Method for preparing high-strength heat-resistant die-casting Mg-Gd-Zr series alloy by regulating and controlling physical property parameters

Abstract

The invention discloses a method for preparing a high-strength heat-resistant die-casting Mg-Gd-Zr alloy by regulating physical parameters, and relates to the technical field of alloy die-casting processing. According to the method for researching and developing the die-casting high-strength heat-resistant Mg-Gd-Zr alloy by adjusting the Gd / Y ratio, the Zn / RE ratio and the Al content in the Mg-Gd-Zr alloy, the feasibility of the scheme is preliminarily verified through low-cost gravity casting starting from alloy component screening, a large number of elements beneficial for improving the fluidity of the alloy are screened in combination with thermodynamic calculation and dynamic calculation, and the high-strength heat-resistant Mg-Gd-Zr alloy is obtained. On the basis of keeping high strength, the die casting defects are reduced, the elongation of the alloy is improved, finally, the high-strength heat-resistant Mg-Gd-Zr alloy subjected to high-pressure die casting is successfully prepared, and the technology starts from the alloy, improves the alloy flowability, reduces the defects brought in the die casting process and improves the alloy performance.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy die-casting processing, and specifically to a method for preparing a high-strength and heat-resistant die-cast Mg-Gd-Zr series alloy by regulating physical properties parameters. Background Art

[0002] Magnesium and magnesium alloys are regarded by materials experts as the green engineering materials with the greatest development and application potential in the 21st century, and in recent years, they have begun to replace aluminum or steel in some cases. Due to their low density, high specific strength, electromagnetic shielding, vibration damping and recyclability, magnesium alloys have become promising materials for various engineering applications in the fields of aerospace, automotive, biomedical and 3C (computers, communications and consumer electronics). High-pressure die-casting of magnesium alloys is a forming technology that injects liquid magnesium alloys into molds and cools and solidifies them under high pressure. Magnesium alloy die-casting has the advantages of high production efficiency, low production cost, high product density and stable performance. Die-casting is one of the important processes for manufacturing magnesium alloy products and is also the most widely used processing technology at present. Die-cast magnesium alloys account for a quite large proportion of the total amount of magnesium alloy products. However, at the same time, high-pressure die-castings also have problems such as insufficient strength, significant deterioration of high-temperature performance and insufficient elongation, which greatly affect the wide use of high-pressure die-castings.

[0003] Adding rare earths to magnesium alloys can bring many benefits, such as (i) improving high-temperature performance by forming precipitates and intermetallic compounds with high melting points and high stability, (ii) enhancing fluidity and casting performance by forming low-melting eutectics, (iii) purifying the melt, improving the microstructure, and enhancing the hot deformation ability, and (iv) producing stronger precipitation and dispersion strengthening effects. In addition, adding rare earth elements (especially Gd, Y) to magnesium alloys can form unique second phases, thereby improving the strength of the material and its performance in specific applications. Therefore, Mg-RE alloys have been widely studied, especially the Mg-Gd-Y-Zn-Zr series. Although Mg-RE alloys are costly, their high strength has led to their widespread application, especially in critical fields such as aerospace and defense. For example, WE43 and Mg-Nd-Zn-Zr alloys have been studied and applied to orthopedic implants (stents and screws). Mg-Y-Nd-Zr and Mg-3Nd-1Gd-0.4Zn-0.5Zr alloys are accepted for use in jet engines and military aircraft, and the WE43C alloy can also be used as structural components such as aircraft seats and integrated reduction gearboxes. Using the Mg-3Nd-1Gd-0.4Zn-0.5Zr alloy can enable military helicopters to achieve faster speeds at higher temperatures. The Mg-10Gd-3Y-0.5Zr alloy has been incorporated into certain types of weapons, such as lightweight missiles and radar components. In addition, Mg-RE alloys also play an irreplaceable role in automotive manufacturing parts, such as the V6 engine block made of the Mg-2.85Nd-0.18Zn-0.45Zr alloy.

[0004] Traditional Mg-RE series alloy materials have achieved certain success in die-casting technology applications, but there are still many deficiencies. For example, the Mg-RE series alloy has poor fluidity. During the solidification shrinkage process, dendrites are likely to be generated, providing channels for gas entrainment and easily causing more casting problems (such as porosity, shrinkage porosity, and shrinkage cavity). High-pressure die-cast Mg-RE series alloys are generally used directly without heat treatment because heat treatment will cause micropores to expand, resulting in dimensional deformation and surface blistering of the castings, but this also severely limits the performance improvement of high-pressure die-cast Mg-RE series alloys. In addition, inevitable die-casting defects (such as hot cracking, cold shut, misrun, inclusion, porosity, and looseness) in high-pressure die-cast Mg-Gd-Zr series alloys with high rare-earth content will seriously reduce the mechanical properties and stability of the castings. Among these defects, porosity and shrinkage porosity are common casting defects in high-pressure die-cast Mg-Gd-Zr series magnesium alloys. To eliminate these defects, currently, the most common methods are to be equipped with a die-casting vacuum system, reasonably select die-casting process parameters, select coatings with good performance, control the spraying amount, appropriately increase the pouring temperature, and shorten the filling time, etc. However, these methods do not start from the root of the problem and have high costs. The present invention fundamentally optimizes the alloy composition, ensures the high strength of the alloy through alloy composition optimization, reduces defects such as porosity by screening alloying elements that improve fluidity, and improves the plasticity of the alloy.

[0005] Therefore, to solve the defects that are likely to occur in Mg-Gd-Zr series alloys, a new solution is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing high-strength and heat-resistant die-cast Mg-Gd-Zr series alloys by regulating physical property parameters. Starting from the alloy composition, by combining thermodynamics calculations, the Gd / Y ratio, Zn / RE ratio, and Al content in the Mg-Gd-Zr series alloys are adjusted, so as to prepare high-strength and heat-resistant Mg-Gd-Zr series alloys for high-pressure die-casting, and to solve the technical problems proposed in the background technology.

[0007] To achieve the above purpose, the present invention provides the following technical solution: A method for preparing high-strength and heat-resistant die-cast Mg-Gd-Zr series alloys by regulating physical property parameters, which at least includes the following steps:

[0008] S1: Screen out a magnesium alloy system that can meet the high-strength and heat-resistant conditions as the basic magnesium alloy system;

[0009] S2: To solve the problems of insufficient strength and plasticity existing in the basic magnesium alloy system, screen out strengthening elements with corresponding high solid solubility to form a primary strengthened magnesium alloy;

[0010] S3: Since the primary strengthened magnesium alloy still cannot completely solve the problems of insufficient strength and plasticity, a new element needs to be introduced at this time to improve the performance, thereby obtaining a secondary strengthened magnesium alloy;

[0011] S4: When die-casting the secondary strengthened magnesium alloy, it is found that the alloy retains some gas porosity and shrinkage porosity. Although the alloy with optimized composition has high strength, its plasticity is still very low. It is determined that the reason affecting plasticity is the high content of defects, and the defects at least include gas porosity and shrinkage porosity. During the tensile deformation process, the defects act as crack sources, leading to premature failure and fracture of the secondary strengthened magnesium alloy, deteriorating the plasticity, and further worsening the mechanical properties of the secondary strengthened magnesium alloy. In order to further eliminate the defects, elements that help improve the thermal physical properties and fluidity of the alloy are screened;

[0012] S5: Combining thermodynamics calculations, starting from the solid-liquid phase line interval, viscosity, and latent heat, elements with the best improvement in the thermal physical properties and fluidity of the alloy are screened. Based on this element and the secondary strengthened magnesium alloy, the final alloy is obtained, which has high strength and excellent elongation at the same time.

[0013] Furthermore, the base alloy system used in S1 is the Mg-9Gd-0.5Zr alloy. Through experiments, it is known that the strength and plasticity of this alloy are insufficient.

[0014] Furthermore, S2 at least includes the following steps:

[0015] Strengthening elements with high solid solubility in magnesium alloy are screened through Pandat calculations, and finally determined to be Y element;

[0016] Set different Gd / Y ratios, and optimize the Gd / Y ratio in combination with the experimental results;

[0017] The primary strengthened magnesium alloy is determined to be the Mg-9Gd-3Y-0.5Zr alloy.

[0018] Furthermore, S3 at least includes the following steps:

[0019] Based on the primary strengthened magnesium alloy system, Zn element is introduced;

[0020] Fine-tune the Zn / RE ratio to control the content and type of the second phase in the alloy;

[0021] The secondary strengthened magnesium alloy system is finally determined to be the Mg-9Gd-3Y-1.5Zn-0.5Zr alloy.

[0022] Furthermore, the elements that help improve the thermal physical properties and fluidity of the alloy in S4 at least include Li, Sr, Bi, Al, B, Ca, Si, and Mn.

[0023] Further, the element finally screened out in S5 is the Al element.

[0024] Further, the final alloy is Mg-9Gd-3Y-1.5Zn-0.5Zr-2Al.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The present invention realizes a method for developing a high-strength and heat-resistant Mg-Gd-Zr series alloy that can be die-cast by adjusting the Gd / Y ratio, Zn / RE ratio, and Al content in the Mg-Gd-Zr series alloy. Starting from the screening of alloy components, the feasibility of the scheme is initially verified by low-cost gravity casting, combined with thermodynamic calculations and kinetic calculations, a large number of elements that help improve the fluidity of the alloy are screened, reducing die-casting defects while maintaining high strength, and improving the elongation of the alloy. Finally, a high-strength and heat-resistant Mg-Gd-Zr series alloy for high-pressure die-casting is successfully prepared. This technology starts from the alloy itself, improves the fluidity of the alloy, reduces the defects brought during the die-casting process, and improves the alloy performance, which has a positive promoting effect on guiding the high-pressure die-casting of high-rare-earth-content magnesium alloys, producing high-quality die-castings, and promoting the method of high-pressure die-casting of magnesium alloys, and has great commercial value and application prospects;

[0027] 2. The present invention does not need to repeatedly adjust die-casting process parameters to reduce defects, effectively avoiding the occurrence of trial-and-error experiments, and shortening the production cycle and production cost;

[0028] 3. The present invention starts from the alloy composition, optimizes the fluidity, reduces the generation of defects such as air holes, and does not require the assistance of high vacuum, which can greatly reduce the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0030] Figure 1 It is the fluidity diagram of Mg-9Gd-3Y-1.5Zn-0.5Zr-zAl of the present invention;

[0031] Figure 2 It is the mechanical property diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0033] Please refer to Figure 1 and Figure 2 , a method for preparing a high-strength and heat-resistant die-cast Mg-Gd-Zr series alloy by regulating physical properties parameters includes at least the following steps:

[0034] S1: Screen out a magnesium alloy system that can meet the high-strength and heat-resistant conditions as the base magnesium alloy system;

[0035] S2: To solve the problems of insufficient strength and plasticity in the base magnesium alloy system, screen out strengthening elements with high solid solubility and form a primary strengthened magnesium alloy;

[0036] S3: Since the primary strengthened magnesium alloy still cannot completely solve the problems of insufficient strength and plasticity, a new element needs to be introduced at this time to improve the performance, and then a secondary strengthened magnesium alloy is obtained;

[0037] S4: When die-casting the secondary strengthened magnesium alloy, it is found that the alloy retains some porosity and shrinkage porosity. Although the alloy after optimizing the composition has high strength, its plasticity is still very low. It is determined that the reason affecting plasticity is the large number of defects, and the defects at least include porosity and shrinkage porosity. During the tensile deformation process, the defects act as crack sources, resulting in premature failure and fracture of the secondary strengthened magnesium alloy, making the plasticity worse, and further deteriorating the mechanical properties of the secondary strengthened magnesium alloy. In order to further eliminate the defects, screen out elements that are helpful for improving the thermal physical properties parameters and fluidity of the alloy;

[0038] S5: Combining thermodynamics calculations, calculate from the solid-liquid phase line interval, viscosity and latent heat, screen out elements with the best improvement in the thermal physical properties parameters and fluidity of the alloy, and obtain the final alloy based on this element and the secondary strengthened magnesium alloy. This alloy has high strength and excellent elongation at the same time.

[0039] The base alloy system used in S1 is the Mg-9Gd-0.5Zr alloy. Through experiments, it is known that the strength and plasticity of this alloy are insufficient.

[0040] S2 includes at least the following steps:

[0041] Screen out strengthening elements with high solid solubility in magnesium alloys through Pandat calculations, and finally determine the Y element;

[0042] Set different Gd / Y ratios and optimize the Gd / Y ratio in combination with the experimental results;

[0043] The primary strengthened magnesium alloy is determined to be the Mg-9Gd-3Y-0.5Zr alloy.

[0044] S3 includes at least the following steps:

[0045] Based on the primary strengthened magnesium alloy system, introduce Zn element;

[0046] Fine-tune the Zn / RE ratio to control the content and type of the second phase in the alloy;

[0047] The secondary strengthened magnesium alloy system is finally determined as Mg-9Gd-3Y-1.5Zn-0.5Zr alloy.

[0048] The elements that help improve the thermal physical properties and fluidity of the alloy in S4 include at least Li, Sr, Bi, Al, B, Ca, Si, and Mn.

[0049] The element selected in S5 is Al element.

[0050] The final alloy is Mg-9Gd-3Y-1.5Zn-0.5Zr-2Al.

[0051] Starting from the alloy composition, the present invention screens out the Mg-Gd-Zr series alloy that meets high performance and has heat-resistant conditions. Although the Mg-Gd-Zr series alloy with a high content of rare earth can solve the heat-resistant problem, different Gd / Y ratios will lead to differences in performance. Therefore, through the Mg-Gd-Y series alloy with different Gd / Y ratios, the Mg-9Gd-3Y-0.5Zr alloy with the optimal performance was screened. To further improve the strength, it is crucial to introduce LPSO. Adding Zn to the Mg-Gd-Y alloy helps to form a long-period stacking order (LPSO) structure during solidification. LPSO can be divided into types such as 6H, 10H, 14H, 18R, 24R, etc. Among them, 18R and 14H are the two most common LPSO phases. However, the Zn / RE ratio will also affect the type and strength of the second phase in the alloy. Therefore, based on the Mg-9Gd-3Y-0.5Zr alloy, the microstructure of the alloy was regulated by fine-tuning the Zn / RE ratio, and then the Mg-9Gd-3Y-1.5Zn-0.5Zr alloy with the best mechanical properties was screened. However, die casting defects will inevitably occur in the Mg-9Gd-3Y-1.5Zn-0.5Zr alloy with a high content of rare earth. These defects will seriously reduce the mechanical properties and stability of the castings, and gas holes and shrinkage porosity are common casting defects in the high-pressure die casting Mg-Gd-Y series magnesium alloy. Therefore, based on the Mg-9Gd-3Y-1.5Zn-0.5Zr alloy, alloying elements that help improve the thermal physical properties of the alloy were screened. Combining thermodynamic and kinetic calculations, the screened elements were filtered, and finally the Mg-9Gd-3Y-1.5Zn-0.5Zr-2Al alloy was determined. Through die casting experiments, it was found that while maintaining high strength, the elongation increased by 221.4%, achieving a huge breakthrough.

[0052] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. A method for preparing a high-strength heat-resistant die-cast Mg-Gd-Zr alloy by regulating physical property parameters, characterized in that: At least the following steps are included: S1: Screen out a magnesium alloy system that can meet the high-strength and heat-resistant conditions as the basic magnesium alloy system; S2: In order to solve the problem of insufficient strength and plasticity in the basic magnesium alloy system, the corresponding strengthening elements with high solid solubility are selected to form the primary strengthening magnesium alloy; S3: Since the primary strengthening of magnesium alloy still cannot completely solve the problem of insufficient strength and plasticity, it is necessary to introduce a new element to improve the performance, thereby obtaining a secondary strengthening magnesium alloy; S4: When die-casting the secondary strengthened magnesium alloy, it was found that the alloy retained some pores and shrinkage. Although the alloy with optimized composition had high strength, its plasticity was still very low. It was determined that the reason affecting the plasticity was the high content of defects. During the tensile deformation process, the defects acted as crack sources, causing the secondary strengthened magnesium alloy to fail and fracture prematurely, making the plasticity worse, and further deteriorating the mechanical properties of the secondary strengthened magnesium alloy. The main reason affecting the defects was the fluidity of the alloy. The defects included at least pores and shrinkage. In order to further eliminate the defects, elements that were helpful in improving the thermophysical parameters and fluidity of the alloy were screened; S5: Combined with thermodynamic calculations, starting from the solid-liquid phase interval, viscosity and latent heat, the elements with the best improvement in the alloy's thermophysical properties and fluidity are screened out. Based on this element and the secondary strengthened magnesium alloy, the final alloy is obtained. This alloy has high strength and excellent elongation.

2. The method for preparing a high-strength heat-resistant die-cast Mg-Gd-Zr alloy by regulating physical property parameters according to claim 1, characterized in that: The basic alloy system used in S1 is Mg-9Gd-0.5Zr alloy. Experiments show that the strength and plasticity of the alloy are insufficient.

3. The method for preparing a high-strength heat-resistant die-casting Mg-Gd-Zr alloy by regulating physical property parameters according to claim 2, characterized in that: The S2 at least comprises the following steps: Through Pandat calculation, strengthening elements with high solid solubility in magnesium alloys were screened and finally determined to be Y elements; Set different Gd / Y ratios and optimize the Gd / Y ratio based on experimental results; The primary strengthening magnesium alloy was determined to be Mg-9Gd-3Y-0.5Zr alloy.

4. The method for preparing a high-strength heat-resistant die-cast Mg-Gd-Zr alloy by regulating physical property parameters according to claim 3, characterized in that: The S3 at least includes the following steps: Based on the primary strengthening of magnesium alloy system, Zn element is introduced; Fine-tune the Zn / RE ratio to control the content and type of the second phase in the alloy; The secondary strengthened magnesium alloy was finally determined to be Mg-9Gd-3Y-1.5Zn-0.5Zr alloy.

5. The method for preparing high-strength heat-resistant die-casting Mg-Gd-Zr alloy by regulating physical property parameters according to claim 4, characterized in that: The elements in S4 that help improve the thermophysical properties of the alloy and the elements that help improve the thermophysical properties and fluidity of the alloy include at least Li, Sr, Bi, Al, B, Ca, Si and Mn.

6. The method for preparing a high-strength heat-resistant die-cast Mg-Gd-Zr alloy by regulating physical property parameters according to claim 5, characterized in that: The element screened out in S5 is Al element.

7. The method for preparing high-strength heat-resistant die-casting Mg-Gd-Zr alloy by regulating physical property parameters according to claim 6, characterized in that: The final alloy was Mg-9Gd-3Y-1.5Zn-0.5Zr-2Al.

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