Method for online monitoring of solid phase ratio of semi-solid die casting slurry

Abstract

The present invention discloses a method for online monitoring of the solid fraction of a semi-solid die-casting slurry, relating to the field of alloy testing. Specifically, the method comprises: measuring the temperature of the slurry using a non-contact temperature measuring device, and calculating the solid fraction of the slurry according to the Scheil-Gulliver equation. Accordingly, the present invention also discloses a method for determining the stirring time in semi-solid die-casting. The implementation of the present invention enables online monitoring of the solid fraction during actual production, providing a good data foundation for control and parameter optimization of the semi-solid rheo-die-casting process.

Description

Technical Field

[0001] The present invention relates to the field of alloy testing, and in particular to a method for online monitoring of the solid phase ratio of a semi-solid die-casting slurry. Background Art

[0002] Semi-solid forming of metal materials is to apply certain treatments to the liquid metal that is still solidifying (such as changing the thermal state of the metal, increasing the solidification rate of the liquid metal, performing strong stirring disturbance, adding grain refiners, etc.) to change the nucleation and growth mode of the primary solid phase, or more fully destroy its dendritic structure, so as to obtain a solid-liquid mixed slurry in which a certain amount of spherical primary solid phase (its solid phase ratio can reach about 50%) will be evenly suspended in the mother liquid of the molten metal. The semi-solid metal slurry is then directly formed. In the semi-solid rheological die-casting process, if qualified semi-solid molded parts are to be obtained, the rheological properties of the semi-solid slurry need to be strictly and accurately controlled. This property has a decisive influence on the apparent viscosity and rheological properties of the slurry, as well as the porosity, mechanical properties, demolding ease, and mold life of the product.

[0003] However, it's currently impossible to obtain accurate online solid fraction data for traditional semi-solid die-cast products. An existing method involves offline analysis, where products are obtained on the die-casting production line and subjected to metallographic examination. The solid fraction of the slurry during mixing is roughly estimated based on data such as the size, number, and roundness of the spherical particles. This offline method presents challenges, not only because the solid fraction cannot be precisely correlated with the changing slurry temperature, but also because when the solid fraction is low, the solid phase agglomerates. Consequently, the observed solid area fraction on different cross sections varies at different shear rates, making it impossible to accurately estimate the slurry solid fraction. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for online monitoring of the solid phase ratio of semi-solid die casting slurry, which can accurately estimate the solid phase ratio of the slurry in real time and provide a data basis for actual production.

[0005] Another technical problem to be solved by the present invention is to provide a method for determining the stirring time in semi-solid die casting.

[0006] In order to solve the above technical problems, the present invention provides a method for online monitoring of the solid phase ratio of semi-solid die casting slurry, which comprises: measuring the temperature of the slurry using a non-contact temperature measuring device, and calculating the solid phase ratio of the slurry according to the Scheil-Gulliver equation.

[0007] As an improvement to the above technical solution, a non-contact temperature measuring device is used to measure the temperature of the liquid alloy in the holding furnace, the temperature of the liquid alloy in the spoon before stirring, the temperature of the slurry in the spoon after stirring, and the temperature of the slurry in the melting cup of the die-casting machine.

[0008] As an improvement of the above technical solution, the slurry is prepared into a semi-solid slurry using an air-cooled stirring device.

[0009] As an improvement of the above technical solution, the air-cooled stirring device includes a soup spoon for holding the slurry, a mechanical stirring rod, a cooling medium inlet pipe, a cooling medium return pipe and a cooling medium circulation device. One end of the cooling medium inlet pipe is connected to the mechanical stirring rod, and the other end is connected to the cooling medium circulation device. One end of the cooling medium inlet pipe is connected to the mechanical stirring rod, and the other end is connected to the cooling medium circulation device.

[0010] As an improvement of the above technical solution, the non-contact temperature measuring device is a radiation temperature measuring device, a spectrum temperature measuring device, a laser interference temperature measuring device or a microwave temperature measuring device.

[0011] As an improvement of the above technical solution, the non-contact temperature measuring device is an infrared temperature measuring device.

[0012] As an improvement of the above technical solution, the non-contact temperature measuring device is movably connected to the cooling medium inlet pipe.

[0013] Accordingly, the present invention also discloses a method for determining stirring time in semi-solid die casting, which comprises:

[0014] S1: Set the initial stirring time;

[0015] S2: stirring the slurry according to the initial stirring time, measuring the temperature of the slurry after stirring using a non-contact temperature measuring device, and calculating the solid phase ratio of the slurry after stirring according to the Scheil-Gulliver equation;

[0016] S3: Determine whether the solid phase ratio of the slurry after stirring satisfies the solid phase ratio>15%;

[0017] If yes, go to step S4, if no, go to step S5;

[0018] S4: changing the value of the initial stirring time to use it as the new initial stirring time, and repeating steps S2 to S3;

[0019] S5: Determine the initial stirring time as the intermediate stirring time;

[0020] S6: stirring and casting the slurry according to the intermediate stirring time;

[0021] S7: Testing the cast alloy parts;

[0022] S8: Determine whether the test result meets the predetermined result;

[0023] If yes, go to step S9, if no, go to step S10;

[0024] S9: Determine the intermediate stirring time as the final stirring time;

[0025] S10: Change the value of the intermediate stirring time as the new intermediate stirring time, and repeat steps S6 to S8.

[0026] As an improvement to the above technical solution, in step S7, the roundness of the grains in the alloy part is tested.

[0027] As an improvement of the above technical solution, the non-contact temperature measuring device is an infrared temperature measuring device.

[0028] The implementation of the present invention has the following beneficial effects:

[0029] 1. The inventors of this invention have demonstrated through extensive validation experiments that the Scheil-Gulliver equation can accurately predict the solid fraction of a slurry based on temperature. Therefore, by measuring the slurry temperature in real time at each stage, the solid fraction of the slurry at that moment can be determined in real time. This provides a robust data foundation for controlling and optimizing parameters in the semi-solid rheo-diecasting process.

[0030] 2. This method utilizes a non-contact infrared temperature measurement device, which overcomes the shortcomings of thermocouple temperature measurement. Contact thermocouples require heat conduction sensing, resulting in slow response times and hysteresis and averaging effects. Furthermore, the thermocouple protective tube is easily corroded by the molten aluminum, causing short circuits and high operating costs. This method can monitor the temperature of the alloy liquid in real time, precisely controlling the temperature of the semi-solid slurry within a 3°C deviation.

[0031] 3. This invention achieves precise control of the semi-die casting process by measuring the temperature of the molten aluminum in the holding furnace, the slurry temperature before and after stirring, and the slurry temperature at the crucible of the die-casting machine. Furthermore, the optimal stirring time is determined by measuring the slurry temperature before and after stirring and by metallographic examination of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The solid phase ratio of AlSi8 alloy obtained by Scheil-Gulliver equation varies with temperature;

[0033] Figure 2 The curve of solid phase ratio of each phase in AlSi8 alloy obtained by Scheil-Gulliver equation versus temperature;

[0034] Figure 3 This is a confocal laser microscope photo of AlSi8 alloy heated to 613.7°C;

[0035] Figure 4 2 is a schematic structural diagram of an air-cooled stirring device according to an embodiment of the present invention;

[0036] Figure 5 This is the metallographic structure of the alloy obtained after stirring for 10 seconds in the stirring time test of the present invention;

[0037] Figure 6 This is the metallographic structure of the alloy obtained after stirring for 15 seconds in the stirring time test of the present invention;

[0038] Figure 7 This is the metallographic structure of the alloy obtained after stirring for 20 seconds in the stirring time test of the present invention;

[0039] Figure 8 This is the metallographic structure diagram of the alloy obtained after stirring for 25 seconds in the stirring time test of the present invention. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to specific embodiments.

[0041] The invention discloses a method for online monitoring of the solid phase ratio of a semi-solid die-casting slurry, which comprises: measuring the temperature of the slurry by a non-contact temperature measuring device, and calculating the solid phase ratio of the slurry according to the Scheil-Gulliver equation.

[0042] The non-contact temperature measuring device may be, but is not limited to, a radiation temperature measuring device, a spectral temperature measuring device, a laser interferometer temperature measuring device, or a microwave temperature measuring device. A radiation temperature measuring device is preferred, and an infrared temperature measuring device is more preferred. Such a temperature measuring device is free of hysteresis and averaging effects, and can monitor the temperature of the slurry, controlling the temperature measurement error of the semi-solid slurry to within 3°C.

[0043] A non-contact temperature measurement device is used to measure the temperature of the liquid alloy in the holding furnace, the temperature of the liquid alloy in the spoon before stirring, the temperature of the slurry in the spoon after stirring, and the temperature of the slurry in the cup of the die-casting machine. This data enables precise control of the semi-die-casting process.

[0044] Specifically, in a semi-solid slurry, since the diffusion coefficient of the solute in the solid phase is 3-5 orders of magnitude smaller than the diffusion coefficient of the liquid phase, during the cooling process of the slurry, there is almost no diffusion of the solute in the solid phase, while the solute diffusion in the liquid phase is completely sufficient. Therefore, the Scheil equation (Scheil-Gulliver equation) can be used to describe the solute redistribution law during the non-equilibrium solidification process of the alloy, and the volume fraction and mass fraction of each phase at each temperature during the solidification process can be obtained, so that the solid phase ratio can be obtained. For example, the temperature-solid phase ratio curve of the AlSi8 alloy obtained by the present invention is as follows: Figure 1 shown.

[0045] Furthermore, the inventors also verified whether the temperature-solid phase ratio curve can accurately predict the solid phase ratio. Specifically, on the one hand, the present invention detects the metallographic photographs of the final solidification state of the AlSi8 alloy and determines the solid phase mass fraction (solid phase ratio, as shown in the following table) of each phase in the final solidification state as follows: w(Si) = 6.6%, w(Al9Fe2Si2) = 3.4%, w(Al) = 89.8%. In the curve obtained by the theoretical model ( Figure 2 ), the solid mass fraction (solid fraction) of each phase in the final solidified state is: w(Si) = 6.0%, w(Al9Fe2Si2) = 3.0%, w(Al) = 91%. On the other hand, the confocal laser microscopy experiment measured the appearance of ripple flow at 613°C, proving that the liquid phase begins to appear, that is, the solid-liquid transition point is about 613.7°C ( Figure 4 ), which is basically consistent with the theoretical prediction of the solid-liquid transition temperature of 613.1℃ ( Figure 1 ). It can be seen that the experimental results are relatively close to the theoretical calculations, which fully proves that the theoretical calculation of the solid phase ratio by the Scheil model is feasible. While the present invention is based on the calculation of the model, the calculation results are also verified in practice, which illustrates the applicability of the model.

[0046] Table 1 Appendix 1 Volume fraction and mass fraction of each phase obtained by quantitative analysis of AlSi8 metallographic photographs

[0047]

[0048]

[0049] The semi-solid die casting slurry in the present invention is prepared by an air cooling and stirring method. That is, the slurry is prepared into a semi-solid slurry by an air cooling and stirring device. Specifically, refer to Figure 4The air-cooled stirring device includes a spoon 1 for holding the slurry, a mechanical stirring rod 2, a cooling medium inlet pipe 3, a cooling medium return pipe 4, and a cooling medium circulation device 5. One end of the cooling medium inlet pipe 3 is connected to the mechanical stirring rod 2, and the other end is connected to the cooling medium circulation device 5. One end of the cooling medium inlet pipe 3 is connected to the mechanical stirring rod 2, and the other end is connected to the cooling medium circulation device 5. Correspondingly, a non-contact temperature measuring device 6 is movably connected to the cooling medium inlet pipe 3. Through this connection, the non-contact temperature measuring device 6 can relatively easily measure the temperature of the liquid alloy in the holding furnace, the temperature of the liquid alloy in the crucible before stirring, the temperature of the slurry in the spoon after stirring, and the temperature of the slurry in the die-casting machine melting cup.

[0050] In addition, the present invention also discloses a method for determining stirring time in semi-solid die casting, which comprises:

[0051] S1: Set the initial stirring time;

[0052] S2: stirring the slurry according to the initial stirring time, measuring the temperature of the slurry after stirring using a non-contact temperature measuring device, and calculating the solid phase ratio of the slurry after stirring according to the Scheil-Gulliver equation;

[0053] S3: Determine whether the solid phase ratio of the slurry after stirring satisfies the solid phase ratio>15%;

[0054] If yes, go to step S4, if no, go to step S5;

[0055] Preferably, in one embodiment of the present invention, if the solid phase ratio is 15%, the temperature of the slurry after stirring is further determined. If 0 < slurry temperature - solid-liquid phase transition temperature ≤ 2°C, the process proceeds to step S5. If slurry temperature - solid-liquid phase transition temperature > 4°C, the process proceeds to step S4.

[0056] S4: changing the value of the initial stirring time to use it as the new initial stirring time, and repeating steps S2 to S3;

[0057] S5: Determine the initial stirring time as the intermediate stirring time;

[0058] S6: stirring and casting the slurry according to the intermediate stirring time;

[0059] S7: Testing the cast alloy parts;

[0060] Among them, the roundness of the spherical grains in the alloy parts is tested.

[0061] S8: Determine whether the test result meets the predetermined result;

[0062] If yes, go to step S9, if no, go to step S10;

[0063] S9: Determine the intermediate stirring time as the final stirring time;

[0064] S10: Change the value of the intermediate stirring time as the new intermediate stirring time, and repeat steps S6 to S8.

[0065] Furthermore, in order to verify whether the above determination method is feasible, the inventors conducted a stirring time test using AlSi8 alloy, that is, stirring the same slurry with different stirring times, and testing the temperature before and after stirring. Figures 5 to 8 As shown in Table 2.

[0066] Table 2 Temperature changes and microstructure characteristics of semi-solid slurry of AlSi8 alloy at different stirring times

[0067]

[0068] First, referring to Table 2, after a stirring time of 30 seconds, the temperature after stirring reached 605°C (the calculated solid fraction was 18.3% > 15%), so extending the stirring time was not appropriate. Therefore, when the semi-solid slurry was die-cast after stirring, the roundness of the particles was examined. It can be seen that the roundness was highest when the stirring time was 25 seconds, so the optimal stirring time was selected as 25 seconds.

[0069] In addition, it can be seen from Table 2 that when the stirring time is greater than 30s, the roundness of the particles will increase with the increase of the stirring time. This is because as the stirring time increases, the collision intensity and frequency will greatly increase, which is conducive to the breaking of the dendrite arms, and is also conducive to the rounding of the sharp corners of the granular grains, thereby transforming them into nearly spherical grains. However, a long stirring time will cause serious air entrainment in the alloy melt, resulting in more pore defects in the structure, which is not conducive to improving the performance of the formed parts. Moreover, on the production process line, a stirring time that is too long will cause the stirring rod to stick to the mold seriously, which is not conducive to continuous casting. This also shows that the idea of ​​relying solely on the roundness of the particles to determine the stirring time is unreasonable, and the idea of ​​first using the temperature-solid phase ratio curve for determination and then using the roundness of the particles for determination in the present invention is reasonable.

[0070] Also, see Figures 5 to 8 As can be seen from the figure, when the stirring time is 20s, the degree of grain refinement is high, but the grain structure is poor. This shows that the conventional idea of ​​using the degree of grain refinement to determine the stirring time is also unreasonable. The idea of ​​the present invention to first use the temperature-solidity ratio curve for determination and then use the particle roundness for determination is reasonable.

[0071] The above is a preferred embodiment of the invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for determining stirring time in semi-solid die casting, characterized in that: include: S1: Set the initial stirring time; S2: stirring the slurry according to the initial stirring time, measuring the temperature of the slurry after stirring using a non-contact temperature measuring device, and calculating the solid phase ratio of the slurry after stirring according to the Scheil-Gulliver equation; S3: Determine whether the solid phase ratio of the slurry after stirring satisfies the requirement of solid phase ratio>15%; If yes, go to step S4, if no, go to step S5; S4: changing the value of the initial stirring time to use it as the new initial stirring time, and repeating steps S2 to S3; S5: Determine the initial stirring time as the intermediate stirring time; S6: stirring and casting the slurry according to the intermediate stirring time; S7: Testing the roundness of spherical grains in the cast alloy; S8: Determine whether the test result meets the predetermined result; If yes, go to step S9, if no, go to step S10; S9: Determine the intermediate stirring time as the final stirring time; S10: Change the value of the intermediate stirring time as the new intermediate stirring time, and repeat steps S6 to S8.

2. The method for determining the stirring time in semi-solid die casting according to claim 1, wherein: In step S2, a non-contact temperature measuring device is used to measure the temperature of the liquid alloy in the holding furnace, the temperature of the liquid alloy in the spoon before stirring, the temperature of the slurry in the spoon after stirring, and the temperature of the slurry in the melting cup of the die-casting machine.

3. The method for determining stirring time in semi-solid die casting according to claim 1, wherein: In step S2 and step S6, the slurry is prepared into a semi-solid slurry using an air-cooled stirring device.

4. The method for determining the stirring time in semi-solid die casting according to claim 3, wherein: The air-cooled stirring device includes a soup spoon for holding the slurry, a mechanical stirring rod, a cooling medium inlet pipe, a cooling medium return pipe and a cooling medium circulation device. One end of the cooling medium inlet pipe is connected to the mechanical stirring rod, and the other end is connected to the cooling medium circulation device. One end of the cooling medium inlet pipe is connected to the mechanical stirring rod, and the other end is connected to the cooling medium circulation device.

5. The method for determining stirring time in semi-solid die casting according to claim 1, wherein: The non-contact temperature measuring device is a radiation temperature measuring device, a spectrum temperature measuring device, a laser interference temperature measuring device or a microwave temperature measuring device.

6. The method for determining stirring time in semi-solid die casting according to claim 1 or 5, characterized in that: The non-contact temperature measuring device is an infrared temperature measuring device.

7. The method for determining stirring time in semi-solid die casting according to claim 4, wherein: The non-contact temperature measuring device is movably connected to the cooling medium inlet pipe.

8. The method for determining stirring time in semi-solid die casting according to claim 1, wherein: In step S3, if the solid phase ratio = 15%, the temperature of the slurry after stirring is further determined; If 0°C < slurry temperature - solid-liquid phase transition temperature ≤ 2°C, proceed to step S5; if slurry temperature - solid-liquid phase transition temperature > 4°C, proceed to step S4.

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