PROPERTIES OF ALUMINIUM/ELECTROLESS Ni-COATED SiC COMPOSITES - A REVIEW

The combination of properties of Al/SiC composites make them very attractive materials for applications in automotive and aerospace industries. Several techniques are used in developing Al/SiC composites but stir casting process is most commonly used because it is the simplest and cost effective technique. However, composites produced via stir casting suffer from limitations such as low wettability and inadequate bonding between the molten Al & SiC particulates and the formation of degrading interfacial products like aluminum carbide (Al4C3) which degrades the mechanical properties of the composite. Some of the techniques to improve Al-SiC wettability include addition of surface active elements such as magnesium, heat treatment of particles and application of metallic coating on the reinforcements before addition to the melt. Wetting agents alter the composition of the matrix alloy, while heat treatment of the reinforcement does not completely prevent the formation of Al4C3 when utilized. To reduce the direct interaction and promote wetting between reinforcements and molten aluminum during processing, the surface of SiC particulates can be modified by coating via oxidation, sol-gel and electroless processes. Of all these methods, electroless nickel deposition produces the best coatings with uniform thickness and adequate strength. In the present study, influence of electroless nickel-coating of SiC on the mechanical, corrosion and microstructural properties of Al/SiC composite has been evaluated. Finally, it can be concluded that the Ni and Ni3P intermetallic phases produced via electroless coating improves the wettability between the SiC and molten aluminium leading to enhanced properties of the composite.

Fabrication and Investigation of Mechanical Properties of SiC Particulate Reinforced AA5052 Metal Matrix Composite

In this present research particulate reinforced aluminium metal matrix composites are developed by using sand mould and liquid stir casting processing route in which AA5052 reinforced with 5 wt. % SiC particulates of 63µm particle size. The density, porosity, micro-hardness, and compressive strength of SiC particulate reinforced AA5052 MMC were investigated and compared these properties with similar properties of unreinforced AA5052. The microstructure of the developed composite was also analysed by using optical microscopy, SEM, and XRD. Developed particulate reinforced Al metal matrix composite gives improved hardness and compressive strength as compared to the unreinforced AA5052. The addition of 5 wt. % SiC particulates increases the density of AA5052.

Effect of SiC Defects on Performance of Particle Reinforced Aluminum Matrix Composites

The effect of segregation defect of SiC particles on the properties of materials was studied. 15% SiCp/2009Al composites were prepared by powder metallurgy (PM). Special SiC/Al samples were added to 15% SiCp/2009Al composites. These SiC/Al samples with different sizes and volume fractions were 25%, 35%, 45% and 60%, respectively, which resulted in SiC particulates segregation defect. The 15% SiCp/2009Al composites with defects were tested by ultrasonic testing. Tensile samples were obtained at the locations, where defects might be detected and the mechanical properties were tested. The results showed that all defective samples were cracked at the defective location. The difference in tensile strength between the samples of defect and the samples without defect was large. The toughness of the sample containing the defect reduced and the brittleness increased. The dimples on the matrix indicate that ductile fracture occurred during the fracture process. The cleavage fracture or cracking of the SiC particulates indicated that the stress can be effectively transferred from the matrix to the particles, and the particulates strengthen the matrix well. However, the sample with defect led to brittle fracture in the defect, and a crack source produced at the interface, resulting in a significant decrease in the mechanical properties of the material. If the inhomogeneous distribution of particulate containing a large area was found in the ultrasonic testing of the aluminum matrix composites, the tensile properties of the products generally cannot meet the requirement for application.

Fabrication and analysis of AA6082/Si3N4 and AA6082/SiC composites

Purpose Sound microstructure components are necessary for reliability and safety; hence, these components are used in aircraft, satellite, automobiles and ships, where many commercial alloys are not suitable. The paper aims to discuss this issue. Design/methodology/approach AA6082/Si3N4 and AA6082/SiC composites were fabricated using the stir-casting process considering 5, 10 and 15 vol.% of reinforcement particles. Density and porosity of AA6082/Si3N4 and AA6082/SiC composites were calculated. Characterization was done using an X-ray (EDX) detector, attached to SEM. The effect of addition of Si3N4 and SiC particulates in the AA6082 was investigated. Findings Results showed that Si3N4 and SiC particulates had good wettability with AA6082 and were uniformly distributed in AA6082 matrix. No adverse effects of reactions were noticed in the microstructure of AA6082/Si3N4 and AA6082/SiC composites. Research limitations/implications AA6082 with more than 15 vol.% of Si3N4 and AA6082/SiC reinforcement particles do not find industrial application where high hardness and tensile strength are required. Practical implications Components made from AA6082/Si3N4 and AA6082/SiC composites find their application where high hardness with better tensile strength is required. Social implications Naturally and locally available materials are utilized for fabrication. Originality/value Little work is available in the literature on fabrication and characterization of AA6082/Si3N4 and AA6082/SiC composites. The authors have identified the process parameters at which proper fabrication is done and sound microstructure is obtained.

Experimental investigation of abrasive assisted hybrid EDM of Ti-6Al-4V

Hybrid electric discharge machining (EDM) has been a promising technique for improving overall machining efficiency for hard-to-cut material. This, to some extent, has been related to the conventional EDM being incompetent for mass production owing to low material removal and reduced surface quality. Hence, the powder mixed electrical discharge machining (PMEDM) hybridized with abrasive jet machining (AJM) has been carried out. The tool wear rate (TWR), material removal rate (MRR) and surface finish study of titanium (Ti-6Al-4V) have been investigated. This hybrid EDM has been performed with and without abrasive jet flushing for evaluation of various eminent responses, namely MRR, TWR and SR, taking into account the input process parameters. Copper electrodes with variable inner hole diameter were used for machining of workpiece in SiCp mixed dielectric fluid. The experiments were planned and analyzed using Taguchi approach. This machining route revealed an appreciable enhancement in MRR when coupled with abrasive jet flushing and enhanced surface finish at the same time. The tool wear was significantly affected by peak current and use of SiC particulates in dielectric. In abrasive mixed flushing technique, an increase in tool erosion was spotted. Moreover, hole size, pulse-off and abrasive mixed dielectric proved to be influential in declining the surface finish of the finished component. The SEM analysis of Ti-6Al-4V samples put forward that pulse-on duration, current and type of dielectric fluid exhibited a vital influence on the topology and microstructure of machined surfaced along with their interactions.

INVESTIGATION ON THE DEPOSITION RATES OF ELECTROLESS Ni–P/NANO-SiC PLATING WITH THE ASSISTANCE OF ELECTROMAGNETIC FIELDS

The nano-SiC/Ni–P composite coatings (nSNCCs) were fabricated on the surface of Glass substrates with the assistance of different electromagnetic fields. Then, the deposition rates of the nSNCCs were calculated by the weighing method. Morphology, chemical composition and crystal structure were characterized by SEM, EDS and X-ray diffraction (XRD), respectively. Experimental results show that the nSNCCs are all built by the accretion of spherical co-deposition product of Ni solid solution and nano-SiC particulates. Moreover, at the same plating time, the deposition rates of the nSNCCs increase with the increasing magnetic strength, and reach the peak by 17.5[Formula: see text]g/h[Formula: see text]m[Formula: see text]. Meanwhile, the spherical particle size and the spaces between spherical co-deposition decrease, which result in the formation of the dense layers. The addition of magnetic fields in preparation process not only promotes the deposition of the nSNCCs, but also has a great influence on the orientation of the deposited products, which is favorable for the formation of a compact and uniform composite coating.