Magnesium alloy casting semi-solid injection molding method and application

Abstract

The invention belongs to the technical field of material processing, and discloses a magnesium alloy casting semi-solid injection molding method and application, and the method comprises the following steps: checking and adjusting a semi-solid injection machine, a casting mold and other equipment to be in a normal state, and placing magnesium alloy particles in a designated area of a hopper; putting a long nozzle of the semi-solid injection platform into the center of a mold sprue; setting the temperature of each section of a mold temperature controller, a charging barrel and a nozzle; preserving heat for a period of time after the temperature of the charging barrel reaches a set value, so that the temperature of materials in the charging barrel is uniform; setting the injection rate, the cooling time, the material return distance and the melt pressure of the semi-solid injection machine; and after a release agent is quantitatively sprayed to the mold, a semi-solid injection program is started, and a casting is obtained. The AS41B magnesium alloy particles with good heat resistance are adopted as the raw material, the semi-solid injection molding method is combined, a melting furnace is not needed, only heating to the semi-solid state is needed, the melt temperature is low, energy is saved, the service life of a mold is prolonged, protective gas is not needed, and the manufactured casting is good in mechanical property and high in heat resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material processing, and particularly relates to a magnesium alloy casting semi-solid injection molding method and application. BACKGROUND

[0002] In recent years, magnesium alloy semi-solid injection process technology has emerged. The principle is that a magnesium alloy ingot is cut into particles with an axial length of 3-6 mm by machining, enters a barrel, and is changed into a semi-solid state through rotation of a screw and heating of the barrel. Then, a mold closing device and an injection seat move forward to close a gate mold. Pressure oil moves the screw forward through an injection cylinder, and at the same time, melts the material at a very high pressure and speed and at a relatively low temperature into the mold. After a certain time of heat preservation and cooling, the mold product is taken out after solidification. The advantages of magnesium alloy semi-solid injection over die casting are: ① low porosity ② easy forming of thin-walled parts ③ long mold life ④ stable filling quality ⑤ high process yield. Compared with liquid die casting, semi-solid injection molding greatly improves the elongation, yield strength and tensile strength of magnesium alloy products.

[0003] The automobile magnesium alloy chain room under cover belongs to a thin-walled shell product, and is produced by using a 950-ton semi-solid injection machine. Magnesium alloy semi-solid materials are mainly magnesium alloy AZ91D and AM60B. However, the automobile magnesium alloy chain room under cover prepared by using the magnesium alloy AZ91D and AM60B through the semi-solid injection molding process has relatively good tensile strength and yield strength, but relatively poor heat resistance. The long-term working temperature requirement of the engine chain room under cover covers the range of-40 DEG C to 130 DEG C. This temperature range is to ensure that the cover material remains stable in performance under the high-temperature environment in the engine compartment, and also needs to have the characteristics of oil resistance, cooling liquid corrosion resistance and the like. As an external part of the engine, the temperature of the cover will be lower than that in the core high-temperature area, but needs to meet the upper limit requirement of 150 DEG C heat resistance, and the magnesium alloy AZ91D and AM60B will slowly creep at this temperature. The under cover is fixed by bolts, and is subjected to the superposition of the bolt pre-tightening force and the engine vibration for a long time. The sealing surface will gradually produce a small deformation, resulting in a large sealing gap originally fitted, and the lubricating oil in the chain room leaks from the sealing gap, causing the "oil leakage" phenomenon. Not only does it pollute the engine compartment, but also causes insufficient lubrication of the chain, and aggravates the wear. When the deformation is serious, the positioning cooperation between the under cover and the cylinder body deviates, which may rub the chain or other moving parts, causing abnormal noise or mechanical damage. SUMMARY

[0004] The application aims to provide a magnesium alloy casting semi-solid injection molding method and application, which uses AS41B magnesium alloy particles with good heat resistance as raw materials, combines the semi-solid injection molding method of the application, does not need a melting furnace, only needs to be heated to semi-solid state, has low melt temperature, saves energy, prolongs the service life of the mold, and does not need a protective gas, meets green manufacturing, and the prepared automobile chain under cover has good mechanical properties and high heat resistance and long service life.

[0005] The specific scheme contents are as follows:

[0006] A magnesium alloy casting semi-solid injection molding method, steps include:

[0007] S1, check the semi-solid injection machine, casting mold and other auxiliary equipment to be in normal state, and place the magnesium alloy particles in the designated area near the hopper;

[0008] S2, adjust the semi-solid injection machine to make the long nozzle enter the center of the mold gate;

[0009] S3, set the temperature of the mold temperature machine, barrel and nozzle;

[0010] S4, after the temperature of the barrel reaches the set value, heat for a period of time to make the temperature of the material in the barrel uniform;

[0011] S5, set the injection rate, cooling time, back material distance and melt pressure of the semi-solid injection machine;

[0012] S6, after the mold is quantitatively sprayed with release agent, start the semi-solid injection program to obtain the casting.

[0013] Further, in step S1, the magnesium alloy particles are AS41B magnesium alloy particles.

[0014] Further, in step S3, the mold cavity of the casting mold is heated by an oil type mold temperature machine, wherein the heating temperature of the moving mold is 230-250℃, and the heating temperature of the static mold is 210-230℃.

[0015] Further, in step S3, the temperature of the first section of the barrel is 480-500℃, the temperature of the second section of the barrel is 480-500℃, the temperature of the third section of the barrel is 600-630℃, and the temperature of the fourth section of the barrel is 600-630℃.

[0016] Further, in step S3, the temperature of the first section of the nozzle is 600-630℃, the temperature of the second section of the nozzle is 600-630℃, the temperature of the third section of the nozzle is 600-635℃, and the temperature of the fourth section of the nozzle is 600-640℃.

[0017] Further, in step S4, the heat preservation time is 10-30min.

[0018] Further, in step S5, the injection rate is gradually increased from a low speed zone 1.2-1.6 m / s, and finally stabilized at 2.3-3.0 m / s, the cooling time is 18-25 s, the back material distance is 130-160 mm, and the melt pressure is 150-200 Bar.

[0019] A magnesium alloy casting semi-solid injection molding method is applied, and the magnesium alloy casting semi-solid injection molding method is prepared, and includes an automobile chain room lower cover.

[0020] Further, the gating system of the automobile chain room lower cover casting is cut off, and mechanical property testing is carried out, the tensile strength of the automobile chain room lower cover is ≥230MPa, the yield strength is ≥130MPa, the elongation is ≥6%, and the creep strain is ≤0.2% under the condition of 150℃-50MPa-100h.

[0021] Further, the automobile chain room lower cover casting is subjected to X-ray flaw detection, and reaches the quality qualified standard of the automobile engine chain room lower cover.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The present application uses AS41B magnesium alloy particles with good heat resistance as raw materials, and combines the semi-solid injection molding method of the present application, without a melting furnace, only the raw material particles need to be heated to semi-solid state, the melt temperature is low, energy saving prolongs the service life of the mold, and without the need for protective gas, reduces the cost and meets the green manufacturing; the prepared automobile chain room lower cover, compared with the die-cast aluminum alloy lower cover, the magnesium alloy lower cover reduces the weight by 31%, realizes lightweight; the tensile strength is ≥230MPa, the yield strength is ≥130MPa, the elongation is ≥6%, and the creep strain is ≤0.2% under the condition of 150℃-50MPa-100h, has excellent mechanical properties and improves the heat resistance, the internal quality is good through X-ray flaw detection, meets the ASTM E505 secondary standard or above. The automobile chain room lower cover prepared by the present application is used in the high temperature environment of the engine compartment for a long time, compared with the automobile chain room lower cover prepared by AZ91D and AM60B, the service life of the lower cover of the present application is longer, and the technical effect is better. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a schematic diagram of the melting curve. DETAILED DESCRIPTION

[0025] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the present application in detail with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0026] The terms used in the present application are merely for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. "Plural" generally includes at least two.

[0027] It should be noted that the terms "front", "back", "inner", "outer", "left", "right" and the like in the present application indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0028] It should be particularly noted that the symbols and numbers present in the specification, if not marked in the description, are not the figure marks.

[0029] The present application provides a magnesium alloy casting semi-solid injection molding method, comprising the following steps:

[0030] S1, check the semi-solid injection machine, casting mold and other auxiliary equipment to be in normal state, and place the magnesium alloy particles in the designated area near the hopper;

[0031] S2, adjust the semi-solid injection machine to enter the mold gate center;

[0032] S3, set the temperature of the mold temperature machine, barrel and nozzle;

[0033] S4, after the barrel temperature reaches the set value, keep warm for a period of time, so that the material temperature in the barrel is uniform;

[0034] S5, set the injection rate, cooling time, back material distance and melt pressure of the semi-solid injection machine;

[0035] S6, after the mold is quantitatively sprayed with release agent, start the semi-solid injection program to obtain the casting.

[0036] In step S1, the magnesium alloy particles are magnesium alloy AS41B particles.

[0037] In the prior art, magnesium alloy AZ91D and AM60B are usually used as raw materials to prepare the under cover of automobile chain. Compared with magnesium alloy AS41B, AZ91D and AM60B, the comprehensive strength of AZ91D is the highest in terms of mechanical properties, and the yield strength and hardness are better than those of the other two, which is suitable for high stress structural parts. The ductility of AM60B is the best, the impact toughness is excellent, and the energy absorption capacity is outstanding. The strength of AS41B is slightly lower, but it has good comprehensive performance, especially suitable for high temperature environment. In terms of heat resistance, the high temperature strength retention rate of AS41B is the highest, which still maintains a high strength at 175℃, and is suitable for high temperature application. The high temperature performance of AZ91D is moderate, and the strength decreases significantly above 120℃. The high temperature strength of AM60B decreases rapidly, and the maximum working temperature is about 120℃. The optimal scheme of the present application uses magnesium alloy AS41B particles as raw materials combined with the preparation method of the present application to prepare the under cover of automobile chain, which takes advantage of its excellent heat resistance. The long-term working temperature requirement of the engine chain under cover is in the range of-40℃ to 130℃. This temperature range is to ensure that the cover material remains stable in performance in the high temperature environment of the engine compartment, and also needs to have the characteristics of oil resistance, corrosion resistance to coolant and the like. As an external part of the engine, the temperature of the cover will be lower than that of the core high temperature area, but it needs to meet the requirement of heat resistance upper limit of 150℃. The under cover prepared by magnesium alloy AZ91D and AM60B will slowly creep at this temperature, and is very prone to deformation and oil leakage. The under cover of the chain prepared by the present application has improved mechanical properties and better heat resistance by using AS41B as raw material combined with the semi-solid injection process of the present application, and meets the working requirements of the under cover of the automobile chain, and has a good service life. The technical scheme of the present application is also applicable to the preparation of other workpieces in high temperature environment.

[0038] In step S3, the mold cavity of the casting is heated by an oil type mold temperature machine, wherein the heating temperature of the moving mold is 230-250℃, and the heating temperature of the static mold is 210-230℃.

[0039] The temperature of the static mold is slightly lower, so that the part close to the static mold solidifies first, forming a directional solidification path from the static mold to the moving mold, which is beneficial to gas discharge and feeding; the high temperature of the moving mold delays local solidification, providing longer feeding time for the casting, significantly reducing internal defects and improving mechanical properties. It can also optimize the demolding performance of the casting, balance the thermal load of the mold, prolong the service life of the mold, and ensure that the characteristics of AS41B magnesium alloy are fully utilized.

[0040] In step S3, the temperature of section 1 of the barrel is 480-500℃, the temperature of section 2 of the barrel is 480-500℃, the temperature of section 3 of the barrel is 600-630℃, and the temperature of section 4 of the barrel is 600-630℃.

[0041] This temperature setting is very suitable for the material change rule of AS41B magnesium alloy semi-solid forming, and the core is to adapt the state transition of the material in the barrel from "solid particles" to "semi-solid slurry" through segmented temperature control, which can ensure smooth conveying and accurately control the semi-solid characteristics.

[0042] In step S3, the temperature of the first section of the nozzle is 600-630 DEG C, the temperature of the second section of the nozzle is 600-630 DEG C, the temperature of the third section of the nozzle is 600-635 DEG C, and the temperature of the fourth section of the nozzle is 600-640 DEG C.

[0043] Through "gradient temperature control", the slurry state in the barrel is connected, the heat loss is compensated, and local abnormalities are avoided, so that the semi-solid slurry is injected into the mold in the best state, and the semi-solid forming requirements of AS41B magnesium alloy are perfectly adapted.

[0044] In step S4, the holding time is 10-30 min.

[0045] This holding time setting perfectly adapts to the state stability requirements of AS41B magnesium alloy semi-solid forming, and through sufficient time, the material realizes thermal uniformity and structural uniformity at the target temperature, avoiding slurry state fluctuations caused by insufficient time.

[0046] In step S5, the injection rate is gradually increased from 1.2-1.6 m / s in the low-speed zone, and finally stabilized at 2.3-3.0 m / s, the cooling time is 18-25 s, the back material distance is 130-160 mm, and the melt pressure is 150-200 Bar. It can avoid common defects (air entrapment, shrinkage, deformation) of semi-solid forming, balance production efficiency and casting precision, and form perfect synergy with the barrel and nozzle temperature before. Every injection of a mold, the melt curve module in the equipment display screen will appear as shown in Figure 1 The front section is controlled below 70 Bar, and the rear end is not more than 180 bar; the process parameters can be adjusted according to the curve trend and display value. The melt back material distance is set according to the forming metering stroke formula, and the formula is as follows: ; wherein: is the product quality (g), is the pipe cross-sectional area (m2), is the material density (kg / m3). . .

[0047] The application also provides a magnesium alloy casting semi-solid injection molding method, which is prepared by the magnesium alloy casting semi-solid injection molding method.

[0048] The gating system of the chain room lower cover casting is cut off, and mechanical property testing is carried out, and the tensile strength is greater than or equal to 230 MPa, the yield strength is greater than or equal to 130 MPa, the elongation is greater than or equal to 6%, and the creep strain is less than or equal to 0.2% under the condition of 150 DEG C-50 MPa-100 h.

[0049] The automobile chain room lower cover casting is subjected to X-ray flaw detection, and meets the ASTM E505 secondary standard or above, reaches the automobile engine chain room lower cover quality qualified standard or above, and meets the actual production use requirement.

[0050] The preparation method can not only be applied to the preparation of the automobile chain room lower cover, but also can be used to prepare other magnesium alloy castings which need to work in a high temperature environment for a long time by using different casting molds.

[0051] The following is combined with Figure 1 The application will be described in detail:

[0052] Example 1:

[0053] Preparation method of AS41B magnesium alloy chain room lower cover:

[0054] 1. Check whether the 950T magnesium alloy semi-solid injection machine, lower cover mold and other auxiliary equipment are in normal state, and after all the equipment are normal, place the AS41B magnesium alloy particles in the designated area near the hopper, and the magnesium alloy particles enter the semi-solid slurry preparation cylinder by relying on negative pressure and gravity, and the semi-solid injection nozzle is aligned with the mold gate;

[0055] 2. The temperature of the mold temperature machine is set to 230 DEG C for the static mold and 240 DEG C for the moving mold;

[0056] 3. The temperature of the cylinder is set to 495 DEG C for the first section, 500 DEG C for the second section, 610 DEG C for the third section and 620 DEG C for the fourth section;

[0057] 4. The nozzle temperature is set to 620 DEG C for the first section, 625 DEG C for the second section, 635 DEG C for the third section and 640 DEG C for the fourth section;

[0058] 5. After the temperature of the molten material in the cylinder reaches the above setting value, heat preservation is carried out for 20 min, so that the temperature of the molten material is uniform.

[0059] 6. The injection rate starts at 1.4 m / s, and the injection rate is gradually increased to finally stabilize at 2.3 m / s. The cooling time is 20 s, the back material distance is 135 mm, and the molten material pressure is 168 Bar.

[0060] 7. The robot finally grasps the casting, and the gating system is automatically cut off to obtain the lower cover blank.

[0061] The obtained lower cover sample is subjected to X-ray flaw detection, mechanical property detection and high temperature creep test to obtain:

[0062] The internal quality is good in X-ray flaw detection, and meets the ASTM E505 first level standard; the tensile strength is 253 MPa, the yield strength is 145 MPa, and the elongation is 8.7%; the creep strain is 0.18% under the condition of 150 DEG C-50 MPa-100 h.

[0063] It can be known from the test result that the automobile chain lower cover casting prepared by the application has high mechanical property and better heat resistance, is suitable for long time use in high temperature environment of an engine, and prolongs the service life.

[0064] Comparative example 1

[0065] The preparation method of the AZ91D magnesium alloy chain lower cover includes the following steps:

[0066] 1. Check whether the 950T magnesium alloy semi-solid injection machine, the lower cover mold and other auxiliary equipment are in normal state, and after all the equipment are normal, place the AZ91D magnesium alloy particles in the designated area near the hopper, and the magnesium alloy particles enter the semi-solid slurry preparation cylinder by relying on negative pressure and gravity, and the semi-solid injection nozzle is aligned with the mold gate.

[0067] 2. The mold temperature machine temperature setting: static mold temperature 230 DEG C, and dynamic mold temperature 240 DEG C.

[0068] 3. The cylinder temperature setting: 1st temperature 495 DEG C, 2nd temperature 600 DEG C, 3rd temperature 600 DEG C, and 4th temperature 600 DEG C.

[0069] 4. The nozzle temperature setting: 1st temperature 600 DEG C, 2nd temperature 600 DEG C, 3rd temperature 600 DEG C, and 4th temperature 590 DEG C.

[0070] 5. After the melt temperature in the cylinder reaches the above setting value, heat preservation is carried out for 20 min, so that the melt temperature is uniform.

[0071] 6. The injection rate can start from 1.4 m / s to make the part, and the injection rate is gradually increased and finally stabilized at 2.3 m / s. The cooling time is 20 s, the back material distance is 135 mm, and the melt pressure is 168 Bar.

[0072] 7. The robot finally grasps the casting, and the lower cover blank is obtained after the gating system is automatically cut off.

[0073] The obtained lower cover sample is subjected to X-ray flaw detection, three-coordinate detection and mechanical property detection; the X-ray flaw detection shows that the internal quality is good, and the tensile strength is 238 MPa, the yield strength is 132 MPa, and the elongation is 6.4%, which meets the ASTM E505 secondary standard; the creep strain is 0.7% under the condition of 150 DEG C-50 MPa-100 h, and the creep strain does not meet the actual production use.

[0074] It can be known from the test results that the mechanical property of the automobile chain room lower cover casting prepared in the comparative example 1 is good, but the heat resistance is poor, and the automobile chain room lower cover casting is not suitable for long-term use in the high-temperature environment of the engine, the service life is short, and the problems such as oil leakage are prone to occur.

[0075] The test results of the samples prepared in the example 1 and the comparative example 1 are listed as follows:

[0076] Tensile strength (MPa) Yield strength (MPa) Elongation (%) Creep strain (%) Flaw detection Example 1 253 145 8.7 0.18 ASTM E505 Grade 1 Comparative Example 1 238 132 6.4 0.7 ASTM E505 Grade 2

[0077] As can be seen from the table, the mechanical property and the heat resistance of the example 1 are higher than those of the comparative example 1, and the automobile chain room lower cover casting is more suitable for long-term use in the high-temperature environment of the engine, the service life is prolonged, and the product quality is improved.

[0078] Compared with the automobile chain room lower cover prepared by using the AZ91D magnesium alloy and the AM60B magnesium alloy as raw materials in the prior art, the mechanical property and the heat resistance of the automobile chain room lower cover prepared by using the AS41B magnesium alloy as raw materials in the preparation method of the application are greatly improved, the automobile chain room lower cover is more suitable for long-term use in the high-temperature environment of the engine, the service life is prolonged, and the product quality is improved. Compared with the die-casting aluminum alloy lower cover, the lower cover of the application is reduced by 31%, and the process yield reaches 64%.

[0079] The above examples are only used to illustrate the technical solutions of the application, but not limit the application; although the application is described in detail with reference to the foregoing examples, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalents; and the modification or replacement does not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solutions of the embodiments of the application.

Claims

1. A semi-solid injection molding method for magnesium alloy castings, characterized in that the steps include... include: S1. Check and adjust the semi-solid injection molding machine, casting mold and other auxiliary equipment to normal condition, and place the magnesium alloy particles in the designated area near the hopper. S2. Adjust the long nozzle of the semi-solid injection stage to enter the center of the mold gate; S3. Set the temperature of each section of the mold temperature controller, barrel, and nozzle; S4. After the barrel temperature reaches the set value, keep it warm for a period of time to ensure that the material temperature inside the barrel is uniform. S5. Set the injection rate, cooling time, return distance, and melt pressure of the semi-solid injection molding machine; S6. After applying a quantitative amount of release agent to the mold, start the semi-solid injection process to obtain the casting.

2. The semi-solid injection molding method for magnesium alloy castings according to claim 1, characterized in that, In step S1, the magnesium alloy particles are magnesium alloy AS41B particles.

3. The semi-solid injection molding method for magnesium alloy castings according to claim 1, characterized in that, In step S3, the mold cavity of the casting is heated by an oil-type mold temperature controller, wherein the heating temperature of the moving mold is 230-250℃ and the heating temperature of the stationary mold is 210-230℃.

4. The semi-solid injection molding method for magnesium alloy castings according to claim 1, characterized in that, In step S3, the temperature of section 1 of the barrel is 480-500℃, the temperature of section 2 of the barrel is 480-500℃, the temperature of section 3 of the barrel is 600-630℃, and the temperature of section 4 of the barrel is 600-630℃.

5. The semi-solid injection molding method for magnesium alloy castings according to claim 1, characterized in that, In step S3, the temperature of nozzle section 1 is 600-630℃, the temperature of nozzle section 2 is 600-630℃, the temperature of nozzle section 3 is 600-635℃, and the temperature of nozzle section 4 is 600-640℃.

6. The semi-solid injection molding method for magnesium alloy castings according to claim 1, characterized in that, In step S4, the heat preservation time is 10-30 minutes.

7. The semi-solid injection molding method for magnesium alloy castings according to claim 1, characterized in that, In step S5, the injection rate gradually increases from a low speed range of 1.2-1.6 m / s to a stable range of 2.3-3.0 m / s, the cooling time is 18-25 s, the return distance is 130-160 mm, and the melt pressure is 150-200 Bar.

8. An application of a semi-solid injection molding method for magnesium alloy castings, characterized in that, The magnesium alloy casting semi-solid injection molding method as described in any one of claims 1-7 is used to prepare the lower cover of the automobile chain chamber.

9. The application of the semi-solid injection molding method for magnesium alloy castings according to claim 8, characterized in that, The gating system of the automotive chain chamber lower cover casting was removed, and its mechanical properties were tested. The tensile strength of the automotive chain chamber lower cover was ≥230MPa, the yield strength was ≥130MPa, the elongation was ≥6%, and the creep strain was ≤0.2% under the conditions of 150℃-50MPa-100h.

10. The application of the semi-solid injection molding method for magnesium alloy castings according to claim 9, characterized in that, X-ray flaw detection was performed on the casting of the lower cover of the automotive engine chain chamber to ensure that it met or exceeded the quality standards for the lower cover of the automotive engine chain chamber.

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