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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 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]

Abstract: In the present study, AZ91 magnesium matrix composites reinforced with six volume fractions (0.5, 1, 1.5, 2, 3 and 5vol.%) of submicron-SiC particulates (0.2μm) were fabricated by stir casting. The as-cast ingots were forged at 420°C with 50% reduction, and then extruded at 370°C with the ratio of 16 at a constant ram speed of 15mm/s. The microstructure of the composites was investigated by optical microscopy, scanning electron microscope and X-ray diffractometer. Microstructure characterization of the composites showed relative uniform reinforcement distribution, significant grain refinement and presence of minimal porosity. The X-ray diffractometer analysis showed that a strong basal plane texture was formed in both AZ91 alloy and SiCp/AZ91 composites during extrusion and the addition of submicron-SiC particulates could weaken the basal plane texture. The presence of submicron-SiC particulates assisted in improving the thermal stability, micro-hardness, elastic modulus and 0.2% yield strength. Both of the 0.2% yield strength and ultimate tensile strength increased with the increasing of submicron-SiC particulate content, however, decreased as the SiC particulate content overrun 2vol.%. [ABSTRACT FROM AUTHOR]

Abstract: SiCp/AZ91 magnesium matrix composite was fabricated by stir casting. The as-cast ingots were cut into cylindrical billets, and then forged at different temperatures (320, 370, 420, 470 and 520°C) at a constant RAM speed of 15mm/s with 50% reduction. The microstructure evolution of the composites during forging was investigated by optical microscope, scanning electron microscope, and transmission electron microscope. The texture of the forged composites was measured by neutron diffraction. Mechanical properties of the composite at different forging temperatures were tested by tensile tests at room temperature. It was found that a strong basal plane texture formed during forging, and the intensity of basal plane texture weakened as forging temperatures increased. The particle distribution in the composite was significantly improved by hot forging. Typical microstructures were obtained after forging at different temperatures and the composite with different microstructures offered different mechanical properties during tensile test. [Copyright &y& Elsevier]

Abstract: The hot deformation behavior of ZK60 magnesium alloy reinforced with 20 vol.% of Al18B4O33 whisker has been studied by employing both processing maps and microstructural observations. The material of investigation was deformed by compression in the temperature range of T =523–723K and strain rate range of . From the hot compression tests, the flow stress data, strain rate sensitivity index (m), power dissipation efficiency (η) and instability parameter () were evaluated and processing maps were developed for the strain of ɛ =0.6. Domains for optimum hot working conditions were obtained using the processing maps and the instability zones were identified. The material showed a regime of dynamic recrystallization in the temperature range of T =623–723K and strain rate range of corresponding to the higher values of efficiency (η). The optimum temperature and strain rate combination for squeeze cast Al18B4O33w/ZK60 composite are T =673K and corresponding to an efficiency of η =24%. In the temperature range of T =573–623K and strain rate range of Al18B4O33w/ZK60 composite exhibited dynamic recovery. At the strain rate higher than 0.3s-1 and temperature range of T =623–723K, the material exhibited flow localization and these conditions should be avoided in processing. [Copyright &y& Elsevier]

Abstract: The effect of Si content on low frequency damping capacities and mechanical properties of as-cast Mg–Si alloys were investigated. Both hypoeutectic alloys with 0.3wt.%Si, 0.8wt.%Si and hypereutectic alloy with 2.3wt.%Si exhibit high damping capacities since these Mg–Si alloys possess large size α-Mg phase with very small amount of soluble atoms in it. The amount of the in situ formed Mg2Si determines the dislocation density and then influences the damping capacity of these Mg–Si alloys. The Mg–0.3wt.%Si alloy exhibits the lowest damping value at small strain region but the highest damping value at large strain region among these Mg–Si alloys. Two damping peaks were found in Mg–Si alloys at 80 and 230°C, respectively. But the addition of Al in Mg–Si alloy impeded the appearance of these two damping peaks since the soluble Al atoms hindered the movement of dislocations and the slide of grain boundaries. The presence of large size, brittle primary Mg2Si particles decreases the tensile strength and ductility of the hypereutectic Mg–Si alloy. [Copyright &y& Elsevier]

Abstract: As-cast hypoeutectic Mg–Si alloy showed a high damping capacity at room temperature. This resulted from the co-effect of damping peaks P 0 and P 1 which were detected at 0°C and 100°C, respectively. P 0 and P 1 were considered to possess similar properties and they were caused by the interaction between dislocations and impurity atoms or vacancies. Heat treatment strongly influenced the damping capacity of this Mg–Si alloy. [Copyright &y& Elsevier]

High quality YBa2Cu3O7 - x films on metallic substrates with high critical current densities well over 106 A/cm2 can be prepared by the rolling assisted biaxially textured substrates (RABiTS) method. Nickel or its alloys have been used as biaxially textured substrates formed through a specific rolling and high temperature annealing procedures. In this paper, we report a newly developed process for developing biaxial texture in rolled Ni tape by argon ion beam bombardment. It is named the ion-beam structure modification (ISM) process. In the ISM processed Ni foils, X-ray diffraction ω scans showed the full width-half maximum (FWHM) value of the (2 0 0) peak was 5.7°. And the electron back scattering diffraction (EBSP) analysis based on scanning electron microscopy showed good {1 0 0} 〈0 0 1〉 cubic orientation and the mean grain size was determined as about 25 μm. The texture evolution of rolled Ni foils during ISM process is reported also. For ISM process, local temperature elevation and distribution arises from the ion bombardment, coupled with anisotropic incident ion penetration and propagation as a result of channeling effects in the metal lattice, are expected to play the major roles in the development of grain reorientation in the Ni foil. Due to the simplicity and efficiency of the ISM process, the technique shows a great promise for application in the industrial scale production of long-lengths of superconductor tapes. [Copyright &y& Elsevier]

SiC particles reinforced AZ91D Mg matrix composites with different particle contents fabricated by a ultrasonic method were extruded at 350 °C. Hot extrusion eliminated the “island” particle distribution, and evidently improved SiC particles distribution of the composites. However, hot extrusion induced particle cracking besides the improvement of SiC particles distribution. There existed more cracked particles in the particle-rich zones. During extrusion, SiC particles stimulated the nucleation of dynamic recrystallization in the matrix. Dynamic recrystallization is also sensitive to the particle content on a local scale in the composites. As SiC contents increased, the yield strength of the composites increased. However, the ultimate tensile strength increases of the composites were small as the SiC contents increased from 10% to 20%, because the improvement of ultimate tensile strength caused by the strengthen effects of SiC particles was offset by extrusion-induced particle cracking. [ABSTRACT FROM AUTHOR]

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: Magnesium matrix composites reinforced with micro-SiC particles were fabricated by semisolid stirring assisted ultrasonic vibration with SiC particle size of 1μm and volume fractions of 3% and 5%, respectively. Compared with as-cast AZ91 alloy, with the addition of the micro-SiC particles grain size of matrix was decreased while most of the phase Mg17Al12 varied from coarse plates to lamellar precipitates in 3vol.% SiCp/AZ91 composite. Although some dispersed micro-SiC particles were found within the grains, most of the micro-SiC particles were located along grain boundaries in both 3vol.% and 5vol.% SiCp/AZ91 composites. The study of the interface between the micro-SiC particle and the alloy matrix suggested that micro-SiC particles bonded well with the alloy matrix without interfacial reaction. The ultimate tensile strength and yield strength of the 3vol.% SiCp/AZ91 composite were improved while elongation to fracture was almost kept. [Copyright &y& Elsevier]

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]

The (micron[m]+submicron[s]+nano[n]) SiC particles (SiCp) reinforced AZ31B magnesium matrix composites (AZ31B/SiCp/m + s + n composites) were fabricated by stirring casting technology followed by hot extrusion. This method has successfully solved the homodisperse problem of SiCp/m + s + n in the magnesium matrix composites. The influence of SiCp/m + s + n on the dynamic recrystallization (DRX) behavior of the magnesium matrix was investigated by researching the TEM microstructures of composites. The results indicated that the addition of SiCp/m + s + n was helpful to increase the ratio of DRXed nucleation and reduce the average grain size of matrix. The particle deformation zone (PDZ) can be formed in the vicinity of micron SiCp, while the region with high dislocation density can be created around submicron SiCp owing to pin dislocation and deformation mismatch between matrix and particles. These regions are ideal sites for the formation of recrystallization nucleus. Meanwhile, the addition of fine SiCp(nano and submicron) may delay or hinder the growth of matrix grain through the pinning effect on the grain boundaries during hot extrusion. The tensile test indicates that the strength of the AZ31B/SiCp/m + s + n composites has a significant improvement. Compared with the single sized or bimodal sized particles reinforced magnesium matrix composites, the tensile strength of the AZ31B/SiCp/m + s + n composites were highlighted. [ABSTRACT FROM AUTHOR]

Multidirectional forging (MDF) under decreasing temperature conditions was adopted to process SiC nanoparticles reinforced magnesium matrix composite. The results showed that grains of the nanocomposite were effectively refined while the amount of precipitated phases was significantly increased after MDF under decreasing temperature conditions. The precipitated phases as well as dispersed SiC nanoparticles could hinder the growth of dynamic recrystallization. The yield strength and ultimate tensile strength of the nanocomposites were increased compared with that of as-cast nanocomposite. This improvement could be attributed to obvious grain refinement as well as Orowan strengthening effect introduced by the dispersed SiC nanoparticles and the precipitated phases. Microcrack could initiate within the SiC nanoparticle dense zones during tensile test at room temperature, resulting in decrease of the elongation. [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]

Abstract: Carbon nanotube (CNTs) reinforced Mg matrix composites were successfully fabricated by a novel approach. After hot extrusion, the influence of CNTs on microstructure and mechanical properties of Mg–6Zn matrix was investigated. The results showed that most CNTs distributed uniformly and individually in the composites, and good interfacial bonding was achieved. CNTs significantly refined the grains of Mg–6Zn matrix, and the CNTs evidently improved the ultimate tensile strength (UTS), yield strength (YS) and Young's modulus. Grain refinement, load transfer mechanism and Orowan strengthening mechanism play important roles on the increase of the yield strength. [Copyright &y& Elsevier]

Abstract: In this paper, 0.2μm SiCp/AZ91 composite was fabricated by stir casting technology. The influence of fine (<1μm) particles on the dynamic recrystallization (DRX) behavior of AZ91 matrix was investigated by researching the microstructure evolution of 0.2μm 1vol% SiCp/AZ91 composite during the hot extrusion process. Results showed that the DRXed ratio of AZ91 matrix increased as well as the average size of DRXed grains reduced due to the addition of fine particles. The SiCp could not only pin dislocation, but also was helpful to generate dislocations owing to the deformation mismatch between matrix and particles, thus causing the increase of dislocation density around SiCp, which was benefit to stimulate DRX nucleation. Meanwhile, the growth of DRXed grains was suppressed in the following deformation process due to the pinning effect of fine particles on grain boundaries. Thus, the fine particles had significant effect on stimulating DRXed nucleation and refining grain size. The yield strength and ultimate tensile strength of the as-deformed 0.2μm 1vol% SiCp/AZ91 composite are 275 and 335MPa, respectively, which are mainly attributed to the grain refinement, basal plane texture and uniform particle distribution induced by hot deformation. [Copyright &y& Elsevier]

Abstract: The dynamic recrystallization (DRX) of a 10μm10% SiCp/AZ91 composite during hot compression was studied using optical microscope and transmission electron microscope. In the as-cast composite, SiC particles were segregated along grain boundaries, which was like necklaces along the grain boundaries. Thus, particles aggregated at transgranular areas while particles were almost absent at the grain interiors. During hot compression, particle deformation zones (PDZs) were formed near particles due to the mismatch between SiC particles and Mg matrix. DRX preferentially started near particles due to “particle-stimulated nucleation (PSN)” in PDZs. Therefore, this necklace particle distribution caused initiation of DRX along the pre-existing (initial) grain boundaries. As a result, the initial grain boundaries were entirely covered by new and fine DRX grains, and necklace structure of DRX grains was formed along the grain boundaries. As DRX further proceeded, DRX extended from the intergranular areas of the initial grains to the initial grain interiors. According to the microstructure investigations and analysis, the necklace mechanism for DRX was established for Mg matrix composites with necklace particle distribution. [Copyright &y& Elsevier]

sAbstract: The Mg/Al laminated composites were fabricated by the accumulative roll bonding (ARB) at ambient temperature using the pure magnesium and commercial pure Al sheets. Mg grains were refined after the primary sandwich preparation and then homogenized during the following ARB process while the grain size of Al layer decreased with increasing of the accumulated strains. Both the yield strength and ultimate strength along rolling direction and transverse direction increased gradually while the elongation to failure along both directions decreased with increasing of the ARB cycles. Formation of the Mg17Al12 phase indicated that the ARB process at ambient temperature could lead to a metallurgic bonding of the Mg/Al interface. [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: SiCp/Mgph name="sbnd" />Ca composites with three volume fractions (5%, 10% and 15%) were successfully fabricated by stir casting. The particle distributions were fairly uniform in all composites, although most particles were segregated along grain boundaries in the micro-scale level. Interfacial reaction products were not observed at the interface between SiCp and matrix. SiCp affected the size and shape of the second phases as well as their distribution in the matrix. In the 5% composite, many large second phases were observed at the particle surfaces. As the particle content was increased up to 10%, large second phases were hardly observed at the SiCp surfaces. Moreover, the second phases mainly existed in the form of fine flake in the 10% and 15% composite, unlike the alloy and 5% composite in which the second phases were large. The effect of SiCp on the second phases significantly influenced the mechanical properties of the composites. Compared with the matrix alloy, 15% composites had good room temperature and high temperature mechanical properties. [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: In the present study, 10vol.% SiCp/AZ91 magnesium matrix composites are fabricated by stir casting. The as-cast ingots are cut into cylindrical billets, and then forged at 420°C with different deformation amounts (40, 50, 60 and 80%) at a constant RAM speed of 15mm/s. The results illustrate that the addition of SiC particles has significant influence on refining grain size and improving tensile strength of AZ91 matrix, however, weakening basal plane texture. After forging SiCp/AZ91 composites, the intensity of basal plane texture increases as deformation amount increases. The grain size of composite matrix grows up slightly as the deformation amount increased to 60%, and then it was refined obviously as the deformation amount continues to increase to 80%. The smaller deformation amount is propitious to improve particle distribution, while lager deformation amount promotes SiC particle agglomeration. Thus, the tensile strength increases as the deformation amount increases to 50%, however, it decreases as the deformation amount continues to increase to 80%. [Copyright &y& Elsevier]

The texture of the Mg/Al laminated composite fabricated by accumulative roll bonding was measured by neutron diffraction. The texture type of the Mg layer was typical rolling texture and the dominant texture of the Al layer was β-fiber rolling texture with scatter around the ideal orientations. The significant waviness structure caused by the shear band reduced both the intensity and the sharpness of the rolling texture of both Mg and Al layers. [Copyright &y& Elsevier]

Abstract: Excellent damping capacities were observed in pure Mg and hypoeutectic Mg–Ni alloys. Two damping peaks (P1,P2) were found at 100°C and 230°C, respectively. P1 was a newly detected damping peak, which was considered to derive from the movement of dislocations; it has great significance for practical applications. [Copyright &y& Elsevier]