CN110749619A - Method for testing volume change of alloy melt in solidification process - Google Patents
Method for testing volume change of alloy melt in solidification process Download PDFInfo
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Abstract
The invention relates to a method for testing volume change of an alloy melt in a solidification process, which comprises the following steps: 1. placing the alloy to be detected in the center of the vacuum suspension coil; 2. suspending a sample by adopting a high-frequency induction power supply, heating the sample by using laser to heat the sample to be molten, and recording interface change in the solidification process in real time by using a high-speed photographic camera; 3. adopting a computer image segmentation technology to carry out single-sheet analysis on the high-speed photographic picture: graying the picture, and segmenting the sample from the picture according to the difference between the brightness of the suspended sample in the picture and the background; 4. combining the contour lines, displaying the sample and the background by a binary image, rotating the cross section area of the sample for a circle around the y axis to obtain a three-dimensional graph similar to the sample, and calculating the volume; 5. and (3) connecting the volume calculation results of the multiple pictures, arranging the volume calculation results according to the time sequence and corresponding to the temperature curve, so that the volume change of the sample at each moment before and after solidification can be obtained. The invention can directly test and obtain the change rule of the alloy volume under the condition of undercooling solidification.
Description
Technical Field
The invention relates to the technical field of volume change measurement in a metal alloy melt solidification process, in particular to a method for testing volume change of an alloy melt in the solidification process.
Background
The volume change behavior of the alloy solidification process can cause the shrinkage of a casting, and the defects of shrinkage cavity and shrinkage porosity are generated, so that the performance of the alloy is influenced. The main problem is that the temperature of the general alloy in the melting state is higher (generally more than 500 ℃), and the general alloy cannot be tested by a drainage method or an Archimedes principle. At present, the common methods for testing the volume change of the alloy along with the temperature are a thermomechanical analysis method (TMA, which can measure 1000 ℃), a fixed volume mould method and a solidification method in molten salt (which can measure 800 ℃). The TMA method tests displacement of the upper surface of a sample material caused by expansion through a displacement sensor and a graphic recorder, and finally obtains a linear shrinkage rate curve of the material. The method for fixing the volume of the mold is also called as a casting mold method, and is characterized in that redundant alloy liquid poured to the upper end of the mold is scraped by a scraper, and then the volume difference between the volume of the alloy liquid in the mold and the volume of a sample after solidification is measured, so that the volume difference before and after the solidification of the alloy is obtained. The method for measuring the volume change of the alloy in the solidification process is a method which is widely applied at present and is used for measuring the volume change of the alloy in the solidification process. Although the method can dynamically measure the volume change of the alloy in the solidification process, the method can only measure the volume change of the supercooled molten metal at present under 800 ℃ due to the limitation of molten salt components, and the volume change of the supercooled molten metal cannot be measured because the alloy liquid is easy to nucleate in the molten salt.
The methods are not applicable to the rapid solidification process of molten metal, and more importantly, the methods need to be in direct contact with alloy liquid, so that the melt is hardly supercooled, and the volume change of the supercooled melt cannot be tested.
Disclosure of Invention
The invention aims to provide a method for testing volume change of an alloy melt in a solidification process, and aims to solve the problems that the change rule of the alloy volume when the alloy melt is solidified under a supercooled condition cannot be directly tested, test data are inaccurate, and test steps are troublesome in the prior art.
In order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a method for testing volume change of an alloy melt in a solidification process, comprising the following steps:
firstly, placing an alloy to be detected in the center of a vacuum suspension coil;
secondly, suspending the sample by adopting a high-frequency induction power supply, heating the sample by using laser to ensure that the sample is heated and melted, and recording interface change in the solidification process in real time by using a high-speed camera;
thirdly, performing single-sheet analysis on the high-speed photographic picture by adopting a computer image segmentation technology: graying the picture, and segmenting the sample from the picture according to the difference between the brightness of the suspended sample in the picture and the background;
and fourthly, displaying the sample and the background by combining the contour line and the binary image, rotating the cross section area of the sample for a circle around the y axis to obtain a three-dimensional graph similar to the sample, and calculating the volume.
And step five, the volume calculation results of the multiple pictures are related and arranged according to the time sequence and correspond to the temperature curve, and the volume change of the sample at each moment before and after solidification can be obtained (figure 6).
In the third step, the difference between the brightness of the sample and the background is separated through a gray level histogram, and the contour line of the sample is found out by searching for a threshold value point on the gray level histogram.
In the fourth step, the coil used by the suspended sample is circular, and the lateral projection is obtained from the picture, so that the lateral cross section of the sample is firstly layered according to the minimum pixel unit, each layer is composed of a line of white pixel points, and the left and right boundaries of the white points can be counted to obtain the imageObtaining the number of pixels of each row of the sample area 2riHalf of the total number, i.e. the length r of the radius of the lineiThe pixel volume of this layer is then π ri 2Then, the volume calculation results of each layer are added up to obtain the volume (pixel volume) of the whole sample, which is equivalent to the volume of the stereogram obtained by rotating the cross section around the y-axis, and then the actual volume of the sample can be obtained by a scale.
In the fourth step, the sample volume calculating step comprises: the formula for calculating the sample volume using discrete integration is as follows:
r in the above formula1,r2……riRespectively the pixel radius of each layer from top to bottom of the lateral cross section of the sample, and V is the volume.
Compared with the prior art, the method has the advantages that:
1. the method can directly test and obtain the change rule of the alloy volume under the condition of supercooling solidification;
2. because the planar graph is shot by adopting a high-speed photography technology and the lateral cross-sectional shape of the sample is obtained by adopting a computer image segmentation technology, a method for obtaining the volume of a space object by a cross-sectional rotation integration method is provided, and the test data is more accurate for the object with a circular coil suspended;
3. the invention applies the image processing technology to the volume measurement in the solidification process of the alloy melt, thereby greatly simplifying the steps of other technology assistance required by the prior method for accurate test;
4. the algorithm for performing gray threshold segmentation on the alloy sample picture, extracting the contour line, obtaining the size of the section and obtaining the sample volume through section rotation integral is simple and feasible and has high calculation speed.
5. The method is simple and easy to implement, and is a new method in image segmentation.
6. The method has wide application range: the device can be used for testing and researching the volume change of various metal alloys capable of being subjected to suspension smelting along with the temperature change, and can be used for measuring the volume change of various alloys before and after solidification in the process of solidifying liquid melts, wherein the volume change comprises aluminum alloy, steel, nickel alloy and the like.
Description of the drawings:
FIG. 1 is a suspension diagram of an alloy sample;
fig. 2 is a picture of a suspension smelting Al-Si alloy obtained by a high-speed camera during a solidification process under a Δ T of 181K;
FIG. 3 is a method of obtaining a sample cross-sectional profile from a picture of a suspended sample;
FIG. 4 is a perspective view of a sample reproduced by section rotation;
FIG. 5 is a schematic diagram of a cross-sectional volume calculation of a rotated sample;
FIG. 6 is a graph of the volume of the sample obtained by calculation as a function of time during the coagulation process.
The specific implementation mode is as follows:
the invention is further described below with reference to the figures and specific examples.
The design principle of the invention is as follows: after the sample is heated and melted by the vacuum electromagnetic suspension furnace, a high-speed camera shoots a picture of the solidification process, and matlab is used for image analysis and processing: high-speed photography-grey scale analysis-sample boundary extraction-sample volume calculation-volume data analysis before and after solidification.
The invention provides a method for testing volume change of an alloy melt in a solidification process, which comprises the following steps:
firstly, placing an alloy to be detected in the center of a vacuum suspension coil (figure 1);
secondly, suspending the sample by adopting a high-frequency induction power supply, heating the sample by using laser to ensure that the sample is heated and melted, and recording the change of the surface of the suspended sample in the solidification process in real time by using a high-speed camera (figure 2);
thirdly, performing single-sheet analysis on the high-speed photographic picture by adopting a computer image segmentation technology (figure 3 a): the picture is grayed (fig. 3b), the sample projection is segmented from the picture through the difference between the brightness of the suspended sample in the picture and the background, the difference can be separated more accurately through a gray histogram (fig. 3c), and the contour line of the sample can be found out by searching a threshold point on the gray histogram (fig. 3 d).
And step four, combining the contour lines, displaying the sample and the background by using a binary image (figure 4a), rotating the cross section area of the sample around the y axis for one circle to obtain a three-dimensional image similar to the sample, and performing volume calculation (figure 4 b). Since the coil used to suspend the sample is circular, the sample should be circular when viewed longitudinally and elliptical when viewed laterally due to gravity we obtain a lateral projection from the photograph, and thus the above method of calculating volume by rotating the cross-section is relatively accurate. The specific volume calculation principle is shown in fig. 5. The cross section of the side surface of the sample is layered according to the minimum pixel unit, each layer is composed of a line of white pixel points, and the number of the pixels in each line of the sample area can be obtained by counting the left and right boundaries of the white pixel pointsiHalf of the total number, i.e. the length r of the radius of the lineiThe pixel volume of this layer is then π ri 2Then, the volume calculation results of each layer are added up to obtain the volume (pixel volume) of the whole sample, which is equivalent to the volume of the stereogram obtained by rotating the cross section around the y-axis, and then the actual volume of the sample can be obtained by a scale. The accuracy of this method can be demonstrated by experimental results (fig. 6), and very small temperature differences, volume changes with temperature can be measured.
In this step, the sample volume is calculated by: firstly, obtaining a contour line and a section image of a sample through a sample boundary, and then calculating the volume of the sample by adopting a discrete integration method, wherein the formula is as follows:
r1 and r2 … … ri in the above formula are the pixel radii of each layer from top to bottom of the lateral section of the sample, respectively, and V is the volume, see fig. 4.
And step five, the volume calculation results of the multiple pictures are related and arranged according to the time sequence and correspond to the temperature curve, so that the volume change of the sample at each moment before and after solidification can be obtained, and the figure 6 is shown.
Claims (4)
1. A method for testing volume change of an alloy melt in a solidification process is characterized by comprising the following steps:
firstly, placing an alloy to be detected in the center of a vacuum suspension coil;
secondly, suspending the sample by adopting a high-frequency induction power supply, heating the sample by using laser to ensure that the sample is heated and melted, and recording interface change in the solidification process in real time by using a high-speed camera;
thirdly, performing single-sheet analysis on the high-speed photographic picture by adopting a computer image segmentation technology: graying the picture, and segmenting the sample from the picture according to the difference between the brightness of the suspended sample in the picture and the background;
step four, combining the contour lines, displaying the sample and the background by a binary image, rotating the cross section area of the sample for a circle around the y axis to obtain a three-dimensional graph similar to the sample, and calculating the volume;
and step five, the volume calculation results of the multiple pictures are related and arranged according to the time sequence and correspond to the temperature curve, and the volume change of the sample at each moment before and after solidification can be obtained.
2. The method of claim 1, wherein in step three, the brightness and background difference of the sample is separated by a gray histogram, and the contour line of the sample is found by searching for a threshold point on the gray histogram.
3. The method for measuring the volume change of an alloy melt during solidification according to claim 1 or 2, wherein in the fourth step, the coil for suspending the sample is circular, and the lateral projection is obtained from the photograph, so that the lateral cross section of the sample is first divided into minimum pixel unitsEach layer is composed of a line of white pixel points, and the number of the pixels in each line of the sample area can be obtained by counting the left and right boundaries of the white pointsiHalf of the total number, i.e. the length r of the radius of the lineiThe pixel volume of this layer is then π ri 2Then, the volume calculation results of each layer are added up to obtain the pixel volume of the whole sample, which is equivalent to the volume of the three-dimensional figure obtained by surrounding the cross section by one circle around the y axis, and then the actual volume of the sample can be obtained by a scale.
4. The method for measuring the volume change of the alloy melt in the solidification process according to claim 3, wherein in the fourth step, the sample volume calculating step comprises: the formula for calculating the sample volume using discrete integration is as follows:
r in the above formula1,r2……riRespectively the pixel radius of each layer from top to bottom of the lateral cross section of the sample, and V is the volume.
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| CN116140593A (en) * | 2023-02-10 | 2023-05-23 | 西北工业大学 | Control method for solidification condition of electrostatic suspension alloy melt |
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