RU2770398C2 - Method for manufacturing metal matrix composite materials - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metallurgy, namely to a method for manufacturing metal matrix composite material with improved mechanical properties and corrosion resistance. The method for manufacturing metal matrix composite material includes following stages: (a) melting of metal or a matrix metal alloy, (b) addition to the melt of metal or a matrix metal alloy from the stage (a) of basalt fibers in a proportion from 1 wt.% to 10 wt.%, (c) mixing of the melt of metal or a matrix metal alloy and basalt fibers from the stage (b) at a rate from 400 rpm to 1200 rpm during a period of time from 1 minute to 60 minutes, (d) processing of the melt of metal or a matrix metal alloy and basalt fibers from the stage (c) with an ultrasound for from 1 minute to 15 minutes at a frequency from 10 kHz to 30 kHz, power from 2 kW to 5 kW and amplitude from 20 mcm to 50 mcm, and (e) casting of the melt of metal or a matrix metal alloy and basalt fibers from the stage (d) at a temperature from 200°C to 780°C to a mold pre-heated at a temperature from 150°C to 500°C during a period of time from 1 hour to 2 hours.EFFECT: obtained materials are characterized by high mechanical properties and high corrosion resistance.20 cl, 45 dwg

Description

The present invention relates to a method for manufacturing a reinforced metal matrix, and in particular a metal matrix composite material with improved mechanical properties and corrosion resistance.

Metal matrix composite materials (MMC; from English: metal matrix composites) combine two or more materials, in the characteristic case, a reinforcing phase and a metal matrix, to improve the properties of the original matrix that does not have reinforcement.

Lightweight metal matrix composite materials are important not only for the transport sector, i.e. for the automotive and aviation industries, but also for other sectors such as renewable energy.

Alternative composite materials according to the prior art include generic polymer-based composites and other MMCs that use aluminum as the metal backbone but use alternative fibers such as E-glass (see US 20050133123) and carbon (see US 20050133123). 4853294).

An aluminum alloy drill rod material with addition of basalt fibers and ceramic particles and a method for producing the same are disclosed in CN 107043901 A (Jilin University).

WO 2006/134405 (Gogoladze et al.) discloses a process for producing an aluminum-based composite material in which molten aluminum is reinforced with basalt fibers having a diameter ranging from 16 µm to 18 µm. The method includes obtaining a layer of fibers with a thickness ranging from 8 mm to 10 mm at the bottom of the crucible and then adding the same volume of aluminum. The mixture is then transferred to an oven at a temperature ranging from 800° C. to 850° C. and stirred for a period of time ranging from 10 minutes to 15 minutes. The mixture is then removed from the oven, molded and cooled. However, the obtained MMC does not have particularly advantageous properties.

The present invention is directed to providing a method for manufacturing a metal matrix composite material with improved mechanical properties.

According to the first aspect of the present invention, a method for manufacturing a reinforced metal matrix is provided, comprising the steps:

(a) at least partial melting of the metal or metal alloy,

(b) adding to the melt from stage (a) basalt fibers in a proportion ranging from 1 wt. % up to 10 wt. %, and

(c) mixing the basalt fibers and the melt from step (b) at a speed ranging from 400 rpm to 1200 rpm for a period of time ranging from 1 minute to 60 minutes.

In a preferred embodiment of the present invention, the method further comprises the step of:

(d) sonicating the basalt fibers and the melt from step (c) for a period of time ranging from 1 minute to 15 minutes, with an ultrasound frequency ranging from 10 kHz to 30 kHz, an ultrasound power ranging from 2 kW to 5 kW, and an ultrasound amplitude ranging from 20 µm to 50 µm.

In a preferred embodiment of the present invention, the method further comprises the step of:

(e) casting the product from step (d) at a temperature ranging from 200°C to 780°C into a mold that has been preheated at a temperature ranging from 150°C to 500°C for a period of time , ranging from 1 hour to 2 hours.

In a preferred embodiment of the present invention, a method for manufacturing a reinforced metal matrix is provided, comprising the steps:

(a) preheating the basalt fibers at a temperature ranging from 100°C to 500°C for a period of time ranging from 1 hour to 3 hours,

(b) rolling an aliquot of fibers into pure aluminum foil,

(c) melting a metal or metal alloy (cast aluminum alloys at a temperature ranging from 550°C to 750°C; zinc at a temperature ranging from 400°C to 440°C; magnesium at a temperature ranging from lying in the range from 600°C to 700°C; tin - at a temperature lying in the range from 200°C to 260°C),

(d) adding from 1 wt. % up to 5 wt. % of basalt fibers from stages (a and b) to the melt from the stage,

(e) mixing the basalt fibers and the melt from step (d) at a speed ranging from 400 rpm to 1000 rpm for a period of time ranging from 10 minutes to 30 minutes,

(f) treating the basalt fibers and the melt from step (d) for 5 minutes with ultrasound at a frequency of 17.5 kHz, a power of 3.5 kW, and an amplitude of 40 µm, and

(e) casting the product from step (e) at a temperature ranging from 200°C to 720°C into a mold that has been preheated at a temperature ranging from 150°C to 500°C for a period of time , ranging from 1 hour to 2 hours.

The proposed material preferably includes an aluminum matrix reinforced with basalt fibers, in particular whiskers, that is, short fibers. Basalt fibers are classified as being between E-glass (low strength) and carbon (high strength) in terms of strength, but these fibers are much cheaper than carbon fibers. In addition to excellent mechanical properties, basalt fibers demonstrate high resistance to corrosion and radiation, including at temperatures up to 600°C, and they are non-combustible; The combination of these properties is unique compared to glass and carbon fibers and makes these fibers an excellent alternative for specific applications.

The excellent properties achieved by the aluminum matrix and basalt fiber composite material obtained by the present inventors are a breakthrough for the next generation of composite materials that can be used as an alternative to steel in order to reduce weight in harsh environments, i.e. in applied tasks related to sea shelves. It is believed that the improvement of material properties is based on a selective chemical reaction between the matrix and basalt fibers. We have performed and investigated a controlled reaction between fiber and matrix in order to fabricate strong polyhedral iron-rich phases at the interface. Diffusion of elements during melting and casting of the composite material occurs from the matrix to the fiber and vice versa, providing stronger bonding (resistance to slip) while maintaining a strong core of the fiber.

The results below show an increase in hardness, tensile strength and corrosion resistance of 30%, all of which were achieved with the addition of as little as 5 wt. % fibers.

Basalt fibers have been widely used to reinforce thermoset and thermoplastic polymers, however, the possibility of using basalt fibers as a reinforcing material for metal matrix composite materials has been limited due to the reduced stability of the fibers during processing at elevated temperatures. In particular, one of the main problems is the dependence of strength on temperature, which usually leads to the loss of strength of the fibers during the exposure of the melts to the high temperatures necessary to ensure the casting. Although the observed micromorphology was the same as before heat treatment, it was found that the addition of a higher volume percentage of fibers was accompanied by an increase in porosity. An evaluation of the optimal process conditions for adding fibers to the melt was performed by Sabet et al. (Production and optimisation of aluminum basalt composites by hand lay-out technique. In: Proceedings of the World Congress on Engineering, vol III; 4-6 July 2012. London, UK), who investigated strength but did not include detailed data in the publication about the chemical/mineralogical interaction occurring at the interface between the fibers and the metal matrix, i.e. limited the results to fibers only without evaluating the overall improvement in the properties of the composite material.

These earlier studies focused on the dispersion of fibers and their ultimate strength in a composite material and did not focus on the fundamental reaction between fibers and matrix and how this reaction can be used to advantage to improve the chemistry and provide intermetallic nucleation within the alloy, which ultimately has influence and improve the overall characteristics of the composite material itself.

Without wishing to be bound by any particular theory, the inventors believe that the present invention is based on enhancing the controlled process of fiber recrystallization as a means to nucleate an advantageous polyhedral iron-rich intermetallic phase at the fiber/matrix interface while maintaining an amorphous central core. It is believed that this fundamental change in matrix and reinforcing phase converts the aluminum-basalt composite material into an aluminum matrix hybrid composite (AMHC; from English: Aluminum Matrix Hybrid Composite). It is believed that in this case the structural integrity of the fiber is maintained, thereby increasing the overall strength of the composite material. Microscopic studies of the interface between the fibers and the matrix in the obtained composite material made it possible to assume an important role for the process of recrystallization of basalt fibers during the casting process. Due to the high content of iron oxides in fibers, crystallization in basalt fiber begins with the oxidation of divalent iron cations and the formation of a phase with a spinel structure on the fiber surface. Calcium, magnesium and iron diffuse from the interior of the fiber to the surface, where they typically react with ambient oxygen to form nanocrystalline oxide layers of these elements. The formation of oxides is followed by the crystallization of the pyroxene phase, the crystallization centers of which are nucleated in the oxides. However, the situation is different if the fibers are in an anoxic environment of molten metal. In this case, as will be explained later, the fibers still reach the recrystallization temperature, so the mineral phases begin to recombine, but oxidation is not possible, so instead the above cations, together with silicon, react with the intermetallic compounds formed in the matrix, which promotes the nucleation of advantageous polyhedral iron-rich phases around the recrystallized outer fiber layer (FIGS. 4, 5 and 6).

The absence of oxygen limits the complete recrystallization of the fiber, maintaining the integrity of the inner core, which increases the strength of the fiber, and in parallel, the iron-silicon phases migrate from the matrix towards the interface with the fiber, where they can combine with cations emerging from the fibers. This process inhibits the formation of intermetallic compounds around the iron fibers, limiting their growth. This is particularly advantageous in the case of iron-rich aluminum alloys, such as alloys made from recycled aluminum, making the present method of adding basalt fibers an excellent means for producing high performance composite materials using recycled aluminum.

The basalt fibers used are available from ZaoMineral. The method for producing these fibers is disclosed in UA 89145, UA 90360, UA 90361, UA 90362.

Several preferred embodiments of the present invention will now be described with reference to the accompanying drawings, where:

Fig. 1 is a schematic representation of the distributive-mixing equipment for carrying out the method of the present invention;

Fig. 2 is a schematic representation of a melt sonicator for carrying out the method according to the present invention;

Fig. 3 is a light microscope image of basalt fibers diffusely distributed in an aluminum matrix obtained according to the present invention;

Fig. 4 is a scanning electron microscope with backscattered electron detector (SEM BSE) image of a fiber in a metal matrix obtained according to the present invention and the corresponding Energy Dispersive X-ray Spectrum (EDS). .: energy-dispersive X-ray spectrum).

Fig. 5 is an SEM BSE image of a cross section of a fiber obtained according to the present invention and the corresponding spectra of this fiber;

Fig. 6 is an SEM BSE image of a cross section of another fiber obtained according to the present invention and the corresponding spectra of this fiber;

Fig. 7 is a stress/strain plot for the LM25 reference alloy;

Fig. 8 is a stress/strain plot for MMC made from LM25 and 5% basalt fibers;

Fig. 9 shows the results of a study of mechanical properties, namely, tensile strength (9A), conditional yield strength at a permanent set of 0.2% (9B) and Vickers hardness (9C);

Fig. 10 shows burnt fibers removed from the surface of the melt prior to casting;

Fig. 11 shows the SEM image of the LM 25 alloy obtained at 800°C (A) and the EDS spectra of the edge zones of the fibers at the interface with the matrix (B);

Fig. 12 shows LM25 made at 720°C;

Fig. 13 shows alloy LM20 produced at 800°C;

Fig. 14 shows LM25 alloy wetted fiber at 720°C (A-D) and EDS elemental composition map (E);

Fig. 15 shows alloy LM20 produced at 720°C;

Fig. 16 shows alloy LM20 produced at 710°C;

Fig. 17 shows alloy LM25 produced at 710°C;

Fig. 18 shows alloy LM20 produced at 690°C;

Fig. 19 shows Mn-enriched fibers wetted with LM20 alloy made at 720°C;

Fig. 20 shows photomicrographs of an AMOFe alloy prepared at 780°C (A), 750°C (B), 720°C (C);

Fig. 21 is an optical micrograph of LM25 alloy that was stirred at 500 rpm for 10 minutes (A and B) and LM20 alloy that was stirred at 1000 rpm for 10 minutes (C);

Fig. 22 is an optical micrograph showing the effect of agglomeration in the absence of sonication;

Fig. 23 is an optical micrograph of the composite material after stirring for 10 minutes at 1000 rpm (A), for 20 minutes (B), and a graph showing the % of fibers in micrographs A and B (C);

Fig. 24 shows the results of EDS area analysis of the spectra of the sample after fiber-melt interaction times of 5 minutes (A), 10 minutes (B), 30 minutes (C);

Fig. 25 are optical micrographs of a cast composed of LM25 and basalt after exposure times of 3 minutes (A), 10 minutes (B), 30 minutes (C), and 80 minutes (D);

Fig. 26 shows the reactions of basalt fibers in LM20, namely - A) EDS area scan for silicon in the case of basalt fibers immersed in LM20 for 5 minutes; B) EDS area scan for silicon in the case of basalt fibers immersed in LM20 for 10 minutes; C) EDS area scan for silicon in the case of basalt fibers immersed in LM20 for 30 minutes;

Fig. 27 is an image of the fiber inside the intermetallic phase (A) and SEM spectra of the intermetallic phase (B), the central part of the fiber (C) and the recrystallized part (D);

Fig. 28 shows images of fibers within intermetallic phases (A, B), SEM spectra of intermetallic phase (C) and fiber (D), nucleation of intermetallic phase from fiber (E, F);

Fig. 29 shows images of fibers within an Al65-Ti35 alloy (A) and the EDS spectrum of Spot 1;

Fig. 30 shows wetted fibers in an LM20 matrix;

Fig. 31 shows EDS analysis of fibers inside LM20 alloy: exposure time of 5 minutes (A), 10 minutes (B), 30 minutes (C);

Fig. 32 is a photomicrograph of basalt-reinforced alloy LM20;

Fig. 33 is an SEM image of fibers within an LM25 alloy: (A) fiber and intermetallic phase cut in the transverse direction, (B) fiber and intermetallic phase cut at an angle in the longitudinal direction, (C) formation of an intermetallic phase on a fiber interacting with the melt;

Fig. 34 is an EDS area map and an EBSD 1_M25/basalt map: aluminum map (A), silicon map (B), ESBD map (C);

Fig. 35 is an SEM image of the fiber in LM12 and the resulting intermetallic compound (A); (B) EDS spectrum of Spot 1 at the fiber edge showing the presence of Al, Si, Fe and Cu (B);

Fig. 36 are views of the fibers within the AZ91 alloy (A); (B) High magnification image showing the formation of an intermetallic phase, (C) formation of an intermetallic phase on a melt-fiber;

Fig. 37 is a BSE image of intermetallic compounds at fiber-melt interfaces. The corresponding linear scanning EDX analysis shows that the intermetallic compounds are enriched in Al and Fe;

Fig. 38 is an optical micrograph showing a good distribution of fibers in the matrix: AZ91 with 5 wt. % fibers obtained at 667°C (A), EDS spectrum of bright intermetallic compounds (B);

Fig. 39 shows the formation of an intermetallic phase around fibers in AZ91 (A) and EDS spectra obtained from intermetallic compounds (B-D);

Fig. 40 is an optical micrograph showing the formation of an intermetallic phase in a mixed alloy after the addition of basalt fibers;

Fig. 41 is the stress-strain curve of LM25 and a composite material based on it;

Fig. 42 reflects data on the density of LM20 and a composite material based on it;

Fig. 43 shows graphs obtained during the wear test of LM20 and a composite material based on it;

Fig. 44 demonstrates the corrosion resistance of samples of LM25, composite material based on it and steel 316L; and

Fig. 45 is a graph of corrosion resistance.

EXPERIMENTAL PROCEDURES

materials

The matrix material used was a commercially available LM25 aluminum casting alloy (US designation A356) supplied by Norton Aluminum Ltd., Staffordshire, UK, in ingot form (actual composition (wt %): Al - 7.50 Si - 0.30 Mg - 0.003 Cu - 0.05 Fe - 0.005 Mn - 0.003 Zn - 0.11 Ti). The reinforcing material used was in the form of short basalt fibers, i. whiskers (their composition in wt. % is shown in Table 1).

Mixing processes

The method for the synthesis of cheap aluminum-based metal-matrix composite materials typically consists of two stages. The first part of the production method involves distributive mixing of the reinforcing material with the matrix, while the second part is dispersive mixing using ultrasonic cavitation before molding.

distributive mixing

In distributive mixing, standard mechanical mixing is used to premix the Al alloy with the reinforcing basalt whiskers. The distributive mixing plant is shown schematically in FIG. 1. The mixing equipment consisted of a drive motor to create the torque of the impeller, a lifting mechanism for the drive unit of rotational movement and an agitator assembly, and a transport pipe for feeding reinforcing whiskers into the melt. The ingot was melted in a cylindrical crucible located inside a top-loaded resistive electric furnace at 750°C.

Accurately measured reinforcing material (5 wt. % basalt fibers) was preheated in an oven at 250°C for 1 hour. The titanium impeller with four blades was coated with boron nitride to prevent reaction with the molten aluminum. A controlled argon atmosphere was maintained inside the furnace during the entire experiment to prevent melt oxidation. Using a transport tube (in the form of whiskers wrapped in aluminum foil), the pre-heated reinforcing whiskers were slowly and continuously transferred into the melt from the side of the vortex created by mixing the melt at a speed ranging from 400 rpm to 600 rpm, within 10 minutes.

The distribution of the reinforcing phase is strongly influenced by many aspects of the flowsheet. According to Bernoulli's theorem, the negative differential pressure existing in the vortex funnel promotes the movement of whiskers added from the outside into the liquid metal. The force created during melt mixing with a mechanical stirrer helps to overcome surface energy barriers caused by poor wettability of basalt whiskers by aluminum alloys. Once the whiskers enter the liquid, their distribution is strongly affected by some flow turbulence. The application of shear force to the added whiskers contributes to their relatively uniform distribution. The design of the impeller plays an important role in ensuring the preferred circulation of the melt and uniform distribution of the reinforcing material in the melt. The axial and radial flows necessary to avoid dead zones are preferably provided by an impeller having an impeller diameter to crucible diameter ratio of 0.4 and an impeller thickness to impeller diameter ratio of 0.35. The mixing of the mixture is carried out in a liquid mode to ensure the spatial uniformity of the distribution of particles (similar volume fractions in any part of the mixture).

The distributive mixing step is important as a way of incorporating reinforcing whiskers and coarsely distributing them in the melt. The degree of mixing is determined by the transfer of momentum from the location of the stirrer to lumps located at a distance from the location of the stirrer. At this stage of mixing, due to the presence of linear velocity gradients within the fluid, the shear applied to the fluid in contact with the impeller results in low shear when averaged over the entire volume of the fluid. The lack of sufficient shear force during distributive mixing leads to the formation of agglomerates in relatively stagnant zones (for example, near the walls of the crucible). To break these agglomerates into individual whiskers in the liquid metal, the applied shear stress (t) acting on the clusters of reinforcing material must exceed the average cohesive force or rupture strength of the lump. Therefore, dispersive mixing should ideally be performed using ultrasonic cavitation.

Dispersive mixing with ultrasonic cavitation

In order to achieve improved mechanical properties of MMS, in particular MMS obtained by casting, it is necessary that the basalt whiskers be homogeneously and uniformly dispersed within the molten aluminum. The agglomeration of fine whiskers hinders the production of high quality castings. Since the cohesive forces keep the agglomerates of the reinforcing material from disintegrating, high hydrodynamic forces are required for their destruction. In the sonication blending method, ultrasonic cavitation forces are used to overcome the cohesive force or slug tear resistance to disperse the fibers. Therefore, the mechanically agitated slurry of the composite material based on Al and basalt is transferred to the apparatus shown in FIG. 2 and sonicated for 5 minutes (17.5 kHz, 3.5 kW, 40 µm amplitude, niobium sonotrode) to obtain a dispersion of basalt whiskers.

The introduction of ultrasonic waves into the melt leads to the effects of acoustic cavitation and acoustic flows (acoustic wind). Acoustic cavitation occurs due to the formation, growth and collapse of cavitation bubbles under the action of alternating acoustic pressure cycles. Acoustic flow is the flow of fluid due to an acoustic pressure gradient resulting in highly efficient mixing. Molten Al at ambient conditions always contains dissolved gases. When the cavitation threshold is exceeded, the trapped gas forms numerous small cavities. During pulsation, these cavitation bubbles grow due to the directed diffusion of gases from the melt. Cavitation bubbles of a certain size collapse during the positive pressure cycle, generating a temperature of 5000°C and a pressure of 1000 MPa, and create a jet of liquid at a speed of 100 m/s in the immediate vicinity of the cavitation implosion zone. At the same time, the acoustic flow with a speed equal to 0.1 m/s, formed due to the pulsation of the cavitation zone, provides a continuous mixing effect throughout the melt. It is believed that during sonication, cavitation and acoustic flow increase the wettability of the reinforcing material. In addition, the cavitation pressure and liquid jet created by bubble implosion disintegrate the agglomerates. The composite material slurry is then cast at 720° C. into a tensile test specimen mold, which is preheated to 400° C. to provide the preferred melt flow and casting porosity.

RESULTS

In the melting mode described above, the fibers were dispersed in the matrix (FIG. 3), while chemical interaction between the matrix and the fiber occurred while maintaining the physical integrity of the fiber. The inventors of the present invention performed a detailed evaluation of the intermetallic phases, and the analysis showed that polyhedral phases of Fe-containing intermetallic compounds (AlFeMnSi) were formed at the fiber-matrix interface (FIG. 4).

In addition, the migration of silicon from the fiber core and aluminum from the matrix to the fiber core is visible, which indicates the reaction between the fiber and the matrix (Fig. 5). In particular, the SEM BSE image of the fiber cross section shows the newly formed polyhedral phases on the fiber surface and their respective composition (Spectrum 5). This clearly demonstrates the changes taking place in the core of the fiber, which loses silicon and gains aluminum, while silicon moves to the surface of the fibers and forms new intermetallic phases.

The same phenomenon is seen in Fig. 6, where one can see the decomposition of the fiber and its recrystallization together with the formation of intermetallic phases. In particular, the core of the fibers retains the chemical composition of the original fiber, although it shows a partial enrichment in aluminum (Spectrum 1), while the recrystallized zone (Spectrum 3) shows a composition with a limited content of aluminum, magnesium and oxygen, and the silicon that was originally present migrates from the recrystallized zones with the formation of i intermetallic phases (Spectrum 4).

The tensile strength of the aluminum composite material reinforced with basalt shows a 30% increase (see Fig. 8) compared to the unreinforced alloy (see Fig. 7).

An additional experimental study was also carried out, the results of which are summarized below. The conclusions are made without wishing to be bound by any theory and are not intended to limit the present invention.

PROGRAM OF EXPERIMENTS

1.0. Studying the Effects of Different Processing Modes

1.1. Investigation of the effects of various alloys

To investigate the potential reactions occurring with different alloys, a series of experiments was performed, each time focusing on one particular alloy. The main elements studied were: iron (Fe), nickel (Ni), titanium (Ti), silicon (Si) and copper (Cu).

1.2. Study of the improvement of mechanical properties in comparison with the standard

1.3. Sample making

After the melt was obtained and allowed to cool, the material was cut and processed using standard metallographic protocols [pouring into resin, plane grinding, polishing (SiC), polishing (diamond paste), fine polishing (colloidal silicon dioxide)].

Each sample was examined using a Zeiss SUPRA FEG-SEM field emission scanning electron microscope equipped with an EDAX Octane Superior EDS detector. Sample images shown below were obtained using a scanning electron microscope (SEM) and elemental composition spectra were obtained using an EDS system.

2.0. STUDYING THE EFFECTS OF DIFFERENT PROCESSING MODES

2.1. Program of Experiments

A series of experiments were carried out to investigate the main characteristics of the formation and production of the composite material. These characteristics are the weight percentage of fibers added, the processing temperature range, the time the melt is exposed to the fiber, and the agitation.

2.1.1. Mass % of fibers

In order to determine the nominal mass fraction of basalt reinforcing material to be added to the aluminum alloy, tensile tests were performed on composite materials reinforced with 1 wt. %, 2.5 wt. % and 5 wt. % basalt, using 4 samples of each type. Cast tensile test specimens were fabricated with a 10 mm gauge diameter, 50 mm gauge length, 14 mm diameter handles, and tensile testing was performed using an Instron® 5569 testing machine. In the case of reference specimens, a strain rate of 0.400%/minute was used and all tests were carried out at ambient temperature. The results obtained were the conditional yield strength, tensile strength (tensile strength) and the calculated Young's modulus.

2.1.2. Temperature range

The effect of temperature range on the formation of intermetallic compounds within the composite material was investigated. The processing temperature was varied in the range from 680°C to 800°C and samples were made for metallographic testing. The samples were then analyzed using EDS and SEM observation systems.

2.1.3. exposition

Two sets of experimental data were obtained to evaluate the effects of matrix/fiber exposure and melt mixing. Exposure time experiments were performed by immersing fibers in molten LM20 aluminum alloy to investigate reactions at interfaces and within the fiber. A series of castings at short intervals was made using alloy LM25 and 5 wt. % of basalt fibers in order to study the formation of an intermetallic phase over time.

2.1.4. Mixing

The mixing experiments involved using an electrically driven paddle agitator immersed in the melt to knead the fibers into the aluminium, varying the agitator speed and mixing time. In all cases, samples of the obtained materials were made for microstructural studies and EDS analysis.

2.2. Mass % of fibers

The reference sample is the baseline for evaluating the effect of the weight percent added fibers. Ultimate Tensile Strength (UTS) is the maximum load that a material can withstand before necking and failure begins. Adding 2.5 wt. % fiber increases UTS slightly (~5%) as shown in FIG. 9A, adding 1 wt. % and 5 wt. % reduces UTS below the reference sample and appears to be potentially detrimental. To increase the tensile strength, the consistent orientation of the fibers is important, with fibers oriented perpendicular to the direction of the applied load, reducing the tensile strength. Data on the conditional yield strength at a residual (plastic) deformation of 0.2% are calculated and presented in Fig. 9B. These data show that the yield stress at 0.2% residual strain improves with the addition of any amount of fibers, however, the greatest improvement was in the sample with the addition of 2.5 wt. % fibers. The sample with the addition of 5 wt. % fibers also showed a significant increase in the conditional yield strength, so the samples with the addition of 5 wt. % and 2.5 wt. % of the fibers were subjected to additional tests.

Hardness tests were carried out using a Vickers micro-indenter, the results of which are consistent with the tensile data. Both samples of composite materials showed increased hardness compared to the reference sample, as can be seen in Fig. 9C.

Adding much more basalt to a composite material is a very difficult task. 5 wt. % is the maximum reached in these experiments. Attempts have been made to add more fibers, but they have resulted in a layer of burnt fibers on the surface of the standard casting. This is shown in FIG. 10. Before casting, deposits are removed from the surface of the melt, removing burnt fibers.

Findings:

- The higher the volume fraction of fibers, the longer it takes to add fibers. Difficulty adding large masses. The % fiber creates the time it takes to mix a large volume of fibers into the melt. 5 wt. % is the maximum amount that can be reached.

- The addition of a large amount of fibers causes the added fibers to float and form a layer of soot.

- In this series of experiments, the addition of 2.5 wt. %. An increase in yield strength and UTS means an overall improvement in mechanical properties.

2.3. Temperature Range Experiments

A series of experiments were performed with small size castings at unusually high temperatures to explore the upper limits of the casting process when fibers are added and to see what intermetallic compounds form inside the composite material samples. The aluminum alloys were placed in small ceramic crucibles and loaded into a furnace to heat up to 800°C. Added 5 wt. % of basalt fibers, mixed and left in the oven for 30 minutes for the reaction to proceed, after which it was poured, cut and analyzed. Fig. 11A shows the difficulty in ensuring sufficient fiber wetting. Samples of LM25 alloy prepared at 800° C. showed fiber agglomeration and reduced reactions due to manual mixing and low melt volume. However, the fibers did recrystallize and show an initial reaction with the matrix, showing an alumina layer at the edge of the fibers, which is a trigger for the formation of intermetallic compounds. Fig. 11B shows the EDS spectra of the investigated intermetallic phase.

The second experiment was performed at a lower temperature of 720°C. Its results can be seen in FIG. 12. The wettability of the fibers was higher due to the larger volume of the melt and mixing with a stirrer (1000 rpm). Fig. 12A shows improved fiber wettability and FIG. 12B shows the formation of an intermetallic compound at the fiber-matrix interface. Analysis of the fiber edge zone shows a composition similar to that shown in FIG. 11B and indicates the formation of an oxide layer, which is associated with the formation of intermetallic compounds. Diffusion of silicon outward from the edge of the fiber and nucleation of the oxide layers trigger the nucleation of dendritic intermetallic compounds (Fig. 11B - initial shape to complete crystallization).

The experiment at 800° C. was then repeated using the LM20 alloy, but the same wettability problems were found due to the manual mixing procedure. However, recrystallization of the fibers is visible and reaction products can be seen. Fig. 13 shows fibers within a composite having an intact core (white in FIG. 13B), an amorphous aluminum-rich layer (light gray in FIG. 13B), and a fully recrystallized alumina layer (dark gray in FIG. 13B).

The studies of the effect of alloy elements, partly performed for section 3, also include experimental work carried out at the upper limit of the temperature range (800°C). See section 3 for details.

Both alloys, LM20 and LM25, were successfully cast at 720°C and showed excellent wettability and strong fiber response. Fig. 14 shows melt-wetted fibers (A-D) and intermetallic compounds (IMCs) formed at the interface. On FIG. 14E shows an area EDS scan of the fiber shown in FIG. 14D. It demonstrates the formation of various IMCs.

Fig. 15 shows fibers inside an LM20 melt made at 720°C. Excellent wetting was achieved and a pronounced reaction was observed between the fiber and the matrix alloy.

Experiments performed at lower temperature (710° C.) with LM20 and LM25 alloys demonstrate fiber recrystallization and formation of intermetallic compounds at the fiber/matrix interface (FIG. 16 and FIG. 17). The observed phenomena seem to agree with the observations at 720°C described above.

Alloys LM20 and LM25 (which are the most common casting alloys, and that is why they were most often used in the experimental procedure) were also investigated at 690°C. At this temperature, recrystallization at the fiber edge was already visible, however, the intermetallic compounds (formed perpendicular to the fiber edges) retain the "Chinese handwriting" type morphology rather than becoming more polyhedral morphology, as shown in FIG. eighteen.

In fact, the effect of temperature seems to be more related to the crystal structure of the resulting intermetallic compounds:

- at 690°C - "Chinese handwriting";

- at 710°С/720°С - polyhedral structure;

- above 720°С - block structure.

However, the interaction between the fibers and the matrix remains the same, and the relationship between the fiber/matrix reaction and the formation of intermetallic compounds appears to remain unchanged.

Manganese (Mn) doped fibers were subjected to the same test to evaluate the importance of fiber composition for their potential wettability and chemical reaction with the matrix. The fibers added to LM20 at 720°C were wetted and reacted in the same way as in the previous experiment. Fig. 19 shows Mn-rich fibers wetted with LM20 melt made at 720°C.

In a separate experiment, an AMOFe melt with the addition of 5 wt. % fibers were obtained at 780°C, 750°C and 720°C. Fig. 20 shows photomicrographs of a composite made at these temperatures. It can be seen that at all temperatures there is a tendency for the formation of intermetallic compounds surrounding the fibers. However, due to the high iron content in this case, the intermetallic compounds tend to block morphology.

Findings:

Temperature range studies have shown that two reactions occur in the presence of molten or partially molten metal:

- The fibers begin to recrystallize with the formation of a chemically active oxide edge zone, which triggers the formation of intermetallic compounds in the matrix;

- A chemical reaction also occurs at the interface, silicon and iron diffuse out of the fibers, promoting the formation of intermetallic compounds, while aluminum diffuses into the fibers, accelerating the formation of an oxide layer, which promotes the formation of intermetallic compounds.

- Different crystal structures of the resulting IMC, namely, dendritic, polyhedral and block, are formed at different processing temperatures.

2.4. Fiber distribution - agitation speed in rpm and agitation time

The distribution and overall wetting of the fibers within the matrix alloy is determined by the stirring speed, stirring time and the application of ultrasonic treatment. Contact time is also a factor, as too long a residence time in the melt causes complete recrystallization of the fibers. Various stirring speeds were tested with the optimum being in the range of 500 rpm to 1000 rpm. Higher rotation speeds provide a more homogeneous distribution, but the fibers can break, and in extreme conditions such speeds can lead to the formation of a non-wettable powder. Fig. 21A and FIG. 21B shows the LM25 based sample after mixing for 10 minutes at 500 rpm, FIG. 21C shows alloy LM20 after mixing for 10 minutes at 1000 rpm. A longer mixing time is useful, but it cannot exceed the interaction time defined in section 2.5. The effect of applying sonication is seen from FIG. 22. She shows a sample obtained using agitation for 10 minutes at 500 rpm without sonication. It is very clearly seen that the fibers are still agglomerated, which significantly reduces the mechanical properties. Therefore mixing is a necessary step (as shown in section 2.3), while sonication is the preferred step. Fig. 23 shows the effect of mixing time on fiber distribution. Fig. 23A shows the LM20 alloy after mixing for 10 minutes, FIG. 23B shows the same alloy after mixing for 20 minutes. Fig. 23C shows data on the percentage of fibers present in the optical micrograph. This confirms the improvement in the penetration of the fibers into the melt and the homogeneous distribution of the fibers in the matrix with stirring for 20 minutes.

Findings:

- Mixing of basalt fibers in the melt is a necessary step.

- Mixing is preferred for a period of time ranging from 10 minutes to 20 minutes.

- Stirring for a long period of time is preferable to ensure good fiber distribution.

- Ultrasonic cavitation is an enhancement step that is useful for producing defect-free castings and helps to separate fiber clumps.

2.5. Exposure time

A series of immersion experiments were performed to investigate the effect of molten aluminum on basalt fibers. For these tests, an LM20 melt was prepared and kept at a temperature of 700°C. The basalt fibers were prepared and ordered before being immersed in the molten metal and kept in the metal for a predetermined period of time (5 minutes, 10 minutes and 30 minutes). The fibers were then removed from the melt and allowed to cool, after which samples were made and analyzed by SEM. EDS scans over the area of the fibers showed that there was significant diffusion from the fiber into the surrounding metal, as well as from the surrounding melt into the fiber. Fig. 24 shows area analysis for aluminum and silicon. The image shows a high content of silicon and a deficiency of aluminum in the fiber after only 5 minutes (Fig. 24A). After 10 minutes (FIG. 24B), the fiber recrystallizes at the fiber/matrix interface and element migration begins. The fiber slowly accumulates aluminum and loses silicon. After 30 minutes, the fiber is almost completely converted (Fig. 24C). These experiments show that the exposure time of the basalt fibers is an important factor in obtaining the preferred chemistry in the final resulting composite material. Ideally, the exposure time should be at least 5 minutes to 10 minutes to allow chemical reactions to begin, and ideally it should not exceed 30 minutes to prevent complete conversion of the fibers.

To understand the response of the fibers in the LM25, a small series of casts were made at exposure times of 5 minutes, 10 minutes, 30 minutes and 80 minutes. Fig. 25 shows optical micrographs of LM25 samples after various exposure periods. It can be seen that reactions start already after 3 minutes (FIG. 25A) and that the fiber is almost completely crystallized after 30 minutes (FIG. 25C and FIG. 25D). It is clear from these experiments that the reactions are very fast and they determine how quickly the fiber will be completely converted. The exposure time for LM25 alloy should be greater than 3 minutes but less than 30 minutes.

Findings:

- From the experiments described above, the exposure time can be determined. Exposure Time Determination: The exposure time when adding basalt fibers should ideally be longer than 5 minutes, but shorter than 30 minutes, to ensure that reactions start but that the amorphous core of the fiber remains intact in the sheath of crystallized material.

3.0. REACTIONS OF ALLOY ELEMENTS (SI. FE, TI, CU, NI, MG)

3.1. Study of the reaction between aluminum alloys and basalt fibers

The previously described exposure time and fiber mass % experiments provided the basis for the elemental response experiments described in this chapter. A suitable amount of fibers should be added, but not too much so as not to interfere with mixing of the small volume of melt. The addition and mixing should ideally also be completed in a relatively short time, i.e. the total interaction time should not exceed 30 minutes. This is illustrated below in FIG. 26 for reaction with silicon. After 5 minutes, the fibers show no visible reaction with hot aluminum. However, after 10 minutes (FIG. 26B), the fiber begins to crystallize, primarily at the interface between the matrix and fiber, while the core of the fiber remains amorphous. After the longest interaction time (30 minutes), the fiber undergoes pronounced crystallization and only a small portion of the amorphous core is retained, as shown in FIG. 26C.

Findings:

- The sequence and timing of adding fibers is important for the successful production of a composite material.

- The total interaction time of the fibers and the melt should ideally not exceed 30 minutes.

- The fibers react very quickly, the reaction is observed after 3 minutes.

3.2. Investigation of the effects of various alloy elements

The experiments described below were performed in order to identify the reactions occurring in the composite material between the main elements of the alloy and the added reinforcing basalt fibers. In this series of experiments, the standard method was used. In each experiment, the following steps were performed:

1. The alloy for the experiment was chosen based on the concentration of the main element of the alloy. Various alloys had a high proportion of specific elements (Fe, Ni, Mg, Ti, Cu).

2. 40 g of the selected alloy was heated in an oven for 1 hour at 800°C.

3. Approximately 5 wt. % basalt fibers. The addition of a large volume of fibers is necessary to provide a suitable percentage of wetted fibers to observe reaction at the interface.

4. Manual mixing of the melt and fibers was performed for 10 minutes (no sonication was performed).

5. After adding the fibers and mixing, the melt was left in the oven for 0.5 hours at 800°C.

6. The crucible was removed from the furnace and left to cool under ambient conditions.

3.2.1. Iron (Fe): Al90-Fe8-Si1

A high iron aluminum alloy (Al90-Fe8-Si1) was chosen to study the reactions that take place between the fibers and the matrix alloy. Fig. 27 shows basalt fibers encapsulated in an intermetallic compound in the form of a large block. A series of spectra was obtained to evaluate the composition of different regions within the micrograph. Fig. 27B shows the composition of a large intermetallic block (light area), which is predominantly composed of aluminum and iron. Fig. 27C and FIG. 27D show the fiber core (C) and the fiber cladding (D).

Findings:

- Fig. 27 shows the formation of a blocky intermetallic compound around two basalt fibers and the resulting EDS spectra showing the elemental composition.

- Apparently, basalt fibers react with iron-rich intermetallic compounds, which causes a change in their shape (from an acicular shape to a block shape, depending on the crystallization temperature of intermetallic compounds) and recrystallization of the fibers.

3.2.2. Nickel (Ni): Al8-Ni2

A high nickel aluminum alloy was chosen to study the reactions that take place between the fibers and the matrix alloy. Alloys with a high nickel content are themselves coarse-grained intermetallic compounds. Fig. 28A shows a low magnification image of the alloy after it has been processed at 800°C. Fig. 28B shows a high magnification image of a basalt fiber encapsulated in a coarse block intermetallic compound. Fig. 28C and FIG. 28D show the corresponding spectra for EDS analysis.

When reacted with alloys with a high nickel content, basalt fibers cause the formation of much larger intermetallic phases than in other aluminum alloys. Fig. 28E and FIG. 28F show a detailed image and EDS analysis of a basalt fiber with intermetallic compounds originating from a crystallized shell, while the core of the fiber appears amorphous.

Findings:

- Intermetallic nickel compounds are found in the form of large blocks.

- Intermetallic compounds originate and grow from the crystallized fiber sheath.

- The interaction between the fibers and the matrix triggers the nucleation of intermetallic compounds.

- When reacted with high nickel alloys, basalt fibers cause the formation of large intermetallic phases compared to the intermetallic phases found in other aluminum alloys.

3.2.3. Titanium (Ti): Al65-Ti35

A study of the reaction between the fibers and the matrix in aluminum alloys with a high titanium content shows that in this case, too, the fibers recrystallize and form an edge zone consisting of aluminum oxide (Fig. 29). A small intermetallic growth is visible near the fiber surface (zone 4). However, as in the case of silicon, the fiber does not appear to be directly responsible for the formation of aluminide intermetallic compounds.

Findings:

- The fibers in this alloy system do not appear to react to form crystallization centers of intermetallic compounds

- Alumina (alumina) is formed along the edge of the fiber, as in other alloys.

3.2.4. Commercial Grade Aluminum: LM0

Elemental analysis was not performed because the fibers appeared to be recrystallized and did not form intermetallic compounds. Fig. 30 shows successfully wetted fibers within an LM0 matrix material. At this stage, apparently, no reactions occur that cause the nucleation and growth of intermetallic compounds surrounding the fiber.

3.2.5. Aluminum casting alloy LM20: Al-SH2

Cast alloy LM20 is similar to LM25 (further in section 3.2.6), except for a slightly higher silicon content. An immersion experiment carried out at a temperature ranging from 700° C. to 730° C. showed a reaction between silicon and aluminum in the matrix and in the fibers. The fiber initially contains little aluminum and captures aluminum; however, the fiber initially also contains a lot of silicon and releases a small amount of it into the matrix. Compared to LM25, in this case, the matrix contains more silicon, so the diffusion of silicon from the fiber is limited, since the alloy contains almost the maximum amount of silicon. Fig. 31 shows the EDS map obtained for the dive experiment. As can be seen, the matrix already initially contains a high percentage of silicon dispersed in the alloy (indicated by the white letter A). On FIG. 31C, there are more pronounced areas of high silicon content protruding from the interface between the fiber and the matrix. This phenomenon is a trigger for the formation of intermetallic compounds; an optical micrograph of the LM20 alloy with the reinforcing material added can be seen in FIG. 32. The fiber reacted with the alloy and generated blocky IMCs surrounding the fiber.

Findings:

- The high silicon content of the alloy reduces the loss of silicon from the fibers, however this diffusion phenomenon still acts as a trigger for nucleation and IMC formation around the fiber cladding.

3.2.6. Aluminum casting alloy LM25: Al-Si7.5

Samples prepared using LM25 as the matrix alloy were tested for the formation of intermetallic compounds. At a high proportion of silicon present (but less than in the case of LM20 (Al-SM2)) the same migration of aluminum and silicon was observed. Fig. 33 shows optical micrographs of basalt fibers inside a matrix. Fig. 33A and FIG. 33B show the formation of silicon-rich intermetallic compounds around the fiber cladding. Fig. 33C shows an intermetallic compound attached to a fiber found on a fracture surface after a tensile test. Fig. 34 illustrates EDS mapping and EBSD mapping showing local silicon concentration in and around the fiber. Fig. 34B shows an EDS map for silicon, the formation of an intermetallic compound of silicon and aluminum surrounding the fiber is visible in the upper right corner (shown by an arrow). Fig. 34C shows an EBSB map of this area. The immersion of the fibers into the melt led to the appearance of recrystallized zones (zones of small crystals). The lower concentration of silicon in the matrix in this case allows additional diffusion of silicon to the interface, which promotes the formation of intermetallic compounds.

Findings:

- The presence of the fibers in the matrix and the process of their recrystallization contribute to the diffusion of silicon to the interface between the fiber and the matrix, which triggers the formation of polyhedral intermetallic compounds that function as an anchor between the fibers and the matrix.

3.2.7. Copper (Cu): LM12

The fibers show complete recrystallization and the copper-aluminum silicide intermetallic compound (FIG. 35B) crystallizes perpendicular to the fiber (FIG. 35A).

Findings:

- In this case, as in other alloys, the fiber recrystallizes, and silicon diffuses into the matrix, starting the crystallization of the fiber.

3.3. Magnesium (Mg): AZ91 (2.5 mass%)

Basalt fibers have been successfully added to magnesium alloy; this alloy is referred to as AZ91, and therefore the main elements of the alloy are aluminum (9%) and zinc (1%). AZ91 was placed in a steel crucible and melted at 730°C for 3 hours. Sulfur hexafluoride (SF ₆ ) was used as a protective gas. The temperature during stirring was equal to 678°C.5 wt. % basalt fibers were added and mixed at 350 rpm for 5 minutes. Ultrasonic cavitation was performed on the mixture for 5 minutes. After completion, the mixture was heated to a casting temperature of 667° C. and cast without pressure into a book-type mold to obtain metallurgical specimens.

Magnesium and aluminum make up 99% of the material in the alloy, and both elements are present in the fiber, so the reaction was expected. The formation of intermetallic compounds was observed as shown in FIG. 36A-36C and FIG. 37. Analysis of the linear EDX scans showed that the IMCs are enriched in Al and Fe (Fig. 37). Good wettability was achieved with a substantially homogeneous distribution as shown in FIG. 38. Some of the initial mechanical properties of the magnesium composite material are presented in Table 3.3.1.

Despite the good fiber distribution, the mechanical properties were found to decrease, except for the hardness, which increased from 54.45 to 68.1 and from 64 to 75.5. As hardness increases, the observed reduction in mechanical properties can be attributed to casting defects that occur during the manufacturing process.

Fig. 39 shows an SEM image of IMCs forming around fibers in the same way as in previous aluminum matrix experiments. EDS analysis showed that these IMCs were high in magnesium and aluminum oxides, but also contained small amounts of iron and manganese.

Findings:

- Just as in the case of the formation of alumina in section 3.2.4 (LM0), the fibers contain magnesium oxide, and therefore magnesium-based intermetallic compounds are formed.

- One of the main elements of the alloy is aluminum, so alumina/spinel formation is expected.

3.4. mixed alloys

It is shown that basalt fibers react with alloy elements that are present in basalt fibers; however, the tests were carried out so that each time only one element was examined. The addition of more than one of these elements provides similar results, several intermetallic compounds are formed around the interface of the fiber and matrix, which are enriched with a specific material present simultaneously in the fiber and matrix, for example, when Al65-Ti35 is added to Al8-Ni2. Fig. 40 shows a photomicrograph of the formation of intermetallic compounds around fibers within this mixed alloy. As expected, there is an intermetallic compound in the form of a large block, together with an oxide layer at the edge of the fibers. It is believed that the formation of this phase is responsible for triggering the nucleation of the intermetallic compound due to the release of silicon from the fibers. If there is very little silicon in the matrix, then all silicon diffuses, and the intermetallic compounds are aluminides; if silicon is present in the matrix in a higher concentration, then the addition of silicon diffusing from the fibers leads to the formation of silicide intermetallic compounds. In all cases, the formed intermetallic compounds are polyhedral at temperatures below 750°C and block, if the melt temperature exceeds 750°C. In all cases, the percentage of acicular intermetallic compounds is extremely limited.

Findings:

- Composites made from mixed alloys show reactions leading to the formation of IMC and the formation of IMC after the addition of fibers.

4.0. STUDY OF MECHANICAL PROPERTIES

4.1. Tensile test

A number of mechanical tests were carried out to evaluate the performance of the composite material. The first series of tests was designed to evaluate the tensile strength (tensile strength) and the conditional yield strength to determine the onset of plastic deformation in the sample. Then, the hardness of the obtained composite material was evaluated.

Tests to evaluate the ability of a metal matrix composite (MMC) to resist wear were performed using a dry sliding abrasion test on a dry finger-disk surface. Wear losses were calculated from the mass of material lost after passing 250 m, 500 m and 750 m.

In all cases, the test results were compared with reference samples, which were made and processed in the same way as the MMC.

The tensile strength of the composite material was evaluated relative to a reference sample without the addition of basalt fibers, but obtained by the same manufacturing method as the samples with basalt. Table 4.1.1 shows the data for the LM25 alloy and also notes the need for ultrasonic cavitation to achieve an excellent combination of properties. Table 4.1.2 shows the results of experiments with LM20 alloy, based on these results, the optimal weight % of added fibers was determined to be 2.5 wt. %. This sample showed the highest UTS value and a significant increase in proof stress. Fig. 41 shows stress/strain curves for samples based on LM25. Obviously, the sample with the addition of 2.5 wt. % fibers have the best performance in terms of tensile strength and yield strength, but this comes at the cost of reduced achievable strain at break.

The tensile strength was examined, and FIG. 9A shows results for samples of LM20 alloy with different amounts of fibers added. It is clear from the results that the addition of 1 wt. % and 5 wt. % led to a decrease in UTS compared to the reference samples. The only set of samples that showed an increase in UTS and, accordingly, the best properties, was a set of samples containing 2.5 wt. % fibers.

The yield strength data shows the load required to initiate plastic deformation of the sample. The results shown in FIG. 9B clearly indicate that large masses. % added fibers are more favorable. Samples with 5 wt. % and 2.5 wt. % fibers show a conditional yield strength, which is 16.92% and 22.16% higher than that of the reference sample, but the sample containing 2.5 wt. % fibers, again has the most favorable properties.

Findings:

- The yield strength increases with the addition of any number of fibers.

- 2.5 wt. % fibers provide the greatest increase in yield strength and increase in UTS.

- UTS increased only by adding 2.5 wt. % fibers and reduced in samples containing 1 wt. % and 5 wt. % fibers.

4.2. Hardness

The tensile data is also supported by the expected results from the hardness test. The results of tensile testing of specimens based on LM20 and LM25 alloys showed that some specimens show an increased load at break. These increased UTS values demonstrate an increase in hardness and a decrease in the overall ductility of the material. The hardness results shown in Fig. 9C show an increase in hardness in samples containing 5 wt. % and 2.5 wt. % fibers compared to the reference sample.

Mechanical tests demonstrate an increase in hardness and tensile strength with the addition of fibers. An additional improvement is found when an additional sonication step is carried out. It is believed that sonication promotes final fiber distribution and minimizes porosity, improving the overall quality of the final casting.

Findings:

- The hardness increases compared to the reference sample.

- Adding 2.5 wt. % of fibers provides the highest hardness of the material.

4.3. wear resistance

The wear resistance test was carried out on LM20 based composite material samples, which were compared with a reference sample without basalt addition. Using the pin and disc wear test and the corresponding material densities (Fig. 42), the wear rate can be calculated. Fig. 43 shows graphs obtained in the wear test for the reference sample and samples containing 5 wt. % and 2.5 wt. % fibers. It has been proven that wear resistance results are related to the hardness of the material, a higher hardness value suggests a corresponding increase in wear resistance. From the wear curves shown in Fig. 43, and the results shown in Table 4.3.1, it can be seen that the sample with the best characteristics was again the sample with the addition of 2.5 wt. % fibers. This sample experiences 50% less abrasion than the reference sample.

With the addition of fibers, a clear increase in wear resistance is seen. An SEM study showed that no outwardly protruding fibers were visible, demonstrating that the formation of intermetallic compounds works as a binding system for the fibers.

Findings:

- Adding 2.5 wt. % fibers provide the best wear resistance.

- Composite material containing basalt shows improved wear resistance compared to the LM20 reference.

4.4. Corrosion resistance

A series of tests were carried out to measure the corrosion resistance of the composite, as shown in Table 4.4.1. The solutions used simulated the potential harsh environments that the composite material might interact with. Since the main purpose of the material is its use in the marine environment, imitations of salt water are the most suitable. In addition to a one molar salt solution, solutions with concentrations equal to 3.5% and 10% were used. However, for testing in particularly harsh environments, a solution containing hydrochloric acid (HCl) was used. Tests carried out using salt water showed such a low corrosion rate of composite samples that the more aggressive HCl solution was preferred. The results of accelerated corrosion tests using HCl are presented in Table 4.4.2.

General corrosion: These tests were carried out under no load conditions on the test piece. This was achieved by immersing the samples in a tank of heated solution (60° C.) for 48 hours to detect corrosion.

Stress Corrosion: These tests were carried out on specimens held in tension in a specially designed stress corrosion tank. The samples were machined to smoothness and subjected to a test in a heated bath of corrosive solution (sea water at 60° C.) for 48 hours. This speeds up corrosion testing by simulating weeks of stress in a shorter amount of time. Each sample was loaded to 75% of the yield strength of the material.

Fig. 44 shows examples of specimens subjected to a corrosion test. In addition to the reference sample and the composite sample, a series of tests were also conducted on 316L stainless steel, which served as the benchmark for corrosion resistant materials currently used in marine applications. Reference samples (without added fibers) proved to be the most unstable product to corrosion. Surface corrosion is visible both on specimens tested for general corrosion and on specimens tested for stress corrosion.

Fig. 45 shows a graph of the corrosion resistance of a composite material based on LM25 and reference samples. The corrosion rate is proportional to l _corr (the kinetic value of the corrosion current density), so this graph shows that the composite sample has a reduced corrosion rate.

Findings:

- Composite material samples showed reduced levels of surface corrosion.

- The composite material samples showed a reduced corrosion rate compared to the reference samples.

All optional and preferred features and modifications of the described embodiments of the present invention and dependent claims can be used in all aspects of the present invention. In addition, individual features of the dependent claims, as well as optional and preferred features and modifications of the described embodiments of the present invention can be combined with each other and replaced with each other.

The contents of the United Kingdom patent application No. 1714401.5, under which this application claims priority, and the abstract accompanying this application, are incorporated into this publication by reference in their entirety.

Claims (25)

1. A method for manufacturing a metal-matrix composite material, including the following steps: (a) melting the metal or metal alloy of the matrix, (b) adding to the melt of the metal or metal alloy matrix from stage (a) basalt fibers in a proportion of from 1 wt.% to 10 wt.%, (c) mixing the molten metal or alloy of the matrix metals and the basalt fibers from step (b) at a speed of 400 rpm to 1200 rpm, for a period of time from 1 minute to 60 minutes, (d) treatment of the metal melt or metal alloy of the matrix and the basalt fibers from step (c) with ultrasound for 1 minute to 15 minutes, with a frequency of 10 kHz to 30 kHz, a power of 2 kW to 5 kW and an amplitude of 20 µm to 50 µm, and (e) casting a molten metal or alloy of matrix metals and basalt fibers from step (d) at a temperature of 200°C to 780°C into a mold preheated at a temperature of 150°C to 500°C for a period of time from 1 hour up to 2 hours. 2. Method according to claim 1, characterized in that the sonication in step (d) is carried out for 5 minutes. 3. Method according to claim 2, characterized in that the sonication in step (d) is carried out at a frequency of 17.5 kHz. 4. The method according to any one of paragraphs. 1-3, characterized in that the sonication in step (d) is carried out at a power of 3.5 kW. 5. The method according to any one of paragraphs. 1-4, characterized in that the sonication in step (d) is carried out at an amplitude of 40 µm. 6. The method according to any one of paragraphs. 1-5, characterized in that the casting in stage (e) is carried out at a temperature of from 200°C to 720°C. 7. The method according to any one of paragraphs. 1-6, characterized in that at least part of the basalt fibers is heated at a temperature of from 100°C to 500°C for a period of time from 1 hour to 3 hours before adding in stage (b). 8. The method according to any one of paragraphs. 1-7, characterized in that at least part of the basalt fibers are wrapped in aluminum foil before being added in step (b). 9. The method according to any one of paragraphs. 1-8, characterized in that the metal or metal alloy is aluminum or an aluminum alloy. 10. The method according to p. 9, characterized in that the temperature during stage (a) is from 550°C to 750°C. 11. The method according to any one of paragraphs. 1-8, characterized in that the metal or metal alloy is zinc or zinc alloy. 12. The method according to p. 11, characterized in that the temperature during stage (a) is from 400°C to 440°C. 13. The method according to any one of paragraphs. 1-8, characterized in that the metal or metal alloy is tin or tin alloy. 14. The method according to p. 13, characterized in that the temperature during stage (a) is from 200°C to 260°C. 15. The method according to any one of paragraphs. 1-8, characterized in that the metal or metal alloy is magnesium or magnesium alloy. 16. The method according to p. 15, characterized in that the temperature during stage (a) is from 600°C to 700°C. 17. The method according to any one of paragraphs. 1-16, characterized in that the proportion of basalt fibers during stage (b) is from 1 wt.% to 5 wt.%. 18. The method according to any one of paragraphs. 1-17, characterized in that the proportion of basalt fibers during stage (b) is 2.5 wt.%. 19. The method according to any one of paragraphs. 1-18, characterized in that the stirring speed during step (c) is from 400 rpm to 1000 rpm. 20. The method according to any one of paragraphs. 1-19, characterized in that the mixing during step (c) is performed over a period of time from 10 minutes to 30 minutes.

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