Method for measuring morphology and position of solidification front in casting process of aluminum alloy

Abstract

A method for testing the morphology and position of a solidification front (4) in a casting process of an aluminum alloy, comprising: preheating a grain refiner (2) to obtain a preheated grain refiner (2); and at a moment A in a casting process, mixing the preheated grain refiner (2) with an aluminum alloy melt (1) flowing through a tundish (5) and continuously injecting the mixture into a casting mold for solidification molding to obtain an aluminum alloy cast ingot (3), and sequentially carrying out longitudinal sectioning, polishing, and etching on part of the aluminum alloy cast ingot (3) in a casting direction passing through the central point of the cross section of the casting mold, thereby visually displaying the morphology and position of the solidification front (4) at the moment A. The method is convenient to operate and easy to implement, and the measurement cost is reduced.

Description

Method for determining the morphology and position of the solidification front during the casting process of aluminum alloys

[0001] This application is based on the Chinese application with CN application number 2023118341090 and application date December 28, 2023, and claims its priority. The disclosed content of the CN application is again introduced as a whole into this application. Technical Field

[0002] The present invention relates to the technical field of aluminum alloy casting, and in particular to a method for measuring the morphology and position of a solidification front during a casting process of an aluminum alloy. Background Art

[0003] Currently, aluminum alloy flat and round ingots for extrusion and rolling are mostly produced using direct water-cooled semi-continuous casting. The main feature of this process is that the liquid metal melt continuously passes through the crystallizer, relying on the crystallizer to achieve metal solidification and constrained shaping. During this production process, the liquid metal area on the upper part of the ingot, surrounded by the crystallization front and the exposed liquid surface of the ingot, is called the liquid pocket (i.e., the solidification front). The shape of the ingot liquid pocket determines the change in the metal crystallization rate in the ingot cross-section, while the depth of the liquid pocket directly reflects the solidification time and solidification rate during the ingot preparation process. Therefore, accurately measuring and adjusting the morphology and position of the solidification front during the casting process is an important indicator and means of reflecting and controlling ingot quality.

[0004] The commonly used method for measuring the morphology and position of the solidification front is the point insertion method. During the casting process, a thin wire or probe is inserted vertically from the molten metal surface into the melt until it contacts the solid phase, then withdrawn. The length of the wire or probe at different locations is measured to determine the position of the solidification front during the casting process. While this method is simple and easy to use, its accuracy is affected by operator experience and the verticality of the probe, resulting in significant errors and inaccurate reflection of changes in the solidification front position. Changes in casting conditions or processes can further increase the error. To compensate for the errors introduced by the wire insertion method, the thermocouple method has emerged. This method involves inserting metal thermocouples online at various locations within the ingot during the casting process. The thermocouples solidify with the ingot, and the temperature changes at these locations are used to reflect the morphology and position of the solidification front during the casting process. This method accurately measures the liquid cavitation value and can quantitatively reflect changes in its morphology and position. However, the metal thermocouple method is complex to operate, and the ingot must be scrapped after measurement, resulting in high costs. When measuring high-strength 7××× and 2××× hard aluminum alloy ingots, the embedded thermocouple increases the stress concentration points inside the ingot, which may cause the ingot to crack or even burst, and the application field is subject to certain restrictions.

[0005] Summary of the Invention

[0006] The main purpose of the present invention is to provide a method for testing the morphology and position of the solidification front during the casting process of aluminum alloy, so as to solve the problems of large errors and high costs in the existing methods for measuring the morphology and position of the solidification front.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for measuring the morphology and position of the solidification front during the casting process of an aluminum alloy is provided. The method comprises: preheating a grain refiner to obtain a preheated grain refiner; at time A in the casting process, mixing the preheated grain refiner with aluminum alloy melt flowing through a runner and continuously injecting the mixture into a casting mold for solidification and forming to obtain an aluminum alloy ingot; wherein the maximum height of the aluminum alloy ingot from the bottom of the casting mold in the casting mold corresponding to time A is denoted as H, and the center point of the cross section of the casting mold at height H is denoted as center point O; and longitudinally sectioning, polishing, and etching a portion of the aluminum alloy ingot along the casting direction through center point O to reveal the morphology and position of the solidification front at time A in the casting process, wherein the maximum height of the longitudinally sectioned portion of the aluminum alloy ingot from the bottom of the casting mold is denoted as L, the diameter of the cross section of the casting mold perpendicular to the casting direction is denoted as φ, and the length of the longitudinally sectioned portion of the aluminum alloy ingot is H'=LH, where H' is 0.1φ to 2φ.

[0008] Furthermore, the mass of the preheated grain refiner and the cross-sectional diameter φ of the casting mold satisfy the following relationship: Where ρ represents the density of the aluminum alloy melt, t A The time after moment A is moment B, and the time of moment B is t B , v cast Indicates the casting speed in the casting mold.

[0009] Furthermore, the mass ratio of the preheated grain refiner to the aluminum alloy melt flowing through the launder is 2-10:1 kg / t.

[0010] Furthermore, in the above-mentioned casting process, the casting process after the casting speed is constant is the stable stage, and the preheated grain refiner is added at different times in the stable stage, and the morphology and position of the solidification front at different times in the stable stage are tested, wherein the thickness H' of the longitudinally sectioned portion of the aluminum alloy ingot is 1φ~2φ, and / or the depth of the solidification front in the stable stage is 0.5φ~1.5φ.

[0011] Furthermore, in the above-mentioned casting process, the casting process before the casting speed reaches a constant value is the initial stage, and the preheated grain refiner is added at different times in the initial stage, and the morphology and position of the solidification front at different times in the initial stage are tested, wherein the thickness H' of the longitudinally sectioned portion of the aluminum alloy ingot is 0.1φ~1φ, and / or the depth of the solidification front in the initial stage is 0~1φ.

[0012] Furthermore, the temperature of the preheating treatment is 350-450°C.

[0013] Furthermore, the model of the above-mentioned aluminum alloy is 7050 or 2024.

[0014] Furthermore, the casting process of the above-mentioned aluminum alloy includes: melting, refining, degassing and standing the aluminum raw material ingot in sequence to obtain an aluminum alloy melt; semi-continuously casting the aluminum alloy melt to obtain an aluminum alloy ingot; the semi-continuous casting process includes a continuous initial stage and a continuous stabilization stage performed in sequence; the temperature of the aluminum alloy melt is 720-740°C, and / or the casting speed in the continuous initial stage is 30-60 mm / min, and after the casting speed linearly increases to 100-125 mm / min within 1 min to 3 min, the continuous initial stage is ended and the continuous stabilization stage is entered.

[0015] Furthermore, cooling water is used to cool the semi-continuous casting process, and the flow rate of cooling water is 4 to 6 m 3 / h, the cooling water temperature is 20~28℃.

[0016] Furthermore, the grain refiner is a rod-shaped grain refiner, which is selected from any one or more of Al-5Ti-B, Al-3Ti-B, and Al-3Ti-0.15C, and / or the length of the rod-shaped grain refiner is 10 to 20 cm.

[0017] Compared to conventional methods for measuring the solidification front morphology and position, the present invention's testing method primarily utilizes an excessive addition of a grain refiner during the casting process (the aluminum alloy melt contains the conventionally added amount of grain refiner required in the art). This method utilizes the enhanced refining effect of the grain refiner and the differences in grain size. After polishing and etching a longitudinally sectioned aluminum alloy ingot, the differences in grain size are utilized to clearly display the solidification front morphology and position during the casting process. This testing method avoids the human error associated with conventional insertion methods for measuring the depth of the solidification front. The present invention provides a more intuitive display of the solidification front morphology and position, significantly improving the accuracy of the measurement results. This allows for a more accurate reflection of the metal crystallization velocity of the aluminum alloy ingot cross section, the solidification time, and the solidification rate of the solidification front during the solidification process of the aluminum alloy melt. This allows for adjustments to the solidification time and rate during the solidification process of the aluminum alloy melt based on the test results, thereby contributing to improved quality of the aluminum alloy ingot. Furthermore, the above testing method is convenient and easy to implement, significantly reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0019] FIG1 shows a schematic diagram of a test process for the morphology and position of the solidification front during the casting process of an aluminum alloy provided in Example 1 of the present application;

[0020] FIG2 is a schematic diagram showing the morphology and position of the solidification front during the casting process (continuous stable stage) of a 7050 aluminum alloy provided in Example 1 of the present application;

[0021] FIG3 is a schematic diagram showing a method of testing the solidification front depth using a thermocouple method according to Comparative Example 2 of the present application.

[0022] The above drawings include the following reference numerals: 1. aluminum alloy melt 1; 2. grain refiner; 3. aluminum alloy ingot; 4. solidification front; 5. runner. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] As analyzed in the background technology of this application, the shape of the solidification front determines the change in the metal crystallization rate of the cross-section of the aluminum alloy ingot, and the depth of the solidification front directly reflects the solidification time and solidification rate during the preparation process of the solidification front ingot. Therefore, accurately measuring and adjusting the morphology and position of the solidification front during the casting of aluminum alloys is an important indicator and means to reflect and control the quality of aluminum alloy ingots. However, the methods for measuring the morphology and position of the solidification front in the existing technology have the problems of large errors and high costs. In order to solve the above problems, the present application provides a method for testing the morphology and position of the solidification front during the casting process of aluminum alloys.

[0025] In a typical embodiment of the present application, a method for measuring the morphology and position of the solidification front during the casting process of an aluminum alloy is provided, the method comprising: preheating a grain refiner to obtain a preheated grain refiner; at time A of the casting process, mixing the preheated grain refiner with the aluminum alloy melt flowing through the flow channel and continuously injecting the mixture into a casting mold for solidification molding to obtain an aluminum alloy ingot; wherein the maximum height of the aluminum alloy ingot from the bottom of the casting mold in the casting mold corresponding to time A is recorded as H, and the center point of the cross-section of the casting mold at the height H is recorded as the center point O; after longitudinally sectioning, polishing, and etching a portion of the aluminum alloy ingot along the casting direction through the center point O, the morphology and position of the solidification front at time A of the casting process can be revealed, the maximum height of the longitudinally sectioned portion of the aluminum alloy ingot from the bottom of the casting mold is recorded as L, the cross-sectional diameter of the casting mold perpendicular to the casting direction is recorded as φ, and the length of the longitudinally sectioned portion of the aluminum alloy ingot is H'=LH, where H' is 0.1φ~2φ.

[0026] Compared with the traditional solidification front morphology and position measurement method, the testing method of the present invention mainly uses the method of excessively adding grain refiners during the casting process (the conventional amount of grain refiners required in the field is added to the aluminum alloy melt), utilizing the enhanced refinement effect of the grain refiners and the difference in refinement effect. After the longitudinal section of the aluminum alloy ingot is polished and corroded, the difference in grain size is used to achieve a clear display of the solidification front morphology and position during the casting process. After adopting the testing method of the present invention, the human error caused by the traditional insertion method when measuring the depth of the solidification front can be avoided. In this application, the morphology and position of the solidification front can be more intuitively displayed, and the accuracy of the measurement results can be significantly improved, so that the metal crystallization rate of the aluminum alloy ingot cross section, the solidification time and solidification rate of the solidification front can be more accurately reflected during the solidification process of the aluminum alloy melt, so that the solidification time and solidification rate during the solidification process of the aluminum alloy melt can be adjusted according to the test results, thereby helping to improve the quality of the aluminum alloy ingot. In addition, the above testing method is easy to operate and easy to implement, which greatly reduces the cost.

[0027] Furthermore, the preheated grain refiner melts rapidly and solidifies within the casting mold along with the aluminum alloy ingot being tested. Specifically, the grain refiner is added at the end of the launder 5 and mixes with the aluminum alloy melt flowing within the launder 5 before entering the casting mold and solidifying along with the aluminum alloy melt. The central longitudinal section of the aluminum alloy ingot is then observed after etching with either an alkaline solution (20% to 30% NaOH solution) or an acid solution (10% to 20% HNO3 solution).

[0028] In one embodiment of the present application, the mass of the preheated grain refiner and the cross-sectional diameter φ of the casting mold satisfy the following relationship: Where ρ represents the density of the aluminum alloy melt, t A The time after moment A is moment B, and the time of moment B is t B , v cast Indicates the casting speed in the casting mold.

[0029] The amount of grain refiner added is related to the size of the aluminum alloy ingot being tested. The larger the ingot, the faster the flow rate of the aluminum alloy melt within the launder 5, and the more grain refiner is added. Preferably, the mass of the preheated grain refiner and the cross-sectional diameter φ of the casting mold satisfy the following relationship. This helps maximize the differences in grain refinement and grain refinement between aluminum alloy ingots of different sizes, thereby enabling testing of the solidification front morphology and position of aluminum alloy ingots of different sizes.

[0030] In one embodiment of the present application, the mass ratio of the preheated grain refiner to the aluminum alloy melt flowing through the launder is 2-10:1 kg / t.

[0031] Adding the grain refiner according to the above ratio and along with the flow of the aluminum alloy melt is more conducive to exerting the uniformity and stability of the grain refiner refinement difference, thereby improving the clarity of the solidification front morphology and position itself.

[0032] Depending on the measurement purpose, grain refiners can be continuously injected at different stages of the casting process, thereby reflecting the changes in the morphology and position of the solidification front at different stages of the casting process, as follows:

[0033] In one embodiment of the present application, in the above-mentioned casting process, the casting process after the casting speed is constant is a stable stage, and the preheated grain refiner is added at different times in the stable stage, and the morphology and position of the solidification front at different times in the stable stage are tested, wherein the thickness H' of the longitudinally sectioned portion of the aluminum alloy ingot is 1φ~2φ, and / or the depth of the solidification front in the stable stage is 0.5φ~1.5φ.

[0034] Controlling the thickness of the longitudinally sectioned portion of the aluminum alloy ingot within the above range helps to more completely reflect the changes in the morphology and position of the solidification front at different times in the stable stage. Preferably, the depth of the solidification front in the stable stage is within the above range, which accurately reflects the starting position of the online annealing applied during the casting process, so as to obtain a balance between forming and loosening control during the casting process.

[0035] In one embodiment of the present application, in the above-mentioned casting process, the casting process before the casting speed reaches a constant value is the initial stage, and the preheated grain refiner is added at different times in the initial stage, and the morphology and position of the solidification front at different times in the initial stage are tested, wherein the thickness H' of the longitudinally sectioned portion of the aluminum alloy ingot is 0.1φ~1φ, and / or the depth of the solidification front in the initial stage is 0~1φ.

[0036] Controlling the thickness of the longitudinally sectioned portion of the aluminum alloy ingot within the above range helps to more completely reflect the changes in the morphology and position of the solidification front at different times in the initial stage. Preferably, the depth of the solidification front in the initial stage is within the above range, which accurately reflects the starting position of the online annealing applied during the casting process, so as to obtain a balance between forming and loosening control during the casting process.

[0037] In one embodiment of the present application, the temperature of the preheating treatment is 350-450°C.

[0038] Preheating the grain refiner can ensure that the grain refiner melts quickly when added to the end of the launder 5. Preheating the grain refiner to the above temperature in a resistance furnace and then keeping it warm can further help improve the accuracy and efficiency of the above test method.

[0039] In one embodiment of the present application, the aluminum alloy is either 7050 or 2024.

[0040] The preferred aluminum alloys of the above types are more suitable for obtaining the morphology and position of the solidification front at different times during the casting process through the above testing method of the present application.

[0041] In one embodiment of the present application, the casting process of the above-mentioned aluminum alloy includes: melting, refining, degassing and standing the aluminum raw material ingot in sequence to obtain an aluminum alloy melt; semi-continuously casting the aluminum alloy melt to obtain an aluminum alloy ingot; the semi-continuous casting process includes a continuous initial stage and a continuous stabilization stage performed in sequence; the temperature of the aluminum alloy melt is 720-740°C, and / or the casting speed in the continuous initial stage is 30-60 mm / min, and after the casting speed linearly increases to 100-125 mm / min within 1-3 minutes, the continuous initial stage is ended and the continuous stabilization stage is entered.

[0042] Controlling the casting process of the aluminum alloy to semi-continuous casting and controlling the casting speed within the above range is more helpful to match the above test method of this application, so as to simply and conveniently obtain the morphology and position of the solidification front at different times during the semi-continuous casting process. Of course, those skilled in the art can also adjust the above specific conditions according to actual conditions, which will not be repeated here.

[0043] In one embodiment of the present application, cooling water is used to cool the semi-continuous casting process, and the flow rate of the cooling water is 4 to 6 m 3 / h, the cooling water temperature is 20~28℃.

[0044] By controlling the flow rate and temperature of the cooling water within the above range, the solidification rate of the aluminum alloy melt of the present application is more consistent with the above test method of the present application, thereby further improving the accuracy of the above test method of the present application.

[0045] In one embodiment of the present application, the grain refiner is a rod-shaped grain refiner, which is selected from any one or more of Al-5Ti-B, Al-3Ti-B, and Al-3Ti-0.15C, and / or the length of the rod-shaped grain refiner is 10 to 20 cm.

[0046] The preferred grain refiners above have excellent refining effects and can melt more quickly after being added to the launder 5 .

[0047] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0048] Example 1

[0049] The test was performed with reference to the schematic diagram of the test flow for the morphology and position of the solidification front during the casting process of the aluminum alloy shown in FIG1 :

[0050] The test method of the present invention mainly includes the following five stages:

[0051] 1) Selection and Preheating of Grain Refiner 2: In this example, the ingot to be tested was a 7050 alloy round ingot. Al-5Ti-B was selected as the grain refiner during the casting process. Preheating the ingot in a resistance furnace enhanced the grain refinement effect and revealed the morphology and position of the solidification front during the casting process. Grain Refiner Preheating: Before casting began, to ensure rapid melting of the grain refiner after adding it to the melt at the end of the launder, multiple rod-shaped Al-5Ti-B grain refiner rods, 10-20 cm in length, were placed in the resistance furnace and preheated to 450°C, then held at that temperature.

[0052] 2) Melting and melt treatment: Place industrial pure aluminum ingots and alloy ingots in an induction furnace at 700°C for melting. After the alloy is melted, transfer it to a heat-insulating standing furnace, and perform furnace refining, degassing and other treatments on the aluminum alloy melt 1. Let it stand for 10 to 20 minutes, and perform semi-continuous casting when the melt temperature drops to 720°C.

[0053] 3) Addition of rod-shaped grain refiner: In this embodiment, the ingot to be tested for the solidification front morphology and position during the casting process is a 7050 round ingot with a diameter of 154 mm. The semi-continuous casting process of the ingot is as follows:

[0054] Before the start of semi-continuous casting, the cooling water flow rate is set to 6m 3 / h, the initial casting speed of the casting machine is 60mm / min, and the speed increases linearly to 100mm / min after the casting process begins. When the ingot length is 1000mm, it enters the continuous stable stage, and the preheated grain refiner is added to the melt at the end of the flow channel 5. That is, the mass of the grain refiner after preheating is 5 kg. At this time, the maximum distance between the aluminum alloy ingot in the crystallizer and the bottom of the crystallizer is recorded to be 1900 mm. The preheated grain refiner enters the crystallizer together with the aluminum alloy melt in the runner 5.

[0055] 4) Display of solidification front morphology and position:

[0056] After casting, a 900-1100 mm section of the aluminum alloy ingot 3 was taken and longitudinally sectioned along the center line. The morphology and position of the solidification front 4 after polishing and etching with 30% NaOH solution were shown in FIG2 . The measured depth of the solidification front was approximately 78 mm.

[0057] Example 2

[0058] The difference from Example 1 is that the cross-sectional diameter φ of the casting mold is 50 mm, and the casting speed v cast The speed is 100mm / min, and the grain refiner is That is, the mass of the grain refiner after preheating is 2.6 kg. After casting, the 950-1050 mm section of the aluminum alloy ingot 3 is taken and longitudinally sectioned along the center line. The morphology and position of the solidification front 4 after polishing and corrosion with 30% NaOH solution are measured. The measured depth of the solidification front is about 25 mm.

[0059] Example 3

[0060] The difference from Example 1 is that the cross-sectional diameter φ of the casting mold is 200 mm, and the casting speed v cast The speed is 100mm / min, and the grain refiner is That is, the mass of the grain refiner after preheating is 8 kg. After casting, the 850-1150 mm section of the aluminum alloy ingot 3 is taken and longitudinally sectioned along the center line. The morphology and position of the solidification front 4 after polishing and corrosion with 30% NaOH solution are measured. The measured depth of the solidification front is about 100 mm.

[0061] Example 4

[0062] The difference from Example 1 is that the mass ratio of the grain refiner to the aluminum alloy melt flowing through the launder after preheating is 2:1 kg / t. After casting, a 900-1100 mm section of the aluminum alloy ingot 3 is taken and longitudinally sectioned along the center line. After polishing and etching with 30% NaOH solution, the morphology and position of the solidification front 4 are measured. The measured solidification front depth is approximately 78 mm.

[0063] Example 5

[0064] The difference from Example 1 is that the mass ratio of the grain refiner to the aluminum alloy melt flowing through the launder after preheating is 10:1 kg / t. After casting, a 900-1100 mm section of the aluminum alloy ingot 3 is taken and longitudinally sectioned along the center line. After polishing and etching with 30% NaOH solution, the morphology and position of the solidification front 4 are measured. The measured solidification front depth is approximately 78 mm.

[0065] Example 6

[0066] The difference from Example 1 is that the mass ratio of the grain refiner to the aluminum alloy melt flowing through the launder after preheating is 1:1 kg / t. After casting, a 900-1100 mm section of the aluminum alloy ingot 3 is taken and longitudinally sectioned along the center line. After polishing and etching with 30% NaOH solution, the morphology and position of the solidification front 4 are measured. The measured solidification front depth is approximately 78 mm.

[0067] Example 7

[0068] 1) Selection and Preheating of Grain Refiner 2: In this example, the ingot to be tested was a 7050 alloy round ingot. Al-5Ti-B was selected as the grain refiner during the casting process. Preheating the ingot in a resistance furnace enhanced the grain refinement effect and revealed the morphology and position of the solidification front during the casting process. Grain Refiner Preheating: Before casting began, to ensure rapid melting of the grain refiner after adding it to the melt at the end of the launder, multiple rod-shaped Al-5Ti-B grain refiner rods, 10-20 cm in length, were placed in the resistance furnace and preheated to 450°C, then held at that temperature.

[0069] 2) Melting and melt treatment: Place industrial pure aluminum ingots and alloy ingots in an induction furnace at 700°C for melting. After the alloy is melted, transfer it to a heat-insulating standing furnace, and perform furnace refining, degassing and other treatments on the aluminum alloy melt 1. Let it stand for 10 to 20 minutes, and perform semi-continuous casting when the melt temperature drops to 720°C.

[0070] 3) Addition of rod-shaped grain refiner: In this embodiment, the ingot to be tested for the solidification front morphology and position during the casting process is a 7050 round ingot with a diameter of 154 mm. The semi-continuous casting process of the ingot is as follows:

[0071] Before the start of semi-continuous casting, the cooling water flow rate is set to 6m 3 / h, the initial casting speed of the casting machine is 60mm / min, 1 minute later, before entering the stable stage, the preheated grain refiner is added into the melt at the end of the launder 5, wherein the preheated grain refiner That is, the mass of the grain refiner is 3 kg. At this time, the maximum distance between the aluminum alloy ingot in the crystallizer and the bottom of the crystallizer is recorded to be 500 mm. The preheated grain refiner enters the crystallizer together with the aluminum alloy melt in the runner 5.

[0072] 4) Display of solidification front morphology and position:

[0073] After casting, a 0-150 mm section of the aluminum alloy ingot 3 was taken and longitudinally sectioned along the center line. After polishing and etching with 30% NaOH solution, the morphology and position of the solidification front 4 were measured. The measured depth of the solidification front was about 20 mm.

[0074] Comparative Example 1

[0075] A common method for measuring the morphology and position of the solidification front is the point insertion method. During the casting process, a thin wire or probe is inserted vertically from the molten metal surface into the melt until it touches the solid phase. The probe is then withdrawn. The length of the wire or probe inserted at different positions is measured to determine the position of the solidification front during the casting process. Table 1 shows the solidification front depth values ​​obtained from five measurements using the point insertion method.

[0076] Table 1

[0077] Comparative Example 2

[0078] In order to compensate for the error caused by the wire insertion method, the thermocouple method came into being. This method is to bury metal thermocouples online at different positions inside the ingot during the casting process. The thermocouples solidify together with the ingot, and the temperature changes of the thermocouples at different positions are used to reflect the morphology and position of the solidification front during the casting process. This method measures the liquid cavity value accurately and can quantitatively reflect its morphology and position changes. As shown in Figure 3, the depth of the solidification front measured by the thermocouple method is 77mm, where T Lis the liquidus temperature, T S is the solidus temperature.

[0079] It should be noted that the method of testing the depth of the solidification front in Comparative Example 2 is highly accurate, but the metal thermocouple method is complicated to operate. After the measurement is completed, the ingot can only be scrapped. In addition, since the embedded thermocouple increases the stress concentration point inside the ingot, it may cause the ingot to crack or even burst, and its application field is subject to certain restrictions.

[0080] In Example 6, the amount of grain refiner added after preheating is relatively low, so the solidification front is not as clear as in Examples 1, 5, and 6.

[0081] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0082] Compared with the traditional solidification front morphology and position measurement method, the testing method of the present invention mainly uses the method of excessively adding grain refiners during the casting process (the conventional amount of grain refiners required in the field is added to the aluminum alloy melt), utilizing the enhanced refinement effect of the grain refiners and the difference in refinement effect. After the longitudinal section of the aluminum alloy ingot is polished and corroded, the difference in grain size is used to achieve a clear display of the solidification front morphology and position during the casting process. After adopting the testing method of the present invention, the human error caused by the traditional insertion method when measuring the depth of the solidification front can be avoided. In this application, the morphology and position of the solidification front can be more intuitively displayed, and the accuracy of the measurement results can be significantly improved, so that the metal crystallization rate of the aluminum alloy ingot cross section, the solidification time and solidification rate of the solidification front can be more accurately reflected during the solidification process of the aluminum alloy melt, so that the solidification time and solidification rate during the solidification process of the aluminum alloy melt can be adjusted according to the test results, thereby helping to improve the quality of the aluminum alloy ingot. In addition, the above testing method is easy to operate and easy to implement, which greatly reduces the cost.

[0083] The above are merely embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for determining the morphology and position of the solidification front during the casting process of an aluminum alloy, characterized in that, The measurement method includes: Preheating the grain refiner to obtain the preheated grain refiner; At moment A during the casting process, mixing the preheated grain refiner with the aluminum alloy melt flowing through the launder and continuously injecting the mixture into a casting mold for solidification molding to obtain an aluminum alloy ingot; Wherein, the maximum height of the aluminum alloy ingot from the bottom of the casting mold at moment A is denoted as H, and the center point of the cross-section of the casting mold at height H is denoted as O center point; After longitudinally cutting, polishing, and etching a part of the aluminum alloy ingot along the casting direction through the O center point, the morphology and position of the solidification front at moment A during the casting process can be revealed. The maximum height of the longitudinally cut part of the aluminum alloy ingot from the bottom of the casting mold is denoted as L, the cross-sectional diameter of the casting mold perpendicular to the casting direction is denoted as φ, and the length of the longitudinally cut part of the aluminum alloy ingot is H' = L - H, where H' is 0.1φ to 2φ.

2. The measurement method according to claim 1, characterized in that, The mass of the grain refiner after preheating and the cross-sectional diameter φ of the casting mold satisfy the following relationship: the where ρ represents the density of the aluminum alloy melt, t A represents the time at moment A, the moment immediately following moment A is moment B, and the time at moment B is represented as t B , v cast represents the casting speed in the casting mold.

3. The measurement method according to claim 1 or 2, characterized in that The mass ratio of the preheated grain refiner to the aluminum alloy melt flowing through the launder is 2 to 10:1 kg / t.

4. The determination method according to claim 1 or 2, characterized in that During the casting process, the casting process after the casting speed becomes a constant value is the stable stage. The preheated grain refiner is added at different moments during the stable stage, and the morphology and position of the solidification front at different moments during the stable stage are tested. Among them, the thickness H' of the longitudinally cut part of the aluminum alloy ingot is 1φ to 2φ, and / or the depth of the solidification front during the stable stage is 0.5φ to 1.5φ.

5. The determination method according to claim 1 or 2, characterized in that During the casting process, the casting process before the casting speed becomes a constant value is the initial stage. The preheated grain refiner is added at different moments during the initial stage, and the morphology and position of the solidification front at different moments during the initial stage are tested. Among them, the thickness of the longitudinally cut part of the aluminum alloy ingot is H' of 0.1φ to 1φ, and / or the depth of the solidification front during the initial stage is 0 to 1φ.

6. The measurement method according to claim 1 or 2, characterized in that The temperature of the preheating treatment is 350 to 450 °C.

7. The determination method according to claim 1 or 2, characterized in that, The type of the aluminum alloy is 7050 or 2024.

8. The determination method according to claim 1 or 2, characterized in that The casting process of the aluminum alloy includes: Successively melting, refining, degassing, and standing the aluminum raw material ingot to obtain an aluminum alloy melt; Performing semi-continuous casting on the aluminum alloy melt to obtain the aluminum alloy ingot; The semi-continuous casting process includes a continuous initial stage and a continuous stable stage that are carried out successively; The temperature of the aluminum alloy melt is 720 to 740 °C, and / or the casting speed during the continuous initial stage is 30 to 60 mm / min. After the casting speed linearly increases to 100 to 125 mm / min within 1 min to 3 min, the continuous initial stage ends and the continuous stable stage is entered.

9. The measurement method according to claim 8, characterized in that, Cooling water is used to cool the semi - continuous casting process, and the flow rate of the cooling water is 4 - 6 m 3 / h, and the temperature of the cooling water is 20 - 28 °C.

10. The determination method according to claim 1 or 2, characterized in that The grain refiner is a rod-shaped grain refiner, and the rod-shaped grain refiner is selected from any one or more of Al-5Ti-B, Al-3Ti-B, and Al-3Ti-0.15C, and / or the length of the rod-shaped grain refiner is 10 to 20 cm.

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