METHOD FOR PRODUCING MULTIPHASE PARTICLE-REINFORCED METAL MATRIX COMPOSITES

FIELD OF TECHNOLOGY

This invention relates to the field of preparation technology of metal matrix composites, in particular to a new method for producing in-situ multiphase particle-reinforced metal matrix composites through the combination of an in-situ reaction process and an in-situ crystallization process under an electromagnetic field.

BACKGROUND

Because the multiphase particle-reinforced metal matrix composites have both excellent toughness and plasticity of metal and excellent strength and modulus of ceramics, compared with conventional materials, the multiphase particle-reinforced metal matrix composites have better physical and mechanical properties and have broad application prospects in the fields of aerospace, automotive, electronics, etc. The in-situ synthesis method is an important method for preparing particle-reinforced metal matrix composites. The reinforcements of this method are formed by in-situ nucleation in the matrix and have high thermodynamic stability, and these reinforcements have high surface cleanliness, good wetting ability with the matrix and high interface bonding strength, which can greatly improve the strength and elastic modulus of the materials, in the mean while ensuring the materials have good toughness and high-temperature performance, so the in-situ synthesis method has become an important method for preparing particle-reinforced metal matrix composites.

In accordance with different generation ways of the reinforcements, the in-situ synthesis method can be divided into in-situ reaction method and in-situ crystallization method. The in-situ reaction method is that the reactants are added into melt followed by the in-situ reaction with the matrix metal to form fine and stable particle-reinforcement phase; and the in-situ crystallization method is using the precipitated phase of the alloy melt during the solidification process as reinforcement particles to prepare the metal matrix composite materials. The in-situ reaction method and in-situ crystallization method have their own characteristics in the preparation method, types and characteristics of reinforcement phase, structure and performance of composite materials.

The in-situ reaction method has the following main advantages:

(1) the number and size of the reinforcements are controlled through controlling the addition amount of the reactants and the reaction time, and the specific preparation methods are flexible;

(2) the reinforcement types have many choices, the particle phase can be ceramic phase, such as Al2O3, TiB2 and ZrB2, or intermetallic compound phase, such as Al3Ti and Al3Zr, and the choice space of the particle phase matched with the matrix is big.

The in-situ reaction method has the following main deficiencies:

(1) the addition of reactants into the melt is prone to being uneven mixed, resulting in severe local reactions and clustered and grown particle phase, unevenly distributed reinforcements, which will seriously affect the performance stability of the composite materials;

(2) when preparing high volume fraction particle phase composite materials, the extent of the in-situ reaction is difficult to control, the heat effect of the reaction will affect the temperature of the reaction system and the nucleation and growth of the particle phase is uncontrolled;

(3) when preparing high volume fraction particle phase composite materials, the efficiency of the in-situ reaction is lower, the generated particles are prone to cluster, the excess reactants and reaction residues easily contaminate the metal, resulting in that high volume fraction of composite materials prepared by in-situ reaction method have many structural defects and the performance will be impact in severe case.

The in-situ crystallization method has the following main advantages:

(1) the types and amount of the particle phase are controlled through controlling the crystallization time, the crystallization temperature and under cooled melt compositions, so the in-situ crystallization process is easy to control;

(2) the particles are in situ precipitated in the melt, there is no problem of contaminating the interfaces, so the interface bonding is better.

The in-situ crystallization method has the following main deficiencies:

(1) the preparation method is single, and the particle reinforcements of the in-situ crystallization are mainly intermetallic compounds and primary phase, such as Mg2Si, Al3Ti, FeAl3 and primary crystal Si, the forms of the particle phase is relatively single, the matching form with matrix is single and the choice space is small;

(2) the in-situ crystal precipitating of the particles is limited by the mass transfer kinetics within the melt, the generation amount of the particle phase is greatly limited, that is to say its volume fraction is greatly limited. Although extending the crystallization time and improving the super cooling degree of the components can increase the volume fraction of the particle phase, too long crystallization time will result in growth and severe aggregation of the primary particles, single in-situ crystallization method is difficult to prepare composite materials with excellent performance and high volume fraction.

In view of the above analysis, the in-situ reaction method has many advantages in the preparation, selection of the particle phase and the matching with the matrix; and the in-situ crystallization method is better than the in-situ reaction method in the control of recombination processes, the combination of particle phase with the matrix and other aspects. The in-situ reaction method and the in-situ crystallization method can be well complemented in the preparation method for in-situ particle-reinforced metal matrix composites, and using the in-situ reaction method and the in-situ crystallization method to prepare the particle-reinforced metal matrix composites can improve the types and the volume fraction of the particle phase, in particular when preparing high volume fraction particle phase-reinforced metal matrix composites, using the in-situ reaction method and the in-situ crystallization method to prepare the multiphase particle-reinforced metal matrix composites can overcome the difficulties existed in the preparation of high volume fraction particle phase-reinforced metal matrix composites by single method.

The preparation method for particle-reinforced metal matrix composites has another important problem: whether the in-situ reaction method or the in-situ crystallization method is employed to prepare particle reinforced metal matrix composites, the formation, appearance and distribution control of the particle phase have decisive impact on the performance of the composite materials, therefore, we must adopt an effective method for the formation, appearance and distribution control of the particle phase.

Based on this background, this invention proposed that in the electromagnetic field, the in-situ reaction method and the in-situ crystallization method are used to integratedly prepare the multiphase particle reinforced metal matrix composites. No report on using the integrated method to prepare the multiphase particle reinforced metal matrix composites has been found in the existing literature search.

SUMMARY

The objective of the present invention is to solve the deficiency of only using the in-situ reaction method or the in-situ crystallization method to prepare particle-reinforced composite materials. The present invention proposes to use the in-situ reaction method and the in-situ crystallization method for integrated preparation of the multiphase particle-reinforced metal matrix composites, and controlling the distribution of the particle phase under the electromagnetic field and resolve the main problems existed in the current preparation processes of particle-reinforced metal matrix composites.

The technical principles of this invention are as the following: the in-situ reaction method and the in-situ crystallization method are combined to prepare multiphase particle-reinforced metal matrix composites, the electromagnetic field is employed to control the in-situ reaction during the in-situ reaction synthesis process, the deficiency of uneven distribution caused by in-situ synthesis reaction is overcome and the cluster and growth of the particle phase is suppressed through controlling the uniformity of the reaction, and due to the stirring action of the electromagnetic field, the utilization ratio of the reactants can be increased to make the in-situ reaction more thoroughly and make for the discharge of impurities and by-products. During the solidification process of the metal matrix composite melt, the same electromagnetic field is employed to make the distribution of the in-situ crystalline phase even, gradient, or directional, and promote the nucleation of the in-situ crystalline phase, using the magnetization and stirring effect of the electromagnetic field. The multiphase particle-reinforced metal matrix composites are prepared by the in-situ reaction synthesized particle phase in cooperation with the in-situ crystalline particle through this method.

Based on the above principle, the technical scheme of the present invention is achieved by two steps:

(1) the composite melt is synthesized and prepared through in-situ reaction under the electromagnetic field

During the synthesis process of the in-situ reaction, after the melt composition is qualified and the temperature reaches the in-situ reaction temperature, the in-situ reactants are added and the magnetic field is employed to control the in-situ reaction and the particle dispersion. The low-frequency traveling wave magnetic field can be selected as the magnetic field of this process, and the electromagnetic parameters are: frequency: 1˜50 Hz, working current: 1-1000 A. The magnetic strength at the melt center is controlled as 0.001˜1 T, the electromagnetic parameters are adjusted according to the mixing intensity of the melt and the magnetic strength at the melt center is most preferably controlled as 0.02˜0.1 T.

The low-frequency electromagnetic stirring magnetic field of this synthesis process can also select rotating and stirring magnetic field with the above range, and the main objective is to stir the melt bath, accelerate the cross-flow and dispersion mass transfer of the reactants and accelerate the transfer of the in-situ reaction heat, so that the system temperature is even and the in-situ reaction can be evenly carried out in the whole melt, while the electromagnetic field can accelerate the transferring and diffusing of the particle phase to reduce the aggregation and control the growth of the particle phase.

(2) the solidification and crystallization of the composite melt are controlled under the electromagnetic field

The above prepared composite melt is solidified under the control of the electromagnetic field after the temperature reaches the casting temperature, and the main purpose of applying the magnetic field is to control the distribution of the particle phase. According to different purposes, the electromagnetic field applied during this process can select low-frequency rotating and stirring magnetic field or high-frequency oscillating magnetic field.

a, for the preparation of homogeneous particle-reinforced composite materials with evenly distributed particles, the rotating electromagnetic stirring magnetic field is applied to control the solidification of the composite melt, and the ranges of the electromagnetic parameters are as follows: frequency: 1˜50 Hz, working current: 1˜1000 A, and the magnetic strength at the crystallization centre is controlled as 0.001˜1 T, and the electromagnetic parameters are adjusted according to the mixing intensity of the melt in the crystallizer, and the magnetic strength at the melt center in the crystallizer is most preferably controlled as 0.02˜0.1 T.

b, for the preparation of composite materials with graded distributed particles or surface reinforced composite materials, the high-frequency oscillating magnetic field is employed during the in-situ crystallization process, and the ranges of the electromagnetic parameters of the high-frequency oscillating magnetic field are as follows: frequency: 1 kHz˜30 kHz, power: 0˜100 kW, and the magnetic strength in the unloaded crystallizer is controlled as 0.005˜1 T, and the magnetic strength in the unloaded crystallizer is most preferably controlled as 0.1˜0.5 T.

Compared with the existing technology, the present invention has the following main advantages:

(1) the multiphase particle-reinforced metal matrix composites are prepared through combination of the in-situ reaction and the in-situ crystallization in the electromagnetic field, which overcomes the deficiency of preparing the particle-reinforced metal matrix composites with single in-situ reaction method or single in-situ crystallization method, makes the in-situ reaction particles in cooperation with the in-situ crystallization particles to strengthen the materials and achieve the complementary of the two strengthening effects, and this strengthening effect is better than the strengthening effect using single in-situ reaction method or single in-situ crystallization method;

(2) the in-situ reaction process is controlled in the electromagnetic field to make the in-situ reaction in the melt more uniform, increase the transferring and diffusing speed of the generated particle phase and suppress the particle aggregation so the particles can be refined and more evenly distributed.

(3) the solidification process of the composite melt and the in-situ crystallization process are acted under the electromagnetic field to control the distribution of the particles and prepare composite materials with evenly distributed multiphase-reinforcement particles or gradient composite materials with the particle phase enriched on the surface and distributed gradiently along the radial direction, or surface-enhanced composite materials.

In summary, using the combination of the in-situ reaction method and the in-situ crystallization method to prepare the multiphase particle-reinforced metal matrix composites can effectively increase the types and amount of the particle phase, achieve multi-phase particle reinforcements, and using the electromagnetic field to effectively control the in-situ reaction process and the in-situ crystallization process can realize preparation of “controllable” and “designable” materials and ensure the performance stability of the materials in industrial production. In addition, this method is simple and easy, the investment in equipment is low and the benefits are obvious, which is very suitable for industrial scale production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the schematic diagram of the in-situ reaction synthesis process under the electromagnetic field.

Explanatory text: 1 argon-air gun (used for blowing the reactant powders or refining powders or argon bowing refining); 2 composite melt; 3 crucible or furnace lining; 4 heating unit; 5 traveling wave magnetic field.

FIG. 2 is the schematic diagram of the in-situ crystallization process under the electromagnetic field.

Explanatory text: 6 melting furnace/refining and maintaining furnace/in-situ synthetic furnace; 7 launder/runner; 8 melt; 9 continuous casting heat-preservation hot top; 10 solidification control magnetic field (rotating magnetic field/high frequency magnetic field); 11 crystallizer; 12 secondary cooling water-spraying device; 13 composite material casting billet.

FIG. 3 is the diagram of the effects in the Embodiment 1 compared with the solidification structures obtained using combination of the in-situ reaction and the in-situ crystallization without magnetic field, and using single in-situ reaction method and single in-situ crystallization method for composite;

FIG. 3 (a) is the result of the present invention; FIG. 3(b) is the result of in-situ reaction+in-situ crystallization with no magnetic field; FIG. 3(c) is the result obtained using single in-situ reaction for composite under the same electromagnetic parameters with the embodiment; FIG. 3(d) is the result obtained using single in-situ reaction for composite with no magnetic field; FIG. 3(e) is the result obtained using single in-situ crystallization for composite under the same electromagnetic parameters with the embodiment; FIG. 3(f) is the result obtained using single in-situ crystallization for composite with no magnetic field;

FIG. 4 is the diagram of the effects in the Embodiment 2 compared with the solidification structures obtained using single in-situ reaction method and single in-situ crystallization method for composite;

FIG. 4(
a) is the result of the present invention; FIG. 4(b) is the result obtained using single in-situ reaction for composite under the same electromagnetic parameters with the embodiment; FIG. 4(c) is the result obtained using single in-situ reaction for composite with no magnetic field; FIG. 4(d) is the result obtained using single in-situ crystallization for composite under the same electromagnetic parameters with the embodiment; FIG. 4(e) is the result obtained using single in-situ crystallization for composite with no magnetic field.

DETAILED DESCRIPTION
Embodiment 1

using the combination of the in-situ reaction method with the in-situ crystallization method to prepare (Al3Zr(s)+Al2O3(s)) particle-reinforced Al-matrix composite materials in the electromagnetic field (Note: reinforcement phase Al2O3(s) were all in-situ reaction generated particles and Al3Zr(s) were mainly in-situ crystallization generated particles).

Raw materials: matrix metal: pure Al, Al-3.8% Zr alloy; solid powder: industrial zirconium carbonate (Zr(CO3)2) powder, refining degasifying agent and slag skimming agent;

The preparation process included the follow three steps:

(1) preparation of reaction salt and matrix metal melt:

The industrial zirconium carbonate powder were ground into fine powder (particle size: less than 100 μm) in a globe mill, dried at 200° C. for 2 hours, weighed and loaded into a blowing tank. The additional weight of Zr(CO3)2 were 20% of metal weight. 90 kg of pure Al and 10 kg Al-3.8% Zr alloy were added into a crucible-type melting furnace and heated to 900° C., degassed and slagged-off.

(2) synthesis of Al2O3(s) reinforced particles through the in-situ reaction under the traveling wave magnetic field

Al2O3(s) generated through the in-situ reaction:

3Zr(CO3)2(s)+4Al(1)==2Al2O3(s)+3Zr+6CO2(g) were in-situ reaction reinforced particles (Note: Zr(CO3)2 further introduced Zr atoms into the melt and the mass fraction of Zr in the melt was increased, which was conductive to improve the amount of Al3Zr(s)) particles precipitated from the in-situ crystallization). The process was as follows:

The temperature of aluminum liquid was kept at 900° C., the slag was skimmed off, and Zr(CO3)2 powder was blown into a melting bath 2 with an Ar air blowing gun 1. At the same time the traveling wave magnetic field 5 was open and the electromagnetic parameters of the magnetic field 5 was 5 Hz and the current was 200 A. The measured magnetic strength at the melt centre was 0.075 T, and after the power blowing, Ar was blew for refining for 3 min followed by stopping the blowing of argon and synthesis for 18 min under the electromagnetic field. Then the magnetic field was closed, and stranded and skimmed off the slag to prepare the handling of the in-situ crystallization compound under the electromagnetic field.

(3) synthesis of Al3Zr(s) reinforced particles through the in-situ crystallization under the rotating magnetic field

The melt-generated Al3Zr(s) particles through in-situ crystallization during the process of cooling, pouring and solidification. In order to crystallize and generate a larger number of Al3Zr(s) during the process of cooling and solidification, the composite material melt prepared by the in-situ reaction was began to pour at about 840° C., and the pouring adopted semi continuous casting (as shown in FIG. 2) to control the casting speed as 0.18 m/min. During the solidification process, the low-frequency rotating and stirring magnetic field 10 was opened and the electromagnetic parameters of the magnetic field 10 were as follows: frequency: 4 Hz, input current: 300 A and the magnetic strength at the melt centre was measured as 0.1 T. The casting billet was round billet with a size of φ120 mm.

The casting billet obtained using the above process has compact interior structure, with particle sizes of Al2O3(s) 0˜0.5 μm, and Al3Zr(s) 0.5˜5 μm.

To compare the effects obtained using the present invention, FIG. 3 shows the diagram of composite materials obtained using the above preparation process of the present invention compared with the solidification structures obtained using combination of the in-situ reaction and the in-situ crystallization without magnetic field, and using single in-situ reaction method and single in-situ crystallization method for composite. FIG. 3 (a) is the result of the present invention; FIG. 3(b) is the result obtained through in-situ reaction+in-situ crystallization with no magnetic field; FIG. 3(c) is Al—Zr(CO3)2(s) component obtained using single in-situ reaction for composite under the same electromagnetic parameters with the embodiment; FIG. 3(d) is the result obtained using single in-situ reaction for composite with no magnetic field; FIG. 3(e) is Al—Zr system obtained using single in-situ crystallization for composite under the same electromagnetic parameters with the embodiment; FIG. 3(f) is the result obtained using single in-situ crystallization for composite with no magnetic field;

It can be seen that, using the present invention, the amount of the in-situ reaction particles Al2O3(s) and the in-situ crystallization particles Al3Zr(s) were significantly increased and the homogenization degree of the particle size distribution was improved.

Embodiment 2

using the combination of the in-situ reaction method with the in-situ crystallization method to prepare (Al3Ti(s)+Mg2Si(s)) particle-reinforced Al-matrix composite materials under the electromagnetic field (Note: reinforcement phase Al3Ti(s) was mainly in-situ reaction generated particles and all Mg2Si(s) were all in-situ crystallization generated particles).

Raw materials: metal: pure Al, Al—Mg alloy, crystal silicon; solid powder: industrial potassium fluotitanate powder, refining degasifying agent and slag skimming agent;

The preparation process included the follow three steps:

(1) preparation of reaction salt and matrix metal melt:

The industrial potassium fluotitanate powder were ground into fine powder (particle size: less than 100 μm) in a globe mill, dried at 200° C. for 2 hours, weighed and loaded into a blowing tank. The additional weight of potassium fluotitanate was 10% of metal weight. 100 kg of industrial pure Al were added into a crucible-type melting furnace and melted and heated to 900° C., degassed and slagged-off, followed by adding 1.5 kg of crystal silicon to the melt, stirring the melting bath to make the silicon melting and uniform, and the temperature of the melt was controlled at 900° C.

(2) synthesis of Al3Ti(s) reinforcement particles through the in-situ reaction under the traveling wave magnetic field

The metal melt was kept at 900° C. and the scum was skimmed off, and potassium fluotitanate powder was blown into a melting bath with an Ar air blowing gun. At the same time the traveling wave magnetic field was open and the electromagnetic parameter of the magnetic field was 15 Hz and the current was 100 A. The measured magnetic strength at the melt centre was 0.05 T, and after the power blowing, Ar was blew for refining for 3 min followed by stopping the blowing of argon. After synthesis for 18 min under the electromagnetic field, 2.4 kg of Al-50% Mg alloy was added into the melt and stirred for 5 min under the magnetic field, and then the magnetic field was closed, standed and skimmed off the scum to prepare the handling of the in-situ crystallization in the electromagnetic field.

(3) synthesis of Mg2Si(s) reinforced particles through the in-situ crystallization in the high frequency magnetic field

The melt generated Mg2Si(s) particles through in-situ crystallization in the molding process. In order to crystallize and generate a greater number of Mg2Si(s) in the process of solidification, the melt began to mould at about 800° C., and the molding and casting speed of the semi-continuous casting was controlled as 0.18 m/min. The high frequency magnetic field was open in the process of solidification and the electromagnetic parameters of the magnetic field were as follows: frequency: 5 Hz, power: 10 kW and the magnetic strength in unloaded crystallizer was 0.1 T. The casting billet was round billet with size of φ120 mm.

Embodiment 3

The raw materials used in this embodiment and the preparation process was exactly identical with the Embodiment 1, and the differences were that the in-situ reaction process and the in-situ crystallization process both adopted the rotating electromagnetic stirring magnetic field, and the electromagnetic parameters used during the in-situ reaction process were as follows: frequency: 5 Hz, working current: 200 A, and the magnetic strength of the melt centre was 0.075 T, but the electromagnetic parameters of the rotating magnetic field used during the in-situ crystallization process was the same as the embodiment 1 to prepare the multiple-phase particle-reinforced composite materials.

Embodiment 4

The raw materials used in this embodiment and the preparation process was exactly identical with the Embodiment 1, and the differences were that the electromagnetic parameters of the traveling wave magnetic field used during the in-situ reaction process were as follows: frequency: 1 Hz, working current: 1000 A, and the magnetic strength of the melt centre was 0.95 T, but the electromagnetic parameters of the rotating magnetic field used during the in-situ crystallization process were as follows: frequency: 50 Hz, working current: 50 A, and the magnetic strength in the crystallizer was 0.01 T to prepare round billet of φ100 mm.

Embodiment 5

The raw materials used in this embodiment and the preparation process was exactly identical with the Embodiment 1, and the differences were that the electromagnetic parameters of the traveling magnetic field used during the in-situ reaction process were as follows: frequency: 50 Hz, working current: 50 A, and the magnetic strength of the melt centre was 0.0075 T, but the electromagnetic parameters of the rotating magnetic field used during the in-situ crystallization process were as follows: frequency: 1 Hz, working current: 750 A, and the magnetic strength in the crystallizer was 0.75 T to prepare round billet of φ200 mm.

Embodiment 6

The raw materials used in this embodiment and the preparation process was exactly identical with the Embodiment 2, and the differences were that the electromagnetic parameters of high frequency magnetic field used during the in-situ crystallization process were as follows: frequency: 30 Hz, power: 100 kW, and the magnetic strength in the unloaded crystallizer was 0.97 T. The casting billet was round billet with size of φ200 mm.

Embodiment 7

The raw materials used in this embodiment and the preparation process was exactly identical with the Embodiment 2, and the differences were that the electromagnetic parameters of high frequency magnetic field used during the in-situ crystallization process were as follows: frequency: 1 kHz, power: 50 kW, and the magnetic strength in the unloaded crystallizer was 0.5 T. The casting billet was round billet with size of φ180 mm.

Embodiment 8

The raw materials used in this embodiment and the preparation process was exactly identical with the Embodiment 2, and the differences were that the electromagnetic parameters of high frequency magnetic field used during the in-situ crystallization process were as follows: frequency: 20 kHz, power: 40 kW, and the magnetic strength in the unloaded crystallizer was 0.4 T. The casting billet was round billet with size of φ160 mm.

From the solidification structures of the composite materials obtained from the above embodiments, compared with the method with no magnetic field or only using the in-situ reaction or only using the in-situ crystallization composite, the particle phase amount of the obtained composite materials was increased and the distribution homogenization degree was improved. The demonstrating comparison was shown in FIG. 3 and FIG. 4.

METHOD FOR PRODUCING MULTIPHASE PARTICLE-REINFORCED METAL MATRIX COMPOSITES

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