CN105154733A - Novel non-rare earth cast magnesium alloy and preparation method thereof - Google Patents

Abstract

The invention is a new type of non-rare earth cast magnesium alloy, the alloy is Mg-Bi-Zr-Zn alloy, the weight percentage of its components is: Bi? 0.5～8wt%; Zr? 0.35～1.0wt%; Zn? 0.1-2.0wt%, and the balance is Mg. The present invention discovers the significant grain refinement effect of Zr element in the Mg-Bi alloy system on the basis of Mg-Bi, thereby improving the strength and plasticity of the alloy. A small amount of zinc is added to increase the strength of the alloy, so that a high-strength cast magnesium alloy has been developed in this alloy series, with a yield strength of 140-155MPa, a tensile strength of 245-285MPa, and an elongation of about 6.5%.

Description

Novel non-rare earth cast magnesium alloy and preparation method thereof

technical field

The invention relates to a magnesium alloy and a preparation method thereof, in particular to a low-cost non-rare earth cast magnesium alloy and a preparation method thereof, which belong to the field of metal materials and metallurgy; the new magnesium alloy can be used as a potential heat-resistant magnesium alloy and Biomedical magnesium alloy materials.

Background technique

Magnesium alloy is the lightest metal structure material. It has many advantages such as high specific strength, high specific stiffness, good electromagnetic shielding performance, excellent casting performance, easy cutting and easy recycling, and has been widely used. Among the existing applications of magnesium alloys, cast magnesium alloys account for more than 90%, and are mainly used in automobiles, aircraft, 3C products and military fields to meet the requirements of weight reduction, noise absorption, shock absorption and radiation protection. In the automotive industry, reducing vehicle weight will improve fuel efficiency and reduce exhaust emissions. 60% of the fuel used by the car is consumed by the car's own weight. For every 10% reduction in the weight of the car, the fuel consumption will be reduced by 8-10%. At the same time, the lightweight of the car can increase the carrying capacity and payload of the vehicle, improve the braking and acceleration performance, and greatly improve the noise and vibration of the vehicle. Commercial cast magnesium alloys with large usage include AZ91D, AM50, AM60B, AS41 and AE42, etc., but the strength of magnesium alloys is not high, which makes the parts using magnesium alloys as stress parts have to increase the wall thickness, which increases the cost, and weaken the advantages of light weight, thus restricting the further popularization and application of magnesium alloys; in addition, the performance of magnesium alloy parts with high Al content is significantly reduced at high temperatures, and the long-term working temperature cannot exceed 120 °C. Therefore, it is urgent to develop low-cost high-strength magnesium alloys to solve the above problems.

By introducing a large number of strengthening phases into magnesium alloys and refining the grains, the strengthening and toughening of magnesium alloys can be achieved, and magnesium alloys with higher strength can be developed. In the prior art, CN102978497A discloses a high-strength and toughness cast magnesium alloy. ~0.7%, the rest is magnesium and a small amount of unavoidable impurity elements. After solid solution and aging treatment, the tensile strength of the alloy is not less than 305MPa, the yield strength is not less than 205MPa, and the elongation is not less than 10%. It has excellent comprehensive mechanical properties . However, the alloy contains Cu and other pure metals with higher melting points as raw materials, and requires long-term (not less than 24 hours) solution treatment and double-stage aging treatment, so the preparation process is complicated. CN102534330A discloses a high-strength casting magnesium alloy. The weight percentage of the alloy components is Gd8-14%, Y1-5%, Al0.6-2%, and the rest is magnesium and unavoidable impurity elements. After aging treatment, the tensile strength of the alloy is between 300-355MPa, the yield strength is between 210-255MPa, and the elongation is between 2-8%. It has high strength, but the elongation is low, and the A large amount of expensive rare earth elements such as Gd and Y need to be added to the alloy, which directly increases the cost of the alloy, increases the density of the alloy, and also leads to poor casting formability. CN1752251 discloses a high-strength magnesium alloy and its preparation method. The weight percentages of its components are: Nd2.5-3.6wt%, Zr0.35-0.8wt%, Zn content not more than 0.4wt%, Ca content not more than More than 0.5wt%, the rest is magnesium and unavoidable impurities. After solid solution and aging treatment, the alloy has high mechanical properties, the tensile strength is 280-320MPa, the yield strength is 140-155MPa, the elongation is 5-12%, and the alloy also contains more precious elements (Nd2. 5-3.6wt%), which increases the cost of the alloy and pollutes the environment. These high-cost magnesium alloys are difficult to commercialize in large quantities.

Therefore, through the development of non-rare earth cast magnesium alloys, and then obtain low-cost high-strength magnesium alloys, it is beneficial to reduce the cost of magnesium alloys and promote the application of magnesium alloys in parts of automobiles and other products, which has important economic and social significance.

Contents of the invention

The purpose of the present invention is to solve the problems existing in the existing high-strength cast magnesium alloys, such as using a variety of high rare earth elements or high-priced alloy elements, resulting in high cost, high density, and poor casting performance of the alloy so that it is difficult to commercialize and apply it. Provide a new type of non-rare earth casting magnesium alloy and its preparation method, the magnesium alloy is a new type of Mg-Bi-Zr-Zn magnesium alloy, the Zr element is added in the form of Mg-Zr master alloy in the smelting process, so that Zr Elements can be easily added to the alloy, so that it has a strong refinement effect in the Mg-Bi alloy, so that the magnesium alloy has excellent comprehensive mechanical properties, and at the same time, the cost of raw materials and processing is low, and it is easy to achieve mass production.

Technical scheme of the present invention is:

A new type of non-rare earth casting magnesium alloy, which is Mg-Bi-Zr-Zn alloy, the weight percentage of its components is: Bi0.5-8wt%; Zr0.35-1.0wt%; Zn0.1-2.0wt%, The balance is Mg.

The preparation method of the novel non-rare earth cast magnesium alloy comprises the following steps:

1) Batching: use pure Mg ingot, pure bismuth block, pure zinc block and Mg-Zr master alloy as raw materials, and carry out batching according to the magnesium alloy composition;

2) Melting: Put the pure Mg ingot into the crucible of the smelting furnace, set the furnace temperature to 700-730°C and keep it. After it melts, put the pure bismuth block, pure zinc block and Add the Mg-Zr master alloy into the molten magnesium; then increase the melting temperature by 10-20°C, keep it warm for 10-15 minutes, and then stir for 2-5 minutes;

3) Pouring: lower the furnace temperature by 10-30°C to the pouring temperature, keep the temperature for 8-10 minutes, pour the magnesium alloy melt into the corresponding mold, and use the gravity casting or pressure casting method to obtain the new type Non-rare earth cast magnesium alloy; wherein, the whole process from smelting to pouring is carried out under the protection of CO ₂ /SF ₆ mixed gas;

The Mg-Zr master alloy is preferably a Mg-20Zr master alloy.

The composition of the CO ₂ /SF ₆ mixed gas is preferably a volume ratio of CO ₂ :SF ₆ =100:1.

The raw materials and equipment used in the preparation method of the above-mentioned novel magnesium alloy are all obtained through known means, and the operation technology used is within the grasp of those skilled in the art.

Substantive features of the present invention are:

The magnesium alloy of the present invention uses Bi as the main alloying element, and Bi can form Mg ₃ Bi ₂ phase with high melting point (melting point is 823° C.) with magnesium in the alloy in situ, and its higher thermal stability can be compared with magnesium-rare earth The thermal stability of the phase is comparable, and the price is low. The Mg ₃ Bi ₂ phase can effectively pin the movement of the grain boundary, hinder the movement of dislocations, and improve the mechanical properties of the alloy. The Zr element is used as the grain refiner. The crystal structure of Zr is similar to that of Mg. It can play the role of heterogeneous nucleation when the alloy is solidified, thereby greatly refining the grain, improving the performance of the alloy, and improving the process of the alloy. Performance, the content of Zr is 0.35-1.0%. A small amount of Zn is also added to the alloy, which can play a certain role in solid solution strengthening, and at the same time adjust the casting performance of the alloy and improve the shrinkage tendency of the alloy.

The beneficial effects of the present invention are

1) The present invention is a cast magnesium alloy based on Mg-Bi alloy system, which is a brand-new cast magnesium alloy series, and a large amount of Mg ₃ Bi ₂ phases are formed in the alloy as the strengthening phase of the alloy. On this basis, it was found that the Zr element has a significant grain refinement effect in the Mg-Bi alloy system, thereby improving the strength and plasticity of the alloy. A small amount of zinc is added to increase the strength of the alloy, so that a high-strength cast magnesium alloy has been developed in this alloy series, with a yield strength of 140-155MPa, a tensile strength of 245-285MPa, and an elongation of more than 6.5%.

2) The preparation method of Mg-Bi-Zr-Zn alloy among the present invention, because metal Bi (271 ℃ of fusing points) and Zn in the raw material that adopts, and the fusing point with Mg-Zr master alloy are all relatively low, and smelting is easy, saves energy. Since the strengthening phase Mg ₃ Bi ₂ phase in the alloy is formed in situ, the existing magnesium alloy smelting and heat treatment equipment can process it without additional improvement, and the requirements for production equipment are low. (simple equipment, high production efficiency)

3) The alloy developed by the present invention has the prospect of being a heat-resistant magnesium alloy. The strengthening phase (Mg ₃ Bi ₂ phase) in the alloy has a relatively high melting point (melting point is 823°C), which is comparable to the high temperature formed by magnesium rare earth. At high temperature, due to its better thermal stability, its strengthening effect can still be maintained. Thereby, the heat resistance of the alloy can be improved.

4) The magnesium alloy of the present invention has low cost. Because it does not contain precious metals such as rare _earths , the metal Bi used to generate the _Mg3Bi2 phase with high thermal stability in situ is cheap, and the alloy cost is low (rare earths are generally 1000 to 5000 yuan per kilogram, while the metal Bi used in this patent is per kilogram Only about 200 yuan); can be widely used in casting parts of civilian products such as automobiles.

5) Bi, the main alloying element of the alloy, has no toxic effect on the environment and the human body, is an environment-friendly material, and is expected to be used as a biomedical material.

6) The as-cast billet alloy of the present invention, because the grain type becomes equiaxed grain with very uniform size, is convenient for plastic processing, can be used for plastic processing such as extrusion, and produces materials with higher performance.

Description of drawings

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described below in conjunction with the accompanying drawings.

Fig. 1 is the microstructure that obtains alloy in embodiment 1

Fig. 2 is the microstructure that obtains alloy in embodiment 2

Figure 3 shows the microstructure of as-cast Mg

Figure 4 is the microstructure of the alloy obtained in Comparative Example 1

Fig. 5 is the SEM photograph of alloy tensile fracture obtained in embodiment 2

The tensile stress-strain curves of the alloy obtained in Fig. 6 embodiment 1,2,3 and the alloy obtained in comparative example 1 at room temperature

Detailed ways

The present invention (technical solution) is described further below with specific embodiment, and following examples are all carried out under the premise of technical solution of the present invention, have provided detailed embodiment and concrete operation process, but protection scope of the present invention It is not limited to the following examples.

Select three alloy components Mg-3.8Bi-0.7Zr-1.0Zn (wt%) (alloy 1), Mg-6.0Bi-0.7Zr-1.0Zn (wt%) (alloy 2), Mg-7.0Bi-0.7Zr -1.0Zn (wt%) (alloy 3) as a typical example.

According to the technical scheme of the present invention, select pure Mg (99.8wt%), pure Bi (99wt%), pure Zn (99.9wt%) and Mg-20Zr (the actual detection content of Zr is 20.01wt%) master alloy as raw material, through Batching, smelting, melt treatment and pouring are used to make low-cost high-strength magnesium alloys, and the mechanical properties and microstructure of the obtained alloys are tested and analyzed.

Example 1

1. Take raw materials by the mass percent of alloy Mg-3.8Bi-0.7Zr-1.0Zn (wt%): pure Bi, pure Zn, Mg-20Ca, all the other are Mg (per 1000 grams of target alloy can be made of 35 grams of Mg-20Zr, 10g of Zn, 38g of Bi and 917g of Mg); and do a good job of surface treatment of raw materials (such as removing dirt, scale, etc.).

② First clean the melting furnace and heat it to 450°C, put the magnesium ingot preheated to 200°C into the crucible of the melting furnace, set the furnace temperature to 720°C, heat slowly, the heating rate is 20-40°C/min, Hold after reaching the set temperature.

③ After the pure magnesium ingots are completely melted, add pure bismuth, pure zinc and Mg-20Zr master alloy preheated to about 200°C.

④Raise the furnace temperature to 740°C, keep it warm for 10-15 minutes, and stir for 2-5 minutes to make all alloy elements evenly distributed in the magnesium alloy melt (this temperature is to make the Zr element fully melt into the alloy melt middle).

⑤ Afterwards, adjust the furnace temperature to 720°C, keep it warm for 8-10 minutes, skim off the scum on the surface of the melt, and then pour it into a mold, cool and solidify, and obtain the required magnesium alloy. The whole process from smelting to pouring is carried out under the protection of CO ₂ /SF ₆ mixed gas, and the volume ratio of CO ₂ :SF ₆ is 100:1.

Samples were taken from the obtained alloy, processed into test bars, and subjected to tensile tests at room temperature. It was measured that the tensile strength of the obtained alloy reached 245 MPa, the yield strength reached 140 MPa, and the elongation was 6.9%.

Example 2

1. take raw materials by the mass percent of alloy Mg-6.0Bi-0.7Zr-1.0Zn (wt%): pure Bi, pure Zn, Mg-20Ca, all the other are Mg; oxide skin, etc.).

② First clean the melting furnace and heat it to 450°C, put the magnesium ingot preheated to 200°C into the crucible of the melting furnace, set the furnace temperature to 720°C, and heat slowly at a heating rate of 20-40°C/min. Hold after reaching the set temperature.

③ After the pure magnesium ingots are completely melted, add pure bismuth, pure zinc and Mg-20Zr master alloy preheated to about 200°C.

④Raise the furnace temperature to 740°C, keep it warm for 10-15 minutes, and stir for 2-5 minutes to make all alloy elements evenly distributed in the magnesium alloy melt (this temperature is to make the Zr element fully melt into the alloy melt middle).

⑤ Afterwards, adjust the furnace temperature to 720°C, keep it warm for 8-10 minutes, skim off the scum on the surface of the melt, and then pour it into a mold, cool and solidify, and obtain the required magnesium alloy. The whole process from smelting to pouring is carried out under the protection of CO ₂ /SF ₆ mixed gas, and the volume ratio of CO ₂ :SF ₆ is 100:1.

Samples were taken from the obtained alloy, processed into test bars, and subjected to tensile tests at room temperature. It was measured that the tensile strength of the obtained alloy reached 272 MPa, the yield strength reached 148 MPa, and the elongation was 6.8%.

Example 3

1. take raw material by the mass percent of alloy Mg-7.0Bi-0.7Zr-1.0Zn (wt%): pure Bi, pure Zn, Mg-20Ca, all the other are Mg; oxide skin, etc.).

② First clean the melting furnace and heat it to 450°C, put the magnesium ingot preheated to 200°C into the crucible of the melting furnace, set the furnace temperature to 720°C, heat slowly, the heating rate is 20-40°C/min, Hold after reaching the set temperature.

③ After the pure magnesium ingots are completely melted, add pure bismuth, pure zinc and Mg-20Zr master alloy preheated to about 200°C.

④ Raise the temperature of the furnace to 740°C, keep it warm for 10-15 minutes, and then stir for 2-5 minutes to make all the alloying elements evenly distributed in the magnesium alloy melt.

⑤ Afterwards, adjust the furnace temperature to 720°C, keep it warm for 8-10 minutes, skim off the scum on the surface of the melt, and then pour it into a mold, cool and solidify, and obtain the required magnesium alloy. The whole process from smelting to pouring is carried out under the protection of CO ₂ /SF ₆ mixed gas, and the volume ratio of CO ₂ :SF ₆ is 100:1.

Samples were taken from the obtained alloy, processed into test bars, and subjected to tensile tests at room temperature. It was measured that the tensile strength of the obtained alloy reached 285 MPa, the yield strength reached 155 MPa, and the elongation was 6.6%.

Comparative example 1

1. take by weighing raw material by the mass percent of alloy Mg-6.0Bi-0.7Zr-1.0Zn (wt%): pure Bi, pure Zn, pure Zr (99.99wt%), all the other are Mg; And do raw material surface treatment (such as Remove dirt, scale, etc.).

② First clean the melting furnace and heat it to 450°C, put the magnesium ingot preheated to 200°C into the crucible of the melting furnace, set the furnace temperature to 720°C, and heat slowly at a heating rate of 20-40°C/min. Hold after reaching the set temperature.

③ After the pure magnesium ingot is completely melted, add pure bismuth, pure zinc and pure Zr (99.99wt%) preheated to about 200°C.

④Raise the furnace temperature to 740°C, keep it warm for 10-15 minutes, and then stir for 2-5 minutes.

⑤ Afterwards, adjust the furnace temperature to 720° C., keep the temperature for 8 to 10 minutes, skim off the scum on the surface of the melt, and then pour it into a mold. After cooling and solidifying, the comparative example 1 magnesium alloy is obtained. The whole process from smelting to pouring is carried out under the protection of CO ₂ /SF ₆ mixed gas, and the volume ratio of CO ₂ :SF ₆ is 100:1.

Samples were taken from the obtained alloy, processed into test bars, and subjected to tensile tests at room temperature. It was measured that the tensile strength of the obtained alloy reached 102 MPa, the yield strength reached 58 MPa, and the elongation rate was 1.3%.

Comparative analysis of microstructure and mechanical properties:

Fig. 1 is the microstructure of the alloy obtained in Example 1, from which it can be seen that the alloy is all made up of uniform equiaxed grains; Fig. 2 is the microstructure of the alloy obtained in Example 2, from which it can be seen that the alloy All are composed of uniform equiaxed grains; Fig. 3 is the microstructure of as-cast Mg obtained under the same experimental conditions as in Example 1, from which it can be seen that the as-cast grains of pure magnesium are very coarse, and most of them are columnar crystal. Figure 4 is the microstructure of the alloy obtained in Comparative Example 1, from which it can be seen that the alloy is mainly composed of two types of grains: equiaxed dendrites and columnar grains. Comparing the as-cast structure of pure magnesium, it can be seen that the comparative example 1 The grains of the obtained alloy are refined, but the grains of equiaxed dendrites in the alloy are still relatively coarse. Comparing Examples 1 and 2 with Comparative Example 1, it can be seen that the alloys obtained in Examples 1 and 2 are all composed of uniform equiaxed grains, and the grain types of equiaxed crystals are from those of the alloy obtained in Comparative Example 1. Axial dendrites transform into cellular equiaxed crystals of the alloy obtained in Examples 1 and 2. It can be seen that when the Zr element is added to the Mg-Bi alloy in the form of an intermediate alloy, it can produce a very strong refining effect, which can greatly improve the strength and plasticity of the alloy, and when the Zr element is in the form of pure Zr in the alloying process When added, it is difficult to obtain a satisfactory refining effect, which shows that adding Zr element in the form of Mg-Zr master alloy has higher alloying efficiency. Figure 5 is a scanning photo of the tensile fracture of the alloy obtained in Example 2. It can be seen from the fracture morphology that the grains of the alloy are very uniform and fine, which once again proves that the Mg-Bi-Zr-Zn alloy is a fine-grained Cast magnesium alloy.

Fig. 6 is the tensile curve of the alloy obtained in Examples 1, 2, 3 and Comparative Example 1. For the mechanical properties of Examples 1, 2, and 3, the yield strength is 140-155MPa, the tensile strength is 245-285MPa, and the elongation is above 6.5%. Compared with the mechanical properties of the alloy in Example 1, the tensile strength reaches 102MPa, and the yield strength reaches 58MPa , The elongation rate is 1.3%, which is a very obvious improvement. Combining the microstructure of each alloy and the strengthening law of general metal materials, it can be speculated that this is mainly the result of the combined effect of grain boundary strengthening and second phase strengthening. On the other hand, as the Bi content increases, the strength of Examples 1, 2, and 3 gradually increases, and the elongation decreases slightly, which is mainly because the number of Mg ₃ Bi ₂ phases increases with the increase of Bi content , on the one hand, it will increase the strength of the alloy, and on the other hand, it will reduce the plasticity of the alloy.

Matters not covered in the present invention are known technologies.

Claims (4)

1. A novel non-rare earth cast magnesium alloy is characterized in that the alloy is a Mg-Bi-Zr-Zn alloy, and the percentage by weight of its components is: Bi0.5～8wt%; Zr0.35～1.0wt%; Zn0 .1～2.0wt%, the balance is Mg. 2. the preparation method of novel non-rare earth cast magnesium alloy as claimed in claim 1 is characterized in that comprising the following steps: 1) Batching: use pure Mg ingot, pure bismuth block, pure zinc block and Mg-Zr master alloy as raw materials, and carry out batching according to the magnesium alloy composition; 2) Melting: Put the pure Mg ingot into the crucible of the smelting furnace, set the furnace temperature to 700-730°C and keep it. After it melts, put the pure bismuth block, pure zinc block and Add the Mg-Zr master alloy into the molten magnesium; then increase the melting temperature by 10-20°C, keep it warm for 10-15 minutes, and then stir for 2-5 minutes; 3) Pouring: Afterwards, lower the furnace temperature by 10-30°C to the pouring temperature, keep the temperature for 8-10 minutes, pour the magnesium alloy melt into the corresponding mold, and use the gravity casting or pressure casting method to obtain the above-mentioned A new type of non-rare earth cast magnesium alloy; wherein, the whole process from smelting to pouring is carried out under the protection of CO ₂ /SF ₆ mixed gas. 3. The preparation method of novel non-rare earth cast magnesium alloy as claimed in claim 2, characterized in that said Mg-Zr master alloy is preferably Mg-20Zr master alloy. 4. The method for preparing a new type of non-rare earth cast magnesium alloy according to claim 2, characterized in that the composition of the CO ₂ /SF ₆ mixed gas is preferably a volume ratio of CO ₂ :SF ₆ =100:1.