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Significant progress has been made in magnesium-based composites during recent decades, especially for the appearance of magnesium matrix composite reinforced by nanoparticles. The nanoparticles added not only exhibit a good strengthening effect, but also maintain the initial toughness of the matrix, effectively balancing the contradiction between the strength and plasticity in the traditional magnesium matrix composites. The magnesium matrix nanocomposites with excellent mechanical properties have pushed the development of magnesium matrix composites to a new stage. However, it is very difficult to disperse the nanoparticles in metal melt especially in magnesium melt which is different from other metal melts and dangerous during the cast processing. This means that the preparation of magnesium matrix nanocomposite is extremely challenging. Further, the magnesium matrix nanocomposites possess a distinctive characteristic in deformation behavior, strengthening and toughening mechanism due to their special size effect of nanoparticles. Accordingly, this review will focus on the new preparation technologies, deformation behavior, mechanical properties and strengthening and toughening mechanisms. The potential applications, development trends and future research ideas of magnesium matrix nanocomposite are also prospected. [ABSTRACT FROM AUTHOR]

In this paper, three volume fractions (2, 5 and 10%) of 10 μm SiCp/AZ91 magnesium matrix composite were fabricated by stir casting. The as cast ingots were forged at 420°C with 50% reduction first and then extruded at 370°C with a ratio of 16∶1. The results show that the grain is refined significantly after hot deformation process, which results in the enhancement of tensile properties. The volume fraction of micrometre SiCp has significant effect on grain size by influencing dynamic recrystallisation of magnesium. By the increase in particle volume fraction, the grain size decreases, the dislocation density increases and the load transfer effect is strengthened, thus leading to the significant improvement of yield strength. The ultimate tensile strength of the composite increases with the increase in particle volume fraction due to the improved deformation uniformity of matrix and the enhanced hindering effect on crack propagation. [ABSTRACT FROM AUTHOR]

Magnesium matrix composites reinforced with two volume fractions (1 and 3%) of SiC particles (1 μm) were successfully fabricated by ultrasonic vibration. Compared with as-cast AZ91 alloy, with the addition of the SiC particles grain size of matrix decreased, while most of the phase MgAl varied from coarse plates to lamellar precipitates in the SiCp/AZ91 composites. With increasing volume fraction of the SiC particles, grains of matrix in the SiCp/AZ91 composites were gradually refined. The SiC particles were located mainly at grain boundaries in both 1 vol% SiCp/AZ91 composite and 3 vol% SiCp/AZ91 composite. SiC particles inside the particle clusters may be still separated by magnesium. The study of the interface between the SiC particle and the alloy matrix suggested that SiC particles bonded well with the alloy matrix without interfacial reaction. The ultimate tensile strength, yield strength, and elongation to fracture of the SiCp/AZ91 composites were simultaneously improved compared with that of the as-cast AZ91 alloy. [ABSTRACT FROM AUTHOR]

Abstract: Magnesium matrix composites reinforced by graphite particles were fabricated using stir casting with graphite particle size of 50μm and graphite particle volume fractions of 5%, 10%, 15% and 20%, respectively. A dynamic mechanical analyzer was used to measure the damping capacities of as-cast composites. The experimental results reveal that the graphite particles play an important role on the damping capacities of as-cast composites. The strain amplitude independent damping of as-cast composites increases significantly as the graphite particle volume fraction increases from 0% to 15%, but decreases when the volume fraction exceeds 15%. The damping values of as-cast composites rise slowly with increasing temperature from room temperature to 125°C, and have no obvious change with increasing temperature from 125°C to 250°C, but rise rapidly with increasing temperature from 250°C to 400°C. [Copyright &y& Elsevier]

Abstract: Grp/AZ91 and SiCp/Grp/AZ91 magnesium matrix composites were fabricated by stir casting with graphite particle size of 50μm and SiC particle size of 10μm. The as-cast composites were extruded at 350°C with an extrusion ratio of 12:1. The experimental results reveal that the reinforcements play an important role on the tensile properties and damping capacities of the composites. The addition of graphite particles improves the yield strength, and the addition of SiC particles further improves the yield strength. The addition of graphite particles improves the strain amplitude independent damping, but the addition of reinforcements does not change the critical strain significantly. Temperature dependence of damping capacities in as-cast and as-extruded materials both can be divided into two regions, and each region has different dominant damping mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: A particulate reinforced magnesium matrix composite fabricated by stir casting was subjected to multidirectional forging (MDF) at a temperature of 420°C. The results showed that grains of matrix in the composite were significantly refined after 1 MDF pass, and gradually refined till 3 MDF passes. The evolution of particle distribution in the composite during MDF was investigated by a window technique. It was shown that MDF led to an increase of the uniformity of the particle distribution. With increasing the MDF passes, both the tensile strength and the elongation to failure of the composite are significantly enhanced till 3 MDF passes. [ABSTRACT FROM AUTHOR]

Abstract: Magnesium matrix composites reinforced by graphite particles were fabricated using stir casting with graphite particle size of 50μm and graphite particle volume fractions of 5, 10, 15 and 20%, respectively. The as-cast composites were extruded at 300°C with an extrusion ratio of 12:1. The experimental results reveal that the graphite particles play an important role on the tensile properties and damping capacities of the composites. The strength increases with the addition of 5% graphite particles, but decreases with further addition of graphite particles. The strain amplitude independent damping increases significantly as the graphite particle volume fraction increases from 0 to 10%, but almost keeps constant when the volume fraction exceeds 10%. Two damping peaks are found at 150 and 350°C, respectively. The damping peak around 150°C is considered to be caused by movable boundary slip, and the damping peak around 350°C is inferred to be recrystallization peak. [Copyright &y& Elsevier]

Abstract: Magnesium matrix composite reinforced by graphite particles was fabricated using stir casting with graphite particle size of 50μm and graphite particle volume fraction of 10%. The as-cast composite was extruded at 250°C, 300°C and 350°C with an extrusion ratio of 12:1. The experimental results reveal that the extrusion temperature plays an important role on the microstructures and damping capacities. The aspect ratio of graphite particles increases as the extrusion temperature rises. Extrusion at 300°C leads to the highest damping values in low strain region at room temperature. It also demonstrates the highest damping values at elevated temperatures when the strain is 4×10−5. In addition, there are two definite damping peaks in the damping-temperature curves which occur at about 150°C and 350°C, respectively. [Copyright &y& Elsevier]

The particle/matrix interfaces in SiCp/AZ91 composite fabricated by stir casting were investigated using transmission electron microscope (TEM) equipped with ultra-thin window energy dispersive X-ray analysis (EDAX) system. Chemical reactions indeed occurred at the interfaces. According to EDAX results, the interfacial reaction products are considered to contain Al4C3, MgO, and Mg2Si phases. The interfaces can be classified into three types (interfaces I, II, and III) according to morphological features of the interfaces: (1) for interface I, interfacial reaction products were in direct contact with the surface of SiCp; (2) for interface II, interfacial reaction products were not in direct contact with the surface of SiCp; (3) for interface III, interfacial reaction products were not observed at the interfaces, i.e., interface III was simply formed by the two surfaces of SiCp and matrix. Mg17Al12 and Al8Mn5 precipitate phases heterogeneously nucleated at the particle/matrix interfaces. [ABSTRACT FROM AUTHOR]

The effect of high temperature exposure on the interface and tensile properties of Al18B4O33w/AZ91 magnesium matrix composite fabricated by squeeze casting was studied. The interfaces of the composites were examined using transmission electron microscopy, and the mechanical properties were evaluated by tensile tests. The interfacial region was composed of MgO which was formed by the reaction between the Al18B4O33 whisker and the Mg matrix. An thin and uniform interfacial reaction layer with a thickness of 10–20 nm formed during squeeze casting could act as a barrier to prevent the further reaction between Al18B4O33 whisker and Mg alloys. The interfacial reaction rate was very low during thermal exposure below the liquidus temperature of AZ91 matrix alloy. Only after exposure above the liquidus temperature of the AZ91 matrix alloy for a long period, the thickness of the interfacial layer increased obviously. However, the interfacial reaction rate was much slower than that in the Al18B4O33w/Al–Mg composites. The interfacial reaction kinetics was controlled by the seepage of Mg and release of Al and B along the narrow diffusion channels between the fine MgO particle. The composite did not show a degradation in the tensile properties after exposure below the solidus temperature of AZ91 for long periods, suggesting that the Al18B4O33w/AZ91 magnesium matrix composite could be subjected to long-term service at elevated temperature. [Copyright &y& Elsevier]

The article reports that aluminum borate whisker has been successfully used as reinforcement in aluminum matrix composites because of its low cost and excellent properties. Recently, aluminum borate whisker reinforced magnesium matrix composites have also been developed, which exhibit almost equivalent mechanical properties to SiCw/Mg composites but with a lower coefficient of thermal expansion. The high cost-effective aluminum borate whisker reinforced magnesium matrix composites have a wide range of possible applications.

The aging behavior of SiC whisker reinforced AZ91 magnesium matrix composites was investigated with Vickers hardness measurement, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The precipitation process observed in the monolithic alloy was not altered by the addition of SiC whiskers. The composite exhibited an accelerated hardening response compared with the unreinforced matrix alloy. However, the addition of SiC whiskers altered the distribution of the Mg17Al12 precipitates. Mg17Al12 precipitated preferentially at the SiCw–AZ91 interface, with a definite orientation relationship with SiC whisker: (1¯10)Mg17Al12//(111)SiCw, [111]Mg17Al12//[011¯]SiCw. The preferential interfacial precipitate decreased the Al content in the matrix, resulting in a decrease in the amount of continuous precipitates. As a consequence, the age-hardening efficiency in the composite was lower. [Copyright &y& Elsevier]

Cites a study on the effect of thermal cycling on the mechanical properties of SiCw/ZK60 magnesium matrix composite. Attraction of the reinforced magnesium matrix composites for space applications due to low density, high specific properties, high wear resistance and low coefficient of thermal expansion; Fabrication of SiCw/ZK60 magnesium matrix composite by squeeze casting with the usage of SiC whisker preform with aluminum phosphate binder; Conclusion on the strength and ductility of the thermally cycled SiCw/ZK60 composite no show of significant degradation by repeated heating and cooling from thermal cycles.

The superplastic deformation behavior of 19.7 vol.% β-SiCw/ZK60 composite was characterized. A maximum elongation of 200% was obtained at 613 K and at 1.67×10−2 s−1 with an m value of 0.35. Basal slip was activated during superplastic deformation. The activation energy (98 kJ/mol) approximates that for grain boundary diffusion (92 kJ/mol) in magnesium. [Copyright &y& Elsevier]

Abstract: A new concept aims at developing genetically intelligent (“gentelligent”) components, which bequeath production or application data to their next generation. For such an approach, it is desirable to store respective information on the component itself. This is accomplished by using its surface to store magnetic data on it. This way, the component itself can be used as its own information carrier throughout the manufacturing process and later throughout the working cycle. The chosen approach is to develop a magnetic magnesium (Mg), integrate it in an appropriate component, and subject the component to recording experiments. [Copyright &y& Elsevier]

Carbon nanotubes (CNTs) reinforced magnesium matrix composite prepared by an improved process was extruded at 350°C with an extrusion ratio of 20:1. Most CNTs were individually and uniformly dispersed in the as-cast and the as-extruded composites. Moreover, good interfacial bonding was achieved, and Raman spectroscopy showed that the damage to CNTs was insignificant. The addition of CNTs could weaken basal plane texture. Meanwhile, the CNTs evidently improved the ultimate tensile strength, yield strength and Young's modulus of the as-extruded composite. Pulling-out CNTs proved that the length of the CNTs was not large enough to be compatible with the high strength of the CNTs. Grain refinement, load transfer mechanism and Orowan strengthening mechanism play important roles on the increase of the yield strength. The composites fabricated by our process showed high strengthening efficiency of CNTs. [ABSTRACT FROM AUTHOR]

Abstract: The pure Mg sheets were processed by ARB at 400°C and 300°C up to 8 cycles and 4 cycles, respectively. The microstructure was refined during the first cycle and only homogenized during the following ARB process due to the high deformation temperature, intermediate reheating and air-cooling. The ARB process did not show an obvious effect on the tensile properties of the as-ARBed pure Mg sheet due to the stable grain size and dominant basal plane texture during ARB. Further deformation should be introduced to improve the bonding quality of the as-ARBed sheet. [ABSTRACT FROM AUTHOR]

SiC particles exhibited necklace-type distribution in SiCp/AZ91 Mg matrix composites fabricated by stir casting , and thus, the SiC particles could be divided into segregated particles region and particle free region. The effects of this particle distribution on the discontinuous precipitation of Mg 17 Al 12 phase during ageing were investigated. The high density dislocations were induced due to the sharp mismatch between the thermal expansion coefficients of SiC and AZ91 alloy. The overlapped mismatch among the segregated particles causes higher density dislocations. And as a result, the discontinuous precipitations as the ageing products started born mainly near particles, especially near segregated particles. However, few Mg 17 A1 12 precipitated in the matrix within the particle segregation. The high-density dislocations and the numerous SiC/Mg interfaces made Mg 17 A1 12 phases much easier and earlier to precipitate in the composite. Thus, the SiCp addition reduced the peak ageing time from 38 h (for AZ91 alloy) to 28 h (for the composite). The ultimate tensile strength of the composite was enhanced by 46% after peak-ageing. SiC particles could also improve the age hardening efficiency of the composite because the high-density dislocations, the fine grain sizes and the numerous SiC/Mg interfaces cause the finer and more uniform precipitation of Mg 17 A1 12 Above all, the addition of SiC particles is effectively to improve the mechanical properties of magnesium matrix composite materials. [ABSTRACT FROM AUTHOR]

High strong magnesium matrix composites can be obtained by refining grain size, heat treatment and severe plastic deformation methods. However, most of the composite enhancing approaches result in the disappointingly poor tensile ductility. Thus, the designing and fabricating of composites with simultaneously good ductility and high strength have become burning issues for the application of light metals/alloys. Simply adding particles or changing particle parameters can not solve the problem of combination of high strength and good ductility. A new method has been developed, wherein the bimodal size grained microstructure formed by adding the bimodal sized SiC particles (SiCp) was selected as favorable microstructure for achieving good ductility and high strength in present work. The fine grains (grain size: <1 μm) were obtained through the particle stimulate of nucleation (PSN) and pin grain boundary effect. However, the coarse grains (grain size: ∼4 μm) were obtained through forming SiCp free zones in the present magnesium matrix composites. The tensile test indicates a significant improvement in the ductility (∼8.3%) and strength (UTS: ∼402 MPa, YS: ∼323 MPa) of the composites. Compared with the conventional single-sized particles (micron or nano) reinforced magnesium matrix composites, the tensile ductility and strength of present composite (AZ31B/SiCp/1n + 9m composite) were highlighted in the current literature. [ABSTRACT FROM AUTHOR]

Magnesium matrix composite reinforced with submicron SiC particles was subjected to room temperature deformation. A stepped tensile method was adopted to observe the development of microstructure at different tensile strain state. The microstructure evolution determined by transmission electron microscopy showed that the existence of submicron SiC particles could promote dislocation multiplication as well as impede dislocation motion. Dislocation density around SiC particles increased with the increase of tensile strain. Compared with the matrix alloy, the composite could withstand greater external loads, which can be related to the pinning effect caused by the submicron SiC particles on the movement of grain and twin boundaries. The study of the interface between the submicron SiC particles and matrix in the composite suggested that single submicron SiC particle bonded well with the matrix alloy after tensile process. Initiation of micro-cracks usually generated in the submicron particle dense zone during tensile process, which could lead to the fracture of composite. [ABSTRACT FROM AUTHOR]

Highlights: [•] The solidification rates significantly affect the CNTs distribution. [•] Uniform CNTs distribution was achieved in the composites. [•] The tensile properties of the composites follow the Kelly–Tyson formula well. [Copyright &y& Elsevier]

Abstract: Bimodal sized (Micro-particles: m and Nano-particles: n) SiC particulates (SiCp) reinforced magnesium matrix composites with different volume fractions of micro-particles (1n+4p, 1n+9p and 1n+14p) were prepared by a semisolid stirring assisted ultrasonic vibration method. Both the as-cast SiCp/AZ31B composites and the AZ31B alloy were extruded at 350°C with the extrusion ratio of 12:1 at a constant ram speed of 15mm/s. The microstructure investigation was carried out by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results show that the distribution of bimodal size SiCp and the mechanical properties of the AZ31B alloy were significantly improved after hot extrusion. When the volume fraction of nano SiCp is 1vol%, both the yield strength and ultimate tensile strength of the AZ31B/SiC/1n+14p composite are stronger than that of the AZ31B/SiC/1n+4p and AZ31B/SiC/1n+9p composites, while the elongation to fracture was decreased comparing with the AZ31B/SiC/1n+4p and AZ31B/SiC/1n+9p composites. [Copyright &y& Elsevier]

Highlights: [•] Submicron-SiCp/AZ31B composites were fabricated.. [•] The influence of submicron SiCp for matrix alloy was determined. [•] Mechanical properties of submicron SiCp/AZ31B composite were enhanced significantly. [Copyright &y& Elsevier]

Highlights: [•] SiC particles inhibit sparking discharge and microarc oxidation coating growth. [•] SiC particles undergo intense oxidation before sparking discharge occurs. [•] Effect mechanism of SiC particle on microarc oxidation process is revealed. [•] SiC particles degrade the corrosion resistance of microarc oxidation coating. [Copyright &y& Elsevier]

Abstract: Fine-grained commercial pure Mg was prepared by equal channel angular pressing. Heat treatments were carried out on ECAP processed samples to modify the microstructures, such as the density of dislocation, grain size and grain boundary, and their effects on internal friction at room and elevated temperatures have been studied in detail by dynamic mechanical analyzer (DMA). The ECAP processed pure Mg shows a high value of strain independence of internal friction, which is reduced after heat treatment due to the decrease of mobile dislocations, while the strain dependent part obviously increases owing to the larger grain size. Three internal friction peaks are observed during the measurements of temperature dependence of internal friction. The low temperature peak around 100–200°C is considered to be caused by thermally activated grain boundary relaxation, and it is obviously broadened compared with a Debye peak for a single relaxation time. The changes of activation energy and relaxation time distribution of this peak with an increase in grain size were also studied. The other two peaks at the temperature range of 200–350°C are frequency independent and associated with some irreversible structural transformation, they are considered to be related to the recrystallization. [Copyright &y& Elsevier]

Abstract: Equal channel angular pressing (ECAP) was performed on the as-extruded commercial pure magnesium at 250°C for 4 passes. The internal friction of the ECAPed pure Mg as a function of strain amplitude was investigated by dynamic mechanical analyzer (DMA), and the cyclic microplasticity of pure Mg was investigated by tensile loading and unloading test. After ECAP processing, the grain size is significantly refined, the texture component with basal planes parallel to extrusion direction is replaced by a new stronger one with basal planes having a tilting angle of about 40° to the extrusion direction. The stress in microplastic region is reduced with increasing ECAP passes, while the internal friction increases. The internal friction of Mg at high strain amplitude is closely related to microplastic deformation and can be interpreted by dislocation mechanism. The Granato and Lücke model only satisfies in anelastic regions, while the internal friction in microplastic deformation region should be explained in terms of the internal friction model postulated by Peguin. The internal friction related to microplasticity can be divided into two parts with different activation volumes of dislocation motion, which correspond to the two regions of microplasctic deformation process. The initial stage associated with dislocation motion on basal plane shows larger activation volume and lower friction stress of dislocations. The second stage related to the annihilation and tangle of dislocations is characterized by larger hardening exponent and friction stress. [Copyright &y& Elsevier]

Abstract: In this paper, three kinds of magnesium matrix composites reinforced by SiCp with the sizes of 0.2, 5 and 10μm, respectively, were fabricated by stir casting technology. Then the as-cast ingots were deformed by the combination of forging and extrusion process. Typical microstructures were obtained in the composites reinforced by different particle sizes. For the composites with lower volume fraction of particles (2%), submicron SiCp had significant influence on grain refinement and strengthening effect, which resulted in better mechanical properties of submicron SiCp/AZ91 composite. However, mechanical properties reduced owing to the obvious agglomerated submicron SiC particles as the volume fraction increased to 5% and 10%. On the contrary, for micron SiCp/AZ91 composite, the grain size was refined and the strengthening effect was enhanced with the increasing of volume fraction. Although particle size has no influence on the texture type, it has different effects on weakening the intensity of texture. [Copyright &y& Elsevier]

Abstract: Particulate reinforced magnesium matrix nanocomposites fabricated by semisolid stirring assisted ultrasonic vibration were subjected to extrusion. The results showed that grains of matrix in the SiCp/AZ91 nanocomposites were gradually refined while the amount of SiC nanoparticle bands was decreased with the extrusion temperature increasing from 250 to 350°C. Under the same extrusion conditions, the grain size of the matrix was gradually decreased while the distribution of SiC nanoparticles was improved in the extruded nanocomposites fabricated by decreasing the stirring time. The yield strength and ultimate tensile strength of the nanocomposites were gradually enhanced with increasing the extrusion temperature. Significant improvement of tensile strength was obtained in the nanocomposites fabricated by decreasing the stirring time. [Copyright &y& Elsevier]

Abstract: A particulate reinforced magnesium matrix composite prepared with stir casting was subjected to multidirectional forging (MDF). The results showed that after 1 MDF pass the grain size of matrix in the composites decreased compared with as-cast composite, and increased with increasing the MDF temperature from 370°C to 450°C. With increasing the MDF passes at 370°C, the particle distribution of the composite was improved until 3 MDF passes while the grain size of matrix in the composite reached a minimum after 4 MDF passes. Both the yield strength and the ultimate tensile strength of the composite were enhanced with increasing the MDF passes. [Copyright &y& Elsevier]

Abstract: SiCp/AZ91 composites fabricated by stir casting were extruded at different extrusion temperatures and ratios. Extrusion reduced the necklace-type particle distribution and improved particle distribution of the composites. As extrusion temperatures and ratios increased, particle distribution was improved, and the grain sizes of matrix increased. The mechanical properties of the composites were improved with the increase of extrusion temperatures and ratios. The microstructure evolution of matrix was not the main influential factor of the mechanical properties of the composites. The particle evolution, which included particle redistribution and particle cracking induced by extrusion, significantly affected the mechanical properties of the extruded composites. [Copyright &y& Elsevier]

Abstract: Microstructure and texture development of the equal channel angular pressed (ECAP) pure Mg with different rotation routes of A, Bc and C were investigated and related to the tensile mechanical property. Results showed that grain size was greatly decreased after 1 pass but varied with processing routes after the following ECAP. Due to a relatively high processing temperature, the refinement degree was limited via these three routes processing. Different preferred orientations of the basal plane were formed with three routes processing and there existed a rotation angle in (0002) pole figure from normal direction to transverse direction. Negative slope of the yield stress versus d−1/2 was obtained with routes Bc processing, which was attributed to the texture modification. Texture strengthening greatly increased the 0.2% yield strength, but decreased the ductility. [Copyright &y& Elsevier]