Papers by Keyword: Magnesium Matrix Composite

Abstract: Hexagonal boron nitride (h-BN) is a ceramic material with high thermal conductivity (TC) and low coefficient of thermal expansion (CTE), which can improve multiple thermal properties of metal-matrix composites as a reinforcing particle, but its wettability with metal melt is very poor. In order to enhance the wettability between the h-BN and magnesium alloy melt, the electroless plating was used to coat a thin layer of pure nickel on h-BN particles, which was proved to be effective and efficient in this study. The results showed that by adding Y element to magnesium alloy melt to consume Ni element melted from the nickel-plating layer, the long period stacking ordered (LPSO) structure composed of Mg-Ni-Y was successfully formed, and the magnesium matrix composite reinforced by hybrid h-BN and LPSO structure was obtained. After ultrasonic treatment (UT), the TC of the magnesium composite containing 3 vol% h-BN and 14.16 vol% LPSO is 99.92 W/(m·K), which is a 8.3% enhancement compare to the composite without UT. The average CTE (293-373 K) of the composite is 18.36×10^-6 K^-1, which is reduced by 29.4% compared with pure magnesium.

Abstract: In the experiment reported in this paper, the friction coefficient (μ) and the mass loss of the metal matrix composite obtained from a powder mixture of Mg, Ti and Al sintered at 640, 650 and 660^ºC, with the other parameters held constant, were determined in the dry sliding test at the total distance of 120 m. The sliding speeds of 0.06, 0.09 and 0.14 m/s, and the loads of 2.3, 5 and 9.3 N were applied, as well as a slider made of the EN-GJL300 cast iron. The value of the friction coefficient decreased with the speed and the load, and, for most of the applied friction parameters, it was very low (0.025-0.2). Some influence of the sintering temperature on the mean value of μ and the profile of μ versus the friction distance curve was revealed, yet in the case of the lowest friction speed and load only. An increase of the composite mass loss with the load was revealed, but the wear was generally very low. For a characterization of the composite and its surface after tribological tests, a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS) was employed. On the worn surface, effects of abrasion and deformation were visible, but no Ti particle degradation or pulling out were found.

Abstract: The application of short carbon fibers in magnesium alloy AZ31 matrix composite fabrication by cold chamber pressure die casting was presented. A technological procedure of small-sized and complex-shaped composite casts manufacturing was shown. The microstructure of the composite was characterized as well as its mechanical properties, friction coefficient and wear resistance. The application of mechanical stirring of melted AZ31 alloy with short fibers and then AZ31-Cf suspension pressure die casting ensured obtaining casts with the reinforcing phase correctly distributed and well bonded with the matrix. Comparision of the AZ31-Cf composite with the AZ31 alloy properties, cast in the same conditions, revealed a considerable increase in bending strength and hardness, and some improvement of ductility and sliding friction parameters as a result of short carbon fibers application.

Abstract: The microstructure and corrosion behaviour of AM50/SiC magnesium matrix composites reinforced with SiC particles were investigated. Composites containing 10 wt. % of SiC were fabricated by means of gravity casting. Technical grade silicon carbide used for the composites fabrication was subjected to a purification procedure leading to the removal of iron containing impurities from its surface. The corrosion resistance of the composite with purified SiC particles was compared to the corrosion resistance of the one containing crude technical grade silicon carbide as well as to the corrosion resistance of the matrix alloy. Voltammetry and an electrochemical noise technique as well as hydrogen evolution rate measurements were utilized for that purpose. Corrosion tests were performed in 0.5 mol dm³ NaCl saturated with Mg (OH)₂. It has been demonstrated that the composite containing purified SiC was less susceptible to corrosion than the one containing crude SiC particles. Both composites were less resistant to corrosion than their matrix itself. Regardless of a purity level of SiC which was used for the composites fabrication, the same constituents were revealed in their microstructure, namely: α-phase (a solid solution of aluminium in magnesium), fully divorced eutectic α + γ (where γ-phase is Al₁₂Mg₁₇), intermetallic compound Al₈Mn₅ and SiC particles uniformly distributed in the whole volume of the matrix.

Abstract: In the presented experiments, the influence of a liquid magnesium alloy with Zr and RE reinforced on glassy carbon particles (GCp) in composites obtained by the mechanical mixing of a suspension, its pressureless solidification and by pressure die casting was examined. The microstructure of the as-received GCp and after their isolation from the composite was characterized by SEM and EDS methods. The presence of a thin oxide type layer with a high RE content was found, independent of the applied composite technology.

Abstract: Magnesium alloys containing yttrium and neodymium are known to have high specific strength, good creep and corrosion resistance up to 523 K. The addition of ceramic particles strengthens the metal matrix composite resulting in better wear and creep resistance while maintaining good machinability. In the present study, WE43 magnesium matrix composite reinforced with SiC and carbon particulates were fabricated by stir casting. The microstructure of the composite was investigated by optical microscopy, quantitative metallography, scanning electron microscope and XRD analysis. Microstructure characterization of WE43 MMC showed inhomogeneous reinforcement distribution and presence of shrinkage porosity. Reinforcing particles are well bonded with the matrix, however, in some cases thin reaction layers was detected. The presence of SiC particles assisted in improving hardness.

Abstract: In-situ micro/nanosized TiB₂ and Al₂(Y, Gd) particles reinforced magnesium matrix composite was successfully fabricated by addition of Al-Ti-B preform into Mg-Gd-Y-Zn matrix alloy, its microstructures and properties were investigated. The results show that the introduction of Al-Ti-B preform causes the precipitation of Al₂(Y, Gd) particles and the SHS synthesis of TiB₂ particles which significantly refine solidification structure. The reinforced Al₂(Y, Gd) particles with average sizes of 5-8 μm are uniformly distributed throughout the magnesium matrix, and have a good bond to the matrix. Tensile tests indicate that, compared with the former matrix alloy, mechanical properties of the multiple in-situ particles reinforced composite are improved all-roundly.

Abstract: The microstructure evolution and mechanical properties of Mg₂B₂O₅ whiskers reinforced AZ31B magnesium composite during extruded were investigated using optical microscope and scanning electron microscope. Mg₂B₂O₅w/AZ31B was fabricated by stir-casting and the as-cast ingot was machined into cylindrical billets. Then the hot extrusion was carried out at 350°C at a constant speed of 10 mm/s with extrusion ratio of 6.25:1. The mechanical properties (strength, ductility and hardness) were tested by tensile tests and hardness tests at room temperature. Typical microstructures of different positions of extruded stock showed the microstructure evolution law during extrusion processing. It was found that DRX took place and whiskers accelerated DRX during hot extrusion. The whisker distribution in the composites was improved by hot extrusion. Additionally, the vickers microhardness of the composites increased first, and then decreased with deformation degree increased.

Abstract: Magnesium alloys have high specific strength, specific stiffness, excellent thermal conductivity and casting properties, which have a great prospects development in the industry, However, its low plasticity and ductility limited its application. Magnesium matrix composites can effectively improve its performance. Magnesium alloy die-casting is the main forming process, the conventional high-pressure die-casting (HPDC) defects in multi-cavity type, easy to volume gas, non-heat-treated. Compared with HPDC, the rheo-diecasting (RDC) process has been greatly developed for near-net shape components. In this paper, Mg2Si /AM60 composites is fabricated by in-situ synthesis and semi-solid magnesium matrix composites which are rheoformed in the die-casting machine are prepared by mechanical stirring. The results indicate that the microstructure of composites is non-dendritic and Chinese script type Mg2Si are fine distributed. The fundamental morphology of microstructure by HPDC is dendrite and liquid-phase distributed between dendrite irregularly. The RDC samples have close-to-zero porosity, less segregation, the most of semi-solid of microstructure in rheo-diecasting is spherical or as-spherical structure.

Abstract: AZ91D alloy composites reinforced by CNTs/SiCp were fabricated using stir casting process. The mechanical properties of the composites were tested, observed and analyzed the microstructure, the fractographs were observed and analyzed via scanning electron microscope. The results showed that CNTs/SiCp could not only refine the grains of the composites, but also bear the load of resistance to deformation. Compared with the matrix alloy, the tensile strength, the elastic modulus, the micro-hardness and the elongation rate of the composites had been enhanced significantly. But the mechanical properties would be fell down with the more addition of CNTs/SiCp.