Magnesium-based Composites Research Articles

Magnesium Matrix Composites: State-of the-Art and what’s the Future

A huge number of different process types are in use to produce magnesium-based composites. Depending on the reinforcement type, all the processes can be subdivided into solid state or powder metallurgical (PM) and liquid phase or ingot metallurgical (IM) processes. In this paper we will focus on ingot metallurgy processes. These liquid state processes result quite often in a very good interface of reinforcement with the magnesium matrix. The liquid processes can be further subdivided into infiltration techniques, casting processes and spray deposition. Those are the most inexpensive processing technologies for discontinuous, reinforced magnesium-based composites. When produced using melting processes, nanoparticle-reinforced magnesium composites are expected to improve in strength, due to the grain refinement described in the Hall-Petch relation. When an isotropic distribution of nanoparticles is achieved, the composites are additionally expected to be Orowan-strengthened. That is why nanosized reinforcements are expected to represent the future for improving the properties of magnesium-based metal matrix composites.

Nanomechanical properties of magnesium-based hybrid composites with graphite nanofiber and alumina short fiber

In this study, an attempt was made to evaluate the nanomechanical properties of magnesium-based hybrid composites with graphite nanofibers (GNFs) and alumina short fibers (Al2O3sf) by nanoindentation. The nanoindentation was performed using continuous stiffness measurement (CSM) method with an indentation depth of 2000 nm. To find out the modulus and hardness of composites of local regions, indentation tests were carried out in different locations of the sample, such as GNFs/Al2O3sf region, Al2O3sf region, GNFs cluster, and Mg matrix. The modulus and hardness values closer to the GNFs/Al2O3sf region are higher than those of the corresponding to the other regions primarily because of a higher constraint to the localized matrix deformation during indentation. Furthermore, the presence of GNFs can act as a barrier for movement of dislocations enhancing the indentation properties. The presence of MgO/Mg17Al12 also can contribute to improve the nanoindentation properties of the present composite system.

Microstructure and Mechanical Properties of Quasicrystal Reinforced Magnesium Matrix Composites

Magnesium-based composites reinforced with stable icosahedral quasicrystal particles have been fabricated via Repeated Plastic Working (RPW) process. The microstructure of the composites has been investigated by XRD, SEM, TEM and HREM, and its mechanical properties have also been studied. The results showed that the RPW process could reduce the matrix grain size significantly, and the average grain size of matrix was only about 500 nm after 200 cycles of RPW. A good metallurgical bond interface between the quasicrystal particles and the Mg matrix was found. The composites exhibited the maximum yield strength of 265MPa and the maximum ultimate tensile strength of 309MPa at room temperature, respectively. The enhancement of mechanical properties is attributed to the strengthening effect of the quasicrystal particles and the fine-grain size of matrix.

Erratum to: Magnesium-based composites with improved in vitro surface biocompatibility

The online version of the original article can be found under doi:10.1007/s10856-010-4165-7.

Magnesium-based composites with improved in vitro surface biocompatibility

In this study, bioactive glass (BG, 45S5) particles were added to a biodegradable magnesium alloy (ZK30) through a semi-solid high-pressure casting process in order to improve the surface biocompatibility of the biomaterial and potentially its bioactivity. The observation of the as-cast microstructures of ZK30-BG composites indicated homogeneous dispersion of BG particles in the matrix. SEM, EDX and EPMA showed the retention of the morphological characteristics and composition of BG particles in the as-cast composite materials. In vitro tests in a cell culture medium confirmed that the composites indeed possessed an enhanced ability to induce the deposition of a bone-like apatite layer on the surface, indicating an improved surface biocompatibility as compared with the matrix alloy.

Hydrogen sorption characteristics of magnesium-based composites with addition of Mg2Ni0.7Co0.3 and graphite

Abstract Magnesium-based composites of 75 wt% Mg — (10, 15, 20) wt% Mg2Ni0.7Co0.3 — (15, 10, 5) wt% C mechanically activated for 30 min under argon in a planetary mill, were obtained. Their absorption-desorption characteristics were investigated under a pressure P = 1 MPa and temperatures of 623, 573, 473, 423 and 373 K. Desorption was carried out at 623 K and 573 K and a pressure of 0.15 MPa. All the three composites showed improved hydriding kinetics as compared to pure magnesium. However, the desorption temperature was somewhat higher than needed for practical application.

Mg/B4C Composites with a High Volume Fraction of Fine Ceramic Reinforcement

The results of a study aimed at establishing an understanding of the role of particulate reinforcement on the hardness and tensile deformation of a magnesium-based matrix discontinuously-reinforced with a high volume fraction (approx. 50 vol%) of boron carbide (B4C) particulates are reported. Composites were fabricated by pressureless infiltration of porous boron carbide preforms with molten magnesium under a flowing nitrogen atmosphere. The capabilities of such a fabrication route for production of magnesium-based composites with a high volume fraction of a bimodal mixture of coarse (d 50 = 44 µm) and fine (d 50 = 0.8 µm) boron carbide particulates uniformly distributed in the matrix were also investigated. The successful initiation of spontaneous infiltration was found to be influenced by several processing parameters which were identified and investigated. Thus, the microstructure and mechanical properties of the fabricated composites were investigated in the light of the influence of the initial perform composition (boron carbide bimodal mixture composition and the wetting agents (Si and Ti powders) applied) and the infiltration parameters. The high volume fraction of particulate reinforcement content successfully achieved by pressureless infiltration was found to improve the hardness and tensile properties of the composites significantly compared to unreinforced counterparts. On the contrary, the reinforcement had a detrimental influence on ductility. Moreover, the experimental findings clearly confirmed that the influence of the reinforcing boron carbide phase on the mechanical response of Mg/B4C composites is predominantly through the volume fraction of ceramic particulate in the matrix, and much less through the average particle size of the ceramic filler applied.

Hydrogen storage of the Mg–C composites

The effect of different kinds of carbon on the hydrogen sorption kinetics by magnesium–carbon composites was analyzed. To prepare magnesium-based composites by ball milling, graphite and carbon nanomaterials (hereinafter CNM) obtained by the electroexplosion technique were used. Phase composition and structure state of the as-milled and hydrogenated magnesium–carbon and magnesium–nickel–carbon composites have been investigated. It was found the crystallite size in the Mg–CNM composite is smaller in comparison with the magnesium–graphite and magnesium–graphite–nickel mixtures. The CNM additives to magnesium essentially improve the hydrogen sorption kinetics. It results in a reduction of hydrogen sorption temperature. The noticeable hydrogen absorption took place already at a temperature of 363K. The hydrogen capacity was about 5wt% for magnesium ball milled with CNM additives.

Effect of length scale of Al 2O 3 particulates on microstructural and tensile properties of elemental Mg

In the present study, magnesium-based composites were fabricated with three different sizes (ranging from nano- to micro-meter scale) of 1.1 vol.% Al 2O 3 particulate reinforcement using blend-press-sinter methodology avoiding ball milling. Microstructural characterization of the materials revealed reasonably uniform distribution of Al 2O 3 reinforcement, significant grain refinement and the presence of minimal porosity. Mechanical property characterization revealed that the incorporation of Al 2O 3 particulates as reinforcement led to a simultaneous increase in hardness, 0.2% yield strength, UTS and ductility of pure magnesium. The results further revealed that the 0.2% yield strength, UTS and ductility combination of the magnesium containing nano-size and submicron size Al 2O 3 remained higher when compared to high strength magnesium alloy AZ91 reinforced with much higher amount of micron size SiC particulates. An attempt is made in the present study to correlate the effect of different length scales of Al 2O 3 particulates on the microstructural and mechanical properties of magnesium.

Effect of particulate size of Al 2O 3 reinforcement on microstructure and mechanical behavior of solidification processed elemental Mg

In the present study, magnesium-based composites were fabricated with three different sizes (ranging from nanometer to micrometer scale) of 1.1 vol.% Al 2O 3 particulates reinforcement using disintegrated melt deposition technique. Microstructural characterization of the materials revealed reasonably uniform distribution of Al 2O 3 reinforcement with good interfacial integrity, significant grain refinement, and the presence of minimal porosity. Mechanical properties characterization revealed that the incorporation of nano and submicron size Al 2O 3 particulates in magnesium matrix led to a simultaneous increase in hardness, 0.2% yield strength, UTS, and ductility of pure magnesium. The results further revealed that the 0.2% yield strength, UTS, and ductility combination of the magnesium containing nano and submicron size Al 2O 3 remained much higher when compared to high strength magnesium alloy AZ91 reinforced with much higher amount of micron size SiC particulates. An attempt is made in the present study to correlate the effect of different length scales of Al 2O 3 particulates on the microstructural and mechanical properties of magnesium.

Hydrogenation Properties of Mg-TiNi Hydrogen Storage Composites Materials

Magnesium and Magnesium alloys have been studied as one of the good lightweight hydrogen storage materials, but the materials have strong difficulties in the fabrication process of mass production until now. The Rotation-Cylinder Method (RCM) has been developed to fabricate magnesium-based composites with moderate rotation under normal atmosphere. Inthis study, the Mg-TiNi hydrogen storage composites materials were manufactured by RCM and evaluated their hydrogenation properties by a Sieverts-type automatic pressure-composition-isotherm (PCI) apparatus at 523, 573 and 623K. The hydrogenation properties of Mg-TiNi composites depended on the behavior of TiNi reinforcements. The formation of Mg hydride, MgH2, on 4h milling samples of Mg-10mass% TiNi intermetallics hinted to the catalytic behavior of TiNi reinforcements. In addition, the dehydriding profile at 573K revealed the two steps of plateau pressure, which were affected by the existence of multi hydride phases.

Electrical and Electrochemical Properties of Poly(P-Phenylene)-Based Carbon for Lithium Rechargeable Batteries

Magnesium and Magnesium alloys have been studied as one of the good lightweight hydrogen storage materials, but the materials have strong difficulties in the fabrication process of mass production until now. The Rotation-Cylinder Method (RCM) has been developed to fabricate magnesium-based composites with moderate rotation under normal atmosphere. In this study, the Mg-TiNi hydrogen storage composites materials were manufactured by RCM and evaluated their hydrogenation properties by a Sieverts-type automatic pressure-composition-isotherm (PCI) apparatus at 523, 573 and 623K. The hydrogenation properties of Mg-TiNi composites depended on the behavior of TiNi reinforcements. The formation of Mg hydride, MgH2, on 4h milling samples of Mg-10mass% TiNi intermetallics hinted to the catalytic behavior of TiNi reinforcements. In addition, the dehydriding profile at 573K revealed the two steps of plateau pressure, which were affected by the existence of multi hydride phases.

Superplasticity and texture of SiC whiskers in a magnesium-based composite

Abstract Superplastic deformation behaviors in a β-SiCw/ZK60 composite were investigated. The samples were tested at temperatures ranging from 613 to 723 K and at initial strain rates ranging from 8.3 × 10 −4 to 8.3 × 10 −2 s −1 . A maximum elongation of 200% was obtained at 613 K and at 1.67 × 10 −2 s −1 with a m -value of 0.35. The activation energy (98 kJ/mol) approximates to that for grain boundary diffusion (92 KJ/mol) in magnesium. A strong 〈 1 1 1 〉 fiber texture was formed in SiC whiskers during superplastic deformation, resulting from the matrix flow and interface sliding. The alignment of SiC whiskers restrains the grain boundary sliding of matrix alloy, and thus facilitates the growth and linkage of cavities, leading to a premature fracture of the composite.

Effect of reinforcements on strength of Mg9%Al composites

Magnesium-based composites reinforced respectively with four types of particulates at different volume fraction were synthesized through powder metallurgy rout. Mechanical properties show that incorporation of TiB 2 particulates leads to a reduction in the yield stress of the composite while use of ZrB 2 and SiC reinforcements enhances mechanical properties. TiC shows less effect on the yield stress of the composite. The strengths of the four composites increase with increasing volume fraction of particulates at initial stage while decrease at high volume fraction. The optimal volume fraction is about 8%.

Effect of the strain rate and temperature on the mechanical behaviour of a Mg–5%Zn alloy reinforced with SiC particles

Metal matrix composites (MMCs) have been found to be promising candidate for mechanical applications under impact and high temperature conditions beyond those possible with conventional alloys. Magnesium-based composites exhibit high specific properties compared to unreinforced magnesium and magnesium alloys. Both magnesium alloy and the same alloy reinforced with particles of silicon carbide were investigated in quasi-static and impact conditions in the temperature range from −150 to 200 °C. Quasi-static tests were performed on the universal testing machine (Instron), whereas impact tests (up to 700 s −1) were carried out on the split Hopkinson bar. Comparative results are presented in terms of the main mechanical parameters, and quantitative conclusions are obtained of the influence of temperature and strain rate on the mechanical behaviour of these materials.

Moisture effect on hydrogen storage properties of nanostructured [formula omitted]–V–Ti composite

In this paper, we present our recent results on the effect of moisture during prolonged cycling on hydrogen storage properties of nanostructured MgH 2 hydride with V and Ti catalysts additions synthesized by ball milling. The hydrogen charge and discharge stability of the nanocomposite hydride has been tested at 300° C for up to 1000 cycles under hydrogen containing 101 ppm moisture. Between the first and the 500th or 1000th cycle, an increase of hydrogen storage capacity by about 5% is observed in dynamic and PCT measurements. This could be due to structural relaxations. While absorption kinetics remain fast, the results show a significant and systematic slow-down of the desorption rates by about a factor of two during cycling. The X-ray diffraction patterns of nanocomposite performed before and after 1000 cycles reveal that the peak shape for magnesium remains unchanged indicating that the crystal growth is negligible. This microstructural stability during cycling suggests that the decreasing desorption rate of the nanocrystalline magnesium-based composite is not induced by any internal structural modification. On the other hand, the presence of moisture in the hydrogen gas during cycling induces surface effects which most likely cause the decrease of the hydrogen discharge flow rate.

Mechanical-stress relaxation in magnesium-based composites

In metal matrix composites (MMCs), the metal matrix is exposed to plastic deformation and damage accumulation in the region close to the reinforcements, following mechanical or thermal stresses. Mechanical spectroscopy has been used to study interface stress–relaxation in Mg–2%Si based MMC reinforced with either C aligned long fibers or Al2O3 short fibers. In the Al2O3/Mg–2%Si composite, the damping capacity is low; the mechanical stresses are relaxed by damage accumulation at interfaces. The elastic shear modulus decreases until rupture, when the composite is cycled at high vibration amplitude. On the contrary, the damping capacity is high in the C/Mg–2%Si composite and the interface stresses are relaxed by reversible motion of dislocations in the matrix, leading to a strong increase in fatigue resistance.

Characteristics of thermal cycling in a magnesium alloy composite

Acoustic emission (AE) and dilatometry were used to monitor the internal thermal stresses and the related structural changes and matrix plastic deformation induced in a magnesium-based composite during thermal cycling. It is shown that the AE response and the residual strain after cycling depend significantly on the upper temperature of cycling. The results are explained in a quantitative analysis using a model that correlates the internal thermal stresses with the change in temperature.

Microstructural factors affecting superplastic properties in magnesium-based composites

Effect of microstructural factors on superplastic behavior in magnesium-based composites was reviewed in order to obtain insights on ways to enhance the superplastic properties, such as highstrain-rate superplasticity, low-temperature superplasticity, and high ductility. The review shows that the reduction in grain size of the matrix directly increases the strain rate and/or decreases the temperature for optimum superplastic flow. The effect of reinforcement addition is shown to reduce the superplastic elongation, but enhance the superplastic strain rate, presumably owing to grain size stability of composites at high temperatures. Ductility enhancement is not necessarily attained by refining initial grain size. It is suggested that it is necessary to disperse the reinforcement uniformly in order to obtain higher ductility.

Low temperature superplasticity in a magnesium-based composite

Low temperature superplasticity in a magnesium-based composite