A method for analyzing die sticking of magnesium alloy profile extrusion

Abstract

A magnesium alloy profile extrusion die sticking analysis method, comprising the following steps: 1) determining the chemical element types of the alloy and the die steel; 2) obtaining the compound composition possibly generated at the interface of all alloys and die steels through a thermodynamic calculation software Thermal-Calc; 3) obtaining the Gibbs free energy size of all possible generated compounds through Thermal-Calc, and inferring the most possible compound generated at the interface of the alloy and the die steel; 4) hot dipping experiment, preheating the die steel and then putting it into the alloy melt with fixed temperature holding; 5) microscopically observing the interface of the die steel and the alloy; 6) analyzing the element distribution of the interface layer by using energy spectrum analysis EDS; 7) combining the results of steps 5) and 6) for judgment. The present application combines thermodynamic calculation, hot dipping interface microscopic characterization and interface element analysis to analyze the die sticking problem in the magnesium alloy profile extrusion process.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy profile extrusion technology, specifically relating to a method for analyzing die sticking during magnesium alloy profile extrusion. Background Technology

[0002] Magnesium alloys have a density only two-thirds that of aluminum alloys, offering advantages such as light weight, high specific strength, good damping and vibration reduction, and excellent electromagnetic shielding performance. They can be widely used in the automotive, aerospace, 3C (computers, communications, and consumer electronics) and defense industries. The research and development and application of magnesium alloys are receiving significant attention worldwide. In recent years, due to improvements in magnesium alloy production capacity and technology, the production cost of magnesium alloy profiles has decreased to a level comparable to that of aluminum alloys. This has greatly stimulated their application in the civilian sector, such as in bicycle frames, wheelchairs, and rehabilitation and fitness equipment, rather than being limited to cutting-edge or defense fields like aerospace. This has significantly broadened the application areas of magnesium alloy profiles, leading to a sharp increase in demand.

[0003] Magnesium alloy profiles are primarily produced through extrusion. However, in actual production, it has been found that some magnesium alloys, especially those with added calcium (Ca), are prone to die sticking during the extrusion process. This phenomenon occurs when the alloy surface adheres to the die steel surface. Die sticking not only degrades the quality of the profile but also makes separation from the die steel difficult, hindering demolding. Furthermore, it reduces production efficiency and increases production costs, thus limiting the large-scale application of magnesium alloy profiles. Therefore, understanding the mechanistic causes of die sticking defects during magnesium alloy profile extrusion is crucial for addressing current defects in magnesium alloy extrusion forming, improving production efficiency, and promoting the large-scale application of these products.

[0004] Currently, analyses of the causes of mold sticking mainly focus on materials, molds, or processes. It is generally believed that the microscopic characteristics of the mold, such as surface hardness, roughness, strength, material composition, and coating, are the primary factors contributing to mold sticking. Some scholars have also analyzed the phenomenon using hot-dip galvanizing. This involves immersing the mold steel in a molten alloy for varying durations, allowing the melt to react with the mold steel surface to form an interface layer. After removing the mold steel and water-cooling it, the width and morphology of the interface layer are analyzed using metallographic (OM) and scanning electron microscopy (SEM) to assess the severity of sticking. Phase diagram analysis is then used to determine the possible compounds formed between the alloy and Fe elements in the mold steel.

[0005] However, in reality, other elements in the die steel may also react with the hot-dip galvanizing process to form compounds, which can lead to die sticking. Therefore, the simple characterization of the hot-dip galvanizing method alone cannot truly explain the interfacial reaction process in die sticking during the extrusion of magnesium alloy profiles.

[0006] Compared to experimental methods, thermodynamic calculations can determine the Gibbs free energy and formation enthalpy of all possible compounds formed between the alloy and the mold steel. By comparing these parameters, researchers can gain a general understanding of which compounds might be formed. New characterization techniques, such as EPMA (electron probe microanalysis), can accurately reflect the types and distribution of elements at the interface, helping researchers analyze the types of compounds at the interface and thus providing a basis for revealing the principles of alloy sticking to the mold. Summary of the Invention

[0007] The purpose of this invention is to provide a method for analyzing die sticking during the extrusion of magnesium alloy profiles. This method combines thermodynamic calculations, microscopic characterization of the hot-dip galvanizing interface, and interface element analysis to analyze the die sticking problem during the extrusion of magnesium alloy profiles. By combining thermodynamic calculations with experimental microscopic characterization analysis, this method can deepen the understanding of the die sticking principle during the extrusion of magnesium alloy profiles.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for analyzing die sticking during extrusion of magnesium alloy profiles, comprising the following steps:

[0010] 1) Determine the types of chemical elements in alloy and die steel;

[0011] 2) In the thermodynamic calculation software Thermal-Calc, select the property diagram module, select the components contained in the alloy and the mold steel, and obtain the composition of all possible compounds that may be generated at the interface between the alloy and the mold steel;

[0012] 3) Calculate the Gibbs free energy of each possible compound as a function of temperature using Thermal-Calc, obtain the Gibbs free energy curves of different compounds, obtain the order of Gibbs free energy of all possible compounds, and infer the most likely compound to be generated at the interface between the alloy and the mold steel.

[0013] 4) Conduct hot-dip galvanizing experiments. After preheating the mold steel, place it in an alloy melt at a fixed temperature for heat preservation. Set different heat preservation times. After the time is up, take out the mold steel and water cool it.

[0014] 5) Conduct microscopic observation of the interface between mold steel and alloy, and analyze the morphology and width of the interface layer, and / or the size, quantity and distribution of the second phase in the interface layer by scanning electron microscopy (SEM) or BSE mode.

[0015] 6) Analyze the elemental distribution of the interface layer using energy dispersive spectroscopy (EDS) to determine which elements are mainly enriched at the interface. Based on the elemental content of EPMA analyzed by electron probe microanalysis and combined with the Gibbs free energy curve results calculated by thermodynamics, comprehensively analyze and determine the specific composition of the products at the interface.

[0016] 7) Combining the analysis results from steps 5) and 6), the following information is obtained:

[0017] ① Whether the alloy composition will stick to the mold can be determined by whether an interface layer appears in the images obtained by SEM or BSE scanning;

[0018] ② The degree of tendency of this alloy composition to stick to the mold is determined by the growth rate of the interface layer based on the thickness of the interface layer and the corresponding holding time. The greater the growth rate, the greater the tendency to stick to the mold.

[0019] ③ By combining Gibbs free energy curves and elemental analysis of EDS or EPMA, the causes of sticking to the mold can be determined.

[0020] Furthermore, the steps for obtaining the Gibbs free energy curve of the compound in step 3) are as follows:

[0021] 3.1 In the Thermal-Calc property graph module, select the corresponding alloy database according to the type of compound, and select the elements of the compound to be calculated;

[0022] 3.2 Define the system size as 1 mol, set the content ratio of each element according to the content of each element in the compound, and set an appropriate temperature range;

[0023] 3.3 Derive the tables of Gibbs free energy and temperature for the system;

[0024] 3.4 Repeat the above steps to derive a table of Gibbs free energy and temperature for all possible compounds, and plot the Gibbs free energy curves for all possible compounds based on the table.

[0025] Furthermore, step 4) of the hot-dip galvanizing experiment is performed as follows:

[0026] 4.1 Place the preheated pure magnesium into a crucible, place it in an electric resistance furnace for heating, and introduce a protective gas mixture of SF6 and CO2 in a ratio of 1:49 to melt the pure magnesium into a liquid state.

[0027] 4.2 Add the intermediate alloy or pure metal containing the alloying elements in sequence, and continue heating until it reaches a completely liquid state;

[0028] 4.3 Process the mold steel into thin sheets, preheat it, and then put it into the melt. Set the resistance furnace temperature and start timing after the temperature reaches the set temperature.

[0029] 4.4 After the set holding time is reached, remove the mold steel sheet from the crucible solution and quickly cool it with water.

[0030] Preferably, in step 4) the hot-dip galvanizing experiment, multiple mold steels can be preheated and then placed in an alloy melt at a fixed temperature for heat preservation, and different heat preservation times can be set. After the time is up, the mold steels can be taken out and water-cooled.

[0031] This invention combines thermodynamic calculations, microscopic characterization of hot-dip galvanizing interfaces, and interface element analysis to analyze the die sticking problem during the extrusion of magnesium alloy profiles.

[0032] Compared with existing methods, the present invention has the following advantages:

[0033] (1) This invention does not consider the microscopic characteristics of the mold or the die casting process, but starts from the interface reaction between the mold and the alloy. By analyzing the reaction between the alloy and the mold interface, it analyzes the cause of sticking from a deeper perspective and reveals the essential behavior of sticking.

[0034] (2) This invention combines thermodynamic calculations and experiments, considers all types of elements in mold steel, predicts all compounds that may be generated at the interface, calculates their Gibbs free energy curves, and combines hot-dip galvanizing experiments and characterization to more accurately analyze the chemical composition of the products generated at the interface, making it more scientific. Attached Figure Description

[0035] Figure 1 A segmented diagram of the Gibbs free energy curves for compounds that may be formed by AZ-based magnesium alloys;

[0036] Figure 2 A segmented diagram of the Gibbs free energy curves for compounds that may form from H13 mold steel;

[0037] Figure 3 The interface morphology and elemental distribution of the Mg-3Al-0.5Zn alloy after holding at a temperature of 0.5 h;

[0038] Figure 4 A schematic diagram of the interface layer after calcium-containing but aluminum-free Mg-1Ca melt and H13 mold steel are kept at a constant temperature for 0.5 h.

[0039] Figure 5 The interface morphology and elemental distribution of the Mg-3Al-0.5Zn-2Ca alloy after holding at a temperature of 0.5 h. Detailed Implementation

[0040] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0041] Example 1

[0042] 1) In this embodiment, AZ-series magnesium alloy and H13 mold steel are selected;

[0043] 2) Using Thermal-Calc software, select the elements Mg, Al, Zn, Ca of AZ series magnesium alloys and Fe, C, Cr, Mn, Si, Mo, V and O from air for H13 mold steel. From the phase and phase composition, the possible compounds that can be generated are Ca2SiO4, CaO, Al2O3, SiO2, MgO, CaMnO3, MnO2, Fe2O3, Al2Fe, Al5Fe2, Al5Fe4, Al13Fe4 and AlFe3;

[0044] 3) Calculate the Gibbs free energy of the possible compounds mentioned above using the property plot module in Thermal-Calc software, with a temperature range of 300~700℃. The results are as follows: Figure 1 As shown;

[0045] 4) Hot-dip galvanizing experiment: Mg-3Al-0.5Zn alloy solution was smelted in an electric resistance furnace using pure magnesium, pure aluminum and pure zinc as raw materials. The protective gas was a mixture of SF6 and CO2 in a ratio of 1:49, and the temperature was set at 710℃. H13 mold steel was processed into thin sheets with a thickness of 2mm, a width of 10mm and a length of 200mm, and placed in the alloy solution. The holding time was set to 0.5h, 1h and 2h. After the holding time was reached, the mold steel sheet was quickly removed and water-cooled.

[0046] 5) Scan and perform energy dispersive spectroscopy analysis on the interface of the hot-dip galvanized coating to obtain the morphology and elemental distribution map of the interface.

[0047] Example 2

[0048] A Mg-3Al-0.5Zn-2Ca alloy solution was smelted in an electric resistance furnace using pure magnesium, pure aluminum, and pure zinc as raw materials. Other steps were the same as in Example 1.

[0049] The following analysis and judgment were made regarding the interfacial adhesion between AZ-based magnesium alloys and H13 mold steel in Examples 1 and 2:

[0050] 1. According to Figure 1 , Figure 2 Considering the elemental content and diffusion capacity, Al and Ca, being present in the magnesium melt, possess strong diffusion capabilities, making them prone to forming Al₂O₃ and CaO at the interface between the magnesium alloy melt and the mold steel. While AlFe has a relatively high compound free energy, Fe is the dominant element in the mold steel, thus increasing the probability of AlFe compound formation. AlFe₃ has the highest Gibbs free energy, making its formation less likely. The Gibbs free energies of the other AlFe compounds are not significantly different. In summary, the most likely compounds to form at the interface between AZ-based magnesium alloys and H13 mold steel are Al₂O₃, CaO, Al₂Fe, Al₅Fe₂, Al₅Fe₄, and Al₂O₃. 13 Several compounds including Fe4 and AlFe3.

[0051] 2. According to Figure 3 In Example 1, after the Mg-3Al-0.5Zn alloy was held at a temperature of 0.5 h, there was no obvious element enrichment at the interface, while from... Figure 4 It can be seen that after 2 hours of heat preservation, there was obvious enrichment of Al at the interface, but no enrichment of O or other elements. Combined with the analysis of the Gibbs free energy curve, it can be concluded that an AlFe compound was formed after 2 hours of heat preservation.

[0052] 3. According to Figure 5 In Example 2, after holding the Mg-3Al-0.5Zn-2Ca alloy at a heat source for 0.5 hours, significant Al segregation was observed at the interface. Figure 2 Compared to Mg-3Al-0.5Zn in Example 1, the segregation of Al was significantly intensified, indicating that the addition of Ca accelerated the enrichment of Al at the interface. Similarly, apart from the segregation of Al, there was no segregation of Ca or other elements at the interface. Combined with the previous analysis of the Gibbs free energy curve, it can also be concluded that AlFe compounds were formed at the interface of the Mg-3Al-0.5Zn-2Ca alloy.

[0053] 4. Based on the above analysis of the Gibbs free energy and hot-dip galvanizing results, it can be concluded that AlFe compounds are generated at the interface between AZ-based magnesium alloys and H13 mold steel. In Mg-3Al-0.5Zn-2Ca, the addition of Ca significantly intensifies the diffusion of Al and promotes the formation of AlFe compounds. In addition, studies have shown that if steel molds are used in the die casting process of aluminum alloys, the tendency of mold sticking is higher than that of magnesium alloys. This is because AlFe compounds are formed at the interface between aluminum alloys and mold steel.

[0054] Therefore, based on the above analysis, the reason why adding Ca during the extrusion process of AZ-based magnesium alloy profiles increases the tendency to stick to the die is that the addition of Ca accelerates the segregation of Al elements at the interface, accelerating the formation of AlFe compounds. The formation of AlFe compounds is the root cause of sticking to the die. Therefore, the addition of Ca increases the tendency to stick to the die during the extrusion process of AZ-based magnesium alloy profiles.

[0055] The above embodiments successfully identified the root cause of the tendency for Ca-added AZ-based magnesium alloy profiles to stick to the die during extrusion using the analytical method of the present invention. However, the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for analyzing die sticking during extrusion of magnesium alloy profiles, characterized in that, Includes the following steps: 1) Determine the types of chemical elements in alloy and die steel; 2) In the thermodynamic calculation software Thermal-Calc, select the property diagram module, select the components contained in the alloy and the mold steel, and obtain the composition of all possible compounds that may be generated at the interface between the alloy and the mold steel; 3) Calculate the Gibbs free energy of each possible compound as a function of temperature using Thermal-Calc, obtain the Gibbs free energy curves of different compounds, obtain the order of Gibbs free energy of all possible compounds, and combine the element content and the diffusion ability of the elements to infer the most likely compound to be generated at the interface between the alloy and the mold steel. 4) Conduct hot-dip galvanizing experiments. After preheating the mold steel, place it in an alloy melt at a fixed temperature for heat preservation. Set different heat preservation times. After the time is up, take out the mold steel and water cool it. 5) Conduct microscopic observation of the interface between mold steel and alloy, and analyze the morphology and width of the interface layer, and / or the size, quantity and distribution of the second phase in the interface layer by scanning electron microscopy (SEM) or BSE mode. 6) Analyze the elemental distribution of the interface layer using energy dispersive spectroscopy (EDS) to determine which elements are mainly enriched at the interface. Based on the elemental content of EPMA analyzed by electron probe microanalysis and combined with the Gibbs free energy change curve calculated by thermodynamics, comprehensively analyze and determine the specific composition of the products at the interface. 7) Combining the analysis results from steps 5) and 6), the following information is obtained: ① Whether the alloy composition will stick to the mold can be determined by whether an interface layer appears in the images obtained by SEM or BSE scanning; ② The degree of tendency of this alloy composition to stick to the mold is determined by the growth rate of the interface layer based on the thickness of the interface layer and the corresponding holding time. The greater the growth rate, the greater the tendency to stick to the mold. ③ By combining the Gibbs free energy change curve and elemental analysis of EDS or EPMA, the cause of the sticking product can be determined.

2. The method for analyzing sticking during extrusion of magnesium alloy profiles as described in claim 1, characterized in that, Step 3) Obtaining the Gibbs free energy change curve of the compound is as follows: 3.1 In the Thermal-Calc property graph module, select the corresponding alloy database according to the type of compound, and select the elements of the compound to be calculated; 3.2 Define the system size, set the content ratio of each element according to the content of each element in the compound, and set the temperature range; 3.3 Derive the tables of Gibbs free energy and temperature for the system; 3.4 Repeat the above steps to derive a table of Gibbs free energy and temperature for all possible compounds, and plot the Gibbs free energy change curves for all possible compounds based on the table.

3. The method for analyzing sticking during extrusion of magnesium alloy profiles as described in claim 1, characterized in that, Step 4) The hot-dip galvanizing experiment is performed as follows: 4.1 Place the preheated pure magnesium into a crucible, place it in a resistance furnace for heating, and introduce a protective gas mixture of SF6 and CO2 to melt the pure magnesium into a liquid state. 4.2 Add the intermediate alloy or pure metal containing the alloying elements in sequence, and continue heating until it reaches a completely liquid state; 4.3 Process the mold steel into thin sheets, preheat it, and then put it into the melt. Set the resistance furnace temperature and start timing after the temperature reaches the set temperature. 4.4 After the heat preservation time reaches the set time, remove the mold steel sheet from the crucible solution and cool it with water.

4. The method for analyzing sticking during extrusion of magnesium alloy profiles as described in claim 1 or 3, characterized in that, Step 4) During the hot-dip galvanizing experiment, multiple mold steels are preheated and then placed in an alloy melt at a fixed temperature for heat preservation. Different heat preservation times are set, and after the time is up, the mold steels are taken out and water-cooled.

Images