WO2024066022A1 - Rare earth-alkaline earth element compounded magnesium-based alloy and preparation method therefor - Google Patents

Abstract

A rare earth-alkaline earth element compounded magnesium-based alloy and a preparation method therefor. The rare earth-alkaline earth element compounded magnesium-based alloy comprises the following components in percentages by mass: Al: 3.0-9.5%, RE: 1.5-5.0%, AE: 1.5-4.0%, Zn: 0.01-0.8%, and Mn: 0.01-0.40%, with the balance being magnesium and inevitable impurities, wherein the RE comprises La, and the AE comprises Ca. The technical difficulties in the aspects of the flame retardance and room-temperature and high-temperature mechanical properties of a magnesium alloy are solved by compositely applying rare earth-alkaline earth elements, and the mechanical properties and technological adaptability of the material are effectively improved by constructing a component-optimized Mg-Al-RE-AE alloy system, such that the material is suitable for various preparation processes such as die casting, extrusion, and forging and pressing.

Description

A rare earth and alkaline earth element composite magnesium-based alloy and preparation method thereof

Related Applications

This application requires an application filed with the China Patent Office on September 28, 2022, with application number 202211196641.X, and invention name “A magnesium-based alloy composite of rare earth and alkaline earth elements and its preparation method”; and an application filed with the China Patent Office on October 24, 2022, with application number 202211307082.5, and name “A magnesium-based alloy composite of rare earth and alkaline earth elements and its preparation method”, all contents of which are incorporated by reference in the application.

Technical Field

The present application relates to the technical field of magnesium alloys, and in particular to a magnesium-based alloy composite of rare earth and alkaline earth elements and a preparation method thereof.

Background technique

The density of magnesium and magnesium alloys is 1.8g/cm3. They are the lightest structural metal materials currently used. They have high specific strength and specific stiffness and are widely used in the automotive and aviation fields. However, the Mg-Al and Mg-Zn magnesium alloys commonly used in the automotive industry, such as AZ91, AM50, and AM60, have a low melting point of the main strengthening phase Mg17Al12 and are the first to melt in a high temperature environment, resulting in a decrease in the high temperature strength of the alloy. They cannot be used in working environments that are higher than room temperature for a long time. Therefore, while developing high-strength magnesium alloys, it is also necessary to improve the high temperature creep resistance of magnesium alloys. In addition, with the development of new energy vehicles, power parts such as battery packs have the risk of catching fire when they fail. This requires that when considering the use of magnesium alloys, the requirements of high strength, high temperature resistance, and flame retardancy must be met at the same time; when magnesium alloys are used in aircraft, they must also meet the stricter flame retardancy and fire protection requirements of aviation regulations. At present, there are still relatively few magnesium alloys that take into account high strength, high temperature resistance, and flame retardancy at home and abroad, and the realization of flame retardancy and fire protection goals is the most challenging.

Considering the requirements of FAA aviation-grade flame retardant, there are only two magnesium alloy grades that have been publicly tested and verified in the world, namely WE43 and EV31, both of which are Mg-RE-Zr alloys. Although this alloy has excellent mechanical strength and flame retardant properties, it has two defects: 1. The existing alloy grades use high content of Gd and Y elements, resulting in high alloy cost and difficult preparation process; 2. The precipitation strengthening mechanism of the alloy leads to low plasticity of the material and requires heat treatment, which makes it difficult to use in the fields of die casting and precision machining.

Poor flame retardancy is one of the technical difficulties that limit the application of Mg-Al alloy system. Traditional commercial AZ/AM/AE alloy system cannot meet FAA flame retardancy requirements, so it cannot be used in high safety requirements such as aviation. Improving the flame retardancy of Mg-Al alloy system is also one of the current research hotspots, especially by adding rare earth elements and alkaline earth elements such as Ca and Sr. There are relatively rich research results. However, there is a technical bottleneck in this field: if the amount of elements with flame retardant effect is low, there will be no significant improvement effect; and a higher amount of alloying elements will lead to higher alloy cost, lower process suitability, and lower mechanical properties of materials.

technical problem

The main purpose of the present application is to provide a magnesium-based alloy, aiming to solve the technical problem of poor comprehensive performance of magnesium-based alloys in the prior art.

Technical Solutions

The magnesium-based alloy composite of rare earth and alkaline earth elements proposed in the present application includes the following components, by mass percentage: Al: 3.0-9.5%, RE: 1.5-5.0%, AE: 1.5-4.0%, Zn: 0.01-0.80%, Mn: 0.01-0.40%, and the rest is magnesium and unavoidable impurities; wherein the RE includes La and the AE includes Ca.

In one embodiment, the Al content ranges from 4.0% to 7.0%, the RE content ranges from 2.0% to 4.0%, the AE content ranges from 1.7% to 3.0%, the Zn content ranges from 0.01% to 0.60%, and the Mn content ranges from 0.1% to 0.2%.

In one embodiment, the RE further includes Sm, Ce and Pr.

In one embodiment, the La content in RE is 70-90%, the Sm content is 10-30%, and the Ce and Pr content combined is no more than 20%.

In one embodiment, the AE also includes Sr.

In one embodiment, in the total content of Ca and Sr, the Ca element content accounts for 80-90%, and the Sr element content accounts for 10-20%.

In one embodiment, the unavoidable impurities include, by mass percentage: Fe≤ 0.02%, Si≤ 0.01%, Cu≤ 0.002%, and Ni≤ 0.001%.

The present application also proposes a method for preparing a magnesium-based alloy composite of rare earth and alkaline earth elements, comprising the following steps:

S1. According to the mass percentage, Mg ingots, Al ingots, Zn ingots, Mg-RE alloy, Mg-AE alloy, and Mg-Mn alloy are prepared;

S2. Under a protective atmosphere, the Mg ingot and the Al ingot are melted, the temperature is raised to 700-730° C., the Zn ingot, the Mg-RE alloy, the Mg-AE alloy, and the Mg-Mn alloy are added in sequence, and the mixture is stirred evenly after melting to obtain an alloy melt;

S3, after standing for 20-35 min, degas and add flux, and refine at 700-710 ℃ for 20-35 min;

S4. After the refining is completed, the mixture is allowed to stand for 0.5-1.0 h, the slag is removed, and the mixture is cast to obtain the magnesium-based alloy.

In one embodiment, the Mg-RE alloy has a RE content of 20-45%.

In one embodiment, in the Mg-AE alloy, the content of Ca or the mixed component of Ca+Sr is 15-40%.

Type your technical solution description paragraph here.

Beneficial Effects

This application solves the technical difficulties in the flame retardancy, room temperature and high temperature mechanical properties of magnesium alloys by composite application of rare earth and alkaline earth elements. By constructing a component-optimized Mg-Al-RE-AE alloy system, the mechanical properties and process suitability of the material are effectively improved, and it is suitable for various preparation processes such as die casting, extrusion, and forging. In order to solve the problems of cost increase, reduced mechanical properties, and poor process suitability caused by adding a large amount of alloying elements, this application realizes multi-element microalloying of rare earth elements by adding La-Sm-Ce (Pr) composite application, maximizes the precipitation efficiency of rare earth elements, and reduces the amount of alloying elements. In addition, this application uses the mechanism that alkaline earth elements can generate dense oxide films on the surface of liquid magnesium alloys through the composite application of Ca-Sr, effectively isolates the contact between the metal liquid and the air, thereby improving the flame retardancy of the alloy. After adding Sr, dispersed Mg17Sr2 phase particles are formed in the alloy, which effectively reduces the size of the Al-Ca brittle phase and improves the plasticity of the alloy. On the premise of ensuring the flame retardant effect of the alloy, the room temperature and high temperature mechanical properties of the alloy are significantly improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a metallographic microstructure of the alloy of the present application, wherein A is an optical metallographic microstructure; and B is a scanning electron microscope microstructure.

Embodiments of the present invention

The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

The following examples will help those skilled in the art to further understand the present application, but are not intended to limit the present application in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present application. These all belong to the protection scope of the present application.

The following will further summarize the addition proportion of various elements:

Al is a commonly used strengthening element for magnesium alloys. It can not only effectively ensure the strength of magnesium alloys, but also improve the casting process performance of magnesium alloys. When the aluminum content is less than 3%, the strength of the alloy is improved little and the casting performance is also poor; when the aluminum content is too high, it will have an adverse effect on the heat resistance. Therefore, the aluminum content of this alloy is in the range of 3-9.5%.

Rare earth elements RE (mainly La) can significantly improve the room temperature and high temperature mechanical properties of the alloy by forming a high melting point Al-La precipitation phase in magnesium-aluminum magnesium alloys, and can effectively change the morphology and distribution of the Mg-Al precipitation phase. La-Sm-Ce is the main alloying element. Through the principle of reducing the solid solubility of each other through multi-element rare earth microalloying, the precipitation quantity of Al-RE phase is effectively increased, the size of the precipitation phase is reduced, and the dispersion of its distribution is improved. In addition, according to the addition effect, the main strengthening element uses the La element with the most significant precipitation effect, and the sharp shape of the rare earth phase is effectively weakened by the combination of Sm. Adding a specific proportion of Ce improves the precipitation efficiency of rare earth elements. The range of RE is 1.5-5.0%.

The content of heavy rare earth elements ranges from 0.02 to 0.3%. Since heavy rare earth elements do not form sharp rod-like phases in magnesium and can be well dissolved in the magnesium matrix, they promote the precipitation of light rare earth elements and increase the nucleation density of the alloy. Therefore, they have better multi-element microalloying strengthening effect when used in combination with light rare earth elements.

Zn has a high solid solubility in magnesium alloys, and can play a strengthening role in magnesium alloys, which is beneficial to the improvement of magnesium alloy casting properties. However, higher Zn content is not conducive to the material's resistance to hot cracking and heat resistance. Therefore, a small amount of zinc is added to this alloy, with a content of 0.01-0.8%.

The Mn element can prevent the recrystallization process of aluminum alloys, increase the recrystallization temperature, and significantly refine the recrystallized grains. The refinement of recrystallized grains is mainly through the Al-Mn compound dispersed particles that hinder the growth of recrystallized grains. Another function of Mn is to dissolve impure iron (Fe) and reduce the harmful effects of iron. The content is 0.01-0.40% %.

AE, taking Ca as an example, can inhibit the high-temperature oxidation of magnesium alloys, increase the ignition point of magnesium alloys, and promote the refinement of magnesium alloy grains during the solidification process. In a high-temperature molten state, calcium diffuses preferentially to the liquid surface and combines with oxygen before magnesium to form a dense oxide film, which hinders further oxidation of magnesium, thereby improving the high-temperature performance of magnesium alloys. However, excessive calcium content will lead to poor hot cracking performance of magnesium alloy castings and significantly reduce the mechanical properties of the material. In this application, the AE addition range is 1.5-4.0%.

For alloys, impurities are inevitable. In the present application, the inevitable impurities include, by mass percentage, Fe, Si, Cu, Ni, etc., and the total impurity content does not exceed 0.1%.

The preparation methods of each embodiment are as follows:

S1. According to the mass percentage, Mg ingots, Al ingots, Zn ingots, Mg-RE alloy, Mg-AE alloy, and Mg-Mn alloy are prepared;

S2. Under a protective atmosphere, the Mg ingot and the Al ingot are melted, the temperature is raised to 700-730° C., the Zn ingot, the Mg-RE alloy, the Mg-AE alloy, and the Mg-Mn alloy are added in sequence, and the mixture is stirred evenly after melting to obtain an alloy melt;

S3, after standing for 20-35 min, degas and add flux, and refine at 700-710 ℃ for 20-35 min;

S4. After the refining is completed, the mixture is allowed to stand for 0.5-1.0 h, the slag is removed, and the mixture is cast to obtain the magnesium-based alloy.

S5. According to the preparation method, the RE content in the Mg-RE alloy is 20%-45%.

S7. According to the preparation method, in the Mg-AE alloy, the content of Ca or the mixed component of Ca and Sr is 15-40%.

The composition of the alloys of various examples is shown in Table 1.

Table 1 Alloy element composition of each example (%)

Example	Al	La	Sm	Ce	Pr	Ca	Sr	Zn	Mn	Gd	Y	Mg
#1	3.0	1.12	0.23	0.07	0.08	1.35	0.15	0.01	0.01	-	-	Remainder
#2	4.0	1.50	0.30	0.10	0.10	1.53	0.17	0.01	0.10	0.05	0.05	Residue
#3	7.0	3.0	0.6	0.20	0.20	2.70	0.30	0.60	0.20	0.10	0.10	Residue
#4	9.5	3.75	0.75	0.25	0.25	3.60	0.40	0.80	0.40	0.15	0.15	Residue
#5	5.5	2.25	0.45	0.15	0.15	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#6	5.5	2.10	0.90	-	-	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#7	5.5	2.70	0.30	-	-	2.25	0.25	0.50	0.25	0.10	0.10	Remainder
#8	5.5	2.10	0.30	0.30	0.30	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#9	5.5	2.10	0.30	-	0.60	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#10	5.5	2.10	0.30	0.60	-	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#11	5.5	1.12	0.23	0.08	0.07	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#12	5.5	1.50	0.30	0.10	0.10	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#13	5.5	3.00	0.60	0.20	0.20	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#14	5.5	3.75	0.75	0.25	0.25	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#15	5.5	2.25	0.45	0.15	0.15	2.00	0.50	0.50	0.25	0.10	0.10	Residue
#16	5.5	2.25	0.45	0.15	0.15	1.35	0.15	0.50	0.25	0.10	0.10	Residue
#17	5.5	2.25	0.45	0.15	0.15	1.53	0.17	0.50	0.25	0.10	0.10	Residue
#18	5.5	2.25	0.45	0.15	0.15	2.70	0.30	0.50	0.25	0.10	0.10	Residue
#19	5.5	2.25	0.45	0.15	0.15	3.60	0.40	0.50	0.25	0.10	0.10	Residue
#20	3.0	2.25	0.45	0.15	0.15	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#twenty one	4.0	2.25	0.45	0.15	0.15	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#twenty two	7.0	2.25	0.45	0.15	0.15	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#twenty three	9.5	2.25	0.45	0.15	0.15	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#twenty four	5.5	2.25	0.45	0.15	0.15	2.25	0.25	0.01	0.01	0.10	0.10	Residue
#25	5.5	2.25	0.45	0.15	0.15	2.25	0.25	0.01	0.10	0.10	0.10	Residue
#26	5.5	2.25	0.45	0.15	0.15	2.25	0.25	0.60	0.20	0.10	0.10	Residue
#27	5.5	2.25	0.45	0.15	0.15	2.25	0.25	0.80	0.40	0.10	0.10	Residue
#28	5.5	3.0	-	-	-	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#29	5.5	2.25	-	-	-	2.5	-	0.50	0.25	0.10	0.10	Residue
#30	5.5	2.25	0.45	0.15	0.15	2.5	-	0.50	0.25	0.10	0.10	Residue

In order to evaluate the performance of the material of the present application, the alloy of the embodiment was melted and die-cast to prepare test samples of various sizes, and tensile strength test (GB/T228.1 Metal Material Room Temperature Tensile Test Method) and flame retardant performance test (DOT/FAA/AR/00/12-Chapter 25, DOT/FAA/AR/00/12-Chapter 26) were performed. The test results are shown in Table 2.

Table 2 Mechanical and flame retardant performance test results of each embodiment

It can be seen from the test results of the embodiments in Table 1 and Table 2 that the alloy of the present application has good mechanical properties and flame retardant properties, and each property is closely related to the Al content of the alloy, the total amount of rare earth, and the content of alkaline earth elements. Among them, it can be seen from the comparative examples 1-5 that the higher the total amount of alloying elements, the higher the mechanical strength (tensile strength and yield strength) and flame retardant properties (weight loss rate) of the material, while the plasticity (elongation) of the material is correspondingly reduced. It can be seen from Examples 6-10 that under the condition of a certain total amount of rare earth, the light rare earth elements with a specific compatibility ratio have basically the same effect on the mechanical properties of the alloy, and all have a good effect of improving the performance. As can be seen from Examples 11-14, the mechanical properties of the material are closely related to the total content of rare earth elements. The strength and flame retardant properties of the material increase with the increase of rare earth elements, while the plasticity of the material decreases with the increase of the rare earth content. When the rare earth content is high, the improvement effect gradually decreases. This is due to the increase in the main strengthening phase Al11La3/Al2La phase of the alloy. The material strength increases with the increase in the number of strengthening phases, but the Al11La3/Al2La phase grows rapidly with the increase in the total amount of rare earths, resulting in the coarsening of the alloy microstructure, which leads to a decrease in the plasticity of the material. As can be seen from the comparison of Examples 5 and 15, the Sr element is a beneficial supplement to Ca. A small amount of Sr can improve the plasticity of the material, but the flame retardant properties of the alloy decrease with the decrease in the Ca content. As can be seen from Examples 16-19, the plasticity of the alloy decreases with the increase in the total amount of alkaline earth elements, and the flame retardant properties of the alloy are positively correlated with the total amount of alkaline earth elements. As can be seen from Examples 20-23, the mechanical properties of the alloy improve with the increase of Al content, but the plasticity and flame retardant properties of the material show the opposite trend. This is because the increase in Al content leads to an increase in the brittle strengthening phase Mg17Al12, so the alloy strength performance is improved, but because the Mg17Al12 phase is relatively brittle, distributed in a network at the grain boundary, and decomposes at a relatively low temperature, the plasticity and flame retardant properties of the material decrease with the increase of the Mg17Al12 phase. As can be seen from Examples 24-27, Zn and Mn elements can increase the yield strength of the material, but the plasticity and flame retardant properties of the material will decrease with the increase of these two elements. As can be seen from the comparison of Example 5 and Example 28, a single rare earth has a better strengthening effect, but is slightly lower than the addition of mixed rare earths. As can be seen from the comparison of Example 5, Example 29, and Example 30, a single addition of Ca has a better flame retardant effect, but is unfavorable for the plasticity of the material.

In order to further evaluate the effect of this application, comparative examples were designed and prepared, among which comparative examples D1 and D2 adopted the standard process scheme of their commercial brands, and other comparative examples adopted the process scheme used in each embodiment of this application. The comparative alloys were subjected to tensile strength test (GB/T228.1 Metal Material Room Temperature Tensile Test Method) and flame retardant performance test (DOT/FAA/AR/00/12-Chapter 25, DOT/FAA/AR/00/12-Chapter 26). The elemental components of each comparative example are shown in Table 3, and the performance test results are shown in Table 4.

Table 3 Element composition of alloys in each comparative example (%)

Example	Al	La	Sm	Ce	Pr	Ca	Sr	Zn	Mn	Gd	Y	Mg
#D1 (AZ91)	8.9	-	-	-	-	-	-	0.85	0.24	-	-	Residue
#D2 (AM60)	5.7	-	-	-	-	-	-	0.05	0.27	-	-	Residue
#D3	5.5	7.0	-	-	-	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#D4	5.5	-	3.0	-	-	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#D5	5.5	-	-	3.0	-	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#D6	5.5	-	-	-	3.0	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#D7	5.5	2.25	0.45	0.15	0.15	-	2.5	0.50	0.25	0.10	0.10	Residue
#D8	5.5	0.25	0.25	-	-	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#D9	5.5	4.50	1.00	0.50	0.50	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#D10	5.5	2.25	0.45	0.15	0.15	4.50	1.50	0.50	0.25	0.10	0.10	Residue
#D11	1.5	2.25	0.45	0.15	0.15	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#D12	12.5	2.25	0.45	0.15	0.15	2.25	0.25	0.50	0.25	0.10	0.10	Residue
#D13	5.5	2.25	0.45	0.15	0.15	2.25	0.25	-	-	0.10	0.10	Residue
#D14	5.5	2.25	0.45	0.15	0.15	2.25	0.25	1.50	0.80	0.10	0.10	Residue

Table 4 Mechanical and flame retardant performance test results of each comparative example

It can be seen from the test results in Table 4 that compared with commercial magnesium alloys (D1, D2), the alloy of the present application has good plasticity and flame retardant properties. It can be seen from Example 5 and Comparative Examples D3-6 that adding a single rare earth element can effectively improve the strength of the material, but the improvement effect is significantly lower than that of a mixed rare earth component with a specific combination. It can be seen from Example 5 and Comparative Example D7 that adding only the Sr element can improve the plasticity of the alloy, but the flame retardant performance of the alloy is not as good as the effect of adding Ca. It can be seen from Example 5, Comparative Examples D8 and D9 that there is no significant strengthening effect when the rare earth addition is insufficient, and when the rare earth content is too high, the material performance begins to decline. It can be seen from Example 5 and Comparative Example D10 that when there are too many alkaline earth elements, the mechanical properties of the alloy decrease rapidly. It can be seen from Example 5, Comparative Examples D11 and D12 that a lower Al content causes a significant decrease in the mechanical properties of the alloy, and too high a content reduces the plasticity and flame retardant properties of the alloy.

It can be seen from Example 5 and Comparative Examples D13 and D14 that not adding Zn and Mn elements leads to a decrease in the yield strength of the alloy, while too high an addition of Zn and Mn elements reduces the plasticity and flame retardancy of the alloy.

The technical features of this application are:

(1) A rare earth component matching scheme based on the effect of rare earth element multi-element microalloying. Different rare earth elements will reduce each other's solid solubility in magnesium alloys, increase the nucleation density and precipitation efficiency while keeping the total amount unchanged, thereby improving strength performance and reducing plasticity loss. In this application, light rare earth La-Sm-Ce (Pr) with low cost and good processability is selected as the main alloying element. Through the principle of reducing the solid solubility of each other by multi-element rare earth microalloying, the precipitation amount of Al-RE phase is effectively increased, the size of the precipitated phase is reduced, and the dispersion of its distribution is improved; in addition, according to the addition effect, the main strengthening element is La, which has the most significant precipitation effect, and the sharp shape of the rare earth phase is effectively weakened by the combination of Sm. The addition of a specific ratio of Ce/Pr improves the precipitation efficiency of rare earth elements.

(2) Composite application design of RE-AE. The Mg-Al/Mg-Al-RE alloy system cannot achieve the flame retardant properties required by FAA. The Mg-Al-Ca flame retardant magnesium alloy system mainly achieves its flame retardant effect through the effect of Ca element forming a dense oxide film on the surface of molten metal. On the one hand, a low content of Ca element cannot form an effective flame retardant effect. On the other hand, too high Ca will aggregate at the grain boundaries of the microstructure, and Al2Ca particles will also grow rapidly, resulting in a significant decrease in the strength and plasticity of the alloy. Therefore, the composite application of rare earth-alkaline earth elements is a technical solution that can not only improve the mechanical properties of the alloy, but also significantly improve the flame retardant properties of the material.

(3) Ca-Sr composite application. Ca is a key element to improve the flame retardant properties of alloys. A higher content of Ca will increase the brittleness of the material, while a lower Ca content will result in the inability to effectively improve the flame retardant properties. Sr is also an alkaline earth element and has good compatibility with Ca. It has a certain substitution effect in the alloy phase. By adding a certain proportion of Sr elements, dispersed Mg17Sr2 phase particles are formed in the alloy, which effectively reduces the size of the Al-Ca brittle phase and improves the plasticity of the alloy. On the premise of ensuring the flame retardant effect of the alloy, the room temperature and high temperature mechanical properties of the alloy are significantly improved.

The above description is only a preferred embodiment of the present application, and does not limit the patent scope of the present application. All equivalent structural changes made by using the contents of the present application specification and drawings under the inventive concept of the present application, or directly/indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims (15)

1. A magnesium-based alloy composited with rare earth and alkaline earth elements, wherein the alloy comprises the following components by mass percentage: Al: 4.0-7.0%, RE: 2.0-4.0%, AE: 1.7-3.0%, Zn: 0.01-0.80%, and Mn: 0.01-0.40%, and the remainder is magnesium and inevitable impurities; the RE comprises La, Sm, Ce and Pr, the La content of RE accounts for 70-90%, the Sm content accounts for 10-30%, and the Ce and Pr content accounts for no more than 20% in total; the AE comprises Ca and Sr, and in the total content of Ca and Sr, the Ca content accounts for 80-90%, and the Sr content accounts for 10-20%.
2. The magnesium-based alloy composite of rare earth and alkaline earth elements as claimed in claim 1, wherein, by mass percentage, the unavoidable impurities include: Fe≤ 0.02%, Si≤ 0.01%, Cu≤ 0.002%, Ni≤ 0.001%.
3. A magnesium-based alloy composite of rare earth and alkaline earth elements, wherein the alloy comprises the following components by mass percentage: Al: 3.0-9.5%, RE: 1.5-5.0%, AE: 1.5-4.0%, Zn: 0.01-0.80%, and Mn: 0.01-0.40%, and the remainder is magnesium and unavoidable impurities; the RE comprises La, Sm, Ce and Pr, the La content of RE accounts for 70-90%, the Sm content accounts for 10-30%, and the Ce and Pr content accounts for no more than 20% in total; the AE comprises Ca and Sr.
4. The magnesium-based alloy composite of rare earth and alkaline earth elements as claimed in claim 3, wherein the total content of Ca and Sr is 80-90% by Ca element content and 10-20% by Sr element content.
5. The magnesium-based alloy composite of rare earth and alkaline earth elements as claimed in claim 3, wherein, by mass percentage, the unavoidable impurities include: Fe≤ 0.02%, Si≤ 0.01%, Cu≤ 0.002%, Ni≤ 0.001%.
6. A magnesium-based alloy composited with rare earth and alkaline earth elements, wherein, by mass percentage, the alloy comprises the following components: Al: 3.0-9.5%, RE: 1.5-5.0%, AE: 1.5-4.0%, Zn: 0.01-0.80%, and Mn: 0.01-0.40%, with the remainder being magnesium and unavoidable impurities; the RE comprises La, and the AE comprises Ca.
7. The magnesium-based alloy composite of rare earth and alkaline earth elements as described in claim 6, wherein the Al content ranges from 4.0% to 7.0%, the RE content ranges from 2.0% to 4.0%, the AE content ranges from 1.7% to 3.0%, the Zn content ranges from 0.01% to 0.60%, and the Mn content ranges from 0.1% to 0.2%.
8. The rare earth and alkaline earth element composite magnesium-based alloy as claimed in claim 7, wherein the RE further comprises Sm, Ce and Pr.
9. The magnesium-based alloy composite of rare earth and alkaline earth elements as claimed in claim 8, wherein the La element content in RE accounts for 70-90%, the Sm element content accounts for 10-30%, and the total content of Ce and Pr elements accounts for no more than 20%.
10. The rare earth and alkaline earth element composite magnesium-based alloy as claimed in claim 8, wherein the AE also includes Sr.
11. The magnesium-based alloy composite of rare earth and alkaline earth elements as claimed in claim 10, wherein, in the total content of Ca and Sr, the Ca element content accounts for 80-90%, and the Sr element content accounts for 10-20%.
12. The magnesium-based alloy composite of rare earth and alkaline earth elements as claimed in claim 6, wherein, by mass percentage, the unavoidable impurities include: Fe≤ 0.02%, Si≤ 0.01%, Cu≤ 0.002%, Ni≤ 0.001%.
13. A method for preparing a magnesium-based alloy composite of rare earth and alkaline earth elements as claimed in claim 6, comprising the following steps:

    S1. According to the mass percentage, Mg ingots, Al ingots, Zn ingots, Mg-RE alloy, Mg-AE alloy and Mg-Mn alloy are prepared;

    S2. Under a protective atmosphere, the Mg ingot and the Al ingot are melted, the temperature is raised to 700-730° C., the Zn ingot, the Mg-RE alloy, the Mg-AE alloy, and the Mg-Mn alloy are added in sequence, and the mixture is stirred evenly after melting to obtain an alloy melt;

    S3, after standing for 20-35 min, degas and add flux, and refine at 700-710 ℃ for 20-35 min;

    S4. After the refining is completed, the mixture is allowed to stand for 0.5-1.0 h, the slag is removed, and the mixture is cast to obtain the magnesium-based alloy.
14. The method for preparing a magnesium-based alloy according to claim 13, wherein the RE content in the Mg-RE alloy is 20-45%.
15. The method for preparing a magnesium-based alloy as described in claim 13, wherein the content of Ca or the mixed component of Ca+Sr in the Mg-AE alloy is 15-40%.