CN103706770B - A kind of disc-type single roller gets rid of the method that amorphous alloy ribbon prepared by band - Google Patents

Abstract

The invention discloses a method for preparing an amorphous alloy thin strip by rapid quenching of the strip by a disc type single roller, belonging to the technical field of alloy thin strip preparation. The present invention adopts a disc-type roller, and the melt is sprayed on the surface of the disc rotating around the central axis of the disc, so that the direction of the centrifugal force on the melt is parallel to the contact surface, that is, the surface of the disc, and the amorphous thin strip on the edge of the disc Cooling self-shrinkage and under the action of centrifugal force, it will separate from the roller automatically to form a thin strip of amorphous alloy. The resulting ribbon is thinner in size, with a higher surface finish and better performance.

Description

A method for preparing amorphous alloy thin strip by disc-type single-roller throwing strip

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 strip stripping 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 melting 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 shows the initial melt pool morphology (solid line) and the melt pool morphology (dotted 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 CoFeSiB alloy melt drawn wire characteristics [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 The dynamic wettability of the molten master alloy on the roller is reflected by θ _d , the smaller the θ _d is, the better the dynamic wettability is, and the more the molten pool changes in the direction of the rotation of the wheel. S.olsen【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 ( The wetting angle reaches 140°-160°), but the presence of tangential stress results in a small dynamic wetting angle and improved wetting ability. M.Allahverdi et al [Huang Shiying. The kinetic equations and verification of the formation of amorphous thin strips by the single-roller quenching method Ⅲ[J]. Instrumentation Materials. 1985,18(4):160-164] Obtained by high-speed photography technology The dynamic wetting of molten metal droplets and the shape of the molten pool at different wheel speeds, the length L and thickness δ of the molten pool; 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, adjusting multiple parameters such as melt injection speed, angle, distance, roller speed, roller material wettability, etc., increase the complexity of the process, for some molten metals with high viscosity, and rollers For molten metal materials with poor wetting, it is difficult to form strips no matter how the process parameters are adjusted, and a smooth and uniform rapid solidification material cannot be obtained [Mao Zhonghan. Manufacturing method of amorphous alloys [J]. Rare metal alloy processing, 1980, 01:11‐15].

Amorphous or metastable phase, with superior mechanical, optical, magnetic and other properties, in order to obtain the required amorphous or metastable phase microcrystalline ribbon, the 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:

${<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; dT</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&tau;</span>}}<span\; class="notranslate">\; )</span>}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; pl</span>}}\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; \&minus;</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>\text{<span class="notranslate"> \&nbsp;\&nbsp;\&nbsp;\&nbsp;\&nbsp;\&nbsp;\&nbsp;\&nbsp;\&nbsp;\&nbsp;\&nbsp;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

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, the cooling speed and the stripping performance cannot be taken into consideration.

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 , and the entire momentum boundary layer δ _V is in the liquid state except the thermal boundary layer δ _T . formed in. When the semi-solid boundary layer flies in the protective gas, since it has already 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 Rayleigh wave to further expand in size and form 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 problem of stripping of some materials. The body can not be well solved【Zhang Bo, Li Wen, Li Hong, Study on the Wettability of Metal Droplets Above and Below the Substrate [J], Surface Technology, 2009, 02:4‐6].

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 stripping, which overcomes the problems in the prior art under the same conditions, that is, solves the splashing of the fast-setting thin strip melt droplets in the single-roller fast-setting thin strip method, which is not easy to form a strip, There are problems such as Rayleigh defects and bubbles in the thin strip, and a rapidly quenched amorphous alloy thin strip with thinner size, higher surface finish and better performance is prepared.

In order to solve the above-mentioned problems, the core solution of the present invention is to change the structure of the roller, adopt a disc-type roller, that is, the surface in contact with the melt is a circular surface, the whole roller is disc-shaped, and the melt is sprayed around the disc. On the surface of the disc rotating on the central axis (as shown in Figure 4), the direction of the centrifugal force on the melt is parallel to the contact surface, that is, the surface of the disc, and the amorphous strip at the edge of the disc cools and shrinks by itself and under the action of centrifugal force, it will automatically separate from the roller , forming a thin strip of amorphous alloy.

The direction of the centrifugal force of the present invention is changed from vertical to the contact surface in the prior art to be parallel to the contact surface. On the one hand, it can reduce the centrifugal force vertical to the contact surface and solve the problem of melt splashing. On the other hand, the centrifugal force is parallel to the contact surface, which can improve Dynamic wettability (as shown in Figure 3), together with F _friction , promotes the rapid spreading of the melt on the contact surface along the radial and tangential directions of the disc.

The present invention develops a new strip-throwing method, and the specific parameters in the strip-throwing process can be adjusted according to specific conditions. The disc type single-roller stripping method of the present invention is characterized in that:

(1) Cooling water is passed through the inside of the disc and rotates along the central axis. The surface of the disc is used as a contact surface and is perpendicular to the central axis. It is preferable that the surface of the disc is horizontal.

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

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

(4) The amorphous thin strip at the edge of the disc will separate from the roller by itself under the action of cooling self-shrinkage and centrifugal force.

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 disc type so that the centrifugal force direction is changed from being perpendicular to the contact surface to being parallel to the contact surface. On the one hand, it can reduce the centrifugal force vertical to the contact surface and solve the problem of splashing from the melt. On the other hand, under the joint action of centrifugal force and F _{friction force} , the strips spread rapidly along the radial direction and tangential direction of the disc surface to form a strip with 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 clogging. The temperature of the molten pool is kept at a certain degree of superheat. Roller materials with high thermal conductivity (such as copper rollers and molybdenum rollers) are used, although the melt can be guaranteed 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 amorphous ribbons with a thickness greater than 20 microns can be obtained, and nozzle clogging, interrupted spray ribbons or broken ribbons often occur, or defects such as voids and Rayleigh waves appear, 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.

Instructions attached

Figure 1 Schematic diagram of thin strip preparation by single roll quenching method

1. Cooling roll 2. Melt metal injection 3. Metal liquid 4. Fast-setting thin strip;

Figure 2 Schematic diagram of single-roll fast-setting thin-belt melt pool

1. Cooling roll 2. Melt metal injection 3. Metal liquid 4. Fast-setting thin strip;

Figure 3 Dynamic wettability under shear stress

1. Liquid metal 2. Roller surface. _θe static contact angle, _θu upstream contact angle, _θd downstream contact angle. Solid line - static shape of molten pool, dotted line - dynamic shape of molten pool

Fig. 4 schematic diagram of centrifugal force and wettability principle of disc-type single-roller stripping method of the present invention

1. Disc-type cooling roll 2. Metal melt 3. Melt pool 4. Fast-setting thin strip;

Figure 5 Schematic diagram of the embodiment of a disc-type single roller

1. Drive motor 2. Roller 3. Melt metal nozzle 4. Valve 5. Pressure gauge 6. Metal melting furnace.

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.

Example 1:

A method for preparing a fast-quenched amorphous alloy thin strip, including batching, smelting, secondary smelting, strip spraying, and harvesting. The mass percentage 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 smelted in an intermediate frequency vacuum induction melting furnace. Before smelting, the vacuum chamber is first evacuated, 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.

In the belt spraying step, the nozzle and the cooling roller form a dynamically stable planar molten pool that spreads in two directions, and the temperature of the molten pool is 700-1300°C.

The disc-type flat roller is made of molybdenum, and the inside of the flat roller is cooled by circulating water. The diameter of the flat roller is 400mm, and the linear speed of the roller edge is 20m/s. In-place finish turning of cooling rolls: Guarantee rolling surface roughness Ra<0.2μm.

The nozzle aperture is 0.5mm, the nozzle is close to the edge of the roller, and 20mm away from the edge of the roller.

The molten metal is sprayed onto the surface of the roller and cooled rapidly to form a fast-setting thin strip. After the molten metal is sprayed onto the surface of the roller, it quickly spreads and cools to form an amorphous thin strip, which will automatically separate from the roller under the action of self-shrinkage and centrifugal force at the edge of the disc. And a thin strip with a uniform thickness of 10-15 microns and a Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 fast-setting thin strip with a surface roughness of less than 0.25 microns is obtained. There is no splashing phenomenon in the process, and there is no α‐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. After making a bonded magnet, the magnetic property is B _r =1.07 T, (BH) _max =22.5MGOe, see schematic diagram 5 for specific preparation equipment.

Parameters such as the composition of Comparative Example 1, the diameter of the roller, the rotating speed of the roller, and the size of the nozzle are the same as those of Example 1, but the difference is that the roller-type stripping method is adopted. In comparative example 1, the shape uniformity of thin strips is poor, and there are many kinds of fast-setting alloys with different shapes and sizes, and some droplet splashing occurs, and spherical particles of Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 fast-setting alloys appear. A large amount of α-Fe, SmFe ₃ phase, the magnetic energy product is small.

Table 1, embodiment and comparative example contrast

Example 2:

The conical fast-setting ribbon method used in this example prepared high-performance Sm _1.0 Zr _0.3 Fe _8.1 Co _0.6 fast-setting ribbons. The thickness and width of the ribbons are shown in Table 2. The difference is that the rotating speed of the roller edge is 40m/s, and others are as in embodiment 1.

Comparative example 2, adopting the roller type fast-setting thin strip method, other parameters are as embodiment 2, extremely unstable in the process of stripping, part of the melt splashing phenomenon has occurred, and the thin strip shape uniformity obtained is relatively poor, and the thickness of the thin strip is 15 ~ 50%. At the same time, there are a large number of granular and rod-shaped fast-setting materials. The XRD diffraction peaks of the granular and rod-shaped α-Fe phase are relatively high. After grinding, nitriding, and bonding, Sm _1.0 Zr _0.3 Fe _8.1 Co The energy product of the _0.6 N _x magnet is small.

Table 2, embodiment and comparative example contrast

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; 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, the spray belt pressure is 0.05Mpa, and the protective atmosphere pressure is 0.01MPa; In the belt spraying step, the nozzle and the cooling roller form a dynamically stable planar molten pool that spreads in two directions, and the temperature of the molten pool is 700-1300°C; The disc-type flat roller is made of molybdenum, and the inside of the flat roller is cooled by circulating water. The diameter of the flat roller is 400mm, and the linear speed of the roller edge is 20m/s; 0.2μm; The nozzle aperture is 0.5mm, the nozzle is close to the edge of the roller, and 20mm away from the edge of the roller; the molten metal is sprayed on the surface of the roller and cooled rapidly to form a fast-setting thin strip; the molten metal is sprayed on the surface of the roller and quickly spreads and cools to form a The crystal thin strip will be separated from the roller by itself under the cooling of the edge of the disc and its own contraction and centrifugal force.