Intensive Shearing Research Articles

Distinctive shear zones demonstrate pervasive laminar cataclastic flow throughout the gigantic Iymek rock avalanche

Intensive fragmentation is a pervasive process during rock avalanche propagation, with a series of typical shearing characteristics being generated, indicating the occurrence of differential shear-induced comminution of clasts. However, much less is known about how shearing evolves within a rock avalanche over long runout. In the Iymek rock avalanche (IRA), pervasive shear zones characterized by multistoried, multiscale, and multistyle shear structures are well developed along the travel path of the IRA, providing an invaluable opportunity to decipher the evolution of shear-induced fragmentation occurred in rock avalanches. In these shear zones, a series of indicative structures, including preserved stratigraphic sequences, jigsaw structures, Riedel shear arrays, sigmoidal shear planes, asymmetrical folds, bookshelf and boudin-like structures, and anastomosing shear networks, are identified. These structures indicate that a laminar-like flow regime characterized by low disturbance but intensive shearing should dominate the emplacement of the IRA, contributing to the formation of these pervasive shear structures and material facies. As indicated by the progressive evolution of these pervasive shear structures, three facies are determined from the transition zone to the accumulation zone, i.e., low-fragmented facies, ductile-dominated facies and brittle-dominated facies. The low-fragmented facies is mainly distributed in the transition zone, similar to a semisolid phase rather than the solid phase of the bedrock in the source area. Conversely, the brittle-dominated facies features a high fragmentation degree and is predominant in the accumulation zone, which mainly consists of a semifluid to fluid phase. This indicates that the rock avalanche mass should evolve from a solid phase to a fully fluid phase during propagation, which involves clast fracturing and comminuting, frictional sliding and rotation. Therefore, we propose that the rock avalanche is a classical cataclastic flow driven by progressive and differential shearing comminution during its laminar-like propagation instead of a granular flow. These results provide a significant basis for interpreting similar structures in other rock avalanche deposits and yield new insights for understanding the emplacement mechanisms of rock avalanches.

Understanding of macro-segregation in direct-chill cast 2024 alloy with intensive melt shearing based on the evolution of microstructure and temperature field

The influence of intensive melt shearing (IMS) on macro-segregation has been systematically investigated. Experimental results show that the negative centerline segregation is effectively suppressed when the IMS is applied. To reveal the mechanism of IMS on macro-segregation, a quantitative study on the evolution of the slurry region, mushy region, solidification interface, morphology, and concentration of microstructure was carried out. It was confirmed that the IMS parameters determine the dominant mechanism affecting centerline segregation by controlling its action region. When IMS is applied above the liquidus, the fine dendritic structure not only has higher solute content, but also effectively limits the penetration depth of the liquid melt. Moreover, the velocity of the shrinkage flow in the horizontal direction decreases due to the flattening of the solidification interface. At this condition, the above factors play a more dominant role in macro-segregation than the increase of the mushy region thickness. When the action region of IMS changes to the slurry region, the solidification interface profile transforms from a “V” shape to a “VVV” shape. In this case, the influence of the magnitude and direction of the shrinkage flow on macro-segregation is balanced by the near-spherical structure (solute-poor), the increase of permeability, and the thickness of the mushy region. A physical model has been proposed to explain the IMS parameters on macro-segregation.

Hot orogenesis in the Paleoproterozoic: Insights from granitic gneiss domes within the Jiao-Liao-Ji belt, North China craton

As a part of the Columbia supercontinent, the North China craton is an ideal object for studying the evolution of supercontinent assembly and the mechanism of orogenesis in the Paleoproterozoic. The Jiao-Liao-Ji belt, located in the eastern part of the North China craton, provides important clues for our understanding of Paleoproterozoic orogenic processes. A series of Paleoproterozoic granitic gneiss domes is preserved in the Liaodong segment of the Jiao-Liao-Ji belt. These domes are cored by the Liaoji granitic gneisses (emplaced at 2250−2150 Ma) and mantled by metamorphosed volcanic-sedimentary rocks (deposited at 2200−1940 Ma). Combining multiple lines of evidence from mesostructures and microstructures, kinematics, magnetic fabrics, and crystallographic fabrics, we suggest that the granitic gneiss domes reflect inhomogeneous shearing of the middle to lower crust during Paleoproterozoic orogenic processes. Intensive layer-paralleling shearing characterized subhorizontal flow during nearly E-W−oriented compression. As a hot orogen formed in the Paleoproterozoic, the orogenic deformation in the Jiao-Liao-Ji belt was characterized by extensive doming due to dominant subhorizontal flow and subsidiary vertical flow in the middle to lower crust.

The control of as-cast structure of 2024 aluminum alloy with intensive melt shearing and its effect on microstructure and mechanical properties after T4 treatment

The newly developed technology of intensive melt shearing direct-chill casting (MS–DC) was used to control the as-cast structure of 2024 aluminum alloy and study its genetic effects in deformation and heat treatment processes. The melt temperature near the bottom of the shearing device (TS) during MS–DC process was proposed as the key parameter to control the as-cast structure. The results showed that the grain refining effect of intensive melt shearing greatly depends on TS. With the decrease of TS, the grain size became smaller, but the grain morphology also got changed. The fine equiaxed dendritic structure was obtained when the TS is slightly above the liquidus of the alloy. The ellipsoid grains was generated when TS was below the liquidus of the alloy. Further work demonstrated that compared with ellipsoid grains, the fine equiaxed dendritic as-cast structure resulted in more refined second phase, smaller size of recrystallized grains, higher mechanical properties and lower intensity recrystallization texture in the samples after cold rolling and T4 treatment.

Numerical simulation of the flow field and temperature field in direct-chill casting of 2024 aluminium alloy under the influence of intensive melt shearing

In the direct–chill (DC) casting process, the application of intensive melt shearing has a significant grain refining effect on the ingot. Understanding the variation of the flow field and temperature field during the DC casting process under the influence of intensive melt shearing is very important to study the mechanism of grain refinement. In this paper, the COMSOL software was used to simulate the flow field and temperature field in the process of DC castingφ300 mm ingots of 2024 aluminium alloy under different casting conditions. The influence of intensive melt shearing and casting speed on the flow field and temperature field were studied. The results showed that intensive melt shearing can increase the width of two-phase zone, change the morphology of the sump, and significantly enhance the convection of the melt.

Grain refinement of Mg-alloys by native MgO particles: An overview

A fine and equiaxed solidification process delivers multidimensional benefits to Mg-alloys, such as improved castability, reduced casting defects, enhanced mechanical properties, increased corrosion resistance and potential for increased recycled contents. Despite extensive research on grain refinement of Mg-alloys in the last few decades, currently, there is no effective grain refiner available for refining Mg-Al alloys, and our current understanding of grain refining mechanisms is not adequate to facilitate the development of effective grain refiners. Under the EPSRC (UK) LiME Hub's research program, substantial advances have been made in understanding the early stages of solidification covering prenucleation, heterogeneous nucleation, grain initiation and grain refinement. In this paper, we provide a comprehensive overview of grain refinement of Mg-alloys by native MgO particles. We show that native MgO particles can be made available for effective grain refinement of Mg-alloys by intensive melt shearing regardless of the alloy compositions. More importantly, we demonstrate that (1) the addition of more potent exogenous particles will not be more effective than native MgO; and (2) MgO particles are difficult to be made more impotent for grain refinement through promoting explosive grain initiation. We suggest that the most effective approach to grain refinement of Mg-alloys is to make more native MgO particles available for grain refinement through dispersion, such as by intensive melt shearing.

High-Pressure Die Casting: A Review of Progress from the EPSRC Future LiME Hub

This article provides an overview of high-pressure die casting (HPDC)-related research undertaken at the EPSRC Future LiME Hub between 2015–2022. The project aimed to identify the cause of variability in the tensile ductility of die-cast structures, and to develop novel processing techniques to address this issue. Variability in tensile ductility was related to the size of large pores and non-metallic inclusions. It was proposed that these non-metallic inclusions formed during the pyrolysis of commercial plunger lubricants in the shot sleeve, and that these large pores derived from dilatational strains introduced during semi-solid deformation. Processing parameters and die design were found to significantly influence the microstructure of die-cast products, and the subsequent variability in tensile ductility. To close, recent progress on the application of intensive melt shearing to HPDC is reviewed. Intensive melt shearing was found to induce significant grain refinement in both Al and Mg alloys due to the effective dispersion of native oxide particles, and the use of these particles as heterogeneous nucleation substrates. The presence of native oxide particles also enabled the use of novel heat treatment procedures that avoided conventional issues such as surface blistering and geometrical distortion.

Formation of intermetallic phases in unrefined and refined AA6082 Al alloys investigated by using SEM-based ultramicrotomy tomography

• Microstructure of AA6082 Al alloys was studied using SEM serial ultramicrotomy tomography. • The formation sequence of intermetallic phases is related to the coarsening of α-Al dendrites. • TiB 2 particles act as nuclei for the formation of β, α intermetallics and Mg 2 Si. • The grain refinement processing causes the severe interconnectivity of α-intermetallics. • Melt shearing is better to uniformly distribute and refine intermetallics than grain refiner. The spatial arrangement, distribution and morphology of Fe-bearing intermetallics in AA6082 alloys depends on the manufacturing process of the alloy and thus influences the macroscopic properties. Here, the microstructure of a near industrial scale casting AA6082 Al alloy fabricated by: (a) direct chill casting, (b) Al-5Ti-1B grain refiner addition and (c) intensive melt shearing has been investigated by three-dimensional visualization using SEM-based serial ultramicrotomy tomography. The formation sequence of phases in AA6082 alloys is generally categorized into four stages: formation of α-Al grains, Fe-bearing intermetallics, Mg 2 Si phase, and eutectic rosettes. Results of three-dimensional visualization of the microstructure indicated that TiB 2 particles not only could nucleate Fe-bearing β-intermetallics, but also could provide substrate for the formation of Fe-bearing α-intermetallics and Mg 2 Si. A further deep analysis reveals that the essential condition for the formation of secondary phases such as Fe-bearing intermetallics and Mg 2 Si phase is the build-up of a supersaturated solute front at the α-Al solid-liquid interface irrespective of the specific nucleation site. In addition, the results indicate that grain refinement processing causes the severe interconnectivity of Fe-bearing α-intermetallics. However, the intensive melt shearing is a better manufacturing process because the intermetallics are more evenly distributed and refined than with the addition of the grain refiner, thereby improving the properties of the alloy.

Hydrophobic agglomeration behavior of rhodochrosite fines Co-induced by oleic acid and shearing

• Agglomeration of rhodochrosite markedly depended on oleic acid concentration and pH. • Hydrophobic attraction drove agglomeration correlated with adsorption of oleic acid. • Large and dense agglomerates formed with increasing stirring rate until 500 rpm. • Excessive shearing could break agglomerates with large-scale fragmentation mechanism. • The broken fragments regrew incompletely as reducing stirring rate to initial value. Efficient separation of fine-disseminated rhodochrosite is a challenge in the purification of manganese carbonate ore and a key to reduce the discharge of electrolytic manganese slag. The agglomeration behavior of the fine particles is of importance for flotation separation. In this study, we investigated the agglomeration behavior and aggregate properties of rhodochrosite fines co-induced by oleic acid (OA) and shearing using particle size and structure analysis, surface properties measurement, extended DLVO (EDLVO) theoretical calculation and shear fracture model analysis. The results showed that rhodochrosite fines agglomerates obviously with the increasing OA concentration and pH value, and the average particle size reaches the maximum at the initial OA concentration of 1 × 10 -3 mol/L and pH of 6. The monolayer physical and chemical saturation adsorption of OA cause stronger hydrophobicity of rhodochrosite. Meanwhile, the hydrophobic attractive force between particles is stronger than electrostatic repulsive force, resulting in hydrophobic agglomeration. The moderate stirring rate is conducive to forming larger-sized and denser agglomerates with the critical rate of 500 rpm. However, intensive shearing will cause significant damage to the formed agglomerates. Besides, the volume concentrations of 10–30 μm and 30–45 μm particles increased with the increase of stirring rate after breakage and with a lower value of γ’ than 0.5, suggesting that the agglomerates breakage is mainly controlled by large-scale fragmentation mechanism. Interestingly, as recovering shearing from the higher rate to the initial rate, a secondary agglomeration is achieved by the regrowth of core (30–45 μm particles) and attach of branches and coatings (some < 10 μm and 10–30 μm particles) under the synergy of hydrophobic attraction and shearing. However, it did not fully recover back to the original balanced state before fragmentation, which was due to irreversible damage caused by excessive shearing. This research will be beneficial for in-depth understanding of agglomeration mechanisms of rhodochrosite fines and provide a basis for subsequent efficient flotation separation.

In-situ microstructural control of A6082 alloy to modify second phase particles by melt conditioned direct chill (MC-DC) casting process – A novel approach

• High shear melt conditioning in the sump during direct chill casting of A6082 billet. • Novelty of maintaining 2–7 °C above alloy liquidus as the sump thermal condition. • In-situ control of solidification during casting by intensive melt shearing. • Precise tailoring of as-cast microstructure to modify second phase particles. • Potential for industries to eliminate homogenisation and use recycled Al alloys. Controlling the formation of noncompact second phase particles during direct chill (DC) casting of aluminium alloys with grain refiner addition remains challenging, as it results in energy intensive homogenisation and deformation problems. In this work, we employed a novel strategy in the DC casting of A6082 alloy to produce billets with a fine-scale dispersion of second phase particles. The strategy involves maintaining 2–7 °C above alloy liquidus as a thermal condition in the sump by in-situ melt conditioning (MC) using a rotor-stator high-shear device operated at a critical rotation speed. As a result, in-situ control of solidification behaviour is achieved to precisely tailor the as-cast microstructure. The billet grain refinement is attained by MC-DC casting without the deliberate addition of chemical grain refiners. The microstructure of the MC-DC cast billet at the critical rotation speed showed a fine-scale dendritic structure with refined secondary dendrite arm spacing (SDAS). The solidification front proceeded with a shallow sump and a corresponding shorter solidification time, higher cooling rate, higher temperature gradient, and smooth solidification rate profile. The ideal fine-scale dendrites with low SDAS divided the remaining eutectic liquid into fine-scale and isolated liquid pockets, resulting in fine-scale, compact morphology, and uniform distribution of second phase particles in the as-cast microstructure. The MC-DC casting process showed the ability to increase the cast house production rate by increasing the casting speed without bleeding the billet. The present approach could be beneficial for eliminating or reducing the homogenisation practice and may also introduce significant flexibility in using recycled Al alloys in the industry.

Improved degassing efficiency and mechanical properties of A356 aluminium alloy castings by high shear melt conditioning (HSMC) technology

• Faster hydrogen removal technology than conventional rotary degassing methods. • Effective elimination of oxide bi-films by innovative rotor-stator design. • High technology efficiency as very low gas flow and rotor speed required. • No covering flux required to maintain good melt quality for long periods after degassing. • Improved casting integrity and mechanical properties due to enhanced melt quality. The degassing of aluminium alloy melts is a crucial step in the production of high-quality casting products, as the presence of dissolved hydrogen and oxide bi-films is detrimental to the mechanical properties. Current rotary degassing techniques are effective, but they lack efficiency because of the high gas flow and long processing times required. This study aims to solve this problem by presenting an innovative rotor-stator degassing technology, that combines controlled inert gas injection with intensive melt shearing. It has been applied to the liquid metal treatment of an aluminium cast alloy to evaluate the effect on melt cleanliness, casting integrity and mechanical properties. The optimum conditions for an efficient bubble dispersion have been obtained by water modelling. The melt quality during and after degassing has been assessed by in-situ measurement of hydrogen concentration and by reduced pressure test sampling for oxide bi-films and porosity content evaluation. This new technology is faster, requires less gas flow consumption and produces higher melt quality than the existing degassing techniques, due to a characteristic combination of distributive and dispersive mixing flow. In addition, re-gassing is minimised, maintaining a high melt quality for longer time after processing. This results in castings with less defects and better mechanical properties. The improved degassing efficiency of this technology makes it an excellent alternative in industry to increase melt quality and casting productivity.

Effect of casting speed on floating grains and macrosegregation of direct-chill cast 2024 alloy with intensive melt shearing

The ingot was prepared by direct-chill (DC) casting technology with different casting speeds under the influence of intensive melt shearing to explore the effect of casting speed and intensive melt shearing on the floating grains and negative centerline segregation. The results indicate that the application of intensive melt shearing in DC casting process can distribute the floating grains uniformly, reduce the area fraction of the floating grains, alleviate the negative centerline segregation, and improve the uniformity of temperature field in the sump. It is also suggested that under the influence of intensive melt shearing, the casting speed plays a crucial role in the amounts and distribution of floating grains. At low casting speed, the intensive melt shearing can significantly reduce the area fraction of the floating grains and distribute them uniformly throughout the ingot. However, this effect gradually disappears with the increase of casting speed.

Microstructure and orientation evolution of microinjection molded β‐nucleated isotactic polypropylene/poly(ethylene terephthalate) blends

AbstractThe influence of different shear stresses induced by changing injection molding speeds on molecular chain orientation and lamellar branching of β‐nucleated iPP/poly(ethylene terephthalate) (PET) microparts was investigated using two‐dimensional wide‐angle X‐ray diffraction and 2D‐small‐angle X‐ray scattering. Results indicated that the prevailing shear stress can promote the formation of parent–daughter α‐crystal structure and twisted shish–kebab structure in subsequent microparts. The diffraction of (300) plane of β‐crystals was also observed at varying injection speeds. Increasing injection speeds can significantly enhance the content of β‐crystals from 24 to 41% for β‐nucleated iPP microparts. Additionally, the content of β‐crystals was further enhanced in β‐nucleated iPP/PET microparts with in situ formation of PET microfibrils under intensive shearing conditions. The addition of both PET and β‐nucleation agents coupling with high shearing conditions exerts a synergetic effect on the development of β‐crystals. However, the orientation degree of crystal lattice decreased with increasing injection speeds for both β‐nucleated iPP and iPP/PET microparts.

Crystallization and Microstructure Evolution of Microinjection Molded Isotactic Polypropylene with the Assistance of Poly(Ethylene Terephthalate).

In this work, a series of isotactic polypropylene/poly(ethylene terephthalate) (iPP/PET) samples were prepared by microinjection molding (μIM) and mini-injection molding (IM). The properties of the samples were investigated in detail by differential scanning calorimetry (DSC), Wide-Angle X-ray Diffraction (WAXD), Polarized light microscope (PLM) and scanning electron microscopy (SEM). Results showed that the difference in thermomechanical history between both processing methods leads to the formation of different microstructures in corresponding iPP/PET moldings. For example, the dispersed spherical PET phase deforms and emerges into continuous in-situ microfibrils due to the intensive shearing flow field and temperature field in μIM. Additionally, the incorporation of PET facilitates both the laminar branching and the reservation of oriented molecular chains, thereby leading to forming a typical hybrid structure (i.e., fan-shaped β-crystals and transcrystalline). Furthermore, more compact and higher degrees of oriented structure can be obtained via increasing the content of PET. Such hybrid structure leads to a remarkable enhancement of mechanical property in terms of μIM samples.

Influence of reinforcing particle distribution on the casting characteristics of Al-SiCp composites

Abstract SiC particulate reinforced A356 alloy metal matrix composites (MMCs) are synthesized using intensive melt shearing. The effect of reinforcing particle distribution on the fluidity of cast A356/10 vol.% SiCp composites is studied. Spiral length representing the fluidity of the composite melt was measured and liquid flow and solidification behaviour were analysed. Improvement in the fluidity of composites is attributed to the uniform distribution of reinforcing particles by intensive melt shearing treatment. From the casting performance point of view, uniform dispersion of reinforcing particles achieved with the aid of intensive shearing improves the mechanical properties of A356/10 vol.% SiCp cast composites. Improved strength, rigidity and wear resistance of composites is attributed to the bulk homogeneity, significantly reducing casting defects.

An investigation of direct-chill cast 2024 aluminum alloy under the influence of high shearing with regards to different shear positions

Abstract The 2024 aluminum alloy ingot with a diameter of 300 mm was prepared by a direct-chill (DC) cast with the application of a high-shear unit in the sump to study the influence of the intensive melt shearing on the 2024 aluminum alloy. During the DC casting process, the head of the high-shear unit was set to different positions in the sump and the corresponding temperature curves were recorded to further study the role of the position of the high shear unit in the DC casting process with the influence of the intensive melt shearing. The experimental results showed that the intensive melt shearing during the DC casting process results in uniform temperature distribution in the sump, significant grain refinement and reduction of negative centerline macrosegregation. The average grain size in the center of the ingot was reduced from 739.7 μm to 193.8 μm, and the negative centerline macrosegregation of Cu element was reduced from -0.094 to -0.041. It was also found that the shear position plays a significant role in uniforming temperature field, eliminating melt superheating and refining grains. When the high shear position lowered to slurry region, the morphology of grain in the center of the ingot transformed from equiaxed dendritic into finer globular equiaxed grain. The reduction of negative centerline macrosegregation is believed to be due to the forced convection caused by the intensive melt shearing and consequently refined microstructure and uniform distribution of floating grains through the whole section of the ingot.

Effect of the Intensity of Melt Shearing on the As Cast Structure of Direct Chill Cast 2024 Aluminum Alloy

Intensive melt shearing was achieved by a stator–rotor high-shear unit and was used in the sump during direct chill (DC) casting process to investigate the influence of the rotation speed on the as cast structure of an aluminum alloy. It has been demonstrated that intensive melt shearing has a significant effect on achieving a uniform temperature distribution and obtaining a fine and uniform as cast structure. We also found that the intensity of the melt shearing plays an important role in the effect. As the rotation speed increases, the melt around the high-shear unit transformed from a liquid to a semisolid state. At a rotation speed of 3000 rpm, intensive melt shearing can only increase the nuclei through fragmentation in the region close to the solidification front by forced convection. When the rotation speed increases to 6000 rpm, intensive melt shearing can also evidently increase the number of effective nuclei, mainly by increased fragmentation in a large volume around the high-shear unit.

Solidification processing of scrap Al-alloys containing high levels of Fe

The accumulation of iron in molten aluminium is one of the main concerns for the recycling and casting industries because it leads to the formation of undesirable Fe-rich intermetallic compounds which are detrimental to mechanical properties. Many methods have been developed in the past to reduce the iron accumulated in molten aluminium scrap, but they all suffer from poor efficiency. Hence, a more efficient method is urgently needed to mitigate the negative effect of high iron levels in the melt, thereby avoiding downgrading secondary aluminium to low quality products or the dilution with expensive primary aluminium. This contribution provides a study of the Fe-rich intermetallic compounds developed in aluminium casting alloys with high levels of Fe as a function of melt processing conditions. Results show that the formation of the Fe-compounds is not only dependent on the cooling rate and holding time before solidification, but more on the initial melt treatment as it enhances the nucleation and growth of the Fe-phases. Elemental addition of Mn leads to the formation of large and compact intermetallic particles, but at slow rate. Physical melt treatment by intensive high shearing produces a much faster nucleation and results in a fine dispersion of smaller iron containing intermetallic particles. The latter could be used either to increase the tolerance to iron contamination or to facilitate the iron removal process, providing huge benefits for the recyclability of scrap aluminium alloys as it would allow the transformation of low-grade feedstock into a low cost and small carbon footprint material for high quality castings.

Effect of High Mixing Intensity on Rheological Properties of Cemented Paste Backfill

Cemented paste backfill (CPB) consists of a mixture of fine particles, mainly consisting of tailings and cement dispersed in water. Therefore, it is necessary to introduce an intensive shearing force into the paste during mixing in order to maintain an equilibrium between agglomeration and dispersion. It is influential for the macroscopical fluidity and rheological properties when changes occur in the microstructure of CPB under shear. However, the research on how mixing affects the properties of CPB is still in its infancy. This paper puts an insight into the relation between the mixing intensity and the rheological behavior of the CPB. It can be demonstrated that two threshold mixing intensities exist in this process. After passing the first or lower threshold, the rheological parameters (yield stress and viscosity) of the paste decrease. After passing the second threshold, a continued increase is observed. The changes in rheological properties are connected with physical and chemical changes in the microstructure of the CPB. The results are discussed in light of the three concepts “structural breakdown”, “thixotropic breakdown”, and “thixotropic behavior” of rheological properties of CPB.

Effect of Nano-SiC on Microstructure and Mechanical Properties of AZ91 Magnesium Alloy Processed by Thixomolding

Magnesium injection molding technology was used to produce Mg based nanocomposites. AZ91 chips were mixed with 5 wt.% of β-SiC nanoparticles in solid state and fed to pre-heated cylinder of prototype injection molding machine. Using screw rotation, granules were transferred to nozzle area at simultaneous intensive shearing and mixing of slurry containing reinforcement phases. Injection process was conducted at 595 °C, which corresponded to about 90% liquid phase and cast to steel die preheated to 150 °C. Detailed characterization of microstructure was performed using SEM and TEM microscopes. Composite microstructure consisted of α(Mg) globular grains with size of about 60 μm and volume of 7-10% surrounded by mixture of proeutectic magnesium solid solution with irregular shape and average size of 12 μm as well as fine eutectic mixture (α(Mg) + β-Mg17Al12). Additionally, TEM-BF image showed β-SiC nanoparticles with size of 20-50 nm in the area of eutectic. Hardness and compression strength of AZ91 nanocomposites increased from 58 to 75 HV and from 200 to 235 MPa, respectively.