CN103114234B - Alloy with excellent room-temperature soft magnetic property and mechanical property, and preparation method thereof - Google Patents

Abstract

The invention discloses an alloy with excellent soft magnetic properties and mechanical properties at room temperature and a preparation method thereof, belonging to the technical field of soft magnetic alloys. The alloy is Fe-49Co-2V-xCr, wherein 0<x≤1.0, and the above are atomic percentages, preferably 0<x<0.5. The preparation method includes the steps of smelting, vacuum diffusion annealing, high temperature forging, hot rolling, cold rolling and final heat treatment. The FeCoVCr alloy provided by the invention has excellent mechanical properties at room temperature, the highest tensile strength reaches 912MPa, the elongation reaches 10.9%, both soft magnetic properties are taken into account, and the coercive force does not exceed 3.58Oe. The preparation process is simple, and it is convenient to prepare larger-sized alloy materials.

Description

An alloy with excellent room temperature soft magnetic properties and mechanical properties and its preparation method

technical field

The invention relates to the technical field of soft magnetic alloys, in particular to a (crystalline) soft magnetic alloy with high saturation magnetic induction, low coercive force, high strength at room temperature and good plasticity and its preparation technology.

Background technique

Soft magnetic materials constitute a very important branch of engineering materials because they can be easily magnetized under the condition of applying a weak magnetic field. Generally, soft magnetic alloys are characterized by high initial magnetization and low coercivity. Their magnetic properties are what determine their applications, including power generation, power distribution, solenoids, magnetic shielding, data storage, and microwave communications. Among the soft magnetic materials, the electronic sheet has a relatively leading market share. FeCo-based soft magnetic alloy has become an ideal material for high magnetic flux density products due to its high saturation magnetization, high Curie temperature, low magnetic crystal anisotropy and high strength. Has been widely used. At present, due to its high saturation magnetization, FeCo alloy has great advantages in reducing the weight or volume of parts. For example, replacing Fe-Si alloy with FeCo alloy can reduce the mass by 20-25%.

In recent years, on the basis of Fe-Co alloys, Fe-Co-V soft magnetic alloys, Fe-Co-based amorphous and Fe-Co-based nanocrystalline materials have been developed. However, although the soft magnetic properties of amorphous and nanocrystalline soft magnetic materials are excellent, they still need breakthroughs in key technologies such as the preparation of larger-sized alloy materials and their high-temperature stability. At present, it is still in the stage of laboratory research.

Adding V to the traditional FeCo alloy improves the cold workability of the alloy. It has also been reported that the addition of V can increase the resistance of the alloy and effectively reduce the loss during use. Some grades of FeCo alloys have been researched and produced abroad, including Permendur, 2V-Pemendur, Hiperco, Supermendur, etc. Among them, the coercive force of Permendur alloy is 0.2Oe, the saturation magnetization is 2.4T, and the tensile strength is 600MPa, but the elongation is only 2%, which has certain limitations in actual production and use.

Since the United States proposed to develop a new generation of more electric aircraft, namely "More Electric Aircraft (MEA)" in the 1990s, the progress in the field of materials applicable to aviation power has become more obvious. The multi-electric aircraft uses electricity to drive different subsystems. Due to the drive of electricity, the time and fuel consumption of the aircraft to reach the cruising altitude are reduced, the reliability and maintainability of the aircraft are greatly improved, and the demand for ground support systems is reduced. Some of the key technologies, such as the integrated generator set, the internal starter/generator of the main propulsion engine, and the magnetic bearing system, require soft magnetic materials that can meet high-temperature service conditions. These requirements include high High magnetic induction (>2T), good mechanical stability (>5000h), and core loss less than 480W kg ^-1 at 5kHz. FeCo-based alloys are of course good suitable materials. However, the mechanical properties of current FeCo-based alloys cannot meet the strength design requirements.

At the same time, as the frequency of use increases, due to the relatively low resistivity of metal soft magnetic materials, large eddy current losses will be caused, and skin effects will be caused at higher frequencies, which severely limits the high-frequency range of FeCo-based alloys. application. For this reason, improving the resistivity of alloys at high frequencies has also become one of the research directions of FeCo-based soft magnetic alloys.

There are currently three grades of Fe-Co soft magnetic alloys in my country, 1J20, 1J21, and 1J22, and a prescribed heat treatment system has been formed. Among them, 1J21 and 1J22 are more commonly used, which are equivalent to foreign 2V-Permendur alloys. The 1J22 alloy is currently widely used in aerospace devices that require light weight and small size. It is also the most widely used soft magnetic alloy for aerospace generators in my country. Difference.

In order to meet the needs of domestic applications and pave the way for the research of high-temperature soft magnetic alloys, it is of great significance to obtain FeCoV-based soft magnetic alloys with excellent soft magnetic properties and balanced mechanical properties.

Contents of the invention

In order to solve the problem that the soft magnetic properties and mechanical properties of the existing FeCoV-based soft magnetic alloys are not well compatible, the invention provides a FeCoVCr alloy and a preparation method thereof. The FeCoVCr-based soft magnetic alloy is Fe-49Co-2V-xCr, wherein 0<x≤1.0, and the above are atomic percentages, preferably 0<x<0.5. The coercive force of the soft magnetic alloy is less than 3.58Oe, the tensile strength is greater than 507MPa, and the elongation is greater than 4.4%. In the microstructure of the soft magnetic alloy, magnetic particles are precipitated at the grain boundaries, the particle size of the precipitated phase is 0.3-1.2 μm, and the volume percentage is 5-16%.

The present invention also provides a method for preparing the above-mentioned FeCoVCr-based soft magnetic alloy, the specific steps are as follows:

In the first step, the raw materials are smelted in proportion, and the smelting method is vacuum electric arc furnace smelting;

The second step is vacuum diffusion annealing, the temperature is ≥900°C, the annealing time is 2-10h, and the molten ingot is cooled with the furnace;

The third step is high temperature forging; the forging temperature is higher than 800°C;

In the fourth step, the forged block is hot-rolled for more than three consecutive passes;

The fifth step is to cold-roll the alloy to produce plates and sheets, with a deformation of 10-95%;

In the sixth step, final heat treatment is carried out on the alloy, the temperature is 350-980° C., the heat treatment time is 2 hours, and the cooling method is air cooling.

The advantages of the present invention are:

(1) The FeCoVCr alloy provided by the present invention has excellent mechanical properties at room temperature, the highest tensile strength reaches 912MPa, the elongation reaches 10.9%, soft magnetic properties are taken into account, and the coercive force does not exceed 3.58Oe.

(2) The preparation process of the soft magnetic alloy provided by the present invention is simple, and it is convenient to prepare larger-sized alloy materials.

Description of drawings

Figure 1 is the EPMA (electron probe) photo (BEI backscattered electron phase) of Fe-49Co-2V-xCr (x=0,0.3,0.5,0.7) alloy after final heat treatment; (a)x=0,(b )x=0.3, (c)x=0.5, (d)x=0.7;

Fig. 2 is the metallographic photograph after final heat treatment of Fe-49Co-2V-0.5Cr alloy;

Fig. 3 is the tensile fracture photo of Fe-49Co-2V-0.7Cr alloy after different final heat treatment temperatures;

Fig. 4 is the coercive force curve of Fe-49Co-2V-xCr (x=0,0.3,0.5,0.7,1.0) alloy after cold rolling and different temperature heat treatment;

Fig. 5 Tensile strength curves of Fe-49Co-2V-xCr (x=0,0.3,0.5,0.7,1.0) alloys after cold rolling and heat treatment at different temperatures;

Fig. 6 Elongation curves of Fe-49Co-2V-xCr (x=0, 0.3, 0.5, 0.7, 1.0) alloys after cold rolling and heat treatment at different temperatures.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

The invention provides a Fe-49Co-2V-xCr alloy, 0<x≤1.0, and the above are atomic percentages. Preferably, 0<x<0.5, more preferably 0<x<0.3. The FeCoVCr alloy has good comprehensive mechanical properties and soft magnetic properties, the tensile strength reaches 912MPa, the elongation reaches 10.9%, soft magnetic properties are taken into account, and the coercive force is less than 3.58Oe. The microstructure analysis of the above alloy shows that there are magnetic particles precipitated on the grain boundaries of the alloy structure, and the particle size of the precipitated phase is 0.3-1.2 μm, and the volume percentage is 5-16%.

The present invention also provides a kind of preparation method of described FeCoVCr soft magnetic alloy, concrete steps are:

The first step is to select raw materials for proportioning melting, and the melting method is vacuum electric arc furnace melting and argon protection. The raw material ratio is Fe-49Co-2V-xCr, 0<x≤1.0, and the above are atomic percentages.

The second step is to carry out vacuum diffusion annealing on the smelted alloy, the temperature is ≥900°C, the annealing time is 2-10 hours, and the molten ingot is cooled with the furnace.

The third step is high-temperature forging, which can eliminate defects such as looseness of the alloy during the smelting process and optimize the microstructure. High temperature forging temperature ≥ 800 ℃.

In the fourth step, the block material obtained after the high-temperature forging in the third step is subjected to hot rolling for more than three consecutive passes, and the hot rolling must be carried out after being kept at 1000° C. for 1 hour. Through high-temperature forging and hot rolling, the coarse grain structure of the alloy in the as-cast state can be destroyed, the microstructure defects can be eliminated, the alloy can be transformed from the as-cast structure to the deformed structure, and its processing performance can be improved, and the processing performance can be improved.

In the fifth step, the alloy is cold-rolled and processed into a plate or sheet, and the deformation of the alloy is 10-95%.

In the sixth step, final heat treatment is performed on the alloy after cold rolling. The final heat treatment temperature is 350-980°C, preferably 760-850°C. The heat treatment time is 2h, and the cooling method is air cooling.

In the soft magnetic alloy obtained by the above preparation method, the grain size in the alloy is 15-20 μm, and there are obvious precipitated phases at the grain boundaries, and a small amount of fine precipitated phases (0.3-1.2 μm in size) in the grains, which are distributed more at the grain boundaries. A small amount exists. After composition determination, the precipitated phase is rich in V and Cr. Through the generation of precipitated phases, the grains have a refining effect compared to the base alloy.

Example 1

Adopt preparation method provided by the invention to prepare Fe-49Co-2V-0.5Cr alloy, concrete steps are as follows:

The first step is the ratio of raw materials and smelting.

Take Fe with a purity of 99.99% and Co, V, and Cr with a purity of 99.9% according to the atomic percentage of Fe-49Co-2V-0.5Cr, and conduct arc melting under argon protection. To ensure homogenization, the raw material was remelted 5 times with negligible mass loss.

The second step is annealing.

After diffusion annealing at a temperature of 1200°C for 4 hours in vacuum, the alloy was cooled with the furnace.

The third step is high temperature forging.

The annealed molten ingot is forged, the forging temperature is 1150° C., and the thickness of the alloy block after forging is 6 mm.

The fourth step is hot rolling.

After the block material in the third step is kept at 1000° C. for 1 hour, it is hot-rolled to a thickness of 2.6 mm.

In the fifth step, the alloy is subjected to intermediate heat treatment under the condition of 750-970° C. for ≥10 minutes.

The sixth step is to perform cold rolling processing with a deformation amount of 30% to obtain alloy sheets.

The seventh step is the final heat treatment.

The cold-rolled alloy sheet is subjected to vacuum heat treatment at different temperatures for 2 hours. The heat treatment temperature is 550°C, 600°C, 670°C, 760°C, 800°C, 850°C, the heating rate is 10°C/min, and the cooling method is air cooling; different The Fe-49Co-2V-0.5Cr soft magnetic alloy of the present invention at the final heat treatment temperature.

Finally Fe-49Co-2V-0.5Cr soft magnetic alloy wire cutting is processed into test piece, the performance of Fe-49Co-2V-0.5Cr is compared with the performance of Fe-49Co-2V, and the coercivity drop of alloy is provided by the present invention To 2.6Oe (0.5Cr alloy 800 ℃ final heat treatment), while the tensile strength reached 912MPa, elongation 10.9%, while maintaining a good coercivity, improve the mechanical properties of the alloy.

The fracture of the cold-rolled alloy sheet in the fifth step is analyzed. The fracture of the alloy is a typical dimple shape with good toughness, but the coercive force is high because the internal microstructure is a rolled structure. The analysis of the alloy after the final heat treatment in the sixth step shows that as the heat treatment temperature of the final heat treatment increases, the fracture morphology of the alloy changes from cleavage fracture to quasi-cleavage characteristics, and the plasticity of the alloy increases. Fig. 2 is a metallographic photograph of the alloy product of Example 1 after treatment at different final heat treatment temperatures, taken by an optical digital metallographic microscope (Olympus BX51M). The metallographic structure shows that when the final heat treatment temperature is higher than 760℃, the rolling structure of the alloy is eliminated, the recovery and recrystallization of the alloy are completed, and the grain morphology is obvious.

Under the same conditions, when the final heat treatment temperature range of Fe-49Co-2V matrix alloy is 760 ℃ ~ 850 ℃, as shown in Figure 1(c), the grain growth of the matrix alloy is obvious as the final heat treatment temperature increases , the grain size increases from 25 μm to 40 μm, and no precipitates are formed. After adding 0.5% Cr, a tiny (0.3-1.2 μm) precipitate phase is formed. Although there are also precipitate phases in the grain, the grain boundary precipitation is more obvious. The small-sized precipitates at the grain boundaries effectively hinder the growth of grains, and the grain size of the alloy corresponding to the final heat treatment at 800 °C is controlled at 15-20 μm (the average grain size of the base alloy after heat treatment at the same temperature is 30 μm). The particle size of the precipitated phase is 0.3-1.2 μm, and the volume percentage is 12%. Grain refinement effectively improves the strength and plasticity of the alloy. On the other hand, the transmission analysis results of the precipitated phase showed that the precipitated phase contained many small-sized (close to nanoscale) particles, and the precipitated phase was magnetic particles with less resistance to domain wall movement and insufficient grain size reduction The coercive force is suddenly increased, so the present invention obtains a soft magnetic alloy with good soft magnetic properties and both mechanical properties. The results of electron probe analysis on the precipitated phase show that the content of V and Cr in the precipitated phase is higher than that in the matrix phase. It can be seen that the addition of Cr is beneficial to the formation of the precipitated phase. The following table 1 shows the performance data of the Fe-49Co-2V-0.5Cr alloy prepared by the present invention.

Table 1 Fe-49Co-2V-0.5Cr alloy properties

The data in Table 1 show that after the addition of Cr element to the matrix alloy Fe-49Co-2V, the increase of the final heat treatment temperature is conducive to the comprehensive maintenance of the soft magnetic properties and mechanical properties of the alloy, especially the final heat treatment temperature is 760 ℃ ~ 800 ℃, the alloy The coercive force is 1.97Oe-2.60Oe, the tensile strength is 824MPa-912MPa, and the elongation is 9.8%-10.9%. Fe-49Co-2V-0.5Cr soft magnetic alloy with good soft magnetic properties and comprehensive mechanical properties has been obtained.

Example 2

Adopting the method provided by the present invention to prepare Fe-49Co-2V-0.3Cr soft magnetic alloy material, the specific process steps are as follows:

Fe with a purity of 99.99% and Co, V, and Cr with a purity of 99.9% are proportioned according to the atomic percentage of Fe-49Co-2V-0.3Cr, and are arc smelted under argon protection. To ensure homogenization, the raw material was remelted 5 times with negligible mass loss. Next, after diffusion annealing in vacuum at 1200°C for 4h, the alloy is cooled with the furnace. After that, the molten ingot was forged, the forging temperature was 1150° C., and the thickness after forging was 10 mm. After that, heat-retain at 1000° C. for 1 hour and then hot-roll to 3 mm. After that, cold rolling processing with a deformation amount of 30% was performed. The cold-rolled alloy sheet was subjected to vacuum final heat treatment at different temperatures for 2 hours. The final heat treatment temperatures were 550°C, 600°C, 670°C, 760°C, 800°C and 850°C, the heating rate was 10°C/min, and the cooling method was air cooling. Finally, the wire cutting is processed into a test piece, and the performance test is carried out on the test piece. The test results are shown in Table 2.

Table 2 Fe-49Co-2V-0.3Cr alloy performance test results

The test results show that after adding 0.3% Cr to the base alloy, as shown in Figure 1(b), after high-temperature final heat treatment (>800°C), tiny precipitates are formed in the alloy structure, and the grain boundary precipitation is more obvious. Compared with the base alloy without precipitation, the small-sized precipitates at the grain boundary hinder the growth of the grains, and the grain size of the alloy corresponding to the final heat treatment at 850 °C is controlled within 18-30 μm. Compared with the base alloy, the grain refinement effectively improves the strength and plasticity of the alloy. The data in Table 2 shows that after adding 0.3% Cr element to the matrix alloy Fe-49Co-2V, the increase of the final heat treatment temperature is conducive to the comprehensive maintenance of the soft magnetic properties and mechanical properties of the alloy, especially the final heat treatment temperature is 800 ℃ ~ 850 ℃ , alloy coercive force 0.63Oe ~ 3.58Oe, tensile strength 507MPa ~ 868MPa, elongation 4.4% ~ 8.3%, obtained better soft magnetic properties and comprehensive mechanical properties Fe-49Co-2V-0.3Cr soft magnetic alloy. Compared with Fe-49Co-2V-0.5Cr soft magnetic alloy, the soft magnetic properties of the alloy are further improved.

Example 3

Adopt the method provided by the present invention to prepare Fe-49Co-2V-0.7Cr soft magnetic alloy material, the specific process steps are as follows:

Fe with a purity of 99.99% and Co, V, and Cr with a purity of 99.9% are proportioned according to the atomic percentage of Fe-49Co-2V-0.7Cr, and are arc smelted under argon protection. Next, after diffusion annealing in vacuum at 1200°C for 4h, the alloy is cooled with the furnace. After that, the molten ingot was forged, the forging temperature was 1150° C., and the thickness after forging was 10 mm. After that, the alloy was kept at 1000°C for 1 hour and then hot rolled to 3mm. After that, cold rolling processing with a deformation amount of 30% was performed. The cold-rolled sheet was subjected to vacuum final heat treatment at different temperatures for 2 hours. The final heat treatment temperatures were 550°C, 600°C, 670°C, 760°C, 800°C, and 850°C. The heating rate was 10°C/min, and the cooling method was air cooling.

Figure 1(d) is the microstructure of the alloy in Example 3 after high-temperature heat treatment (760°C-850°C). It can be seen from the figure that the addition of 0.7% Cr produces a large number of precipitates, forcing the grains to disperse. After treatment at 760°C, the dispersion of grains is uneven, and there are still some large grains. After treatment at 800°C, the area of uneven dispersion, the grain size becomes smaller, and heat treatment at 850°C, the dispersion of grains is very uniform. , the grain size is within 10 μm. As the heat treatment temperature increased, the precipitated phase content also increased. Due to the joint effect of precipitation strengthening and fine grain strengthening, the tensile strength of Fe-49Co-2V-0.7Cr alloy is higher, and the grain refinement also improves the plasticity of the alloy.

Fig. 3 is a fracture morphology diagram of the alloy test piece in Example 3, taken by a scanning electron microscope (CamScan3400). The fracture of as-rolled alloy is a typical dimple morphology, the alloy has better toughness and higher elongation. The order-disorder transition temperature of FeCo alloy is 730℃, and the addition of V will lower this transition temperature. The final heat treatment is carried out in the temperature range lower than the ordered-disordered transition, that is, the alloy is heat treated in the ordered area, the degree of ordering of the alloy is relatively high, the fracture is a typical brittle cleavage fracture, and the river patterns are clearly visible, so the alloy is relatively brittle , the elongation rate is low; the final heat treatment is carried out in the temperature range higher than the order-disorder transition, because the cooling method is air cooling, the alloy will still produce a certain order phase, but the order degree is reduced, and the fracture is a typical The quasi-cleavage fracture, as shown by the dotted line in the figure, has cleavage lines expanded by dimples. Although there are certain river patterns, the area is reduced and the length is shortened, so the plasticity of the alloy is improved and the elongation is increased.

Example 4

Using the preparation method provided by the present invention, an alloy with a Cr content of 0.3-1.0 is also prepared in this embodiment, and the rest of the preparation process is the same as that in Embodiment 2.

Figure 4 is the coercive force curve of the Fe-49Co-2V-xCr alloy in the cold-rolled state and after heat treatment at different temperatures, which was tested by a DC B-H loop tracer. The sample without heat treatment after cold rolling has a very large residual stress after cold rolling, resulting in high coercive force of the alloy. Through heat treatment, the coercive force will be reduced; as the heat treatment temperature increases, the sample undergoes recrystallization and the degree of crystallization increases, and the coercive force will increase due to the resistance of the grain boundary to the movement of the domain wall; As the temperature further increases, the grain grows, the grain boundary density decreases, and the coercive force decreases; when the temperature is higher than 800°C, the precipitates rich in V and Cr increase significantly, and they are distributed around the grains to form domain walls. Movement resistance, coercive force increased. With the increase of Cr content, the coercive force curve moves up as a whole, that is, the coercive force of the alloy after heat treatment at the same temperature increases.

Figure 5 and Figure 6 are the result curves of tensile strength and elongation of Fe-49Co-2V-xCr alloy in cold-rolled state and heat treatment at different temperatures, and the data are tested by tensile tester (INSTRON5565-50kN). The samples without heat treatment after cold rolling have work hardening effect, and the alloy strength is higher. As the heat treatment temperature increases, defects such as dislocations decrease, the lattice distortion weakens, the effect of work hardening decreases, and the strength of the alloy decreases. The higher the temperature, the higher the degree of ordering), the alloy brittleness is obvious. However, when the heat treatment is higher than 700 ℃, it enters the heat treatment in the disordered area, the degree of ordering is relatively reduced, and the plasticity is improved. At the same time, when the temperature is higher than 760 °C, the heat treatment temperature increases, the grain refinement and precipitation strengthening are obvious, and the strength increases.

The matrix alloy described in the present invention is Fe-49Co-2V alloy, which is prepared by the method provided in the present invention. After heat treatment, the soft magnetic properties are excellent, and the coercive force can reach 0.45-2Oe. However, in terms of structure, after the final heat treatment in the range of 760-850 °C, as shown in Figure 1(a), there is no obvious precipitation. As the heat treatment temperature increases, the grain size grows, and the mechanical properties will increase with the grain size. The tensile strength is only 495MPa at 800°C, which does not meet the needs of practical applications. The specific performance is shown in Table 3.

Table 3 Fe-49Co-2V matrix alloy performance table

Claims (4)

1. a FeCoVCr magnetically soft alloy, is characterized in that: described FeCoVCr magnetically soft alloy is Fe-49Co-2V-0.5Cr, after described magnetically soft alloy 800 DEG C of finished heat treatment, tensile strength reaches 912MPa, elongation reaches 10.9%, and soft magnet performance is taken into account, coercive force 2.6Oe; In described magnetically soft alloy microscopic structure, grain boundaries be magnetic particle separate out, precipitated phase particle size 0.3 ~ 1.2 μm, percentage by volume is 12%.

2. a preparation method for magnetically soft alloy according to claim 1, is characterized in that comprising the steps:

The first step, carries out proportioning melting by raw material, and melting mode is vacuum arc furnace melting;

Second step, diffusion in vacuum is annealed, temperature >=900 DEG C, annealing time 2 ~ 10h, and melted ingot cools with stove;

3rd step, high temperature forging; Forging temperature is higher than 800 DEG C;

4th step, to the hot rolling of forging bulk through the above passage of continuous three passage;

5th step, alloy carries out cold rolling processing sheet material, sheet material, deflection 10 ~ 95%;

6th step, alloy carries out finished heat treatment, and temperature is 350 ~ 980 DEG C, and heat treatment time is 2h, and the type of cooling is air cooling.

3. the preparation method of magnetically soft alloy according to claim 2, is characterized in that comprising the steps:

The first step, carries out proportioning melting by raw material, and melting mode is vacuum arc furnace melting;

Second step, diffusion in vacuum is annealed, temperature >=1200 DEG C, annealing time 4 ~ 10h, and melted ingot cools with stove;

3rd step, high temperature forging; Forging temperature is higher than 1100 DEG C;

4th step, to the hot rolling of forging bulk through the above passage of continuous four-pass;

5th step, alloy carries out intermediate heat-treatment, and condition is 750 ~ 970 DEG C, >=10min;

6th step, alloy carries out cold rolling processing sheet material, sheet material, deflection >=30%;

7th step, alloy carries out finished heat treatment, and temperature is 550 ~ 850 DEG C, and heat treatment time is 2h, and the type of cooling is air cooling.

4. the preparation method of the magnetically soft alloy according to Claims 2 or 3, is characterized in that: the temperature of described finished heat treatment is 760 ~ 850 DEG C.