Lift liquid low-pressure casting method for aluminum alloy chassis

Abstract

The invention relates to the field of low-pressure casting, in particular to an aluminum alloy chassis liquid rising low-pressure casting method which comprises the steps that a liquid rising pipe is connected with an ingate, a liquid outlet of the liquid rising pipe is connected with an inlet of the ingate, and the inner diameter of the liquid rising pipe is gradually reduced from the end away from the ingate to the end close to the ingate; the inner diameter of the ingate is gradually increased from the end close to the liquid rising pipe to the end away from the liquid rising pipe, and the caliber of the liquid outlet is larger than that of the inlet. By directly connecting the riser tube with the ingate, the configuration of a sprue and a cross gate is reduced, and the flowing path of molten aluminum is shortened, so that the loss of pressure transmitted to the body mold is reduced, the feeding capability is favorably improved, and the attachment of the molten aluminum on the sprue and the cross gate is reduced, namely the loss of the molten aluminum is reduced.

Description

Technical Field

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

[0002] Compared with traditional gravity casting, low-pressure casting has controllable filling speed, stable aluminum liquid flow and reduced secondary inclusions. Compared with sand casting, metal mold casting has fast cooling speed, is easier to obtain fine and dense structure and high mechanical properties, and is easier to achieve automated and clean production. Therefore, metal mold low-pressure casting is widely used in the production of aluminum alloy wheels, chassis parts, engine parts and other automotive parts production fields and aerospace and other military production fields. Low-pressure casting usually includes process stages such as liquid lifting, filling, pressurization, pressure holding 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 objects of the present invention include, for example, providing a method for low-pressure casting of an aluminum alloy chassis by liquid lifting, which 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.

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

[0006] The present invention provides a method for casting an aluminum alloy chassis by liquid lifting at low pressure, comprising: connecting a liquid lifting pipe and an ingrate, wherein a liquid outlet of the liquid lifting pipe is connected to an inlet of the ingrate, an inner diameter of the liquid lifting pipe gradually decreases from an end away from the ingrate to an end close to the ingrate, an inner diameter of the ingrate gradually increases from an end close to the liquid lifting pipe to an end away from the liquid lifting pipe, and a diameter of the liquid outlet is larger than a 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 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 8-66.7 mbar / s, and the boost pressure is 450±50 mbar;

[0011] The pressure holding process includes a pressure-reducing 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-reducing and pressure-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 condition, 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 ingrowth 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 ingrowth; 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 and the ingrown, and the step surface is distributed around the circumference of the inlet.

[0020] In an optional embodiment, the riser includes a riser body and a base connected to the outer circumference of the riser body, the base is provided with an annular groove, the annular groove is distributed around the outer circumference of the riser body, and the annular groove is arranged adjacent to the ingrate; the riser body is provided with a liquid outlet;

[0021] An air cooling pipe is arranged in the annular groove, and the air cooling pipe comprises an annular pipe and a plurality of air outlet nozzles connected to the annular pipe. The plurality of air outlet nozzles are distributed in sequence along the circumference of the annular pipe at intervals, and the air outlet nozzles all 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 30-40 m / s. 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 aluminum alloy chassis low-pressure casting method of the embodiment of the present invention include, for example: by directly connecting the riser pipe and the entrapment, the configuration of the straight runner and the cross runner is reduced, the flow path of the aluminum liquid 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 aluminum liquid to the straight runner and the cross runner, that is, reducing the loss of aluminum liquid.

[0024] At the same time, the inner diameter of the riser pipe gradually decreases from the end away from the ingrow to the end close to the ingrow, so that the riser pipe conveys molten aluminum to the ingrow in the form of reduced diameter, which can increase the pressure of the molten aluminum when conveying to the ingrow and reduce the bubbles in the molten aluminum; while the inner diameter of the ingrow gradually increases from the end close to the riser pipe to the end away from the riser pipe, and the diameter of the liquid outlet is larger than the diameter of the inlet, so that the ingrow is set to expand the diameter for conveying, which can make the molten aluminum entering the ingrow rise steadily after reducing the gas. In this way, after reducing the gas in the molten aluminum, it can be ensured that the molten aluminum can rise steadily and fill up, so as to fully improve the shrinkage compensation capacity.

[0025] The aluminum alloy chassis low-pressure casting method for liquid raising provided in an embodiment of the present invention, after liquid raising, also adopts a segmented method to fill the mold, and maintains the pressure at a relatively low pressure, and starts air cooling after maintaining the pressure for a period of time. 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 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 drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

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

[0028] Figure 2 It is a 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 pouring channel; 300-air cooling pipe; 310-annular pipe; 320-air outlet nozzle. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 here 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 claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are 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, further definition and explanation thereof is not required in subsequent drawings.

[0033] In the description of the present invention, it should be noted that if the terms "inside" or "outside" appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the invention is usually placed when in use. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, if the terms "first" or "second" appear, they are only used to distinguish the description, and cannot be understood 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 rising, comprising: connecting a liquid rising pipe 100 and an ingrate 200, wherein the liquid outlet of the liquid rising pipe 100 is connected to the inlet of the ingrate 200, the inner diameter of the liquid rising pipe 100 gradually decreases from an end away from the ingrate 200 to an end close to the ingrate 200, the inner diameter of the ingrate 200 gradually increases from an end close to the liquid rising pipe 100 to an end away from the liquid rising pipe 100, and the diameter of the liquid outlet is larger than the diameter of the inlet.

[0036] By directly connecting the riser 100 and the ingode 200, that is, the riser 100, the ingode 200 and the cast chassis body are directly connected and then connected to the riser, the configuration of the sprue and the runner is reduced, and the ceramic body between the riser 100 and the chassis body mold is eliminated, shortening the path of the aluminum liquid flow, thereby reducing the loss of pressure transmitted to the body mold, which is beneficial to improving the shrinkage compensation capacity and reducing the adhesion of aluminum liquid to the sprue and the runner, that is, reducing the loss of aluminum liquid. In addition, the sprue and the runner are eliminated, and the process of painting the sprue and the runner is also reduced, which is beneficial to improving production efficiency and reducing costs.

[0037] At the same time, the inner diameter of the riser 100 gradually decreases from the end away from the ingrow 200 to the end close to the ingrow 200, so that the riser 100 conveys the aluminum liquid to the ingrow 200 in the form of a reduced diameter, which can increase the pressure of the aluminum liquid when conveyed to the ingrow 200, squeeze out the gas in the aluminum liquid, and reduce the bubbles in the aluminum liquid; and the inner diameter of the ingrow 200 gradually increases from the end close to the riser 100 to the end away from the riser 100, and the diameter of the liquid outlet is larger than the diameter of the inlet, so that the ingrow 200 is set to expand the diameter for conveying, which can make the aluminum liquid entering the ingrow 200 after reducing the gas rise steadily. In this way, after reducing the gas in the aluminum liquid, it can be ensured that the aluminum liquid can rise steadily and fill up, so as to fully improve the shrinkage compensation capacity.

[0038] It should be noted that by directly connecting the riser 100 and the ingrate 200, the runners and sprues 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 required clamping force of 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 is not specifically limited here; the diameter of the liquid outlet is 55-65mm, for example: 55mm, 58mm, 60mm, 63mm, 65mm, etc., which is not specifically limited here. Such a configuration can, on the one hand, increase the pressure of the aluminum liquid when the riser tube 100 transports the aluminum liquid to the inner runner 200, so as to squeeze out the gas in the aluminum liquid, reduce the bubbles mixed in the aluminum liquid, so as to reduce the formation of defects such as shrinkage cavities and shrinkage, and improve the shrinkage compensation capacity; on the other hand, it can also ensure that the transportation of the aluminum liquid will not be adversely affected, 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. Such a configuration can ensure that the aluminum liquid entering the ingrow 200 rises smoothly without rising too fast, which is conducive to fully reducing the formation of defects such as shrinkage cavities and shrinkage porosity, and improving the shrinkage compensation capability.

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

[0042] Optionally, the diameter of the liquid outlet is 3-5 mm larger than the diameter of the inlet, for example, 3 mm, 4 mm, 5 mm. When the aluminum liquid flows from the larger liquid outlet to the smaller inlet, a certain slow flow effect can be formed to prevent the aluminum liquid from entering the inner runner 200 in the direction of gushing, thereby causing the problem of holes formed during casting, thereby further reducing the formation of defects such as shrinkage cavities and shrinkage porosity, and improving the shrinkage compensation capability.

[0043] Optionally, the junction of the riser 100 and the ingrate 200 has a step surface 101, and the step surface 101 is distributed around the circumference of the inlet. The setting of the step surface 101 can ensure the slow flow effect formed when the aluminum liquid flows from the outlet to the inlet, that is, the step surface 101 can form a certain blocking and buffering effect on the aluminum liquid flowing from the outlet to the inlet, that is, the aluminum liquid in the riser 100 can enter the ingrate 200 from the inlet under the guidance of the step surface 101, thereby improving the problem of aluminum liquid entering the ingrate 200 in the direction of gushing, resulting in the formation of holes in casting, thereby further reducing the formation of defects such as shrinkage cavities and shrinkage porosity, and improving the shrinkage compensation capability.

[0044] Optionally, see Figure 1 and Figure 2 The riser 100 includes a riser body 110 and a base 120 connected to the outer periphery of the riser 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 body 110, and the annular groove 121 is arranged adjacent to the inner runner 200; the riser 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 periphery of the riser 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 arrangement, on the one hand, can make the wind blow toward the ingrate 200 and the mold connected to the ingrate 200, which is beneficial to improve the efficiency of air cooling, and on the other hand, 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 aluminum alloy chassis low-pressure casting method of this embodiment includes: liquid raising, mold filling, pressurization, pressure maintenance and air cooling; wherein,

[0046] The rate of liquid lifting is 12.7-21 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 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 a first stage and a second stage 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 20 mbar / s. 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 here), 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 here);

[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 includes a pressure-reducing and pressure-holding stage and a stable pressure holding stage, wherein the time of the pressure-reducing and pressure-holding stage is 35-45s (for example, 35s, 37s, 40s, 43s, 45s, etc., not specifically limited here), and the pressure of the stable pressure holding stage is 350±50mbar (for example, 300mbar, 330mbar, 350mbar, 380mbar, 400mbar, 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 at the stable pressure maintenance stage, and the air cooling flow rate is 30 to 80 m 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 stages 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 martensitic 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 of the first stage is lower than that of the second stage. Filling the mold at a lower rate first can reduce the turbulence generated when the aluminum liquid enters the mold cavity in the early stage of filling, thereby reducing the amount of gas drawn into the air or molding sand, which helps to reduce the formation of pores; it also helps to make the aluminum liquid uniform, thereby helping to form a finer and more uniform grain structure and improve mechanical properties; at the same time, slow early filling can also play a preheating role, which is beneficial to reduce the temperature difference of subsequent filling and reduce the risk of cracks; slow filling in the early stage can also ensure the uniformity of each metal element in the aluminum liquid, which is beneficial to promote the element uniformity of the entire casting later, and can reduce the impact of aluminum liquid on the mold, which is beneficial to protect the mold. Then, filling the mold at a higher rate can not only improve production efficiency, but also reduce the oxidation of 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 molten aluminum, which helps the molten aluminum to better fill complex or small casting cavities, reduce under-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 compensation 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 down at the same time, reduce the temperature difference between different parts of the casting, and help reduce the occurrence of cracks.

[0053] Optionally, the rate at which the pressure of the boost pressure drops to the pressure of 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. A 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 stage of solidification of the casting, when the fluidity of the molten aluminum decreases. The boost pressure can improve the shrinkage compensation efficiency, reduce the formation of shrinkage cavities and shrinkage porosity, and help fill the tiny gaps inside the casting, improve the density of the casting, thereby improving its mechanical properties, and help reduce the temperature difference between different parts of the casting, reduce thermal stress, and thus reduce the formation of cracks. Appropriately reducing the holding pressure after boost pressure can effectively improve the problem of increased internal stress of the casting under 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 rate of pressurization is greater than the rate of filling. In this way, the shrinkage compensation efficiency can be improved, that is, a higher pressurization rate can ensure that the aluminum liquid in the riser can quickly flow to the area that needs shrinkage compensation when the casting solidifies, improve the shrinkage compensation efficiency, and reduce the formation of shrinkage cavities and shrinkage porosity; it can also promote the flow of aluminum liquid, that is, pressurization can increase the fluidity of aluminum liquid, help aluminum liquid overcome resistance during the flow process, and ensure that aluminum liquid can fully fill various parts of the casting, especially those small or complex areas; at the same time, it can improve the density of the casting, that is, a high pressurization rate helps to reduce the voids and pores inside the casting, improve the density of the casting, and thus improve its mechanical properties; control the solidification sequence, that is, the aluminum liquid in the riser can be solidified last, providing continuous shrinkage compensation for the casting, thereby improving the shrinkage compensation effect; reduce thermal cracks, that is, a larger pressurization rate helps to reduce the temperature difference between different parts of the casting and avoid 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 pores and sand flushing, and improve the problem of aluminum liquid splashing and excessive turbulence, which leads 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 30-40 m / s. 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 time can achieve a certain pre-cooling effect, which is conducive to the subsequent uniform cooling at a high wind speed, and low wind speed cooling in a short time can give atoms a certain chance to migrate and form a small amount of lath-shaped martensite structure. There are certain gaps between the lath-shaped martensite, which is prone to dislocation movement, thereby increasing the toughness of the casting, but the slow cooling time is short and will not form a large amount of lath-shaped martensite structure, 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, and good toughness. Moreover, subsequent rapid cooling at 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 ingrowth are connected; wherein, the liquid outlet of the riser tube is connected to the inlet of the ingrowth, the inner diameter of the riser tube gradually decreases from the end away from the ingrowth to the end close to the ingrowth, and the inner diameter of the ingrowth 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 ingrowth 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 liquid rise is 200 mbar;

[0062] The filling process includes the first stage and the second stage 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 for the last 190s is 40m 3 / h.

[0066] Example 2

[0067] The riser tube and the ingrowth are connected; wherein, the liquid outlet of the riser tube is connected to the inlet of the ingrowth, the inner diameter of the riser tube gradually decreases from the end away from the ingrowth to the end close to the ingrowth, and the inner diameter of the ingrowth 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 ingrowth 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 liquid rise is 210 mbar;

[0070] The filling process includes the first stage and the second stage 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] The pressure was reduced at a rate of 11.4 mbar / s to a stable pressure of 350 mbar;

[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 ingrowth are connected; wherein, the liquid outlet of the riser tube is connected to the inlet of the ingrowth, the inner diameter of the riser tube gradually decreases from the end away from the ingrowth to the end close to the ingrowth, and the inner diameter of the ingrowth 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 ingrowth 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 liquid rise is 190 mbar;

[0078] The filling process includes the first stage and the second stage 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 ingrowth have the same inner diameter and are both straight tubes of equal diameter, and the inner diameter is 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 stage and the second stage 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 stage and the second stage 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 maintenance is equal to the pressure of the pressure boosting; other process parameters refer to 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 70 mbar / s, and the pressure is directly increased at 50 mbar / s. 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 holes, cracks, tensile strength, yield strength and elongation, wherein the tensile strength, yield strength and elongation were measured using an Instron 8801 tensile testing machine; metallographic microscope observation and image analysis were used to analyze the percentage of the area covered by holes and cracks in each embodiment and comparative example with a cross-sectional size of 10 cm×10 cm to the total area; 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 known that the coordinated cooperation of the reduced diameter riser 100 and the expanded diameter ingrowth 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 ingrowth 200. That is, after reducing the gas in the molten aluminum, it can be ensured that the molten aluminum can rise and fill smoothly, so as to fully improve the shrinkage compensation capacity, thereby fully improving the strength and elongation of the product and reducing cracks.

[0102] By 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 compensation when the casting solidifies, thereby improving the shrinkage compensation efficiency, reducing the formation of shrinkage cavities and shrinkage porosity, thereby reducing cracks, and improving strength and elongation.

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

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

[0105] By 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] Comparing Examples 1-3 and Comparative Example 7, it can be seen 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 compensation capability.

[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 only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for casting aluminum alloy chassis by low pressure casting, characterized in that: include: Connecting a liquid riser (100) and an ingrate (200), wherein the liquid outlet of the liquid riser (100) is connected to the inlet of the ingrate (200), the inner diameter of the liquid riser (100) gradually decreases from an end away from the ingrate (200) to an end close to the ingrate (200), the inner diameter of the ingrate (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 comprises: liquid raising, mold filling, pressurization, pressure holding and air cooling; wherein, The rate of the liquid rising is 12.7-21 mbar / s, and the pressure of the liquid rising is 200±10 mbar; The filling includes a first stage and a 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; The boosting rate is 8-66.7 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 30-80m 3 / h condition, and last for at least 200s.

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

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

7. The aluminum alloy chassis liquid rising 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 ingrate (200); and the diameter of the liquid outlet is 3-5 mm larger than the diameter of the inlet.

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

9. The aluminum alloy chassis liquid rising 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 circumference 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 circumference of the riser tube body (110), and the annular groove (121) is arranged adjacent to the ingrate (200); the riser tube body (110) is provided with the liquid outlet; An air cooling pipe (300) is arranged 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 liquid rising 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 which are performed sequentially. The flow rate of the first air cooling stage is 30-40 m / s. 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.

Images