RU2437949C1 - Cast composite material on base of magnesium alloy and procedure for its manufacture - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: composite material consists of matrix alloy on base of magnesium and 5-10 wt % of strengthening particles of carbide of titanium, silicon or boron at contents of components in matrix alloy wt %: 0-12 Al, 0-4 Cu, 045 Zn, 0-1 Zr, to 3 Mn, to 10 REM, from 0.1 to 10 Ca, magnesium - the rest; structure of matrix alloy contains inter-metallide phases of composition (X)₂Ca, where X - Mg or Al. The procedure consists in preparation of semi-finished product of matrix alloy, in placing it in a reactor over reinforcing particles of carbide of titanium, silicon or boron heated to 650-670°C, in melting matrix alloy and in mechanical mixing in air during 5-10 min.

EFFECT: raised quality of composite material, reduced cost and raised ecological safety of material manufacture.

4 cl, 1 dwg, 2 tbl

Description

The invention relates to the field of metallurgy, in particular to the production of a cast composite material based on a magnesium alloy reinforced with discrete reinforcing particles, and can be used in the automotive industry, aviation, rocket and nuclear technology to obtain structural material for parts, as well as bearing and case products with minimum weight and improved mechanical characteristics.

As you know, magnesium alloys are characterized by low strength, hardness, wear resistance, as well as a tendency to scratch during sliding friction. To eliminate these disadvantages, reinforcement of magnesium matrices with ceramic particles is used. With a uniform distribution of particles in the matrix, composite materials (CM) based on magnesium alloys, in addition to high specific values of strength and stiffness, high hardness and wear resistance, have high casting properties and are easily machined.

The main methods for the manufacture of dispersion-strengthened CMs with a magnesium matrix are:

1) solid-phase combination of powder components - matrix powders and ceramic particles;

2) liquid-phase combination of components during mechanical mixing of ceramic particles in magnesium melts. Solid-phase methods of powder metallurgy do not provide CM with a 100% density and controlled bond quality at the matrix / filler boundaries; in addition, they involve the acquisition of expensive equipment, the high cost of matrix alloy powders, the implementation of complex technological processes for the preparation of components and compaction, i.e. are very expensive. Liquid-phase, or foundry, methods make it possible to obtain higher-quality CMs (fewer pores, better interfacial coupling) and are more economical. However, due to the affinity for oxygen and the tendency to ignite magnesium melts, liquid-phase methods also have several disadvantages.

So, there is a method of producing molten magnesium KM liquid-phase impregnation without pressure [N. KANEDA and T. CHON. Fabrication of particulate reinforced magnesium composites by applying a spontaneous infiltration phenomenon. // J. Mater. Sci. No. 32 (1) (1997). P.47], including the following steps:

but. Preparation of a mixture of a hardener (SiC particles) and an impregnation reagent (SiO ₂ ) in a mill;

b. Loading a mixture of powders into a crucible of an impregnation plant and laying a magnesium alloy ingot over a mixture of powders; evacuation of the assembly;

at. Hot impregnation of the powder mixture with a melt in a pure argon atmosphere at 700 ° C for 20 minutes, followed by stepwise cooling.

The presence of an impregnation reagent — amorphous silicon oxide — on the surface of SiC particles can also be achieved by prolonged oxidation of the particles in air: 30 hours at 1000 ° C [T. EPICIER, F.BOSSELET and J.C. VIALA. Microstructure of interfaces between a magnesium matrix and preoxidized silicon carbide particles. // INTERFACE SCIENCE. No. 1 (1993). P.213]. The further procedure of combining such particles with the melt requires even more thorough protection against oxidation and is carried out in sealed ampoules filled with argon.

In these methods, a uniform distribution in the matrix of reinforcing ceramic particles is not achieved due to the lack of mixing of the composite melt.

Another method is to mix pre-heated particles of TiC (up to 20 vol.%) Or AIN (up to 15 vol.%) In a magnesium melt at a temperature of 700 ° C in argon atmosphere [Suk-Won Urn, T. Imai, Y. Nishida and D.Jiang. Superplacity of ceramic particulate reinforced magnesium alloy composites, fabricated by melt stirring method. Proc. of Eleventh Intern. Conf. of comp. Mater. (1997) P.486].

In this method, during mechanical stirring, the gas is saturated with the melt due to gases adsorbed on the filler particles and the protective gas, which negatively affects the properties of the CM.

A method of manufacturing a semi-finished product KM in the form of a magnesium alloy with the addition of nanoscale powders TiC, Al ₂ O ₃ , SiC or nanotubes in an amount of from 0.01 to 10% by injection into the melt using protective gas (Ar, mixtures Ar + N ₂ or N ₂ + CO ₂ ) is proposed in US patent [US Patent No. US 2010/0075064 A1, Method for making magnesium-based composite material; TSINGHUA UNIVERSITY, Beijing (CN); HON HAI Precision Industry CO., LTD., Tu-Cheng (TW) (Mar. 25, 2010)]. To achieve uniform distribution of particles in the matrix, the melt is subjected to vibration processing in the protection of gases N ₂ or a mixture of N ₂ + SF ₆ .

In this method, during gas injection of the filler into the melt, the melt is saturated with gas due to gases adsorbed on the particles of the filler and the protective gas, which negatively affects the properties of CM.

A known method of manufacturing CM with a magnesium matrix, including the introduction by mechanical mixing of SiC particles into the AZ91 alloy melt, heated in a protective atmosphere CO + SF ₆ to a liquid-solid state (590 ° C) [XJWang, XSНu, К.Wu, MYZheng, L.Zheng, QJZhai. The interfacial characteristics of SiC _p / AZ91 magnesium matrix composites fabricated by stir casting. // J. Mater. Sci. No. 44 (2009). P.2759] or up to a temperature of 700 ° C [A.Luo. Effect of matrix alloy composition on the interfacial phenomena and microstructure of cast Mg / SiC _p composites. Proc. of Tenth Intern. Conf. of comp. Mater., (1995) P.287].

As in the previous examples, the method requires careful protection from oxidation of the melt, which complicates mixing and worsens the uniformity of the distribution of particles in the matrix.

A known method of protecting liquid magnesium melt prepared for combining with a preform of short fibers Al ₂ O ₃ , a flux of graphite powder or a mixture of boric acid and sulfur [S. JAYALAKSHMI, S. SESHAN, SVKAILAS, K. KUMAR and S. SRIVATSAN. Influence of processing and reinforcement on microstructure and impact behavior of magnesium alloy AM100. // Sâdhâna, Vol. 29. No. 5 (2004). P.509]. In the patent of the Russian Federation No. 2217512 [RU 2217512 C2, FLUX FOR REFINING AND PROTECTION AGAINST BURNING OF MAGNESIUM AND ITS ALLOYS; Putin O.A., Putin A.A., Gulyakin A.I., Nechaev N.P., Rubel O.A., Lyamin S.G., Novikov S.M., Zhulanov N.K., Belkin N .A., Temnikov V.V., Remeslov M.N .; OJSC "Russian Research and Design Institute of Titanium and Magnesium" (02/05/2002)] is proposed to use flux containing magnesium chloride, potassium chloride, calcium fluoride, sodium bromide and potassium fluoroborate to protect Mg melt. However, the protective layer of fluxes on the surface of the melt does not provide 100% protection of magnesium from ignition and desorption of gases from the surface of the filler particles and prevents the introduction of particles into the melt during mechanical mixing.

Thus, the use of special technological methods and materials for protecting molten matrix metal and gas desorption from the surface of filler particles makes the casting process of mechanical mixing of reinforcing particles into the melt difficult to implement.

Closest to the proposed invention (prototype) is a method of manufacturing CM with a matrix of magnesium and its alloys [US Patent No. 84657065, Composite materials having a matrix of magnesium or magnesium alloy reinforced with discontinuous silicon carbide particles; Tsuguyasu Wada, Ann Arbor; George T. Eldis, Ypsilanti; Darryl L. Albright, Ann Arbor, all of Mich. Amax Inc., Greenwich, Conf. (Apr. 14, 1987)]. KM contains as a hardener short fibers or particles of silicon carbide or titanium carbide in an amount of up to 24 vol.% And up to 5 vol.%, Respectively, which are introduced into the magnesium melt by mechanical mixing for the time required for uniform distribution of the filler in the matrix. In order to improve the wetting of the filler, lithium (metallic or in the composition of the ligature) is introduced into the melt of magnesium or magnesium alloy in an amount of from 0.2 to 0.7 wt.%. The process of mixing the filler into the melt can be carried out in an atmosphere of air. The disadvantage of this method is the difficulty of maintaining a constant concentration of lithium in Mg due to the rapid evaporation at temperatures of the existence of a magnesium melt.

The problem to which the present invention is directed, is to develop a composition and method for the production of magnesium CM, which eliminates the use of protective media from the process of combining the hardener and matrix, to achieve 100% assimilation of discrete particles of the reinforcing ceramic filler by the melt, uniform distribution of these particles in the matrix, additional hardening KM. The technical result is to increase the quality of the CM, reduce the cost of its manufacture, improve working conditions.

The technical result is achieved by the fact that a cast composite material based on a magnesium alloy is proposed, consisting of a matrix alloy based on magnesium and reinforcing discrete particles, characterized in that it contains titanium, silicon or boron carbide in an amount of 5 to 10 as reinforcing discrete particles wt.%, and the matrix alloy based on magnesium contains calcium in the following components, wt.%:

- aluminum from 0 to 12;

- copper from 0 to 4;

- zinc from 0 to 15;

- zirconium from 0 to 1;

- manganese up to 3;

- REM up to 10;

- calcium from 0.1 to 10;

- magnesium - the rest,

moreover, the matrix alloy contains discrete inclusions of intermetallic phases of the composition X ₂ Ca, where X is Mg or Al.

Reinforcing discrete ceramic particles of titanium, silicon or boron carbide have an average size of up to 40 microns. Discrete inclusions of intermetallic phases X ₂ Ca, appearing in the magnesium matrix with the introduction of calcium in an amount of 5 to 10 wt.%, Have a size of less than 10 microns.

The method of producing a cast composite material based on a magnesium alloy, comprising mechanically mixing a molten magnesium matrix alloy with reinforcing discrete particles, is characterized in that a semi-finished magnesium alloy matrix product is prefabricated with the following content of components, wt.%:

- aluminum from 0 to 12;

- copper from 0 to 4;

- zinc from 0 to 15;

- zirconium from 0 to 1;

- manganese up to 3;

- REM up to 10;

- calcium from 0.1 to 10;

- magnesium - the rest.

The semi-finished product is placed in the reactor over reinforcing discrete particles heated to 650-670 ° C, which are used as titanium, silicon or boron carbide in an amount of from 5 to 10 wt.%. After melting the matrix alloy, stirring is carried out in air for 2-5 minutes.

The process of manufacturing KM begins with the preliminary casting of a semi-finished product from a magnesium alloy containing from 0 to 12 wt.% Aluminum, from 0 to 4 wt.% Copper, from 0 to 15 wt.% Zinc, from 0 to 1 wt.% Zirconium, up to 3 wt.% manganese, up to 10 wt.% rare-earth metals with the addition of 0.1 to 10 wt.% calcium to reduce the tendency to ignite when heated and to ensure uniform distribution of filler particles in the matrix due to better wetting ability and the possibility of intensive mixing of the melt. Doping with calcium is carried out by adding ligatures to the semi-finished product (14.7 wt.% Ca, Mg - the rest). Then the finished semi-finished product is placed in the reactor over reinforcing discrete ceramic particles heated to a temperature of 650-670 ° C and heated. After the matrix alloy is melted, stirring is carried out for 2-5 minutes and then the mixture is poured by any known casting method. The manufacturing process of KM is carried out in air without the use of protective environments.

The minimum calcium content was experimentally obtained by determining the start time of burning a magnesium alloy in air when heated to 650-670 ° C. The maximum calcium content in the KM matrix of magnesium alloys was selected on the basis of data on a decrease in the strength and ductility of Mg alloys doped with calcium in an amount of more than 10 wt.% (~ 7 at.%) [LING-LING SHI, JIANXU and EVAN MA. Mg-Al-Ca In-Situ composites with a refined eutectic structure and their compressive properties. // Metall. Mater. Trans. A No. 39A (2008). P.1225].

The introduction of calcium into the magnesium matrix leads to a decrease in the cellular-dendritic parameter, i.e. dispersing the structure of the matrix and its hardening.

The invention can be illustrated by the following examples:

According to the above technology, cast KMs were obtained:

Example 1. Cast CM with a matrix made of Mg90 alloy (in wt%: Fe <0.04, Si <0.009, Mn <0.03, Ni <0.001, Al <0.02, Cu <0.004, Na <0.01, PZM 0.006, total impurities < 0.12, Mg - the rest) + 0.1 wt.% Ca, reinforced with particles of silicon carbide α-SiC in an amount of 10 wt.% With an average size of 14 microns; stirring at a melt temperature of ~ 660 ° C for 3 minutes

Example 2. Cast KM with a matrix made of an alloy of type AZ91 (Al - 9 wt.%, Zn - 1 wt.%, Mn <0.03 wt.%, PZM <0.01 wt.%, Mg - the rest) + 0.5 wt.% Ca reinforced with particles of silicon carbide α-SiC in an amount of 5 wt.% with an average size of 40 microns; stirring at a melt temperature of ~ 660 ° C for 2 minutes

Example 3. Cast KM with a matrix made of an AZ91-type alloy (Al - 9 wt.%, Zn - 1 wt.%, Mn <0.03 wt.%, PZM <0.01 wt.%, Mg - the rest) + 0.5 wt.% Ca reinforced with particles of silicon carbide α-SiC in an amount of 10 wt.% with an average size of 14 microns; stirring at a melt temperature of ~ 660 ° C for 5 minutes.

Samples for studying the microstructure and mechanical properties were cut from the obtained cast CMs. The drawing (a, b, c) shows the microstructure of cast KM from examples 1, 2 and 3, respectively. A uniform distribution of reinforcing filler particles in the matrix volume is seen. Reinforcing filler particles (silicon carbide, titanium carbide) retain cleavage, which indicates the absence of intense interfacial interaction when combined.

Adding more than 5 wt.% Calcium to the alloy leads to the appearance of intermetallic phases, which provide additional hardening of the alloy. The composition of the intermetallic phases (X) is ₂ Ca, where X is Mg or Al or other metal components of the magnesium alloy.

Flammability results are presented in table 1. It is seen that an increase in the mass content of calcium in the alloy sharply increases the resistance to ignition of magnesium alloys in the atmosphere of air, which makes it possible to obtain a uniform distribution of filler particles with vigorous stirring.

Samples of cast cylindrical CMs (h / d ratio - 2/3, where h is the height, d is the cylinder diameter in mm) were tested for compression (strain rate 1 mm / min), their strength was determined to be _{0.2 SJ} and σ _{B. SJ} . Hardness measurements of HB samples were carried out on a Wolpert Wilson TESTOR 930 setup (ball diameter 2.5 mm, load 62.5 kgf, loading duration 14 s). The mechanical properties of the obtained CMs are presented in Table 2. It can be seen that the addition of calcium in the matrix alloy even in an amount of 0.1 wt.% Makes it possible to obtain CM samples reinforced with SiC particles by mixing the melt without the use of protective media. The strength gain of cast KM, additionally doped with calcium, compared with the base alloys was: 95% with the introduction of 10 wt.% SiC in Mg90 alloy; 3.8% with the introduction of 5 wt.% SiC in the alloy AZ91; 28.5% with the introduction of 10 wt.% SiC in the alloy AZ91. The increase in hardness of cast KM in comparison with base alloys was respectively: 62%, 74% and 65.6%.

The reduction in the cost of CM is achieved by eliminating the use of expensive equipment in the manufacturing process of CM to protect the surface of a heated matrix alloy from oxidation, and the refusal to use protective materials harmful to humans leads to improved working conditions. Reducing the time for introducing the hardener and the rejection of sophisticated protective equipment increases the energy efficiency and environmental friendliness of the manufacturing process of CM.

Table 1 The content of Ca in the alloy, wt.% Flammability at 670 ° C, min Particle introduction Melt without stirring Melt with stirring 0.05 5 3 - 0.1 12 8 + 0.5 twenty fifteen + one > 20 > 20 + Note: (-) - particles could not be entered; (+) - particles were introduced successfully.

table 2 Example No. Material σ _{0.2 SG.,}
MPa σ _{B. S.J.,} MPa Hardness, HB one Mg90 + 0.1 wt.% Ca + 10% SiC _p 195 228 51.5 2 AZ91 + 0.5 wt.% Ca + 5% SiC _p 273 319 108.8 3 AZ91 + 0.5 wt.% Ca + 10% SiC _p 338 371 103.5 Mg90 one hundred 130 31.8 AZ91 263 358 62.5

Claims (4)

1. Cast composite material based on a magnesium alloy, consisting of a matrix alloy based on magnesium and reinforcing discrete particles, characterized in that as reinforcing discrete ceramic particles it contains titanium, silicon or boron carbide in an amount of from 5 to 10 wt.%, and the magnesium-based matrix alloy contains calcium in the following components, wt.%:
aluminum from 0 to 12 copper from 0 to 4 zinc from 0 to 15 zirconium from 0 to 1 manganese until 3 REM to 10 calcium from 0.1 to 10 magnesium rest,
moreover, the matrix alloy contains discrete inclusions of intermetallic phases of the composition X ₂ Ca, where X is Mg or Al. 2. The material according to claim 1, characterized in that the reinforcing discrete particles of titanium carbide, silicon or boron have an average size of up to 40 microns. 3. The material according to claim 1, characterized in that the discrete inclusions of intermetallic phases X ₂ Ca have a size of less than 10 microns. 4. A method of obtaining a cast composite material based on a magnesium alloy, comprising mechanically mixing a melt of a magnesium-based matrix alloy with reinforcing discrete particles, characterized in that the prefabricated magnesium-based matrix alloy is prefabricated with the following components, wt.%:
aluminum from 0 to 12 copper from 0 to 4 zinc from 0 to 15 zirconium from 0 to 1 manganese until 3 REM to 10 calcium from 0.1 to 10 magnesium rest,
place the semi-finished product in the reactor over reinforcing discrete particles heated to 650-670 ° C, which use titanium, silicon or boron carbide in an amount of 5 to 10 wt.%, and stirring is carried out after the matrix alloy is melted in air for 2-5 min

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