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Many interesting studies on composites with nano or submicron SiCp have been performed since the size advantages of fine SiC particles. However, it is extremely hard to disperse fine particles in metal melts due to their poor wettability and large surface-to-volume ratio, especially the fabrication of composites with multisized SiCp (5 µm, 0.5 µm, and ∼60 nm) is very difficult. The use of multisized reinforcements is required to solve the dispersion problem. The stir casting technology and hot extrusion method could be used to disperse the multisized SiCp in the matrix. The effects of multisized SiCp on the dynamic recrystallization behavior of the composites are discussed. The large-scale dynamic recrystallization caused by adding multisized SiCp results in a fine matrix microstructure. Compared with the as-accepted AZ31B alloy (YS: 195 MPa, UTS: 277 MPa), the yield strength and ultimate tensile strength of the AZ31B/SiCp/n-1 + S-4 + 5-10 composite were enhanced to 73.8 and 44.8%, respectively. The better tensile properties were attributed to the uniform distribution of reinforcement, strengthening effect of multisized SiCp, and grain refinement of magnesium matrix. [ABSTRACT FROM AUTHOR]

Melting plays a critical role in cast parts production, and an electromagnetic field can affect heat transfer in the induction melting process. This paper studied a mathematical model of coupled electromagnetic and temperature fields based on a simplified physical model of the induction melting process. The '' method was applied to solve the electromagnetic governing equations, while the finite difference method of the uneven mesh was used to discretise all the control equations. The simulation results of the self-developed program and ANSYS software for electromagnetic fields had the same distribution trend and both demonstrated a good agreement of current skin effect and magnetic edge effect. However, the result comparisons illustrated that the simulation results of this program were more accurate. The simulation results explained the heat transfer mechanism of cast steel in the induction melting process, and the impact of current and frequency on heat transfer was also discussed. [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: Electrophoretic deposition (EPD) method has been developed for the fabrication of TiO2 and MnO2 films. Benzoic acid and phenolic molecules, such as 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, gallic acid, salicylic acid and salicylic acid sodium salt were investigated as charging additives for the EPD of TiO2 and MnO2 particles. The deposition yield has been studied as a function of the additive concentration and deposition time for cathodic deposits obtained from the suspensions, containing benzoic acid, 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid and anodic deposits prepared from the suspensions, containing gallic acid and salicylic acid sodium salt. The results obtained for the phenolic molecules with different number of OH groups were analyzed and compared with corresponding experimental data for benzoic acid without OH groups. The adjacent OH groups, as well as adjacent OH and COOH groups bonded to the aromatic ring of the phenolic molecules were beneficial for adsorption of the molecules on oxide particles. The adsorption mechanisms involved the interaction of COOH groups and OH groups of the organic molecules with metal ions on the particle surfaces and complexation. Gallic acid was shown to be an effective charging additive, which provided stabilization of TiO2 and MnO2 particles in the suspensions and enabled their deposition. It was shown that composite TiO2–MnO2 films can be obtained using gallic acid as a common dispersing agent for TiO2 and MnO2. The Ti/Mn ratio in the composite films was varied in the range of 0–1.3. The thickness of the films was varied in the range of 0–10μm. The mechanisms of particle charging and deposition were discussed. [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: Equal channel angular pressing (ECAP) of the in situ Mg2Si reinforced Mg composite was performed with route Bc up to 8 passes using a 90° die. Refinement and re-distribution of the reinforced phase Mg2Si was investigated. Bulk texture development during ECAP was characterized by neutron radiation. Results showed that only the eutectic Mg2Si (Type-II) was proposed to be effective for preparing the in situ Mg2Si/Mg composite. Neutrons texture analysis briefly illustrated that a 〈00.2〉 basal fiber with the obtainment of less shear effect was formed. But the asymmetry of basal fiber around the ECAP direction was also observed. Both uniform texture and homogeneity distribution of Mg2Si particles played an important role in the tensile behavior of ECAPed composite. [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 deformation and fracture behavior of as-solutionized SiCw/AZ91 magnesium matrix composite was observed during the in-situ tensile straining in a transmission electron microscope. The results indicated that the dislocation slip was impeded by the SiC whiskers, a large number of dislocation pile-ups occurred around the whiskers. Microcracks nucleated predominately at the SiC whisker rich regions and the matrix near SiCw-AZ91 interfaces. The SiC whiskers and twins prohibited the crack propagation. The microcracks linked with each other and connected with the main crack, leading to the catastrophic failure of the composite. The fracture processes of the composite were found to be matrix-controlled. The poor ductility of the composite was attributed to the low inherent ductility of the magnesium alloy matrix and the local stress concentration because of the addition of the SiC whiskers. [ABSTRACT FROM AUTHOR]

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.

In this study, both AZ91 alloy and nano-SiCp/AZ91 composite were subjected to multi-pass forging under varying passes and temperatures. The microstructure and mechanical properties of the alloy were compared with its composite. After six passes of multi-pass forging at a constant temperature of 400 ℃, complete recrystallization occurred in both the AZ91 alloy and composite. The decrease of temperature and the increase of passes for the multi-pass forging led to further refinement of dynamic recrystallized grains and dynamic precipitation of second phases. The grain size of the nano-SiCp/AZ91 composite was smaller than that of the AZ91 alloy under the same multi-pass forging condition, which indicated that the addition of SiC nanoparticles were beneficial to grain refinement by pinning the grain boundaries. The texture intensity for the 12 passes of multi-pass forging with varying temperatures was increased compared with that after nine passes. The ultimate tensile strength is slightly decreased while the yield strength was increased unobviously for the AZ91 alloy with the decrease of temperature and the increase of the passes for the multi-pass forging. Under the same condition of multi-pass forging, the yield strength of the composite was higher than that of the AZ91 alloy due to the Orowan strengthening effect and grain refinement strengthening resulting from externally applied SiC nanoparticles and internally precipitated second phases. By comparing the microstructure and mechanical properties between the AZ91 alloy and nano-SiCp/AZ91 composite, the strength-toughness properties of the composites at room temperature were affected by the matrix grain size, texture evolution, SiC nanoparticles distribution and the precipitated second phases. [ABSTRACT FROM AUTHOR]

Variable-stiffness shells are thin composite structures in which the reinforcement direction is a function of its surface co-ordinates. This paper presents a numerical investigation into the buckling and post-buckling of two variable-stiffness cylinders under axial compression. Both shell walls are made from unidirectional carbon fiber slit tapes that are steered to give them a piecewise-continuous fiber-angle variation around the circumference. Dynamic analyses of the complete loading and unloading cycles are computed using a time-integrated finite element model (Abaqus). The numerical results generated herein are compared with test data and are found to be in good agreement, in terms of axial force versus end-shortening and global displacement fields. The analyses provide significant new insight into the mechanisms underpinning collapse behavior of the shells. For example, the development of the initial nonlinear buckle, its dynamic snap-through, and the formation of a post-buckled configuration are clearly visible. One effect elucidated by this investigation is the symmetry-breaking mechanism of the circumferential stiffness variation. In contrast to a constant-stiffness cylinder, in which the total strain energy is invariant to the translation of a dimple of fixed dimensions, the present structures exhibit a single dominant post-buckling mode that are associated with the formation of ‘trapped’ surface dimples. In one case, this dominant mode is found to be stable over a significant amount of further end shortening. [ABSTRACT FROM AUTHOR]

Abstract: A ceramic coating was synthesized on the surface of SiCw/AZ91 magnesium matrix composite by means of microarc oxidation (MAO) technique. Scanning electron microscope (SEM) was employed to characterize the surface morphology and cross-section microstructure of the coating. The phase structure and the chemical composition of the ceramic coating were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the coating was evaluated by immersion test and electrochemical method. The results showed that the corrosion rate of the coated SiCw/AZ91 composite was decreased greatly compared with that of the bare composite because of the protective microarc oxidation coating. [Copyright &y& Elsevier]

This study investigates the precipitation behavior in the graphene nanoplatelets (GNPs) reinforced bimodal structural Mg-6Zn (wt%) matrix composite. The GNPs with an increasing content progressively accelerate the age-hardening response in the local regions of the composite. The composite takes only half the time that the Mg-6Zn alloy needs to reach the peak strength when aging at 200 °C. The observation reveals that the planar and wrinkled GNPs in the composite act as the effective trigger of dislocations and collector of solute atoms to accelerate the precipitation. It is concluded that GNPs have a pronounced effect on the development of matrix microstructure. Moreover, the orientation relationship between the aligned GNPs towards the extrusion direction and the matrix grains with a fiber type texture makes the GNPs and [0001] Mg precipitate rods constitute a hybrid strengthening architecture in the composite. As a result, the synergistic strengthening effect of the GNPs and the precipitates is realized. [ABSTRACT FROM AUTHOR]

Nano-SiCp/AZ91 magnesium matrix composite was fabricated by stir casting. The as-cast ingots were extruded at 350 °C, then processed by equal channel angular pressing (ECAP) at various temperatures (250 °C, 300 °C and 350 °C). Grains are significantly refined after the extrusion and the ECAP. A basal fibre texture was detected by neutron diffraction after the extrusion, which inclines about 45° to the extrusion direction (ED) after the ECAP. Nano-scaled SiC particles agglomerate in the as-cast composite. After the extrusion, the agglomeration tends to form continuous or discontinuous strips along the extrusion direction. By application of the ECAP, the agglomerated SiC particles are partly dispersed and the strips formed during the extrusion tend to be thinner and broken with the increasing pass number. The yield tensile strength (YTS) and the ultimate tensile strength (UTS) of the composite are dramatically increased after the extrusion. ECAP for one pass at various temperatures further increases the strength, however, the YTS decreases with the increasing ECAP temperature and the pass number. The Orowan equations predict the maximum YTS of the composite may be up to 400 MPa providing SiC particles are homogenously distributed in the matrix. [ABSTRACT FROM AUTHOR]

The effect of fly ash cenospheres (FACs) on the electromagnetic interference (EMI) shielding effectiveness (SE) of the magnesium matrix was investigated. Raw FACs and FACs modified by Ca(OH) 2 were employed as reinforcements. The two kinds of FACs dispersed uniformly in the matrix. Most unmodified FACs were severely broken in the composites, but the majority of FACs kept complete integrated in the composites reinforced by modified FACs. In the range of the testing frequency, raw FACs did not evidently improve the EMI SE of matrix. However, the modified FACs with better ball structure improved the EMI SE of matrix to 75–90 dB. This improvement is attributed to the reflection loss occurred at the outer face (R), absorption at interior place (A) of the composites as well as multiple reflection (B) between different modified FACs. [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: [•] Bimodal size SiCp/AZ31B composites were fabricated. [•] The influence of bimodal size SiCp for matrix alloy was determined. [•] Mechanical properties of bimodal size SiCp/AZ31B composite were enhanced significantly. [ABSTRACT FROM AUTHOR]

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: Particulate reinforced magnesium matrix nanocomposite prepared with semisolid stirring assisted ultrasonic vibration was subjected to extrusion at 350°C with an extrusion ratio of 12:1. Extrusion of the SiCp/AZ91 nanocomposite induced large scale dynamic recrystallization resulting in a fine matrix microstructure. There were two kinds of zones in the extruded nanocomposite: SiC nanoparticle bands parallel to the extrusion direction and refined-grain zones between the SiC nanoparticle bands. In the SiC nanoparticle bands, there were SiC nanoparticles along the boundaries of refined grains. The distribution of SiC nanoparticles was uniform although some agglomerates of SiC nanoparticles still existed in the SiC nanoparticle bands. The ultimate tensile strength, yield strength and elongation to fracture of the SiCp/AZ91 nanocomposite were simultaneously improved by extrusion. Results from the extruded SiCp/AZ91 nanocomposite tensile testing at different temperatures (75, 125, 175 and 225°C) revealed an increase of the tensile strength and ductility values compared with the unreinforced and extruded AZ91 alloy. [Copyright &y& Elsevier]

Abstract: The influence of various annealing temperatures on microstructure evolution of oxidized Ni(20nm)/Au(20nm) ohmic contact to p-GaN was studied by synchrotron X-ray diffraction (XRD). In association with the variation of the specific contact resistance (ρ c), it is observed that NiO and Au began to form partially epitaxial structure on p-GaN at 450°C, which played a critical role in lowering down the ρ c. At 500°C, the epitaxial structure of Au and NiO was improved further while the lowest ρ c was reached. However, at 600°C, the epitaxial structure of NiO was transformed to polycrystalline structure again with a sharp increase of ρ c. Therefore, it is suggested that the degradation of the epitaxial structure of NiO is responsible for the sharp increase of ρ c. [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]