Synthesis and characterization of 356-SiC_p composites by stir casting and compocasting methods

Stir casting is one of the simplest ways of producing aluminum matrix composites.However,it suffers from poor incorporation and distribution of the reinforcement particles in the matrix.These problems become especially significant as the reinforcement size decreases due to greater agglomeration tendency and reduced wettability of the particles with the melt.Development of new methods for addition of very fine particles to metallic melts which would result in more uniform distribution and effective incorporation of the reinforcement particles into the matrix alloy is therefore valuable.In this work,356-5%SiCp(volume fraction) composites,with average SiCp sizes of about 8 and 3 μm,were produced by injection of different forms of the reinforcement particles into fully liquid as well as semisolid slurries of 356 aluminum alloy and the effects of the injected reinforcement form and the casting method on distribution of the reinforcement particles as well as their porosity,hardness and impact strength were investigated.The results reveal that addition of SiC particles in the form of(Al-SiCp)cp composite powder and casting in semisolid state decreases the SiCp particle size,enhances the wettability between the molten matrix alloy and the reinforcements and improves the distribution of the reinforcement particles in the solidified matrix.It also increases the hardness and the impact energy of the composites and decreases their porosity.

Compocasting of A356-CNT composite

A356 aluminum alloys reinforced with carbon nano-tubes (CNTs) were produced by stir casting and compocasting routes and their microstructural characteristics and hardness were examined.In order to alleviate the problems associated with poor wettability, agglomeration and gravity segregation of CNTs in the melt, CNTs were introduced into the melts by injection of CNT deposited aluminum particles instead of raw CNTs.Aluminum particles with mean diameters of less than 100 μm were first deposited by CNTs using Ni-P electroless plating technique and then injected into the melt agitated by a mechanical stirrer.The slurry was subsequently cast at temperatures corresponding to full liquid as well as 0.15 and 0.30 solid fractions.The results show that addition of CNTs to A356 matrix can significantly refine both full liquid and semi-solid cast microstructures.Hardness of the samples is also significantly increased by addition of CNTs and A356-CNT composite cast at 0.3 solid fraction produces the highest hardness.

Effects of compocasting process parameters on microstructural characteristics and tensile properties of A356-SiC_p composites

The effects of compocasting process parameters on some structural and tensile characteristics of the A356-10% SiCp (volume fraction) composites were studied. Semisolid stirring was carried out at temperatures of 590, 600 and 610 °C with stirring speeds of 200, 400 and 600 r/min for 10, 20 and 30 min. The distribution of the SiC particles within the matrix, porosity content and tensile properties of the obtained samples were examined. The structural evaluations show that by increasing the stirring time and decreasing the stirring temperature, the uniformity in the particle distribution is improved;however, by increasing the stirring speed the homogeneity firstly increases and then declines. It is also found that by increasing all of the processing parameters, the porosity content is enhanced. From the tensile characteristics viewpoint, the optimum values of the speed, temperature and time are found to be 400 r/min, 590 °C and 30 min, respectively. The contribution of the reinforcement distribution uniformity prevails over that of the porosity level to the tensile properties.

Comparison of microstructure and wear resistance of A356-SiC_p composites processed via compocasting and vibrating cooling slope

The influences of SiC content on the microstructure, porosity, hardness and wear resistance of A356？SiCp composites processed via two different methods of compocasting and vibrating cooling slope （VCS） were compared with each other. In the as-cast condition, the matrix of VCS and compocast processed composites exhibited globular and dendritric structures, respectively. While a more uniform distribution of SiC particulates in the matrix alloy as well as higher hardness values were obtained for the VCS processed samples, the composites produced via compocasting exhibited less porosity. The increased SiC content （up to 20% in volume fraction） resulted in a more uniform distribution of SiC particles within the matrix alloy and improved wear resistance for both the composite series. However, for the VCS processed composites, the increased SiC content, resulted in the decreased size and shape factor of globules as well as better tribological properties when compared with compocast composites. It was concluded that the improved properties of the VCS processed composites when compared with their compocast counterparts was a consequence of a more uniform distribution of SiC particulates in the matrix alloy as well as the globular microstructure generated during the VCS process.

Microstructure, mechanical and tribological properties of A390/SiC composite produced by compocasting

Aluminum A390 alloys reinforced with 10 wt.%SiC composite,were produced by the compocasting method.The effects of temperature,time,and stirring speed of this compocasting method on the microstructure,mechanical and tribological properties of composite were investigated.The results indicated that with increasing the rotational speed from 450 to 550 r/min,the distribution of the SiC particles becomes more uniform.A sudden increase in porosity due to gas absorption results in a downtrend of elongation with an increase in stirring speed from 550 to 650 r/min.Furthermore,as the stirring time increases,the amount of agglomerates of primary Si particles is reduced,and a more uniform microstructure of SiC and Si particles is formed.Although the fracture mode is a combination of both brittle and ductile fractures,the main mechanism of the fracture in the compocast sample is ductile.The formation of a protective layer at a high temperature can result in a very low wear rate as compared to a wear test performed at a low temperature.Optimal particle uniformity and mechanical properties were obtained at processing parameters of 610刟C,550 r/min,and 20 min.

Production and characterization of rich husk ash particulate reinforced AA6061 aluminum alloy composites by compocasting

Rice husk ash(RHA) is a potential particulate reinforcement to produce aluminum matrix composites(AMCs)economically.Compocasting method was applied to produce aluminum alloy AA6061 reinforced with various amounts(0,2%,4%,6%and 8%,mass fraction) of RHA particles.The prepared composites were characterized using X-ray diffraction and scanning electron microscopy.X-ray diffraction patterns of AA6061/RHA AMCs revealed the presence of RHA particles without the formation of any other intermetallic compounds.The scanning electron micrographs showed a homogeneous distribution of RHA particles all over the aluminum matrix.Intragranular distribution of RHA particles was observed.Further,RHA particles were bonded well with the aluminum matrix and a clear interface existed.The reinforcement of RHA particles enhanced the microhardness and ultimate tensile strength(UTS) of the AMCs.The tensile behavior is correlated to the microstructure of the AMCs.

Tribological behavior of A356-CNT nanocomposites fabricated by various casting techniques

Tribological behaviors of monolithic A356 aluminum alloy castings and A356.CNT nanocomposite castings, fabricated by fully liquid and semisolid routes were examined. Samples were prepared by melt agitation, rheocasting, stir casting, and compocasting techniques. Effects of addition of carbon nanotubes (CNTs), casting process and the applied load on wear properties and mechanisms were investigated. It was found that wear loss, wear rate and friction coefficient of nanocomposite samples remarkably declined by the addition of CNTs. Moreover, changing the casting process from fully liquid to semisolid routes, plus increasing fractions of the primary phase were the two factors that improved the wear properties of the investigated samples, especially nanocomposite ones. In addition, it was revealed that adhesion and delamination were the dominant wear mechanism of the monolithic samples produced by fully liquid and semisolid routes, respectively. However, regardless of fabrication techniques, the abrasion was the main wear mechanism of nanocomposite samples.

Processing and Mechanical Properties of Al2O3 and Red Mud Particle Reinforced AA6061 Hybrid Composites

Aluminum 6061 alloy metal matrix composites (MMCs) reinforced with four different weight fractions of (Al2O3 + red mud) particles up to 10 wt% were fabricated by a vortex method. The effects of reinforcement content on the mechanical properties of the composites such as hardness and tensile strength were investigated. The density measurements showed that the samples contained little porosity, and the amount of porosity in the composites increased with increasing weight fraction of particles. Scanning electron microscopic observations of the microstructures revealed that the dispersion of the particles was uniform with small clusters at some places and porosity. The results showed that the hardness and the tensile strength of the composites increased with increasing weight fraction of particles.

Erosive wear properties of ZA-27 alloy-based nanocomposites: Influence of type, amount, and size of nanoparticle reinforcements

Metal matrix nanocomposites(MMnCs)comprise a metal matrix filled with nanosized reinforcements with physical and mechanical properties that are very different from those of the matrix.In ZA-27 alloy-based nanocomposites,the metal matrix provides ductility and toughness,while usually used ceramic reinforcements give high strength and hardness.Tested ZA-27 alloy-based nanocomposites,reinforced with different types(Si C and Al2O3),amounts(0.2 wt.%,0.3 wt.%,and 0.5 wt.%)and sizes(25 nm,50 nm,and 100 nm)of nanoparticles were produced through the compocasting process with mechanical alloying pre-processing(ball milling).It was previously shown that the presence of nanoparticles in ZA-27 alloy-based nanocomposites led to the formation of a finer structure in the nanocomposites matrix and an improvement in the basic mechanical properties(hardness and compressive yield strength)through the enhanced dislocation density strengthening mechanism.Solid particle erosive wear testing demonstrated that these improvements were followed with an increase in the erosive wear resistance of tested nanocomposites,as well.Additionally,by analyzing the influences of type,amount,and size of nanoparticles on the erosive wear resistance of nanocomposites,it was demonstrated that there is an optimal amount of nanoparticles,which in our case is 0.3 wt.%,and that the presence of SiC nanoparticles and smaller nanoparticles in nanocomposites had more beneficial influence on erosive wear resistance.