Magnesium Metal Matrix Composites Research Articles

An investigation of the microstructure and mechanical properties of B4C reinforced PM magnesium matrix composites

Due to their excellent properties such as high specific stiffness, strength/weight ratio, and wear resistance, metal matrix composites (MMCs) with particulate reinforcement and related manufacturing methods have become important research topics in recent years. Magnesium MMCs are materials that are commonly used for fabrication of light-weight functional components. Magnesium MMCs that are reinforced with various fractions of B4C (3, 6, and 9 wt.%) were fabricated by powder metallurgy (PM) technique using a sintering cycle in a vacuum furnace at 590°C for 9 h. A qualitative analysis of X-ray diffraction (XRD) patterns indicated the formation of Al2O3, MgO, and MgB2 phases in the structure of Mg/B4C MMCs. The sintered density of the MMCs decreased with an increase in the amount of B4C addition. The hardness of the MMCs was found to be higher than that of unreinforced Mg. The compressive test results also showed a significant effect of 3 wt.% B4C content on the compressive strength of magnesium MMCs manufactured by the PM technique.

Grain Refinement of AZ61/SiCp Magnesium Matrix Composites for Tubes Extruded by Hot Extrusion Processes

Magnesium (Mg) alloys are gaining more recognition as a lightest structural material for light-weight applications, due to their low density and high stiffness-to-weight ratio. Nevertheless, their ductility is still not good for further metal forming and their strength is not large enough for real structure applications. The aim of this paper is to develop new magnesium metal matrix composites (Mg MMCs) reinforced with SiC particles by the stir-casting method for the hot extrusion processes to produce tubes. AZ61/SiCp MMCs ingots reinforced with 1, 2, and 5 wt% SiC particles are fabricated by the melt-stirring technique. AZ61/SiCp MMCs tubes are manufactured by hot extrusion using a specially designed die-set for obtaining uniform thickness distribution tubes. Finally, the mechanical properties of the reinforced AZ61/SiCp MMCs and Mg alloy AZ61 tubes are compared with those of the billets to manifest the advantages of extrusion processes and addition of SiC particles. The microstructures of the billet and extruded tubes are also observed. Obvious grain size refinement both by addition of particles and extrusion process are discovered.

Tribological Properties of Magnesium Nano-Alumina Composites under Nano-Graphite Lubrication

The tribological behavior of magnesium metal matrix composites lubricated with graphite nanoparticles as additives in paraffin oil was investigated using a pin-on-disc wear tester. The results of nano-graphite-lubricated conditions are compared with the results of the tribotests carried out with micro-graphite additives in paraffin oil, pure paraffin oil, and dry sliding conditions. Wear tests were conducted at loads ranging from 15 to 60 N and sliding speeds varying from 1.25 to 3.15 m/s for a constant sliding distance of 1,600 m. The worn surfaces of the composites were analyzed through scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX) spectroscopy. Characterization of the tribolayer and subsurface deformation layer of worn-out composites was accomplished using a novel focused ion beam (FIB) milling technique. The wear resistance of the metal matrix composite was observed to decrease with increasing severity of testing conditions (i.e., applied load and sliding speed) when tested under a dry sliding condition and paraffin oil lubrication. Nevertheless, the wear rate of the composites when tested under nano- and micro-graphite lubrication conditions showed very little variation over the entire range of loads and sliding speeds. The low-order coefficient of friction for the nano-graphite-lubricated condition arose from the formation of a thick continuous graphite layer at the contact zone. The operating wear mechanism for micro-graphite and nano-graphite lubrication was established as a combination of smearing, forming, and transfer of the graphite layer.

Microstructure and Properties of Stir Cast AZ91 Mg Alloy – SiC<sub>p</sub> Composites

Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. Using stir casting process, AZ91 magnesium alloy metal matrix composites have been produced with different weight percentages (5, 10, 15, 20 and 25) of silicon carbide particles (SiCp) addition. Microstructural characterization reveals uniform distribution of SiC particles with good interfacial bonding between the matrix and reinforcement. Electrical conductivity and Co-efficient of Thermal Expansion (CTE) measurements carried out on these composites have yielded better properties. Improved mechanical properties such as hardness, ultimate tensile strength, and compressive strength are obtained. The microfracture mechanisms involved during tensile fracture is analyzed and correlated with the properties obtained.

Characterisation of magnesium matrix composite reinforced with SiC particulates manufactured by powder metallurgy method

Particle reinforced magnesium metal matrix composites (MMCs) and related manufacturing methods are among important research topics because of their low density, high specific stiffness, strength and wear resistance. SiCp/Mg composites are commonly used materials for fabrication of light-weight functional components. Magnesium powders with mean size of 69 mm were used as raw material while reinforcement material was selected as SiCp with the average particle size of 84 mm. Different amounts of SiCp (3, 6, and 9 wt. %) were added to the magnesium matrix and the composite materials were sintered in a vacuum furnace at 590°C. Structural characterisation of the produced composites was performed using several techniques such as scanning electron microscopy (SEM) and X-ray diffraction. The green density of the composite materials increased with SiCp addition. The hardness of the composites was found to be higher than the pure Mg. Reinforcement with 9 wt. % SiCp showed significant increase in the compressive strength of magnesium matrix composites.

G040036 Zn-22A1超塑性合金の摩擦撹拌重ね接合

Friction stir welding (FSW) is a relatively new solid state joining process primarily for aluminum alloys. FSW process can also be applied to the welding of a variety of other materials, including magnesium alloys, titanium alloys, stainless steels and metal matrix composites. However, very little information is available regarding FSW characteristics of superplastic alloys. In this study, trials with friction stir lap welding of superplastic Zn-22Al alloy were carried out on a modified milling machine. The results of FSW performed on superplastic Zn-22Al alloy were discussed in terms of the possibility of the development of bulk superplastic Zn-22Al alloy.

Development of Friction Stir Welding Apparatus for Steels

Friction stir welding (FSW) is a relatively new solid-state joining process primarily for aluminum alloys. FSW process can also be applied to the welding of a variety of other materials, including magnesium alloys, titanium alloys, stainless steels and metal matrix composites. While considerable experimental work has been done in FSW, there is little published information about FSW apparatus for steels. The development of new FSW apparatus for steels needs to proceed with caution and attention to detail and the reduced cost and time.The objectives of this study are to develop a FSW apparatus for steels and to discuss some initial results on FSW of mild steel.

Advanced Production Process and Properties of Die Cast Magnesium Composites Based on AZ91D and SiC

The driving force behind the efforts to develop magnesium metal matrix composites (MMC) via high-pressure die casting is the requirements for advanced applications under severe operational conditions in terms of stress, temperature, and corrosion resistance. Therefore this study aims to explore the mechanical properties of die cast Mg-MMC in terms of hardness and strength, as well as its corrosion resistance. AZ91D was chosen as the most commonly used magnesium alloy. The choice as the reinforcement agent that has to be an economical and non-reactive addition was silicon carbide particles (SiCP) with an average particle size of 10 μm. The challenge was production of high quality, homogeneous material with good mechanical properties and acceptable corrosion resistance. The results revealed the advantages of a die cast Mg-MMC as a new attractive alternative for advanced structural applications that can be used for mass production.

Coating formation by plasma electrolytic oxidation on ZC71/SiC/12p-T6 magnesium metal matrix composite

Plasma electrolytic oxidation (PEO) of a ZC71/SiC/12p-T6 magnesium metal matrix composite (MMC) is investigated in relation to coating growth and corrosion behaviour. PEO treatment was undertaken at 350 mA cm −2 (rms) and 50 Hz with a square waveform in stirred 0.05 M Na 2SiO 3.5H 2O/0.1 M KOH electrolyte. The findings revealed thick, dense oxide coatings, with an average hardness of 3.4 GPa, formed at an average rate of ∼1 μm min −1 for treatment times up to 100 min and ∼0.2 μm min −1 for later times. The coatings are composed mainly of MgO and Mg 2SiO 4, with an increased silicon content in the outer regions, constituting <10% of the coating thickness. SiC particles are incorporated into the coating, with formation of a silicon-rich layer at the particle/coating interface due to exposure to high temperatures during coating formation. The distribution of the particles in the coating indicated growth of new oxide at the metal/coating interface. The corrosion rate of the MMC in 3.5% NaCl is reduced by approximately two orders of magnitude by the PEO treatment.

Corrosion behaviour of carbon fibres/magnesium metal matrix composite and electrochemical response of its constituents

The corrosion behaviour of carbon fibres reinforced magnesium metal matrix composite (MMC) was investigated with emphasis on the galvanic corrosion arisen between the magnesium matrix alloy and the carbon fibres. The susceptibility of carbon/magnesium interface to degradation was also ascertained. The corrosion behaviour was studied in both neutral and alkaline aqueous solutions containing different concentrations of NaCl, using electrochemical techniques, hydrogen evolution test, optical microscopy and scanning electron microscopy (SEM) coupled with EDX and WDX capabilities. Two matrix alloys were used, AS41 and AS41(0.5% Ca). The latter monolithic alloy had a significantly higher corrosion resistance marked by Ca-addition, but the presence of carbon fibres in MMCs invalidated the beneficial effect of Ca. Carbon, as an electrically conductive element, is electrochemically unstable despite its almost chemical stability in aqueous chloride environments. Therefore, the polarisation diagrams of MMCs were demonstrated in terms of the electrochemical activity of carbon fibres. This necessitated performing the electrochemical polarisation tests, individually, on both Mg MMC, monolithic magnesium matrix alloy and carbon fibres electrode.

221 FSPによるZn-22Al共析合金の組織制御(加工による機能創製)

Friction stir welding (FSW) is a relatively new solid-state joining process primarily for aluminum alloys. FSW process can also be applied to the welding of a variety of other materials, including magnesium alloys, titanium alloys, stainless steels and metal matrix composites. In addition, FSW has been generating interest because of its association with friction stir processing (FSP), a new technique that essentially employs FSW tooling. FSP is being explored as a thermo-mechanical processing technique to transform a heterogeneous microstructure into a more homogenous microstructure. In this study, trials with FSP of superplastic alloys were carried out on a modified milling machine. The results of FSP on superplastic Zn-22Al alloy are discussed in terms of residual microstructure and the damping capacity.

Corrosion characterisation of alumina–magnesium metal matrix composites

Alumina magnesium metal matrix composites are a precious alternative for aerospace and automotive applications because of their high stiffness-to-weight ratio. A considerable deal of investigations had been devoted to their processing and mechanical properties, while the corrosion behaviour is still uncertain. In this study, the corrosion behaviour of Al 2O 3 fibres strengthened magnesium AS41 composite, in aqueous solutions containing various concentrations of NaCl at different pH values, was studied and compared with the behaviour of pure AS41 magnesium matrix alloy using electrochemical techniques, hydrogen evolution test, optical microscopy, and scanning electron microscopy (SEM) coupled with EDX and WDX capabilities. The results showed that the corrosion behaviour of the composite was comparable to its pure matrix alloy, yet a reduction in the corrosion resistance was observed in the composite at higher chloride concentrations. The corrosion mechanism involved, as well as the corrosion characteristics, was extensively discussed in terms of the effect of Al 2O 3 fibres. Also, an appropriate model describing the corrosion mechanism was proposed.

Effect of volume fraction and particle size on the microstructure and plastic deformation of Mg–Y 2O 3 composites

The plastic behaviour at room temperature of magnesium and magnesium metal matrix composites reinforced with yttria particles of two sizes is studied. All the materials are produced by powder metallurgy. During extrusion both the unreinforced magnesium and the composites develop a fibre texture with the { 1 0 1 ¯ 0 } planes perpendicular to the extrusion direction. The fibre intensity decreases as the volume fraction of yttria particles increases. A tension/compression asymmetry is observed. The extrusion texture prevents deformation by the basal slip system in both tension and compression. Deformation in the { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 1 〉 twinning system is only possible in compression. As the volume fraction of yttria particles increases, the texture becomes more random and the tension/compression asymmetry tends to decrease and is eventually reversed. The composites reinforced with the smallest ceramic particles present the highest yield stress.

Study on Properties of Carbon Nanotube/Magnesium Matrix Composite

Under the protection of argon gas, carbon nanotube reinforced magnesium metal matrix composite was made by stirring carbon nanotube into magnesium melts and formed by die casting. TEM and EDS methods were introduced to analyze boundary structure and chemical composition between carbon nanotube and magnesium metal matrix. The mechanical carbon nanotube properties of the composite were tested. Nickel chemical plating surface of carbon nanotube is favorable to adhesion of carbon nanotube to magnesium. Tests show that carbon nanotube, especially chemical nickel-plated one, has excellent role in strengthening the magnesium. The structure of magnesium was fined .The tensile strength, elongation, hardness and elastic modulus of the composite are improved.

Fabrication of TiB 2 particulate reinforced magnesium matrix composites by powder metallurgy

Magnesium metal matrix composites (MMCs) reinforced with 10, 20 and 30 vol.% TiB 2 particulates, respectively, were fabricated by powder metallurgy. The microstructure, porosity, hardness and abrasive wear behavior of the composites were evaluated. Microstructural characterization of Mg MMCs showed generally uniform reinforcement distribution. As compared with pure Mg, the hardness (HB) values of Mg MMCs reinforced with 10, 20 and 30 vol.% TiB 2 particulates were increased by 41%, 106% and 181%, respectively. The abrasive wear tests showed that the wear resistance of Mg MMCs is increased with the increasing of the reinforcement volume fraction. This was due to the strong particulate-matrix bonding and high hardness of the TiB 2 particulate.

Fabrication of B 4C particulate reinforced magnesium matrix composite by powder metallurgy

Magnesium metal matrix composites (MMCs) reinforced with various fractions of 10, 15 and 20 vol.% B 4C particulates fabricated by powder metallurgy (P/M) technique were investigated. Microstructure characterization of the composites revealed necklace distribution of B 4C particulates in the matrix material and the presence of minimal micro-porosity. The X-ray diffraction (XRD) showed the formation of MgO and MgB 2 in B 4C/Mg composites. Moreover, the results revealed that the hardness and wear resistance of the composites were higher than those of as-cast Mg ingot and increased with increasing amount of B 4C particulates from 10 to 20 vol.%.

YAG laser cladding of an Al-Si alloy onto an Mg/SiC composite for the improvement of corrosion resistance

Magnesium metal–matrix composites (MMCs) show great potential for industrial applications. But galvanic corrosion between magnesium matrices and the reinforcing constituents is a major concern when using these materials. Laser cladding onto an Mg/SiC composite was carried out for the enhancement of corrosion resistance in the present study. Results show that laser parameters, especially scanning velocity, have significant influences on both the microstructure and the corrosion resistance. When laser power was kept at 500 W, the laser-clad coating at 8 mm s −1 displayed three layers, i.e. the undiluted layer, the diffusive layer and the interfacial layer. Increasing scanning velocity to 10 mm s −1 caused the elimination of the diffusive layer whilst decreasing scanning velocity to 5 mm s −1 induced the absence of the undiluted layer. An increase of laser power to 600 W resulted in rough surface and porosity in the coating. The undiluted layer has a fine Al–Si eutectic structure and the diffusive layer consists of aluminium, Al–Si eutectic and Mg 2Si phase. The corrosion resistance of the Mg/SiC composite has been significantly improved by using YAG laser cladding treatment, especially, at a scanning velocity of 10 mm s −1.

Application of model for work hardening behaviour of SiC reinforced magnesium based metal matrix composites

An understanding of the work hardening behaviour of particulate reinforced metal matrix composites is crucial in optimising the parameters for deformation processing of these materials. In the present study, SiC reinforced magnesium metal matrix composites were produced using a liquid phase process. The microstructure of the composite was characterised and the mechanical properties were determined. The results of the ambient temperature tensile testing on the extruded Mg and Mg/SiC specimens revealed that an increase in the weight percentage of SiC particulates in pure magnesium increases the elastic modulus, does not affect the 0·2% yield strength, and reduces the ultimate tensile strength and ductility. A modified continuum model was applied to relate the work hardening behaviour of the composites to microstructural parameters and to predict the fracture strain of the composites. The model is shown to predict the fracture strain of the composites quite accurately for all the three weight fractions of reinforcements evaluated in the present study.

Processing, microstructure, and mechanical behavior of cast magnesium metal matrix composites

Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. This article presents a liquid mixing and casting process that can be used to produce SiC particulate-reinforced magnesium metal matrix composites via conventional foundry processes. Microstructural features, such as SiC particle distribution, grain refinement, and particle/matrix interfacial reactions of the cast magnesium matrix composites, are investigated, and the effects of solidification-process parameters and matrix alloys (pure Mg and Mg-9 pct Al-1 pct Zn alloy AZ91) on the microstructure are established. The results of this work suggest that in the solidification processing of MMCs, it is important to optimize the process parameters both to avoid excessive interfacial reactions and simultaneously achieve wetting, so that a good particle distribution and interfacial bonding are obtained. The tensile properties, strain hardening, and fracture behavior of the AZ91/SiC composites are also studied and the results are compared with those of the unreinforced AZ91 alloy. The strengthening mechanisms for AZ91/SiC composite, based on the proposed SiC particle/matrix interaction during deformation, are used to explain the increased yield strength and elastic modulus of the composite over the magnesium matrix alloy. The low ductility found in the composites is due to the early appearance of localized damages, such as particle cracking, matrix cracking, and occasionally interface debonding, in the fracture process of the composite.

On the wear of aluminium and magnesium metal matrix composites

The effect of fibre reinforcement of aluminium, magnesium and Mg-9Al-1Zn on the wear properties has been investigated. Dry sliding, two- and three-body abrasion and solid particle erosion testing were performed. The results show that the tribological behaviour of metal matrix composites (MMCs) depends very much on the type of MMC and the type of contact situation, i.e. tribosystem. The dominant wear mechanisms are identified by light optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. In dry sliding an optimum wear resistance was obtained at a fibre content of approximately 10%. Magnesium and the magnesium alloy showed an increasing two-body abrasion resistance with increasing fibre content while no positive effects were observed in three-body abrasion. The abrasion rate of aluminium was not affected by the fibre content. In erosion, aluminium and magnesium displayed decreasing wear resistance with higher fibre content whereas the magnesium alloy was hardly affected. The relations between wear rate, wear mechanisms and matrix parameters are discussed.