. Filling the mold at a lower rate first can reduce turbulence generated when the molten aluminum enters the mold cavity in the early stages of filling, thereby reducing the amount of gas entrained in air or molding sand, helping to reduce the formation of pores. It also helps to even out the molten aluminum, thereby helping to form a finer, more uniform grain structure and improve mechanical properties. At the same time, slow early filling can also serve as a preheating agent, helping to reduce temperature differences during subsequent filling and lowering the risk of cracks. Slow early filling also ensures the uniformity of various metal elements in the molten aluminum, which promotes the subsequent elemental uniformity of the entire casting. It can also reduce the impact of the molten aluminum on the mold, which helps protect the mold. Filling the mold at a higher rate afterwards can not only improve production efficiency, but also reduce the oxidation of the molten aluminum, that is, reduce the formation of oxides, and ensure the strength and toughness of the casting; filling at a high rate can also improve the fluidity of the molten aluminum, which helps the molten aluminum to better fill complex or small casting cavities, reduce insufficient pouring or cold shut defects, and improve the efficiency of the riser, that is, it can ensure that the molten aluminum in the riser is quickly replenished to the shrinkage area of ​​the casting, improve the shrinkage feeding efficiency, and reduce the formation of shrinkage cavities and shrinkage porosity; at the same time, increasing the rate in the later stage of filling can also help all parts of the casting to cool simultaneously, reduce the temperature difference between different parts of the casting, and help reduce the occurrence of cracks.

[0053] Optionally, the rate at which the boost pressure drops to the pressure in the stable pressure holding stage is 4.4 to 11.4 mbar / s, that is, the pressure reduction rate in the pressure reduction and pressure holding stage is 4.4 to 11.4 mbar / s, for example: 4.4 mbar / s, 5 mbar / s, 6 mbar / s, 7 mbar / s, 8 mbar / s, 9 mbar / s, 10 mbar / s, 11 mbar / s, 11.4 mbar / s, etc., which is not specifically limited here. Higher boost pressure can more effectively drive the molten aluminum in the riser to flow to the shrinkage area of ​​the casting, especially in the late solidification stage of the casting when the fluidity of the molten aluminum decreases. Boosting can improve the shrinkage feeding efficiency, reduce the formation of shrinkage cavities and shrinkage porosity, and help fill the tiny gaps inside the casting, increase the density of the casting, thereby improving its mechanical properties. At the same time, it helps to reduce the temperature difference between different parts of the casting, reduce thermal stress, and thus reduce the formation of cracks. Properly reducing the holding pressure after boosting can effectively improve the problem of increased internal stress in the casting caused by higher boost pressure, so as to further effectively reduce the problem of deformation or cracking of the casting and ensure the density of the casting.

[0054] Optionally, the pressurization rate is greater than the filling rate. This can improve feeding efficiency. A higher pressurization rate ensures that the molten aluminum in the riser can quickly flow to the areas requiring feeding during solidification, improving feeding efficiency and reducing the formation of shrinkage cavities and porosity. It can also promote aluminum flow. Pressurization increases the fluidity of the molten aluminum, helping it overcome resistance during flow and ensuring it can fully fill all parts of the casting, especially those with small or complex shapes. It can also improve casting density. A high pressurization rate helps reduce voids and pores within the casting, increasing its density and thus improving its mechanical properties. It can also control the solidification sequence, allowing the molten aluminum in the riser to solidify last, providing continuous feeding for the casting and thus improving feeding effectiveness. It can also reduce thermal cracking. A higher pressurization rate helps reduce temperature differences between different parts of the casting, avoiding cracks caused by local overheating. Compared with increasing the pressure to reduce the filling rate, it can improve the problem of excessive filling rate leading to an increase in air holes and sand blasting, and improve the problem of aluminum liquid splashing and excessive turbulence leading to a decrease in casting quality.

[0055] It should be noted that if the pressurization rate is too fast, it will easily lead to higher stress inside the casting, increase the risk of deformation or cracking of the casting, and easily cause the aluminum liquid to flush the surface of the mold, affecting the surface roughness and dimensional accuracy of the casting.

[0056] Optionally, the air cooling step includes a first air cooling stage and a second air cooling stage performed sequentially, and the flow rate of the first air cooling stage is 30-40m 3 / h(for example: 30m 3 / h、32m 3 / h、35m 3 / h、37m 3 / h、40m 3 / h, etc., not specifically limited here), the flow rate of the second air cooling stage is 40~80m 3 / h(for example: 40m 3 / h、50m 3 / h、60m 3 / h、70m 3 / h、80m 3 / h, etc., not specifically limited here); wherein, the flow rate of the first air cooling stage is less than the flow rate of the second air cooling stage, and the time of the first air cooling stage is less than 15s. First, cooling at a low wind speed in a short period of time can achieve a certain pre-cooling effect, which is conducive to achieving uniform cooling at a high wind speed later. Moreover, cooling at a low wind speed in a short period of time can give atoms a certain chance to migrate and form a small amount of lamellar martensite structure. There are certain gaps between the lamellar martensite, which is prone to dislocation movement, thereby increasing the toughness of the casting. However, the slow cooling time is short and will not form a large amount of lamellar martensite structure, thereby avoiding adverse effects on the strength and hardness of the casting. Then, through subsequent high wind speed cooling, the migration of atoms is suppressed, ensuring the formation of fine needle-shaped martensite structure, so that the low-pressure cast aluminum alloy chassis has good hardness and strength, as well as good toughness. Moreover, subsequent rapid cooling at a high wind speed can also reduce the time of the crystallization pressure holding stage, accelerate the cooling and solidification of the product, and shorten the production cycle.

[0057] The present invention will be further described in detail below with reference to specific embodiments.

[0058] Example 1

[0059] The riser tube and the ingrown runner are connected; wherein, the liquid outlet of the riser tube is connected to the inlet of the ingrown runner, the inner diameter of the riser tube gradually decreases from the end away from the ingrown runner to the end close to the ingrown runner, and the inner diameter of the ingrown runner gradually increases from the end close to the riser tube to the end away from the riser tube; the diameter of the liquid outlet is 3mm larger than the diameter of the inlet, and the liquid outlet has a step surface; the angle between the inner wall of the riser tube and its axis is 3°; the diameter of the liquid outlet is 60mm; the angle between the inner wall of the ingrown runner and its axis is 6°.

[0060] Aluminum alloy chassis liquid low pressure casting process steps:

[0061] The rate of liquid rise is 12.7 mbar / s, and the pressure of the liquid rise is 200 mbar;

[0062] The filling process includes the first and second stages in sequence. The rate of the first stage is 2 mbar / s and the pressure of the first stage is 230 mbar. The rate of the second stage is 5 mbar / s and the pressure of the second stage is 300 mbar.

[0063] The boost rate is 8 mbar / s and the boost pressure is 400 mbar;

[0064] Reduce the pressure at a rate of 4.5 mbar / s to 300 mbar and maintain the pressure steadily;

[0065] Air cooling starts at the stable pressure holding stage, and the air cooling flow rate for the first 10 seconds is 30m 3 / h, the air cooling flow rate in the last 190s is 40m 3 / h.

[0066] Example 2

[0067] The riser tube and the ingrown runner are connected; wherein, the liquid outlet of the riser tube is connected to the inlet of the ingrown runner, the inner diameter of the riser tube gradually decreases from the end away from the ingrown runner to the end close to the ingrown runner, and the inner diameter of the ingrown runner gradually increases from the end close to the riser tube to the end away from the riser tube; the diameter of the liquid outlet is 5mm larger than the diameter of the inlet, and the liquid outlet has a step surface; the angle between the inner wall of the riser tube and its axis is 2°; the diameter of the liquid outlet is 55mm; the angle between the inner wall of the ingrown runner and its axis is 7°.

[0068] Aluminum alloy chassis liquid low pressure casting process steps:

[0069] The rate of liquid rise is 21 mbar / s and the pressure of the liquid rise is 210 mbar;

[0070] The filling process includes the first and second stages in sequence. The rate of the first stage is 20 mbar / s and the pressure of the first stage is 250 mbar. The rate of the second stage is 30 mbar / s and the pressure of the second stage is 320 mbar.

[0071] The boost rate is 66.7 mbar / s and the boost pressure is 500 mbar;

[0072] Reduce the pressure at a rate of 11.4 mbar / s to 350 mbar and maintain the pressure steadily;

[0073] Air cooling starts at the stable pressure holding stage, and the air cooling flow rate for the first 12 seconds is 40m 3 / h, the air cooling flow rate in the last 200s is 80m 3 / h.

[0074] Example 3

[0075] The riser tube and the ingrown runner are connected; wherein, the liquid outlet of the riser tube is connected to the inlet of the ingrown runner, the inner diameter of the riser tube gradually decreases from the end away from the ingrown runner to the end close to the ingrown runner, and the inner diameter of the ingrown runner gradually increases from the end close to the riser tube to the end away from the riser tube; the diameter of the liquid outlet is 4mm larger than the diameter of the inlet, and the liquid outlet has a step surface; the angle between the inner wall of the riser tube and its axis is 4°; the diameter of the liquid outlet is 65mm; the angle between the inner wall of the ingrown runner and its axis is 5°.

[0076] Aluminum alloy chassis liquid low pressure casting process steps:

[0077] The rate of liquid rise is 15 mbar / s and the pressure of the liquid rise is 190 mbar;

[0078] The filling process includes the first and second stages in sequence. The rate of the first stage is 10 mbar / s and the pressure of the first stage is 250 mbar. The rate of the second stage is 20 mbar / s and the pressure of the second stage is 310 mbar.

[0079] The boost rate is 40.5 mbar / s and the boost pressure is 450 mbar;

[0080] Reduce the pressure at a rate of 7.8 mbar / s to 330 mbar and maintain the pressure steadily;

[0081] Air cooling starts at the stable pressure holding stage, and the air cooling flow rate for the first 8 seconds is 35m 3 / h, the air cooling flow rate in the last 200s is 50m 3 / h.

[0082] Comparative Example 1

[0083] The difference between Comparative Example 1 and Example 1 is that the riser and the ingrown channel have the same inner diameter and are both straight tubes of equal diameter, with an inner diameter of 60 mm; other process parameters refer to Example 1.

[0084] Comparative Example 2

[0085] The difference between Comparative Example 2 and Example 1 is that the pressurization rate is equal to the rate of the second stage of filling; other process parameters refer to Example 1.

[0086] Comparative Example 3

[0087] The difference between Comparative Example 3 and Example 1 is that the first and second stages of filling are not distinguished, and only the first stage of filling is followed; other process parameters refer to Example 1.

[0088] Comparative Example 4

[0089] The difference between Comparative Example 4 and Example 1 is that the first and second stages of filling are not distinguished, and only the second stage of filling is followed; other process parameters refer to Example 1.

[0090] Comparative Example 5

[0091] The difference between Comparative Example 5 and Example 1 is that the pressure of the pressure-maintaining process is equal to the pressure of the pressure-increasing process; other process parameters refer to those of Example 1.

[0092] Comparative Example 6

[0093] The difference between Comparative Example 6 and Example 1 is that the pressurization rate is 70 mbar / s; other process parameters refer to Example 1.

[0094] Comparative Example 7

[0095] The difference between Comparative Example 7 and Example 1 is that: 3 / h flow rate for 200s; other process parameters refer to Example 1.

[0096] Comparative Example 8

[0097] The difference between Comparative Example 8 and Example 1 is that: the first and second stages of filling are not distinguished, and only the first stage of filling is followed; the rate of pressurization is 70mbar / s, and the pressure is directly 3 / h flow rate for 200s; other process parameters refer to Example 1.

[0098] The castings of each embodiment and comparative example were tested for pores, cracks, tensile strength, yield strength, and elongation. The tensile strength, yield strength, and elongation were measured using an Instron 8801 tensile testing machine. Metallographic microscopy and image analysis were used to analyze the percentage of the area covered by pores and cracks relative to the total area of ​​each embodiment and comparative example with a cross-section size of 10 cm × 10 cm. The results are shown in Table 1.

[0099] Table 1

[0100]

[0101] According to the records in Table 1, by comparing Examples 1-3 with Comparative Example 1, it can be seen that the coordinated cooperation of the reduced diameter riser tube 100 and the expanded diameter ingrown 200 can effectively squeeze out the gas in the molten aluminum, reduce the bubbles in the molten aluminum, and ensure that the molten aluminum rises smoothly in the ingrown 200. That is, after reducing the gas in the molten aluminum, it can be ensured that the molten aluminum can rise smoothly and be filled, thereby fully improving the shrinkage feeding capacity, thereby fully improving the strength and elongation of the product, and reducing cracks.

[0102] Comparing Examples 1-3 and Comparative Example 2, it can be seen that controlling a larger pressurization rate can ensure that the molten aluminum in the riser can quickly flow to the area requiring shrinkage feeding when the casting solidifies, thereby improving the shrinkage feeding efficiency, reducing the formation of shrinkage cavities and shrinkage porosity, thereby reducing cracks, and improving strength and elongation.

[0103] Comparing Examples 1-3 with Comparative Examples 3 and 4, it can be seen that segmented filling can effectively reduce the entrainment of air into the aluminum liquid, helping to reduce the formation of bubbles and thus reduce cracks; it also helps to make the aluminum liquid uniform, thereby helping to form a finer and more uniform grain structure and improve mechanical properties.

[0104] Comparing Examples 1-3 and Comparative Example 5, it can be seen that maintaining pressure at a pressure lower than the boost pressure can reduce the formation of defects such as cracks and improve mechanical strength and elongation.

[0105] Comparing Examples 1-3 and Comparative Example 6, it can be seen that if the pressurization speed is too fast, it is easy to cause higher stress inside the casting, increasing the risk of deformation or cracking of the casting, not only increasing the cracks, but also easily leading to a decrease in mechanical strength and elongation.

[0106] Comparison of Examples 1-3 and Comparative Example 7 shows that direct high-speed air cooling increases the risk of deformation or cracking of the casting, which not only increases the cracks but also easily leads to a decrease in mechanical strength and elongation.

[0107] By comparing Examples 1-3 and Comparative Example 8, it can be seen that the technical solution provided by the present invention can further ensure the reduction of holes and cracks and fully ensure the mechanical strength and elongation by segmented filling, controlling a lower pressurization speed, and a lower cooling speed.

[0108] According to Table 1, it can be seen that the method disclosed in the present invention can effectively reduce the porosity and cracks of the casting, ensure the tensile strength, yield strength and elongation, and ensure good shrinkage feeding ability.

[0109] In summary, the aluminum alloy chassis low-pressure casting method of the present invention can improve the shrinkage compensation capability and reduce the loss of aluminum liquid, thereby achieving the purpose of improving the qualified rate and saving costs.

[0110] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A low-pressure casting method for an aluminum alloy chassis, characterized in that: include: Connecting a liquid riser (100) and an ingrowing (200), wherein the liquid outlet of the liquid riser (100) is connected to the inlet of the ingrowing (200), the inner diameter of the liquid riser (100) gradually decreases from an end away from the ingrowing (200) to an end close to the ingrowing (200), and the inner diameter of the ingrowing (200) gradually increases from an end close to the liquid riser (100) to an end away from the liquid riser (100), and the diameter of the liquid outlet is larger than the diameter of the inlet; The aluminum alloy chassis liquid raising low-pressure casting method includes: liquid raising, mold filling, pressurization, pressure holding and air cooling; wherein, The rate of the liquid rising is 12.7 to 21 mbar / s, and the pressure of the liquid rising is 200 ± 10 mbar; The filling process includes a first stage and a second stage in sequence, wherein the rate of the first stage is 2-20 mbar / s and the pressure of the first stage is 240±10 mbar, and the rate of the second stage is 5-30 mbar / s and the pressure of the second stage is 310±10 mbar; The boosting rate is 8 to 66.7 mbar / s, and the boosting pressure is 450 ± 50 mbar; The pressure holding includes a pressure reduction and pressure holding stage and a stable pressure holding stage. The pressure in the stable pressure holding stage is 350±50mbar, and the time of the pressure reduction and pressure holding stage is 35-45s. The air cooling starts at the stable pressure holding stage, and the flow rate of the air cooling is 30 to 80 m 3 / h conditions, and last for at least 200s.

2. The aluminum alloy chassis low-pressure casting method according to claim 1, characterized in that: The rate of the first stage is smaller than the rate of the second stage.

3. The aluminum alloy chassis liquid rising low pressure casting method according to claim 1, characterized in that: The pressure reduction rate in the pressure reduction and pressure maintenance stage is 4.4-11.4 mbar / s.

4. The aluminum alloy chassis low-pressure casting method according to claim 1, characterized in that: The rate of pressurization is greater than the rate of filling.

5. The aluminum alloy chassis low-pressure casting method according to claim 1, characterized in that: The angle between the inner wall of the rising pipe (100) and its axis is 2-4°; the diameter of the liquid outlet is 55-65 mm.

6. The aluminum alloy chassis low-pressure casting method according to claim 1, characterized in that: The angle between the inner wall of the ingrown channel (200) and its axis is 5-7°.

7. The aluminum alloy chassis low-pressure casting method according to claim 1, characterized in that: The axial height of the liquid riser (100) is greater than the axial height of the ingrown channel (200); and the diameter of the liquid outlet is 3-5 mm larger than the diameter of the inlet.

8. The aluminum alloy chassis low-pressure casting method according to claim 1, characterized in that: A step surface (101) is provided at the junction of the riser pipe (100) and the ingrown channel (200), and the step surface (101) is distributed around the circumference of the inlet.

9. The aluminum alloy chassis low-pressure casting method according to claim 1, characterized in that: The riser tube (100) comprises a riser tube body (110) and a base (120) connected to the outer periphery of the riser tube body (110); the base (120) is provided with an annular groove (121), the annular groove (121) is distributed around the outer periphery of the riser tube body (110), and the annular groove (121) is provided adjacent to the ingrowth (200); the riser tube body (110) is provided with the liquid outlet; An air cooling pipe (300) is provided in the annular groove (121), and the air cooling pipe (300) comprises an annular tube (310) and a plurality of air outlet nozzles (320) connected to the annular tube (310), wherein the plurality of air outlet nozzles (320) are distributed in sequence and spaced apart along the circumference of the annular tube (310), and the air outlet nozzles (320) all blow air toward the bottom of the annular groove (121).

10. The aluminum alloy chassis low-pressure casting method according to claim 1, characterized in that: The air cooling step includes a first air cooling stage and a second air cooling stage performed sequentially, wherein the flow rate of the first air cooling stage is 30-40 m 3 / h, the flow rate of the second air cooling stage is 40~80m 3 / h; wherein, the flow rate of the first air cooling stage is less than the flow rate of the second air cooling stage, and the time of the first air cooling stage is less than 15s and greater than 0s.

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