CN103658574B - A kind of method that circular cone type single roller rapid quenching prepares amorphous alloy ribbon - Google Patents

Abstract

The invention discloses a method for preparing an amorphous alloy thin strip by conical single-roll rapid quenching, which belongs to the technical field of alloy thin strip preparation. Conical rollers are used, and the melt is sprayed on the conical slope rotating around the central axis of the cone, so that the direction of the centrifugal force on the melt changes from perpendicular to the contact surface to an angle with the contact surface, and the edge of the conical slope is very The crystal thin strip will shrink and separate from the roller automatically under the action of centrifugal force. The thin strip prepared by the invention has thinner size, higher surface finish and better performance.

Description

A method for preparing amorphous alloy thin strip by conical single-roll rapid quenching

technical field

The invention belongs to the technical field of alloy thin strip preparation, and relates to a novel single-roll strip stripping method to solve the problems of liquid droplets splashing and difficult strip formation during the strip stripping process, in particular to a disc-type single-roll quick quenching method.

technical background

Single roll quick quenching method, also known as melt cooling roll spin coagulation method, continuous casting thin strip method. The method of producing amorphous ribbons invented by Bedell is shown in Figures 1 and 2. The molten metal sprays on the surface of the cooling roll rotating at high speed and spreads under the action of gravity and wetting to form a molten pool; the interface layer between the molten pool and the cooling roll is quenched and solidified, and rotates with the cooling roll to continue cooling to form a thin metal strip; Thin metal strip detaches from the rim surface of the roller under the action of self-shrinkage and centrifugal force [Xian Chunchun, Li Derong. Characteristics of the molten pool of planar flow casting technology [J]. Journal of Harbin Institute of Technology, 2000, 24(4): 273-274] .

F _Friction : The contact surface between the roller and the melt forms a thin solidified layer and adheres to the surface of the roller and is accelerated by the rotating roller. There is a velocity gradient in the melt. Small, the force on the mutual movement inside the melt is expressed as F _{friction force} .

F _Adhesion : Refers to the ability of a certain material to adhere to the surface of another material, specifically the ability of the melt to adhere to the surface of the roller.

F _{Centrifugal force} : The molten metal is accelerated by the roller and rotates with the roller, resulting in a centrifugal force away from the center of rotation.

In the single-roll quick quenching process, the melt is subjected to centrifugal force F _{centrifugal force} , adhesion force F _{adhesion force} , and tangential stress F _{friction force} .

Melting pool: It refers to the liquid-solid metal expansion area where the molten metal comes out of the nozzle and forms a certain shape on the surface of the roller, and the molten metal is spread and solidified in this area.

The high-speed rotation of the roller provides a tangential stress F _friction to the molten pool and drives the molten pool to move in the same direction. Figure 3 is the initial melt pool morphology (solid line) and the melt pool morphology (dashed line) during the process of preparing amorphous wire from the melt. It can be seen from the figure that the molten master alloy and the There is a clear difference between wetting and static wetting between rollers [Yu Shengsheng, Sun Jianfei. Research on the characteristics of CoFeSiB alloy melt drawn into wires [D]. Harbin Institute of Technology (Harbin), 2011: 5-6]. During the melt pulling process, the shape of the molten pool changes drastically along the direction of roller rotation; at the same time, the wetting angle changes from the static wetting angle θ _e to the upstream contact angle θ _u and the downstream contact angle θ _d , where the Reflecting the dynamic wettability of the molten master alloy on the roll is θ _d . The smaller θ _d is, the better the dynamic wettability is, and the more the molten pool changes in the direction of the wheel rotation. [M.Allahverdi, Robin ALDrew, Strom-Olsen. Wetting and melt extraction characteristics of ZrO2-Al2O3 based materials[J].Journal of American Ceramic Society.1997,80:2910-2916] found that although the static wettability is very Poor (wetting angle up to 140°-160°), but the presence of tangential stress results in a small dynamic wetting angle and improved wetting ability. M.Allahverdi et al [M.Allahverdi, RALDrew, Strom-Olsen.Melt extraction and properties of ZrO2-Al2O3-Based fibers[J].Ceramic Engineering and Science Proceedings.2008:1015-1025], [Huang Shiying. Kinetic equations of amorphous thin strips and its verification Ⅲ [J]. Instrumentation Materials., 1985,18(4):160-164】The images of molten metal droplets under different wheel rotation speeds were obtained by high-speed photography Dynamic wetting and melt pool morphology, melt pool length L and thickness δ; as the wheel speed V increases, the tangential stress F _friction increases, and the melt spread area increases.

In the prior art, the melt is subjected to centrifugal force perpendicular to the contact surface of the roller, and the centrifugal force makes the melt tend to fall off the surface of the roller instead of spreading on the surface of the roller. When the centrifugal force is greater than the adhesion force, the molten metal falls off the roller before it is fully cooled. On the surface of the wheel, a droplet splash phenomenon is formed. For example, the rotational speed is 40m/s, the diameter of the roller is 0.4m, and the centrifugal acceleration of the liquid metal is as high as 816g, which is prone to splashing of droplets.

In the prior art, in order to enable the melt to spread effectively on the surface of the roller and improve the wettability of the roller and the melt, it is necessary to consider viscosity (μ), surface tension (γ), wettability, surface roughness (Ra), Temperature (T), phase change factors, adjustment of multiple parameters such as melt injection speed, angle, distance, roll speed, roll material wettability, etc., increase the complexity of the process [Mao Zhonghan. Manufacturing method of amorphous alloys [J ]. Rare metal alloy processing, 1980, 01: 11-15]. For some molten metal materials with high viscosity of molten metal and poor wetting with rollers, no matter how the process parameters are adjusted, it is difficult to form strips and cannot obtain Smooth and uniform rapid solidification material ^[5] .

Amorphous or metastable phase, with superior mechanical, optical, magnetic and other properties, in order to obtain the required amorphous or metastable phase microcrystalline ribbon, a cooling rate above 10 ⁶ ~ 10 ⁸ K/s is required . It is known that the overall heat transfer method in the rapid quenching process is mainly Newtonian cooling:

${<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&tau;</span>}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; h</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

ρ _l is the density of the metal liquid, С _pl is the specific heat of the metal liquid at constant pressure, and the heat transfer coefficient of the α alloy liquid and the cooling roll. h is the thickness of the metal strip. It can be seen that the cooling rate is inversely proportional to the thickness of the alloy strip and directly proportional to the rotational speed of the roller.

The existing technology adopts increasing the rotational speed of the roller to increase the cooling rate. When the rotation speed of the wheel disc increases to a certain level, the thickness of the strip does not decrease much, but the pulling marks on the surface of the strip are too large, the surface roughness increases, and meshes and cavities appear, which affect the quality of the thin strip. At the same time, the centrifugal force increases, Under the action of centrifugal force, the melt is likely to cause droplet splashing, which affects production safety. Therefore, the speed of the cooling roll should generally not be too large, and the line speed should be less than 35m/s.

The existing technology is to reduce the size of the nozzle to reduce the thickness of the strip and increase the cooling speed. However, due to the influence of the purity of the molten metal, the nozzle is easily blocked by impurities in the molten metal and the spray strip is stopped. At the same time, it flows through the nozzle per unit time. The flow rate of molten metal is too small, and the molten metal at the nozzle will block the nozzle due to continuous cooling and solidification, so the diameter of the nozzle should not be too small, generally 0.6-0.12 mm, and the molten metal must maintain a certain degree of superheat to ensure continuous flow spray tape. In the existing technical conditions, due to the limitations of technology and methods, only 30-60 micron amorphous alloy strips can be prepared by spraying.

The existing technology is to use the roller material with high thermal conductivity, but with the increase of the thermal conductivity of the wheel, after the melt is pulled for a unit time, the remaining temperature of the melt inside the molten pool will gradually decrease, and the time required for solidification will be shorter. The smaller the spread area of the melt on the roller, the worse the wettability and the worse the belt forming performance. When choosing a metal roulette, cooling speed and strip forming performance cannot be balanced [Yu Shengsheng, Sun Jianfei. Research on CoFeSiB alloy melt drawn wire characteristics [D]. Harbin Institute of Technology (Harbin), 2011: 5-6].

Rayleigh wave: refers to the regular periodic ripples of liquid column or unsolidified metal under the combined action of surface tension and gravity

Rayleigh wave defects and entrained gas holes are easily formed on the surface of the amorphous strip prepared by the prior art. When the rotation speed of the roller is low, eddy currents are formed around the free surface of the strip to cause the disturbance of the melt pulling layer, and Rayleigh waves are easily formed on the surface of the amorphous strip. The formation process of the entire Rayleigh wave can be divided into three stages: (1) The melt is in contact with the roller; (2) The melt pulling layer moves together with the roller; (3) The melt pulling layer is separated from the roller . When the roller is in contact with the melt, a very thin solidification layer is formed due to the chilling effect of the tip of the roller, which can be regarded as the thermal boundary layer δ _T . The momentum boundary layer δ _V is much larger than the thermal boundary layer δ _T , the entire momentum boundary layer δ _V is in the liquid state except the thermal boundary layer δ _T , and the melt pulling layer rollers move together. After the melt is disturbed, the Rayleigh wave is in the liquid state. formed in. When the semi-solid boundary layer is flying in the protective gas, since it has separated from the rim at this time, the solidification process mainly conducts heat through convection and radiation, and the cooling rate decreases rapidly, causing the size of the Rayleigh wave to further expand, forming a Rayleigh wave defect. When the rotating speed of the wheel is high, the entrainment of protective gas causes the melt drawing layer to break before it is completely solidified.

The patent (200810247383.7) proposes a method to obtain a smooth and uniform rapid solidification material by increasing the injection speed of the liquid metal alloy, but it can only determine the stripping problem of some materials. For high-viscosity, non-wetting alloy melt The body is still not well resolved.

Therefore, how to solve the strip forming performance of the single-roll quick quenching method, it is necessary to develop new equipment and new processes.

Contents of the invention

The purpose of the present invention is to provide a new method of throwing strips, which overcomes the problems in the prior art, that is, solves the splashing of the melt droplets of the fast-setting thin strips in the single-roller fast-setting thin strip method, the difficulty of forming strips, and the existence of thin strips. To solve problems such as defects, bubbles, etc., a rapidly quenched amorphous alloy thin strip with thinner size, higher surface finish and better performance is prepared.

In order to solve the above problems, the core solution of the present invention is: change the structure of the roller, adopt the conical cooling roller, and melt spray on the conical slope surface (as shown in Figure 4) that rotates around the central axis of the cone, so that the melt is subjected to centrifugal force The direction of the contact surface changes from being vertical to the contact surface upwards to form an angle with the contact surface, and the amorphous strip at the edge of the conical slope surface cools and shrinks by itself and under the action of centrifugal force, it separates from the roller by itself.

The component force of the centrifugal force includes the outward force of the vertical conical contact surface and the parallel conical contact surface. Compared with the prior art, on the one hand, the upward centrifugal force on the vertical contact surface is reduced, which can solve the problem of melt splashing. On the other hand, the force parallel to the contact surface The centrifugal force component can improve the dynamic wettability (as shown in Figure 3), and together with the F _{friction force} , promote the rapid spread of the melt on the contact surface along the radial and tangential directions of the disc.

Conical cooling roll single roll stripping method of the present invention is characterized in that:

(1) The conical cooling roll passes cooling water inside and rotates along the central axis, and the angle between the conical slope surface as the contact surface and the central axis is greater than 0° and less than 90°, preferably 45-80°.

(2) The molten material is melted in the furnace and sprayed on the conical slope surface through the nozzle.

(3) The melt forms a molten pool on the conical slope surface, and under the joint action of centrifugal force, friction force and gravity, the melt spreads and cools to form a thin and smooth amorphous ribbon.

(4) The amorphous strip at the edge of the conical slope surface is cooled and self-shrinks and centrifugal force separates itself from the roller.

(5) The tape throwing method of the conical cooling roller type single roller of the present invention can adjust the parameters of the strip throwing process according to specific conditions.

Compared with prior art, the beneficial effect of the present invention is:

1. In the prior art, the metal is sprayed on the outer surface of the roller, and the metal melt is subjected to centrifugal force perpendicular to the contact surface of the roller (Figure 1), and the melt cannot be effectively spread on the surface of the roller. When the centrifugal force is greater than the wetting force , The molten metal falls off the surface of the roller before it is fully cooled, forming a phenomenon of droplet splashing. In the present invention, the roller type is changed to a conical type so that the direction of the centrifugal force is changed from being perpendicular to the contact surface upward to forming an angle with the contact surface. On the one hand, the centrifugal force vertical to the contact surface can be reduced and the problem of splashing by the melt can be solved. On the other hand, under the combined action of the centrifugal force component parallel to the slope surface of the roller and the F _{friction force} , it spreads rapidly along the radial and tangential directions of the conical slope surface, forming a strip with a smooth surface and uniform thickness. Thinner amorphous ribbons that require faster cooling can be produced.

2. The existing technology is necessary to ensure the stability of the melt and prevent the nozzle from being clogged. Cooling speed, but after the melt is pulled for a unit time, the remaining temperature of the melt inside the molten pool is low, and the time required for solidification is too short, and the melt solidifies before it can spread on the rollers, which is not conducive to the spread of the melt and the formation of belts The performance is poor; the melt-drawn layer of the present invention spreads faster under the action of F _{centrifugal force} and F _{friction force} , the spread area of the melt is larger, and the belt-forming performance is better.

3. The existing technology uses high speed to obtain sufficient supercooling degree. High speed is easy to make the protective gas around the molten pool get involved in the molten pool. At the same time, the melt deflects with the rotation of the roller. Too high speed is easy to This leads to the fracture of the melt-drawing layer. On the one hand, in the present invention, due to the rapid spreading of the melt-drawn layer under the pulling action of F _{centrifugal force} and F _{friction force} , sufficient cooling speed and thin strip spreading area can be obtained at low roller speed without excessively high speed.

4. Under the existing technical conditions, only narrow amorphous strips with a thickness greater than 20 microns can be obtained, and there are often nozzle blockages, interrupted spray strips or broken strips, or defects such as voids and Rayleigh waves, and the production efficiency is not high. . The melt of the present invention accelerates the speed of spreading under the pulling action of F _{centrifugal force} and F _{friction force} . After the melt is pulled for a unit time, the remaining temperature of the melt pool rises, and the spread area of the melt on the roller increases and the thickness is small. A very thin amorphous strip can be obtained by using too small a nozzle without nozzle clogging, and at the same time, the width of the amorphous strip and the efficiency of spraying the strip can be improved.

5. In the prior art, Rayleigh wave defects are easily formed during the stripping process. In the present invention, the melt spreads very thinly under the pulling action of F _{centrifugal force} and F _{friction force} , and quickly condenses into a solid state. Rayleigh waves can only be formed in a liquid state, which reduces the occurrence of Rayleigh wave defects and obtains a surface Smooth thin strip.

6. The conical slope of the present invention has an angle with the rotation axis, so that the melt is subjected to a centrifugal force component and the vertical slope faces outward, so that the cooled amorphous belt can be more easily detached from the surface of the cooling roller under the action of centrifugal force.

Description of drawings

Figure 1 Schematic diagram of the cylinder single-roller fast-setting thin-belt method

1. Conical cooling roll 2. Nozzle 3. Metal liquid 4. Fast-setting thin strip;

Fig. 2 Schematic diagram of the cylindrical single-roll fast-setting thin-belt melt pool

1. Conical cooling roll 3. Metal liquid 4. Fast-setting thin strip 7. Melt metal spraying;

Fig.3 Dynamic wettability diagram under shear stress

8. Liquid metal 9. Cooling roll surface. θe static contact angle, θu upstream contact angle, θd downstream contact angle. Solid line - static shape of molten pool, dotted line - dynamic topography of molten pool;

Figure 4 Schematic diagram of conical single-roller stripping method

1. Conical cooling roll 2. Nozzle 4. Fast-setting thin strip 10. Melting pool;

Fig. 5 Sectional view of conical single-roller stripping method

1. Conical cooling roll 2. Nozzle 10. Melting pool;

Figure 6 is a schematic diagram of an embodiment of the conical single-roller stripping method

1. Conical cooling roller 2. Nozzle 5. Pressure gauge 6. Metal melting furnace 11. Drive motor 12. Valve.

detailed description

The specific embodiments of the present invention are described in detail below in conjunction with the examples, but the specific embodiments of the present invention are not limited to the following examples. The schematic diagram of equipment for the conical single-roller stripping method in the following embodiments is shown in FIG. 5 .

Example 1:

A method for preparing a fast-quenched amorphous alloy thin strip, including batching, smelting, secondary smelting, strip spraying, and harvesting. The mass percent of its chemical composition is: 21.57% Sm, 72.84% Fe, 1.66% Zr, 3.93% Co.

Using 99.5% metal samarium, industrial pure iron, metal cobalt, and metal zirconium as raw materials, it is melted in an intermediate frequency vacuum induction melting furnace. Before melting, the vacuum chamber is first vacuumed, and then high-purity argon is used as a protective gas to avoid alloy oxidation. . The melting temperature is 1600°C. Secondary melting is carried out in the induction ladle, and the spray belt pressure is established in the nozzle package, and the spray belt pressure is 0.05Mpa. The protective atmosphere pressure is 0.01Mpa.

The conical cooling roll is made of molybdenum, the angle between the conical slope surface and the central axis is 80°, and the inside of the conical cooling roll is cooled by circulating water. The diameter of the conical cooling roll is 400mm, and the linear speed of the cooling roll edge is 24m/s. In-place finish turning of conical cooling rolls: Guarantee rolling surface roughness Ra<0.2μm.

The hole diameter of the nozzle is 0.5mm, and the nozzle is close to the edge of the cooling roll and 20mm away from the edge of the cooling roll.

After the molten metal is sprayed onto the conical slope surface, it spreads and cools rapidly to form a fast-setting thin strip, which is separated from the cooling roll by itself under the contraction of cooling and centrifugal force, and obtains Sm _1.0 Zr _0.3 with a thickness of 12-14 microns and a surface roughness of less than 0.3 μm. Fe _8.1 Co _0.6 fast-setting thin strips, there is no splashing phenomenon in the process of throwing the strips, and there is no a-Fe soft magnetic phase in the alloy. After grinding and nitriding, Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 N _x is formed, and the sticky After the magnet is combined, the magnetic properties are B _r =0.95T, (BH) _max =23.4MGOe.

Parameters such as composition, roller diameter, roller speed, nozzle size of Comparative Example 1 are the same as in Example 1, and the factors are the same, except that the roller type strip method (Fig. 1) is adopted. Due to the centrifugal force, the molten metal is easy to splash, and a small amount of discontinuous thin strips are obtained. The thickness of the thin strips is thicker, the roughness is larger, and the magnetic energy product is smaller.

Table 1, embodiment and comparative example contrast

Example 2:

The conical fast-setting thin strip method used in this example prepared the Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 fast-setting thin strip. The difference is that the angle between the conical slope surface and the central axis is 45°, and other parameters are as in Example 1. . A thin ribbon with a uniform thickness of 18-19 microns and a Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 fast-setting thin ribbon with a surface roughness of less than 0.3 μm was obtained, and there was no splashing during the ribbon throwing process. There is no a-Fe soft magnetic phase in the alloy, and Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 N _x is formed by grinding and nitriding. After making a bonded magnet, the magnetic properties are B _r ＝0.97T, (BH) _max ＝ 22.3 MGOe.

Claims (1)

1. A method for preparing a fast-quenched amorphous alloy thin strip, including batching, smelting, secondary smelting, spraying, and collecting, the mass percent of its chemical composition is: 21.57% Sm, 72.84% Fe, 1.66% Zr, 3.93% Co; It is characterized in that, using 99.5% metal samarium, industrial pure iron, metal cobalt, and metal zirconium as raw materials, it is smelted in an intermediate frequency vacuum induction melting furnace. Protective gas to avoid alloy oxidation; melting temperature is 1600°C; secondary melting in induction heating ladle, spray belt pressure is established in nozzle package, spray belt pressure is 0.05Mpa, and protective atmosphere pressure is 0.01Mpa; The conical cooling roll is made of molybdenum, the angle between the conical slope surface and the central axis is 80°, and the inside of the conical cooling roll is cooled by circulating water; the diameter of the conical cooling roll is 400mm, and the edge speed of the conical cooling roll is 24m/s ;The conical cooling roller is guaranteed to have rolling surface roughness Ra<0.2μm after finish turning; The diameter of the nozzle hole is 0.5mm, the nozzle is close to the edge of the cooling roll, and 20mm away from the edge of the cooling roll; After the molten metal is sprayed onto the conical slope surface, it spreads and cools rapidly to form a fast-setting thin strip. After cooling, the thin strip automatically separates from the cooling roll under the action of its own shrinkage force and the centrifugal force of the cooling roll; and obtains a thin strip with a uniform thickness of 12-14 microns , Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 fast-setting thin strips with surface roughness less than 0.3μm, there is no splashing phenomenon in the stripping process, no a-Fe soft magnetic phase appears in the alloy, and Sm _1.0 is formed after grinding and nitriding Zr _0.3 Fe _8.1 Co _0.6 N _x , after being made into a bonded magnet, the magnetic properties are B _r =0.95T, (BH) _max =23.4MGOe.