CN102925775B - Low-deformation-resistance wrought magnesium alloy and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of non-ferrous metal alloys, and specifically discloses a deformed magnesium alloy with low deformation resistance and a preparation method thereof. On the basis of AZ61 magnesium alloy, in terms of weight percentage, Mn in its alloy elements is increased to 0.65-1.2%, and RE0.4-1.0% and Bi0.2-1.0% are added at the same time. The invention carries out multi-element alloying on the basis of the AZ61 magnesium alloy, and the obtained novel deformed magnesium alloy has low thermal deformation resistance, and the obtained deformed material has high strength at room temperature. Not only is it very beneficial to solve the problem of difficulty in extrusion of large thin-walled and complex-shaped magnesium alloy profiles due to the excessive extrusion force required, but also to improve the strength of the deformed material at the same time. It has practical application value for the preparation and application of high-performance large-size, thin-walled and complex-shaped magnesium alloy profiles. In addition, the preparation method of the present invention is easy to operate; due to the relatively low addition of rare earth elements and bismuth with high prices, the increase in the preparation cost of the alloy is limited.

Description

A kind of low deformation resistance wrought magnesium alloy and preparation method thereof

technical field

The invention belongs to the technical field of non-ferrous metal alloys, and relates to a deformed magnesium alloy with low deformation resistance and a preparation method thereof.

Background technique

Magnesium alloy is currently the lightest metal structural material available, with a series of advantages such as high specific strength, high specific stiffness, strong vibration damping, electromagnetic shielding and radiation resistance, easy cutting, easy recycling, etc., known as "21 Century commercial green environmental protection and ecological metal structural materials". It has broad application prospects in high-tech fields such as aerospace, weaponry, automobiles, and 3C products. With the increasing tension of international energy sources and environmental protection issues in recent years, the demand for lightweight structural materials has become increasingly urgent, which has greatly stimulated the development of magnesium alloys.

Since magnesium has a hexagonal close-packed crystal structure, magnesium alloys have poor plastic deformation ability, so most magnesium alloy products are realized by casting process. The current magnesium alloy products are mostly castings, especially die castings. However, compared with cast magnesium alloys, wrought magnesium alloys have higher strength and toughness, and can obtain more diverse sizes and specifications. Therefore, one of the main developments of magnesium alloys in the future is to devote itself to the development and application of wrought magnesium alloy products with excellent plastic deformation properties and performance. Among all the plastic deformation methods of magnesium alloys, extrusion deformation can maximize the plasticity of the material. Moreover, various magnesium alloy deformed products such as rods, tubes, and profiles can be obtained by extrusion, which has broad application prospects in the fields of construction, transportation, and aviation industry. Therefore, extrusion deformation is the main means to obtain deformed magnesium alloy materials. However, due to the inherent hexagonal close-packed crystal structure of magnesium alloys, even with extrusion deformation, the plastic deformation ability is still poor. The specific performance is that the extrusion rate is low (only a quarter of the extrusion rate of aluminum alloy, otherwise, the extruded product will appear transverse cracks), and the extrusion force required for large-sized and complex-shaped thin-walled extruded profiles is too large. Extrusion processing is difficult. At present, with the development of high-speed trains, rail transit and aerospace industries and their urgent requirements for lightweight, there is an increasingly urgent demand for high-performance (mainly high-strength), large-scale, and complex-shaped thin-walled magnesium alloy extrusion profiles. Therefore, it is of great significance to develop a new wrought magnesium alloy with low deformation resistance (reduced extrusion force) and high room temperature strength after deformation.

Currently used wrought magnesium alloys mainly include Mg-Al series, Mg-Zn-Zr series, Mg-Li and Mg-Mn series. Among them, Mg-Zn-Zr and Mg-Li series are expensive and difficult to prepare, and Mg-Mn series have low strength. The Mg-Al series has medium strength, low cost, relatively mature preparation technology, and good weldability and corrosion resistance, so it is currently the most widely used wrought magnesium alloy series. A small amount of zinc and manganese are also contained in the Mg-Al alloy. Among them, AZ61 alloy (containing about 6% aluminum) has good strength and plasticity, and has a good application prospect.

If multi-element microalloying can be carried out on the basis of AZ61 wrought magnesium alloy, while improving the room temperature strength of the wrought material, by changing the plastic deformation mechanism and reducing the deformation resistance of hot working, it will undoubtedly solve the problem of large-size, thin-walled magnesium alloys. 1. Existing in the preparation of profiles with complex shapes, the problems of extrusion difficulties and insufficient strength of extrusion materials due to the excessive extrusion force required are of great significance.

The inventor's research group once conducted research on "the influence of Mn and RE on the microstructure and properties of AZ61 deformed magnesium alloy" (10,000 yuan, the influence of Mn and RE on the microstructure and properties of AZ61 deformed magnesium alloy [D], Zhengzhou University, year 2011). The results show that when the Mn content is 0.7312% and the rare earth content is 0.39%, the deformation resistance is low, but the strength of the alloy is low; with the decrease of the "Mn/RE" ratio, the strength increases, but the deformation resistance increases with the increase. Further research conducted by the research group on the basis of this master's thesis showed that the morphology and distribution of the aluminum-manganese phase and the rare earth phase have a significant impact on the deformation resistance and room temperature strength of the alloy. Therefore, on the basis of the previous research, it is of great research and practical value to take measures to further reduce the deformation resistance of the alloy and at the same time make the deformed material have a higher room temperature strength.

Contents of the invention

The object of the present invention is to provide a wrought magnesium alloy with low deformation resistance and high profile room temperature strength and a preparation method thereof.

In order to achieve the above object, the technical scheme that the present invention takes is as follows:

A low deformation resistance wrought magnesium alloy, on the basis of AZ61 magnesium alloy, in terms of weight percentage, Mn (manganese) in the alloy element is increased to 0.65-1.2%, and RE (rare earth) 0.4-1.0%, Bi ( Bismuth) 0.2-1.0%.

Preferably, RE is Ce (cerium) or cerium-rich mixed rare earths. The content of cerium in the cerium-rich mixed rare earth is greater than 60wt%.

Preparation method, the steps are as follows:

① Prepare materials according to the weight percentage of alloy elements: pure magnesium ingot, pure aluminum ingot, pure zinc ingot, anhydrous MnCl ₂ , pure cerium or cerium-rich mixed rare earth, pure bismuth ingot; (the above purities refer to industrial pure)

②Heat the cast steel crucible to dark red, sprinkle the covering agent evenly on the inner wall and bottom of the crucible, add the preheated pure magnesium ingot and pure aluminum ingot, and sprinkle the covering agent evenly on it, and the temperature rises to 700 -740°C;

③ After all the charge is melted, add the preheated pure zinc ingot;

④ After the pure zinc ingots are completely melted, add preheated anhydrous MnCl ₂ , and stir with argon gas when adding; after the furnace charge is melted, let it stand still, and then stir with argon gas until the alloy composition is uniform;

⑤Raise the temperature to 760-780°C, add preheated pure cerium or cerium-rich mixed rare earth and pure bismuth ingots, after keeping warm, manually remove the bottom and stir, then stir with argon until the alloy composition is uniform, after standing still, clear the bottom of the pot and oxide slag on the surface;

⑥Reduce the temperature to 700-720°C, let it stand still, and cast it into an alloy.

Preferably, the covering agent is JDMF. The total addition amount of the covering agent is 2-3% of the total weight of the alloy element stock.

Preferably, in step ④, stand still for 15-30 minutes and stir with argon for 5-10 minutes.

Preferably, in step ⑤, heat preservation for 20-40 minutes, manual bottom stirring for 1-3 minutes, argon stirring for 1-2 minutes, and standing for 10-30 minutes.

Preferably, in step ⑥, stand for 15-30 minutes.

The function of the preheated raw materials described in steps ②, ③, ④, ⑤ is to remove moisture, and the temperature is preferably 150-200°C.

For the convenience of analyzing and testing alloy properties, the alloy ingot prepared by the present invention can be further processed as follows:

Extrusion of profiles:

Homogenize the ingot (homogenization temperature 350-420°C, time 6-24 hours), heat the homogenized magnesium alloy billet at 360-420°C for 1-3 hours, then put it into the preheating In the extruding cylinder, it is extruded into rods on a horizontal hydraulic extruder. Used to characterize deformation resistance and bar strength during extrusion.

Deformation resistance and deformation strength test method:

1) Characterization of deformation resistance

The deformation resistance (σ) is characterized by the extrusion power (N), extrusion speed (V), billet cross-sectional area (S), and extrusion ratio (α) of the extrusion machine during the extrusion process.

2) Bar strength

Refer to the GB6397-86 standard to process tensile samples, and use a tensile testing machine to measure the strength of the bar.

The invention point of the present invention: on the basis of the AZ61 magnesium alloy, increase the content of manganese, add an appropriate amount of rare earth and bismuth at the same time, control the morphology and distribution of the aluminum-manganese phase and rare earth phase through the action of bismuth and make it refined, and then change Twin ratio during hot deformation, promote dynamic recrystallization, change deformation mechanism, and form particle strengthening and fine-grain strengthening at the same time, to achieve the purpose of reducing the deformation resistance during hot extrusion and improving the room temperature strength of the profile; for extrusion Large-size, thin-walled, complex-shaped magnesium alloy profiles provide a new wrought magnesium alloy with low deformation resistance and high profile room temperature strength.

Advantage and positive effect of the present invention:

(1) On the basis of AZ61 magnesium alloy, multi-element alloying is carried out, and the obtained new wrought magnesium alloy has low hot-working deformation resistance, and the obtained wrought material has high room temperature strength. Not only is it very beneficial to solve the problem of difficulty in extrusion of large thin-walled and complex-shaped magnesium alloy profiles due to the excessive extrusion force required, but also to improve the strength of the deformed material at the same time. It has practical application value for the preparation and application of high-performance large-size, thin-walled, and complex-shaped magnesium alloy profiles;

(2) In addition, the preparation method of the present invention is easy to operate; due to the relatively low addition of rare earth elements and bismuth with high prices, the increase in the preparation cost of the alloy is limited.

Detailed ways

The following is an example of the preparation and extrusion of the alloy of the present invention, wherein the weight percent composition of cerium-rich mixed rare earths is 65% cerium, 10% neodymium, 20% lanthanum, and 5% praseodymium; the purity of the raw materials involved refers to industrial purity; and, The following examples are only some special points in the alloy composition and preparation process conditions of the present invention, and the present invention includes it but is not limited to it.

Example 1

Alloy composition (by weight percentage, the same applies below): Al 5.8%, Zn 0.8%, Mn 0.65%, Ce 0.6%, Bi 0.3%, Mg balance. Prepare materials according to the above alloy composition: pure aluminum ingot, pure zinc ingot, anhydrous MnCl ₂ , pure cerium, pure bismuth ingot, pure magnesium ingot.

Magnesium alloy ingot preparation process: ① Heat the cast steel crucible to dark red (about 500°C), sprinkle JDMF covering agent evenly on the inner wall and bottom of the crucible, add pure magnesium ingots and pure aluminum ingots preheated to 200°C, And sprinkle JDMF covering agent evenly on it, the temperature rises to 700 ℃, wherein the total addition amount of JDMF covering agent is 2% of the total weight of the alloy element stock. ② Add pure zinc ingots preheated to 200°C after all the charge is melted. ③ After the pure zinc ingots are completely melted, add anhydrous MnCl ₂ preheated to 150°C, and stir with Ar gas when adding. After the charge is melted, let stand for 16 minutes, and then stir with argon for 10 minutes. ④Raise the temperature to 760°C, add pure cerium and pure bismuth ingots preheated to 200°C, keep warm for 30 minutes, manually remove the bottom and stir for 2 minutes, then stir with argon for 1 minute, and after standing for 10 minutes, clear the bottom of the pot and Oxidized slag on the surface. ⑤Reduce the temperature to 700°C, let it stand for 15 minutes, and cast it into an alloy rod ingot of φ120mm.

Specifically, the homogenization and extrusion process of the present embodiment are as follows:

Extrusion process: ingot homogenization treatment temperature 360°C, time 15 hours. 800t horizontal forward extruder is used to extrude alloy rods of φ30mm. The bar heating temperature is 360°C, and the holding time is 2 hours. The temperature of the extrusion cylinder was 340° C., and the extrusion speed was 2.5 m/min.

As a comparison, the same process was used to prepare AZ61 magnesium alloy ingots (composition: Al 5.8%, Zn 0.8%, Mn 0.2%, Mg balance), and the same homogenization and extrusion process was used to prepare φ30mm AZ61 magnesium alloy rods .

As a comparison, the same process was used to prepare alloy ingots for the previous work. The previous work alloy 1: Al 5.8%, Zn 0.8%, Mn 0.73%, cerium-rich mixed rare earth 0.39%, Mg balance; the previous work alloy 2: Al 5.8% , Zn 0.8%, Mn 0.68%, cerium-rich mixed rare earth 0.67%, Mg balance (refer to 10,000 yuan, the influence of Mn and RE on the microstructure and properties of AZ61 wrought magnesium alloy [D], Zhengzhou University, alloy composition in 2011 ), and the same homogenization and extrusion process was used to prepare φ30mm magnesium alloy rods.

The calculated deformation resistance and the extruded bar strength are listed in Table 1.

Example 2

Alloy composition: Al 6.2%, Zn 0.6%, Mn 0.8%, pure cerium 0.8%, Bi 0.4%, Mg balance. Prepare materials according to the above alloy composition: pure aluminum ingot, pure zinc ingot, anhydrous MnCl ₂ , pure cerium, pure bismuth ingot, pure magnesium ingot.

Magnesium alloy ingot preparation process: ① Heat the cast steel crucible to dark red (about 500°C), sprinkle JDMF covering agent evenly on the inner wall and bottom of the crucible, add pure magnesium ingots and pure aluminum ingots preheated to 200°C, And sprinkle JDMF covering agent evenly on it, the temperature rises to 720 ℃, wherein the total addition amount of JDMF covering agent is 2.5% of the total weight of the alloy element stock. ② Add pure zinc ingots preheated to 200°C after all the charge is melted. ③ After the pure zinc ingots are completely melted, add anhydrous MnCl ₂ preheated to 150°C, and stir with Ar gas when adding. After the charge is melted, let stand for 20 minutes, then stir with argon for 8 minutes. ④Raise the temperature to 760°C, add pure cerium and pure bismuth ingots preheated to 200°C, keep warm for 30 minutes, manually drag the bottom and stir for 3 minutes, and then stir with argon for 1 minute. After standing for 20 minutes, remove the oxidized slag on the bottom and surface of the pot. ⑤Reduce the temperature to 710°C, let it stand for 20 minutes, and cast it into an alloy rod of φ120mm.

Specifically, the homogenization and extrusion process of the present embodiment are as follows:

Extrusion process: the ingot homogenization treatment temperature is 380°C, and the time is 14 hours. 800t horizontal forward extruder is used to extrude alloy rods of φ30mm. The bar heating temperature is 380°C, and the holding time is 2 hours. The temperature of the extrusion barrel is 360° C., and the extrusion speed is 2.5 m/min.

As a comparison, the same process was used to prepare AZ61 magnesium alloy ingots (composition: Al 6.2%, Zn 0.6%, Mn 0.2%, Mg balance), and the same homogenization and extrusion process was used to prepare φ30mm AZ61 magnesium alloy rods .

The calculated deformation resistance and the extruded bar strength are listed in Table 1.

Example 3

Alloy composition: Al 6.5%, Zn 0.6%, Mn 0.8%, cerium-rich mixed rare earth 0.8%, Bi0.6%, Mg balance. Prepare materials according to the above alloy composition: pure aluminum ingot, pure zinc ingot, anhydrous MnCl ₂ , cerium-rich mixed rare earth, pure bismuth ingot, pure magnesium ingot.

Magnesium alloy ingot preparation process: ① Heat the cast steel crucible to dark red (about 500°C), sprinkle JDMF covering agent evenly on the inner wall and bottom of the crucible, add pure magnesium ingots and pure aluminum ingots preheated to 200°C, And sprinkle JDMF covering agent evenly on it, the temperature rises to 720 ℃, wherein the total addition amount of JDMF covering agent is 3% of the total weight of the alloy element stock. ② Add pure zinc ingots preheated to 200°C after all the charge is melted. ③ After the pure zinc ingots are completely melted, add anhydrous MnCl ₂ preheated to 150°C, and stir with Ar gas when adding. After the charge is melted, let stand for 20 minutes, then stir with argon for 6 minutes. ④Raise the temperature to 770°C, add cerium-rich mixed rare earth and pure bismuth ingots preheated to 200°C, keep warm for 30 minutes, manually drag the bottom and stir for 2 minutes, and then stir with argon for 2 minutes. After standing for 10 minutes, remove the oxidized slag on the bottom and surface of the pot. ⑤Reduce the temperature to 720°C, let it stand for 20 minutes, and cast it into an alloy rod of φ120mm.

Specifically, the homogenization and extrusion process of the present embodiment are as follows:

Extrusion process: the ingot homogenization treatment temperature is 380°C, and the time is 14 hours. 800t horizontal forward extruder is used to extrude alloy rods of φ30mm. The bar heating temperature is 380°C, and the holding time is 2 hours. The temperature of the extrusion barrel is 360° C., and the extrusion speed is 2.5 m/min.

As a comparison, the same process was used to prepare AZ61 magnesium alloy ingots (composition: Al 6.5%, Zn 0.6%, Mn 0.4%, Mg balance), and the same homogenization and extrusion process was used to prepare φ30mm AZ61 magnesium alloy rods .

The calculated deformation resistance and the extruded bar strength are listed in Table 1.

Example 4

Alloy composition: Al 7.0%, Zn 0.65%, Mn 1.0%, cerium-rich mixed rare earth 1.0%, Bi 0.8%, Mg balance. Prepare materials according to the above alloy composition: pure aluminum ingot, pure zinc ingot, anhydrous MnCl ₂ , cerium-rich mixed rare earth, pure bismuth ingot, pure magnesium ingot, and the weight percentage of cerium-rich mixed rare earth is cerium 65%, neodymium 10%, lanthanum 20%, praseodymium 5%.

Magnesium alloy ingot preparation process: ① Heat the cast steel crucible to dark red (about 500°C), sprinkle JDMF covering agent evenly on the inner wall and bottom of the crucible, add pure magnesium ingots and pure aluminum ingots preheated to 200°C, And sprinkle JDMF covering agent evenly on it, the temperature rises to 740 ° C, wherein the total amount of JDMF covering agent added is 2% of the total weight of the alloy element stock. ② Add pure zinc ingots preheated to 200°C after all the charge is melted. ③ After the pure zinc ingots are completely melted, add anhydrous MnCl ₂ preheated to 150°C, and stir with Ar gas when adding. After the charge is melted, let stand for 20 minutes, then stir with argon for 10 minutes. ④Raise the temperature to 780°C, add cerium-rich mixed rare earth and pure bismuth ingots preheated to 200°C, keep warm for 30 minutes, manually stir for 3 minutes, and then stir for 2 minutes with argon. After standing for 30 minutes, remove the oxidized slag on the bottom and surface of the pot. ⑤Reduce the temperature to 710°C, let it stand for 20 minutes, and cast it into an alloy rod of φ120mm.

Extrusion process: ingot homogenization treatment temperature 400°C, time 12 hours. 800t horizontal forward extruder is used to extrude alloy rods of φ30mm. The bar heating temperature is 400°C, and the holding time is 1.5 hours. The temperature of the extrusion barrel was 380° C., and the extrusion speed was 2.5 m/min.

As a comparison, the same process was used to prepare AZ61 magnesium alloy ingots (composition: Al 7.0%, Zn 0.65%, Mn 0.5%, Mg balance), and the same homogenization and extrusion process was used to prepare φ30mm AZ61 magnesium alloy rods .

The calculated deformation resistance and the extruded bar strength are listed in Table 1.

As can be seen from the above table: adopt extrusion technology described in the present invention to extrude, and the alloy of the present invention has thermal working deformation resistance to reduce by more than 20% compared with AZ61 magnesium alloy, and ultimate strength and yield strength increase by more than 10% and 30% respectively; The performance of "significantly increasing the strength of the deformed material while significantly reducing the hot working deformation resistance" possessed by the alloy of the present invention is obtained.

Claims (9)

1. one kind low resistance to deformation wrought magnesium alloys, it is characterized in that: on the basis of AZ61 magnesium alloy, by weight percentage, in its alloying element, Mn is increased to 0.65-1.2%, add RE 0.4-1.0%, Bi 0.2-1.0%, described RE is Ce or cerium-rich mischmetal simultaneously; The preparation process of this wrought magnesium alloys is as follows:

1. get the raw materials ready by the weight percent composition of alloying element: pure magnesium ingot, fine aluminium ingot, pure zinc ingot, anhydrous MnCl ₂, pure cerium or cerium-rich mischmetal, pure bismuth ingot;

2. by cast steel crucible heating to dark red, sprinkle insulating covering agent at crucible internal walls and bottom even, add pure magnesium ingot, fine aluminium ingot through preheating, and sprinkle insulating covering agent equably thereon, temperature rises to 700-740 DEG C;

3. after furnace charge all melts, add the pure zinc ingot after preheating;

4., after pure zinc ingot all melts, the anhydrous MnCl after preheating is added ₂, stir with argon gas time reinforced; After load melting, leave standstill, then it is even to be stirred to alloying constituent with argon gas;

5. be warming up to 760-780 DEG C, add the pure cerium after preheating or cerium-rich mischmetal and pure bismuth ingot, after insulation, manually drag for the end and stir, then it is even to be stirred to alloying constituent with argon gas, after leaving standstill, remove the oxidation sludge on the bottom of a pan and surface;

6. be cooled to 700-720 DEG C, after leaving standstill, be cast into alloy.

2. low resistance to deformation wrought magnesium alloys as claimed in claim 1, is characterized in that: in described cerium-rich mischmetal, cerium content is greater than 60wt%.

3. prepare a method for low resistance to deformation wrought magnesium alloys as claimed in claim 1 or 2, it is characterized in that step is as follows:

1. get the raw materials ready by the weight percent composition of alloying element: pure magnesium ingot, fine aluminium ingot, pure zinc ingot, anhydrous MnCl ₂, pure cerium or cerium-rich mischmetal, pure bismuth ingot;

2. by cast steel crucible heating to dark red, sprinkle insulating covering agent at crucible internal walls and bottom even, add pure magnesium ingot, fine aluminium ingot through preheating, and sprinkle insulating covering agent equably thereon, temperature rises to 700-740 DEG C;

3. after furnace charge all melts, add the pure zinc ingot after preheating;

4., after pure zinc ingot all melts, the anhydrous MnCl after preheating is added ₂, stir with argon gas time reinforced; After load melting, leave standstill, then it is even to be stirred to alloying constituent with argon gas;

5. be warming up to 760-780 DEG C, add the pure cerium after preheating or cerium-rich mischmetal and pure bismuth ingot, after insulation, manually drag for the end and stir, then it is even to be stirred to alloying constituent with argon gas, after leaving standstill, remove the oxidation sludge on the bottom of a pan and surface;

6. be cooled to 700-720 DEG C, after leaving standstill, be cast into alloy.

4. preparation method as claimed in claim 3, is characterized in that: described insulating covering agent is JDMF.

5. the preparation method as described in claim 3 or 4, is characterized in that: the total addition level of insulating covering agent is that alloying element is got the raw materials ready the 2-3% of gross weight.

6. preparation method as claimed in claim 5, is characterized in that: step 4. in, leave standstill 15-30 minute, argon gas stirs 5-10 minute.

7. preparation method as claimed in claim 6, is characterized in that: step 5. in, insulation 20-40 minute, manually drag for the end and stir 1-3 minute, argon gas stirs 1-2 minute, leaves standstill 10-30 minute.

8. preparation method as claimed in claim 7, is characterized in that: step 6. in, leave standstill 15-30 minute.

9. preparation method as claimed in claim 8, is characterized in that: step 2., 3., 4., 5. described in preheating temperature be 150-200 DEG C.