CN101391291A - A method for in-situ synthesis of metal matrix composites under combined electromagnetic fields - Google Patents

Abstract

The invention provides a method for continuous production of particle-reinforced metal-matrix composite materials on an industrial scale. The metal-matrix composite materials are synthesized under a combined magnetic field. It is characterized in that: in the in-situ synthesis process of the composite material, a combination of a rotating magnetic field and a traveling wave magnetic field is used to synthesize and prepare a particle-reinforced metal matrix composite material melt. A low-frequency rotating magnetic field is placed outside the molten pool of composite material, and the center of the magnetic field coil is at the same height as the center of the melt; a traveling wave magnetic field is applied at the bottom of the molten pool of composite material, and the center of the traveling wave magnetic field coil is at the same position as the center of the molten pool of composite material. The particle reinforcement phase of the composite material prepared by the method is evenly and finely distributed, the internal structure is dense without looseness, shrinkage cavity and other structural defects, the outer surface of the billet has high smoothness and no defects, and the friction and wear resistance of the composite material is obviously improved.

Description

A method for in-situ synthesis of metal matrix composites under combined electromagnetic fields

technical field

The invention relates to the technical field of material preparation, in particular to a new method for synthesizing a metal-based composite material of an endogenous particle-reinforced phase by combining a melt reaction under an electromagnetic field.

Background technique

Particle-reinforced metal matrix composites have become a new type of metal functional material that is more and more widely used because of its composite structure characteristics and good physical, chemical and mechanical properties. According to the morphology of the reinforced phase, metal matrix composites are mainly divided into two categories: particle reinforced metal matrix composites and fiber reinforced metal matrix composites. The outstanding advantages of particle-reinforced metal matrix composites are high specific strength, low reinforcement cost, relatively uniform microstructure, isotropic material properties, and secondary molding by traditional processing techniques. At present, there are mainly two mature methods for the preparation of particle-reinforced metal matrix composites: the method of adding reinforced particles and the method of in-situ reaction formation. The method of adding reinforced particles is mainly based on the stirring and synthesis of metal melts with reinforced particles; the principle of preparing particle-reinforced metal matrix composites by the in-situ reaction to generate particles is to add or introduce alloying elements that can form a second phase in the metal matrix melt. Or compounds, react with the metal matrix melt at a certain temperature to form in-situ reinforced particle composites.

The above two methods of preparing particle-reinforced metal matrix composites have their own characteristics, but the biggest difficulty in the preparation process is the same problem, that is, how to control the size and distribution of the particle-reinforced phase under the premise of ensuring the performance of the metal matrix , morphology, and the wettability of the interface between the particle phase and the matrix metal to ensure that the composite material has uniform and dense structure, fine and dispersed particles, and excellent comprehensive performance of the material. The most effective way to solve this problem is to use the melt stirring method. The stirring methods used in research reports and industrial applications include mechanical stirring, gas stirring and electromagnetic stirring. The mechanical stirring method is the most simple and direct method. Due to the disadvantages of low efficiency, the stirring device pollutes the metal melt and carries slag into the melt, it is not conducive to the adoption of large-scale continuous production and the improvement of product quality. The disadvantages of the gas stirring method are mainly limited stirring intensity, uneven stirring and slag contamination of the melt by blown gas, which is also not conducive to improving product quality. Electromagnetic stirring realizes non-contact stirring, does not damage the oxide film and top slag protective layer of the molten pool, and does not pollute the melt. Moreover, the stirring intensity is easy to achieve precise control, and it is more and more widely used in metallurgy and material preparation processes.

At present, there are several patented technologies for the preparation of metal matrix composites under the action of single electromagnetic field stirring, such as Chinese patent: CN1667147C, the publication date is: 2005.9.14, and the name of the invention is: an industrial scale preparation of endogenous particle reinforced aluminum matrix composites The preparation method of the patent proposes the use of melt reaction method + electromagnetic stirring treatment + semi-continuous casting molding integration technology. The method is to add a compound containing elements that enhance particle formation into molten aluminum or aluminum alloy at a certain temperature, and at the same time apply electromagnetic stirring to make it fully react, and make the endogenous particles distribute more uniformly in the melt to obtain The composite material melt is semi-continuously cast into rods. Chinese patent: CN 101199989, method for continuous casting of particle-reinforced metal matrix composites under different-frequency composite electromagnetic fields, which proposes to apply low-frequency alternating magnetic fields during the preparation of composite material melts: the frequency is 5-50Hz, and the power range is 5-60kW. Perform electromagnetic stirring. The magnetic fields used in the preparation of particle-reinforced composite materials under the above electromagnetic fields are all single rotating stirring magnetic fields, and the electromagnetic field also plays an obvious role. However, with the development of technology and the improvement of performance and quality requirements for composite materials, synthetic The problems existing in metal matrix composites have gradually emerged, especially when stirred under a single magnetic field, the particle phase is prone to segregation, forming a local dense or cluster-like distribution, resulting in inhomogeneity in the structure and properties of the material. The reasons for this problem are analyzed as follows:

Due to the difference in physical properties between the particle-reinforced phase and the matrix metal melt, the metal melt containing the particle-reinforced phase has the characteristics of heterogeneity and discontinuity, and the difference in electromagnetic properties between the particle-reinforced phase and the matrix metal makes both The electromagnetic force is inconsistent, and due to the difference in density and wettability between the particle phase and the matrix metal liquid, the particle phase is easy to segregate in the metal melt. For example, when a rotating magnetic field is applied to stir, if the density of the particle phase is greater than that of the melt The density is higher, and the particle phase is segregated to the periphery of the melt under the action of rotating centrifugal force. When stirring with a traveling wave magnetic field, the non-magnetic particle phase is not affected by the electromagnetic force. During the up and down stirring process of the melt, due to the density difference between the particle phase and the melt, the particle phase is easy to float or settle, and the yield of the phase is enhanced. decline. Therefore, it is difficult to achieve very ideal results by applying electromagnetic stirring with a single magnetic field to the metal melt containing the particle-reinforced phase.

In order to solve the above problems under single magnetic field stirring, the applicant proposed a new method of synthesizing metal matrix composites under combined magnetic field, so that the particle phase can be more effectively refined in the matrix metal melt and achieve an ideal uniform distribution effect .

Contents of the invention

The purpose of the present invention is to provide a method for the continuous synthesis of particle-reinforced metal-matrix composites on an industrial scale in view of the main problems in the current synthesis of particle-reinforced metal-matrix composites, that is, the melt of particle-reinforced metal-matrix It is synthesized under the action of stirring (EMS), and is formed by semi-continuous casting to obtain a billet or molded to make a casting.

The basic idea of the present invention is: during the synthetic process of the particle reinforced composite material, a rotating magnetic field (R-EMS) and a traveling wave magnetic field (T-EMS) are simultaneously applied to carry out electromagnetic stirring under the composite magnetic field, and the electromagnetic stirring of the rotating magnetic field realizes the melting of the metal melt. Circular motion, that is, rotational motion, and the traveling wave magnetic field realize the vertical (up and down) stirring motion of the metal melt. Therefore, under the joint action of the rotating magnetic field and the traveling wave magnetic field, the metal melt realizes a spiral motion. The helical stirring under the combined magnetic field can overcome the deficiency of electromagnetic stirring in a single magnetic field, and make the distribution of the particle phase in the melt more uniform and refined. The principle is combined with Figure 1, and the analysis is as follows:

Applying a rotating magnetic field 1 to electromagnetically stir the composite material melt 2 on the outside of the composite material molten pool 3 made of thermal insulation refractory material, the composite material melt is dominated by horizontal circular motion (Fig. 1A) (naturally under forced stirring) Convection can be ignored), which is the low-frequency rotating magnetic field electromagnetic stirring (R-EMS) mentioned in the Chinese patent: CN101199989. Under the action of the stirring magnetic field, the rotating laminar flow motion of the melt is difficult to overcome the sedimentation or floating of particles, resulting in particles in different height directions Moreover, under the centrifugal force of circular motion, the particle phase tends to agglomerate into large particles around the molten pool and is captured by the refractory lining. This is the shortcoming of single application of R-EMS. If the rotating magnetic field 1 is not applied, but a traveling magnetic field 4 is applied at the bottom of the molten pool of the composite material (Fig. 1B), that is, the traveling magnetic field electromagnetic stirring (T-EMS) is implemented, the composite material melt is vertical under the action of the magnetic field ( Up and down) movement, the disadvantage of using this stirring method alone is that there are local dead zones and local strongly stirred zones in the molten pool, that is, the uniformity of stirring is poor. The yield is not high, resulting in poor compounding effect. If the rotating magnetic field 1 and the traveling wave magnetic field 4 (Fig. 1C) are applied at the same time, that is, the combined magnetic field proposed by the present invention is adopted, the composite material melt presents the effect of spiral stirring, and the stirring intensity is effectively improved, especially the "dead zone" of stirring can be effectively eliminated ", the combined magnetic field stirring combines the advantages of both R-EMS and T-EMS stirring, and makes up for the shortcomings of using a single magnetic field stirring.

Based on above-mentioned train of thought, realize the technical scheme of the present invention is:

A method for synthesizing metal matrix composites by melt reaction under a combined magnetic field: after the metal melt is refined, it is adjusted to the initial temperature of reaction synthesis, and reactants that can react with the melt in situ to form a particle phase are added to carry out the synthesis reaction. During the synthesis process, a rotating magnetic field and a traveling wave magnetic field are simultaneously applied; after the reaction is completed, it is left to stand at the pouring temperature before pouring.

In the method of the present invention, the rotating magnetic field and the traveling wave magnetic field are simultaneously applied during the reaction synthesis process. The specific operation is: install a low-frequency rotating magnetic field outside the molten pool of the composite material. The installation position is determined according to the height of the melt in the molten pool. The center of the magnetic field coil At the same height as the center of the melt, the range of electromagnetic parameters of the low-frequency magnetic field is frequency: 0.5-100Hz, working current: 1-1000A, and the electromagnetic parameters are adjusted according to the stirring intensity of the melt; a traveling wave magnetic field is applied at the bottom of the molten pool of composite materials, The center of the traveling wave magnetic field coil is at the same position as the center of the molten pool of the composite material. The electromagnetic parameters of the traveling wave magnetic field range from frequency: 0.5 to 100Hz, and working current: 1 to 1000A. The electromagnetic parameters are adjusted according to the stirring intensity of the melt.

The method is characterized in that a rotating magnetic field is applied from the side of the molten pool during the synthesis of the metal matrix composite, a traveling magnetic field is applied from the bottom of the molten pool, and the synthesis is carried out under the combined magnetic field composed of the rotating magnetic field and the traveling magnetic field. The method can be used to prepare composite materials by adding particle-reinforced phase to melt and in-situ reaction synthesis.

The specific features of applying this invention are:

After the composition of the matrix metal melt in the composite material molten pool and the initial reaction temperature are reached, the reactants that can react with the molten metal to form a particle-reinforced phase are sprayed into the composite material molten pool 2 through the spray gun 5, and the combined magnetic field is turned on to adjust the combined magnetic field The electromagnetic parameters are used to stir the composite material melt for a certain period of time to obtain a composite material melt. If synthesis under vacuum conditions is adopted, a sealed furnace cover 6 (Fig. 2) is added on the molten pool.

Compared with the prior art, the advantages of the present invention are mainly that the stirring efficiency of the molten pool is improved, the stirring time is shortened, the stirring effect is improved, the phase of the prepared composite material melt particles is finer and denser, the dispersion is more uniform, and the temperature difference control range of the melt is wider. precise.

Description of drawings:

Figure 1 Schematic diagram of electromagnetic stirring

Figure 2 Schematic diagram of equipment

Fig.3 SEM images of the microstructure of the composite billet

In the figure: 1-rotating magnetic field, 2-composite melt, 3-melting pool, 4-traveling magnetic field, 5-spray gun, 6-sealing furnace cover.

Detailed ways

Implementation example: preparation of (Al ₃ Zr _(s) + Al ₂ O _{3 (s)} ) particle reinforced A356 matrix composite material

Raw materials: base metal: A356 alloy; solid powder: industrial zirconium carbonate (Zr(CO ₃ ) ₂ ) powder (purity 99.20%), refining degasser and slag removal agent;

In situ reaction equation: 7Al _(l) +Zr(CO ₃ ) _2(s) ＝Al ₃ Zr _(s) +2Al ₂ O _3(s)

Particle reinforcement phase: Al ₃ Zr _(s) and Al ₂ O _3(s)

The preparation process is divided into two steps:

(1): Metal smelting and powder preparation:

The A356 alloy is melted in a 60kW industrial frequency aluminum melting furnace and heated up to 900°C for degassing and slag removal. The reagents used were fully dried at 250°C to 300°C, among which Zr(CO ₃ ) ₂ was ground into fine powder (particle size less than 100 μm), weighed and put into the injection tank, the weight of Zr(CO ₃ ) ₂ added was 10% of metal weight (note: the theoretical volume fraction of the particle phase is about 13.68vol%).

(2): In situ reaction synthesis under compound electromagnetic field to prepare composite material melt:

As shown in Figure 1C, the molten metal 2 that has been refined and meets the requirements of the initial reaction temperature (870° C.) is poured from the metal refining holding furnace into the insulated composite material molten pool 3, and is blown into the molten pool 3 with Zr ( CO ₃ ) ₂ powder, turn on R-EMS1 and T-EMS 4, and carry out electromagnetic stirring under the combined magnetic field, the frequency of R-EMS stirring magnetic field 1 is 15Hz, the current is 300A, the frequency of T-EMS stirring magnetic field 4 is 15Hz, and the current is 300A , the horizontal magnetic induction intensity and vertical magnetic induction intensity of the coil center are both 0.1T at no load, after 20 minutes of reaction, refining with Ar gas for 5 minutes, and standing for 5 minutes, the composite material melt is obtained, and the composite material is obtained by semi-continuous casting. The scanning electron micrograph of the material round billet is shown in Figure 3.

The diameter of the continuous casting slab is 200mm. The outer surface of the composite casting slab is smooth, the internal structure is dense, there is no solidification structure defect such as porosity and shrinkage cavity, and the particle size is 1-2 μm.

Claims (3)

1, the method for synthetic metal-base composites under a kind of combination field, comprise and to adjust to the synthetic reaction initial temperature after the metal bath refining, adding can generate particle reactant mutually with the metal bath reaction in-situ carry out synthetic reaction, and question response finishes, and pours into a mould after leaving standstill pouring temperature; It is characterized in that, in the synthetic preparation process of composite, carry out outer field action under the resultant field that adopts rotating excitation field and travelling-magnetic-field to be combined into.

According to the method for synthetic metal-base composites under the said combination field of claim 1, it is characterized in that 2, said resultant field is to make up and form by the rotating excitation field that applies from the side, molten bath with from the travelling-magnetic-field that the molten bath base plate applies.

3, according to the method for synthetic metal-base composites under the said combination field of claim 2, it is characterized in that, the low frequency rotating excitation field is settled in the outside, composite molten bath, the installation site is determined according to melt height in the molten bath, field coil center and melt center are at sustained height, the electromagnetic parameter scope of low frequency magnetic field is frequency: 0.5～100Hz, operating current: 1～1000A; Bottom in the composite molten bath applies travelling-magnetic-field, and the center in travelling-magnetic-field hub of a spool and composite molten bath is at same position, and the electromagnetic parameter scope of travelling-magnetic-field is frequency: 0.5～100Hz, operating current: 1～1000A.

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