CN101220432A - High-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum - Google Patents

Abstract

The invention relates to a high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum. 0.01%-1.5%, La 0.01%-1.5%, impurity elements Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium. The alloying material used is cerium-lanthanum rare earth, and the remaining cerium-lanthanum rare earth is separated from the Nd and Pr in the common cerium-rich mixed rare earth. Currently, the rare earth material is cheap and has a large backlog in the market. The invention avoids the waste of rare earth resources, and the mechanical properties and plasticity of the alloy are better than those of the AZ91 alloy, and the corrosion resistance can be increased several times to dozens of times.

Description

High-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum

technical field

The invention relates to a high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum, belonging to the field of metal materials.

Background technique

Magnesium alloy has the advantages of light specific gravity, high specific strength, good thermal conductivity, strong electromagnetic shielding ability, good vibration damping and easy recycling. The use of magnesium-aluminum light alloy instead of steel is the key to reducing weight, reducing fuel consumption and improving quality of current vehicles. measures and directions for development. With the light weight and high strengthening requirements put forward by modern industry for products, the demand for Mg-Al series magnesium alloys with excellent comprehensive properties continues to increase. This type of alloy represented by AZ91 has the advantages of excellent casting process performance, small hot cracking tendency, and low cost. It accounts for about 90% of the total magnesium alloys and is the most widely used cast magnesium alloy. However, traditional magnesium alloys have inherent disadvantages such as poor casting performance, corrosion resistance, heat resistance, fatigue and impact resistance, which limit their further application. In order to solve these shortcomings, rare earth elements are introduced as the most valuable and potential alloying elements to develop magnesium alloys with high strength and corrosion resistance. After a long period of extensive research and development work, domestic and foreign research institutes and manufacturers currently recognize that rare earth elements are effective components of advanced magnesium alloys such as heat resistance, high strength, corrosion resistance, and flame retardancy, and are used as additives to improve the comprehensive performance of magnesium alloys.

The rare earths used in magnesium alloys include single and mixed rare earths, and cerium-rich mixed rare earths are one of the most widely used mixed rare earths in magnesium alloys, and the main components are La, Ce, Pr, and Nd. However, due to the expansion of the application and price rise of Pr and Nd metals, they were separated from the cerium-rich misch metal. At present, there is a large backlog of low-cost cerium-lanthanum rare earths. If these rare earths cannot be fully utilized, it will be a great waste of resources and a great pollution to the environment. To sum up, it is necessary and urgent to develop the application market of cerium-lanthanum rare earths, and it is of great economic and scientific significance to make comprehensive utilization and balanced development of rare earth elements.

Due to the unique chemical activity of cerium, the addition of magnesium alloy can play the role of purifying the melt, activating the interface, refining grains and alloying/microalloying. Compared with other rare earth elements, cerium and lanthanum have better deoxidation and impurity removal and purification effects on magnesium alloys, and the improvement of the comprehensive performance of magnesium alloys has been recognized by the academic circles. Make full use of cerium-lanthanum rare earths separated from high-priced elements, and develop new high-strength and corrosion-resistant magnesium alloys on the basis of traditional magnesium alloy AZ91, which will not only improve the competitiveness of the magnesium industry, but also help solve the contradiction between production and demand of cerium-lanthanum rare earth resources and the imbalance between production and sales problems, to achieve mutual benefit and win-win between industries. (Xing Bin. Stabilizing product prices to promote healthy development of the industry. Rare Earth Information 2007.10: 13)

Contents of the invention

In order to improve the performance defect of the currently widely used AZ91 die-casting magnesium alloy, the invention provides a high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum. On the basis of AZ91 alloy, by adding a certain amount of cerium-lanthanum mixed rare earth for alloying and modification treatment, the mechanical properties and corrosion resistance of the magnesium alloy are significantly improved compared with AZ91, which is in line with the development direction of light alloy materials and meets Future industry needs for magnesium alloys.

The composition and mass percentage of the high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum are: the composition and mass percentage of the high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum are: Al is 8.5% to 9.5%, Zn is 0.4 to 0.9%, and Mn is 0.2%～0.6%, rare earth is Ce 0.01%～1.5%, La 0.01%～1.5%, impurity elements Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, the balance is magnesium AZ91-based alloy and magnesium-20% cerium-lanthanum master alloy are selected as raw materials, and the magnesium-20% cerium-lanthanum master alloy is 80% of magnesium and 20% of cerium-lanthanum; the magnesium-cerium-lanthanum master alloy is The cerium-lanthanum raw material is made of cerium-lanthanum mixed rare earth after separating Nd and Pr, wherein the composition and mass percentage of cerium-lanthanum rare earth are: Ce is 20%-80%, La is 80%-20%.

The preparation method of the high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum provided by the present invention, the steps and conditions are as follows: weigh the material according to the proportion, preheat the base alloy to 200°C, and put it into a crucible with a preheating temperature of 300°C Melt, and pass through the SF ₆ -CO ₂ protective gas with a volume ratio of SF ₆ : CO ₂ of 1:100. When the magnesium alloy is completely melted and the melt temperature reaches 720°C-740°C, add magnesium-cerium-lanthanum master alloy, magnesium - The cerium-lanthanum master alloy is preheated to 200°C, then continuously stirred and introduced with SF ₆ -CO ₂ protective gas until the magnesium-cerium-lanthanum master alloy is completely melted; when the temperature reaches 730-740°C, it is stirred and refined with argon for 5 ~ 10 minutes, then stand still for 25-35 minutes, when the melt temperature drops to 680°C ~ 700°C, carry out die-casting production on a cold chamber die-casting machine to obtain a high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum;

Beneficial effects of the present invention:

(1) cerium-lanthanum mixed rare earth is the element that the present invention is used to improve alloy strength and plasticity, and its strengthening mechanism is: one, fine-grain strengthening, because rare earth is surface-active element in magnesium alloy melt, cerium-lanthanum is in solidification process Rare earths are enriched at the front of the solid-liquid interface, forming supercooled components that hinder grain growth and effectively refine the alloy structure. The combination of rare earth and aluminum in the alloy forms the rare upper phase Al ₁₁ RE ₃ , which is mainly dispersed in the grain boundary, reducing and inhibiting the formation and growth of the brittle second phase Mg ₁₇ Al ₁₂ , thereby strengthening the alloy matrix and making the plasticity Uniform deformation. The rare earth phase can effectively pin the grain boundary, inhibit dislocation climbing in the grain, and increase the resistance of dislocation movement, thereby improving the strength and plasticity of the alloy, so the comprehensive performance of the new magnesium alloy has been significantly improved.

(2) During the smelting process, the cerium-lanthanum rare earth can remove impurities in the melt, so as to achieve the effects of degassing, slag removal, and purifying the melt. When the alloy is smelted, cerium and lanthanum accumulate on the surface of the alloy liquid, and have a strong interaction with elements such as O, S, H, and N, and produce products such as RE ₂ O ₃ , RE ₂ S ₃ , REH ₂ , REN, etc., which can make The gas content in the alloy melt is reduced by 16%, thereby significantly reducing the harmfulness of harmful gas elements in the alloy. In magnesium alloys, the oxidized inclusions are mainly MgO. Since the affinity between rare earth elements and O is greater than that between Mg and O, rare earth oxides will be formed after adding rare earth elements to the magnesium alloy liquid to reduce MgO inclusions. Rare earth can also reduce the weakening effect of harmful trace metals in metal materials such as Fe, Cu, Si, Ni, etc., and generate binary or multi-element compounds with higher melting points. Hazards of substances in solid metals. Through the above three aspects, the cerium-lanthanum rare earth improves the corrosion resistance of the AZ91 magnesium alloy.

(3) The cerium-lanthanum rare earth raw material used in the new magnesium alloy is the remaining cerium-lanthanum rare earth after separating Nd and Pr from ordinary cerium-rich mixed rare earths (including La, Ce, Pr, and Nd). Since the 1990s, rare earth experts at home and abroad have paid great attention to the unbalanced application of rare earths. One of the problems affecting the comprehensive utilization and balanced development of rare earths is the large backlog of cerium and lanthanum rare earths. In China alone, there is a backlog of about 120,000 tons of cerium-lanthanum rare earths worth hundreds of millions of dollars each year, which have not been used in large quantities, resulting in a great waste of resources and a great threat to the environment. The invention utilizes the low-cost cerium-lanthanum rare earth to develop the high-strength corrosion-resistant die-casting magnesium alloy. First, it finds a new utilization method for the backlog of cerium-lanthanum rare earth resources, alleviates the problem of unbalanced production and sales of rare earth resources, and enables the coordinated development of the utilization of many rare earth elements; The second is to reduce the cost of this type of magnesium alloy, and replace the traditional cerium-rich mixed rare earth with cheap cerium-lanthanum rare earth, so that the cost of the product is reduced by 50%, and the scarce Pr and Nd rare earth resources are saved. In addition, the rich rare earth resources of cerium and lanthanum ensure the sustainable development of the alloy, which is conducive to improving the competitiveness of my country's magnesium alloy industry and promoting the sound and rapid development of rare earth magnesium alloys.

Description of drawings

Fig. 1 is the microstructure of scanning electron microscope and transmission electron microscope of embodiment 2 of the present invention AZ91+CeLa (Ce=0.6%, La=0.4%) alloy. It can be seen that the fine-grain strengthening of the alloy produced by the refined alloy grains and the dispersion strengthening of a large number of fine high-melting point Al-RF relative to the alloy at the grain boundary are the main reasons for the excellent mechanical properties of the alloy.

Detailed ways

Embodiment 1 AZ91+CeLa (Ce=0.01%, La=1.0%) alloy

The composition and mass percentage of the high-strength corrosion-resistant die-casting magnesium alloy containing cerium-lanthanum rare earth are: aluminum: 9%, Zn: 0.9%, manganese: 0.2%, cerium: 0.01%, lanthanum: 1.0%, impurity element Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium; AZ91 base alloy and magnesium-20% cerium-lanthanum master alloy are selected as raw materials, and the magnesium-20% cerium-lanthanum master alloy is magnesium Accounting for 80%, cerium lanthanum accounts for 20%; The cerium lanthanum raw material of described magnesium-cerium lanthanum intermediate alloy is made with the cerium lanthanum mixed rare earth after separating Nd, Pr, wherein the composition and mass percentage of cerium lanthanum rare earth are : Ce is 20% to 80%, and La is 80% to 20%.

Alloy properties are shown in Table 1 and Table 2.

Weigh the material according to the proportion, preheat the base alloy to 200°C, put it into a crucible with a preheating temperature of 300°C and melt it, and inject SF ₆ -CO ₂ with a volume ratio of SF ₆ :CO ₂ of 1:100 Protective gas, when the magnesium alloy is completely melted and the melt temperature reaches 720°C-740°C, add the magnesium-cerium-lanthanum master alloy, preheat the magnesium-cerium-lanthanum master alloy to 200°C, then continuously stir and feed SF ₆ -CO ₂ Protective gas until the intermediate alloy is completely melted; when the temperature reaches 730-740°C, pass argon gas to stir and refine for 5-10 minutes, and then stand still for 25-35 minutes. When the melt temperature drops to 680-700°C, the Die-casting production is carried out on a chamber die-casting machine to obtain a high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum.

Embodiment 2 AZ91+CeLa (Ce-0.6%, La=0.4%) alloy

The composition and mass percentage of the high-strength corrosion-resistant die-casting magnesium alloy containing cerium-lanthanum rare earth are: aluminum: 9%, Zn: 0.9%, manganese: 0.2%, cerium: 0.6%, lanthanum: 0.4%, impurity element Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium; AZ91 base alloy and magnesium-20% cerium-lanthanum master alloy are selected as raw materials, and the magnesium-20% cerium-lanthanum master alloy is magnesium Accounting for 80%, cerium lanthanum accounts for 20%; The cerium lanthanum raw material of described magnesium-cerium lanthanum intermediate alloy is made with the cerium lanthanum mixed rare earth after separating Nd, Pr, wherein the composition and mass percentage of cerium lanthanum rare earth are : Ce is 20% to 80%, and La is 80% to 20%.

Alloy properties are shown in Table 1 and Table 2.

Weigh the material according to the proportion, preheat the base mixture to 200°C, put it into a crucible with a preheating temperature of 300°C and melt it, and inject SF ₆ -CO with a volume ratio of SF ₆ :CO ₂ of 1:100 ₂ Protective gas, when the magnesium alloy is completely melted and the melt temperature reaches 720°C to 740°C, add the magnesium-cerium-lanthanum master alloy, preheat the magnesium-cerium-lanthanum master alloy to 200°C, then continuously stir and feed SF ₆ -CO ₂ Protective gas until the intermediate alloy is completely melted; when the temperature reaches 730-740°C, pass argon gas to stir and refine for 5-10 minutes, then stand for 25-35 minutes, when the melt temperature drops to 680-700°C, in Die-casting production is carried out on a cold chamber die-casting machine to obtain a high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum.

Embodiment 3 AZ91+CeLa (Ce=0.2%, La=0.3%) alloy

The composition and mass percentage of the high-strength corrosion-resistant die-casting magnesium alloy containing cerium-lanthanum rare earth are: aluminum: 9%, Zn: 0.9%, manganese: 0.2%, cerium: 0.2%, lanthanum: 0.3%, impurity element Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium; AZ91 base alloy and magnesium-20% cerium-lanthanum master alloy are selected as raw materials, and the magnesium-20% cerium-lanthanum master alloy is magnesium Accounting for 80%, cerium lanthanum accounts for 20%; The cerium lanthanum raw material of described magnesium-cerium lanthanum intermediate alloy is made with the cerium lanthanum mixed rare earth after separating Nd, Pr, wherein the composition and mass percentage of cerium lanthanum rare earth are : Ce is 20% to 80%, and La is 80% to 20%.

Alloy properties are shown in Table 1 and Table 2.

Weigh the material according to the proportion, preheat the base alloy to 200°C, put it into a crucible with a preheating temperature of 300°C and melt it, and inject SF ₆ -CO ₂ with a volume ratio of SF ₆ :CO ₂ of 1:100 Protective gas, when the magnesium alloy is completely melted and the melt temperature reaches 720°C-740°C, add the magnesium-cerium-lanthanum master alloy, preheat the magnesium-cerium-lanthanum master alloy to 200°C, then continuously stir and feed SF ₆ -CO ₂ Protective gas until the intermediate alloy is completely melted; when the temperature reaches 730-740°C, pass argon gas to stir and refine for 5-10 minutes, and then stand still for 25-35 minutes. When the melt temperature drops to 680-700°C, the Die-casting production is carried out on a chamber die-casting machine to obtain a high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum.

Embodiment 4 AZ91+CeLa (Ce=0.6%, La=0.01%) alloy

The composition and mass percentage of the new high-strength corrosion-resistant die-casting magnesium alloy containing cerium-lanthanum rare earth are: aluminum: 9%, Zn: 0.9%, manganese: 0.2%, cerium: 0.6%, lanthanum: 0.01%, impurity element Fe≤0.02% , Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium; AZ91 base alloy and magnesium-20 % cerium-lanthanum master alloy are selected as raw materials, and the magnesium-20% cerium-lanthanum master alloy is magnesium Accounting for 80%, cerium lanthanum accounts for 20%; The cerium lanthanum raw material of described magnesium-cerium lanthanum intermediate alloy is made with the cerium lanthanum mixed rare earth after separating Nd, Pr, wherein the composition and mass percentage of cerium lanthanum rare earth are : Ce is 20% to 80%, and La is 80% to 20%.

Alloy properties are shown in Table 1 and Table 2.

Weigh the material according to the proportion , preheat the base alloy to 200°C, put it into a crucible with a preheating temperature of 300°C and melt it, and inject SF ₆ -CO ₂ with a volume ratio of SF ₆ :CO ₂ of 1:100 Protective gas, when the magnesium alloy is completely melted and the melt temperature reaches 720°C-740°C, add the magnesium-cerium-lanthanum master alloy, preheat the magnesium-cerium-lanthanum master alloy to 200°C, then continuously stir and feed SF ₆ -CO ₂ Protective gas until the intermediate alloy is completely melted; when the temperature reaches 730-740°C, pass argon gas to stir and refine for 5-10 minutes, and then stand for 25-35 minutes, when the melt temperature drops to 680-700°C, Die-casting production is carried out on a chamber die-casting machine to obtain a high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum.

Table 1

Alloy No. Tensile strength (MPa) Yield strength (MPa) Elongation (%) Example 1 Example 2 Example 3 Example 4AZ91 242260235240220 150155145150145 57563

Table 1 compares the room temperature mechanical properties of the alloys of Example 1, Example 2, Example 3, and Example 4 of the present invention and AZ91.

Table 2

alloy composition Corrosion rate (mg/cm ² day)

AZ91 7.70 Example 1 0.95 Example 2 0.55 Example 3 1.03 Example 4 0.77

Table 2 is a comparison of the corrosion resistance of the alloys of Example 1, Example 2, Example 3, and Example 4 of the present invention and AZ91.

Claims (5)

1. A high-strength corrosion-resistant die-casting magnesium alloy containing cerium and lanthanum, characterized in that the composition and mass percentage are: Al is 8.5% to 9.5%, Zn is 0.4% to 0.9%, Mn is 0.2% to 0.6%, and the rare earth is Ce is 0.01% %～1.5%, La is 0.01%～1.5%, impurity elements Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium; select AZ91 base alloy and magnesium-20% cerium Lanthanum master alloy is used as a raw material, and the magnesium-20% cerium-lanthanum master alloy accounts for 80% of magnesium and 20% of cerium-lanthanum; the cerium-lanthanum raw material of the magnesium-cerium-lanthanum master alloy is separated from Nd and Pr It is made of cerium-lanthanum mixed rare earth, wherein the composition and mass percentage of cerium-lanthanum rare earth are: Ce is 20% to 80%, and La is 80% to 20%. 2. The cerium-containing lanthanum high-strength corrosion-resistant die-casting magnesium alloy as claimed in claim 1 is characterized in that the composition and mass percentage are: Al is 9%, Zn is 0.9%, Mn is 0.2%, Ce is 0.01%, La 1.0%, impurity elements Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium. 3. The cerium-containing lanthanum high-strength corrosion-resistant die-casting magnesium alloy as claimed in claim 1 is characterized in that the composition and mass percentage are: Al is 9%, Zn is 0.9%, Mn is 0.2%, Ce is 0.6%, La 0.4%, impurity elements Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium. 4. The cerium-containing lanthanum high-strength corrosion-resistant die-casting magnesium alloy as claimed in claim 1 is characterized in that the composition and mass percentage are: Al is 9%, Zn is 0.9%, Mn is 0.2%, Ce is 0.2%, La 0.3%, impurity elements Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium. 5. The cerium-containing lanthanum high-strength corrosion-resistant die-casting magnesium alloy as claimed in claim 1 is characterized in that the composition and mass percentage are: Al is 9%, Zn is 0.9%, manganese is 0.2%, cerium is 0.6%, lanthanum 0.01%, impurity elements Fe≤0.02%, Cu≤0.002%, Si≤0.01%, Ni≤0.001%, and the balance is magnesium.

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