Strong, Ductile Magnesium-Zinc Nanocomposites (original) (raw)
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Materials Science and Engineering: A, 2021
The microstructure, compression, and creep responses of the squeeze-cast AZ91 alloy; the AZ91 alloy with 0.6Sb (wt.%) addition; and the AZ91 alloy with 0.6Sb (wt.%) + 2.0SiC (wt.%) (1.2 vol%) nanoparticles addition have been evaluated. The additions of 0.6Sb and 0.6Sb+2.0SiC to the AZ91 alloy reduce the grain size and decrease the β-Mg 17 Al 12 phase, and result in improved compression and creep responses. The AZ91 + 0.6Sb+2.0SiC np nanocomposite exhibits the best compression properties and the highest creep resistance. The dislocation climb controlled by pipe diffusion is the dominant creep mechanism in the alloys and nanocomposite. The superior compression responses are attributed to the reduction in grain size, and the improved creep resistance is attributed to the decrease in the β-Mg 17 Al 12 phase for both the AZ91 + 0.6Sb alloy and AZ91 + 0.6Sb+2.0SiC np nanocomposite. The strengthening due to CTE mismatch between the alloy and SiC nanoparticles, as well as the Orowan strengthening for the nanocomposite additionally contributed to the improved compression and creep responses.
International Journal of Metalcasting, 2008
Magnesium based metal matrix composites (MMCs) have been extensively studied as an attractive choice for automotive and aerospace applications due to their low density and superior specific properties including strength, stiffness and creep resistance. Xi et al [1] studied the Ti-6Al-4V particulate (TAp) reinforced magnesium matrix composite which is fabricated by powder metallurgy route. The tensile strength of the composite was markedly higher than that of the unreinforced magnesium alloy. Xi et al [2] also studied the SiC whiskers-reinforced MB15 magnesium matrix composites by powder metallurgy and found that the mechanical properties of SiCw/MB15 composite were significantly influenced by powder-mixing methods of PM. Li et al [3] studied the hot deformation behavior of SiC whiskers reinforced AZ91 magnesium matrix composites in compression. It was found that the microstructure evolutions involved the movement of SiC whiskers and the changes of the matrix, and the rotation and the broken SiC whiskers tended to be obvious with the increasing strain, and also high density of dislocation was observed in the AZ91 matrix at the initial stage of compression (1%). Jiang et al [4] studied that magnesium metal matrix composites (MMCs) reinforced with B4C particulates fabricated by powder metallurgy. The hardness and wear resistance of the composites were higher than those of as-cast Mg ingot and increased with increasing amount of B4C particulates from 10 to 20 vol.%. Zhang et al [5] studied that carbon nanotube reinforced magnesium metal matrix composite by stirring the carbon nanotube into magnesium melts. It was found that carbon nanotube, especially chemical nickel-plated one, This paper presents the results from our recent development in cast bulk Mg nanocomposites. SiC nanoparticles reinforced magnesium and magnesium alloys including pure magnesium, and Mg-(2, 4)Al-1Si and Mg-4Zn were successfully fabricated by ultrasonic cavitation based dispersion of SiC nanoparticles in magnesium melt. As compared to un-reinforced magnesium alloy matrix, the mechanical properties including tensile strength and yield strength were improved significantly while the ductility was retained or even improved. In the microstructure, the grain size was refined considerably by SiC nanoparticles. While some micro SiC clusters still exist in the magnesium matrix, ultrasonic cavitation based processing is very effective in dispersing SiC nanoparticles. A SEM study showed that SiC nanoparticles were dispersed quite well in the areas outside micro SiC clusters. A TEM study on the interface between SiC nanoparticles and magnesium alloy matrix indicates that SiC nanoparticles bonded well with Mg matrices without forming an intermediate phase.
Materials, 2019
In the present study, Mg nanocomposites with a high volume fraction (10 vol %) of SiC particles were fabricated by two approaches: mechanical milling and mixing, followed by the powder consolidation steps, including isostatic cold pressing, sintering, and extrusion. A uniform distribution of the high content SiC particles in a fully dense Mg matrix with ultrafine microstructure was successfully achieved in the mechanically milled composites. The effect of nano- and submicron-sized SiC particles on the microstructure and mechanical properties of the nanocomposites was evaluated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), and X-ray diffractometry (XRD) were used to characterize microstructures of the milled and mixed composites. Mechanical behavior of the Mg composites was studied under nanoindentation and compressive loading to understand the effects the microstructural modification on the strength and ductility o...
Development and Characterization of Mg-SiC Nanocomposite Powders Synthesized by Mechanical Milling
Key Engineering Materials, 2017
Magnesium powder in micron scale and various volume fractions of SiC particles with an average diameter of 50 nm were co-milled by a high energy planetary ball mill for up to 25 h to produce Mg-SiC nanocomposite powders. The milled Mg-SiC nanocomposite powders were characterized by scanning electron microscopy (SEM) and laser particle size analysis (PSA) to study morphological evolutions. Furthermore, XRD, TEM, EDAX and SEM analyses were performed to investigate the microstructure of the magnesium matrix and distribution of SiC-reinforcement. It was shown that with addition of and increase in SiC nanoparticle content, finer particles with narrower size distribution are obtained after mechanical milling. The morphology of these particles also became more equiaxed at shorter milling times. The microstructural observation revealed that the milling process ensured uniform distribution of SiC nanoparticles in the magnesium matrix even with a high volume fraction, up to 10 vol%.
Semi-solid casting (SSC) of zinc alloy nanocomposites
Journal of Materials Processing Technology, 2009
An innovative casting method that combines semi-solid casting (SSC) and metal matrix nanocomposite (MMNC) technology was successfully demonstrated. The method uses the grain refining properties of the nanoparticles in the MMNC to produce slurry with the appropriate globular structure for semi-solid casting. In this way no additional material processing or mechanical agitation is necessary to achieve the desirable slurry microstructure. The grain refining attributes of the nanoparticles were shown to stem from the promotion of nucleation in the solidifying matrix alloy. Differential scanning calorimetry (DSC) showed a reduced undercooling necessary for nucleation owing to the nucleation catalytic potency of the nanoparticles. Using this method zinc alloy AC43A nanocomposite with 0.5 wt.% SiC  nanoparticle additions were cast at a 30% solid fraction. The resulting castings showed increased ductility, reduced shrinkage, and increased strength compared to their monolithic liquid cast counterparts.
Fabrication and Characterizations of Mg/SiC Composite Via Compo-Casting Technique
The present work deals with applying compo-casting technique for fabrication of magnesium matrix composite under an inert gas atmosphere. A 15 Micrometer average diameter size of -SiC particulate was used as a reinforcement material with different volume fractions. The effect of processing technique on SiC distribution within alloy matrix was investigated using light optical microscope and scanning electron microscope. Also, microstructural characterization studies conducted on the composites produced by compo-casting technique revealed a uniform distribution of SiC particulates (at the microscopic scale) and less porosity content. The mechanical properties of pure Mg and Mg-SiC composites have been evaluated. The results show a remarkable increasing in hardness value, tensile strength and 0.2% yielding strength. The increasing in overall mechanical properties revealed to SiC addition to base matrix. However, it is also evident that the strain to failure significantly decreased as the volume fraction of the particulate increased. Also, a good bonding between Mg matrix and SiC reinforcement material was observed in fracture surface SEM micrograph.
In this work, an attempt has been made to fabricate novel hybrid nanocomposites from Mg-Zn-Yttrium (traceable) alloy with 1.0 wt. percent nano-SiC P (fixed) and 0.5, 1.0, and 1.5 wt. percent nano-hBN P as reinforcing particles. The combined effect of stir-ultrasonication and squeeze casting was applied to mix the nanoparticles in the Mg matrix. The nanocomposite samples were heat-treated at T5 condition. Optical microscopy evaluates the refined grains. SEM pictures represent the uniform nanoparticle dispersion in the Mg matrix. As compared with base alloy, higher dislocation density is observed in the nanocomposite samples which were confirmed by the TEM images. XRD validates the occurrence of SiC and BN phases in the hybrid nanocomposites. The combination of 1.0 wt% SiC P and 1.5 wt% hBN P reinforced hybrid nanocomposite show 31% more microhardness and 42% more tensile strength than the base alloy. Various strengthening models employed to assess the influence of nanoparticles on yield strength, which were then, compared to the experimental yield strength values. Experimental and theoretical yield strength values were found to be in closer agreement.
Metals and Materials International, 2020
In this study, first, AZ80 magnesium alloy and AZ80/SiC nanocomposite were manufactured through a stir casting approach. Then built samples underwent five passes of DECLE process at a constant temperature of 300 °C. Changes in microstructures, hardness, and tensile strength were measured in the annealed alloy and nanocomposites as well as samples with 1, 3, and 5 passes of DECLE to determine the effects of sic. strengthening nanoparticles and number of the DECLE passes. Results show that there is a most significant decrease in grain size due to adding the nanoparticles.The microstructure of the initial AZ80 samples made by large grains and inhomogeneous structure with an average grain size of 60.3 µm. After five DECEL passes for samples with nanoparticles, the structure is turned into fine and homogenous grains with an average size of 4.5 µm. Along with this decreasing trend in the grain size, hardness shows a 20.7% increasing. The results of the uniaxial tensile test show that yield strength and ultimate tensile strength have increased respectively from 74 to 131.8 MPa for initial samples to 113 and 221.9 MPa in nanocomposites. Finally, their values reach to 191.3 and 288.3 MPa after applying five passes of DECLE process. The results indicate that it is possible to significantly improve the microstructure and mechanical properties of the AZ80 magnesium alloy through enriching by nanoparticles. Using severe plastic deformation processes such as DECLE can induce a further decrease in grain size and significant improvement in the mechanical properties without causing changes in the samples' dimensions.
Processing-microstructure relationships in compocast magnesium/SiC
Journal of Materials Science, 1992
Compocasting experiments were conducted to investigate the feasibility of the process as applied to the AZ91 D magnesium alloy-SiC particles system. Processing-macro/ microstructure relationships were examined. Three temperature-time processing sequences were investigated: stirring temperature maintained above liquidus; stirring temperature in the semi-solid temperature range; and lastly, an imposed temperature rise above the liquidus after stirring in the mushy zone. Stirring temperature and particle size significantly affect spatial particle distribution and porosity level. The easy incorporation and even dispersion of particles in the matrix suggest good wetting of SiC particles by the magnesium matrix. Impact fracture surfaces show strong bonding at the particle/matrix interface. A reaction takes place at the matrix/particle interface whilst stirring at temperatures above the liquidus. Reaction products have been identified. Finally, the mechanical properties of a compocast ingot which was extruded have been studied and are reported. This work clearly points out that there is a preferred procedure to follow during compocasting to obtain an optimum microstructure. The procedure is to add the reinforcing materials to the semi-solid alloy followed by stirring above the liquidus temperature.
Materials Science and Engineering: A, 2000
The microstructure and heterogeneous nucleation phenomena in cast SiC particles reinforced magnesium composite have been studied using optical and transmission electron microscopy (TEM). The microstructure of magnesium composites showed that most SiC particles were pushed and segregated at the grain boundaries while few SiC particles (3%) were entrapped in the magnesium grain. The SiC particles in the magnesium composite were identified as 6Ha-SiC structure. Stacking faults and pits defects were also observed within the SiC particles. The primary magnesium phase which heterogeneously nucleated on the SiC particle surface has been identified with a small lattice disregistry (2.3%) while their crystallographic orientation relationship was (101( 0) Mg //(0001) SiC . Examination of the composite interface indicated that the eutectic and Cu 5 Zn 8 phases were able to wet the SiC particles and heterogeneously nucleate on the SiC particles while the crystallographic orientation relationships between them were (011( 1) SiC //(110) Mg17Al12 and (0001) SiC //(001) Cu5Zn8 , respectively. Finally, the factors that influence the heterogeneous nucleation of primary magnesium phase, eutectic and Cu 5 Zn 8 phases on the SiC particles are discussed.