Al-metal matrix composites (AMMCs) reinforced with diverse volume fraction of SiC nanoparticles were synthesized using microwave sintering process. The effects of the reinforcing SiC particles on physical, microstructure, mechanical, and electrical properties were studied. The phase, microstructural, and surface analyses of the composites were systematically conducted using X-ray diffraction (XRD), scanning electron microscope (SEM), and surface profilometer techniques, respectively. The microstructural examination revealed the homogeneous distribution of SiC particles in the Al matrix. Microhardness and compressive strength of nanocomposites were found to be increasing with the increasing volume fraction of SiC particles. Electrical conductivity of the nanocomposites decreases with increasing the SiC content.
The weight reduction in automotive industry is very critical as it improves the engine efficiency and greatly contributes to improve the fuel economy with current power trains. This is the reason that the aluminum alloys are widely used in engine and chassis components. The practice of using aluminum and magnesium castings in the automotive industry had grown rapidly in the past few years, aiding engineers to design and fabricate more fuel-efficient automobiles. Metal Matrix Composites (MMCs) are widely used in different areas of automotive, aerospace, and many other industries, along with the wide applications in the individual’s daily life [
Among all the metal matrix composites, Al composites are the focus point in the leading up growing industries and technology. It can be used in aircraft and in cars and automotive vehicles. They also can be widely used in aerospace and military defence equipment due to their resistance and strength, which help in reducing the gas emissions and improve the future of the fuel economy, by developing a light weight material with the possible acquired performance [
AMMCs are known to possess high performance and light weight that combines all its metallic properties with ceramic properties to create light and at the same time hard materials. Many extensive researches are being done to investigate and enhance the AMMCs performance to meet the commercial conditions applications, which is one of the most important parameters that control the manufacturing process and cars leading market. The industrial demands and manufacturing conditions keep changing with time, which is the main reason to find and investigate new materials, new alloys, and new metal-metal composites [
Most of the recent studies show an interest in metal matrix composites especially the Al composites, since they have many applications in many areas. One of many problems facing this kind of research is the type of the proper bonding between the reinforcement particles and the matrix. Researchers focus on the importance of the reinforcement bonding, chemical stability, and compatibility, in order to produce materials with proper mechanical characters that satisfy the fabrication stand points [
In general, the metal oxides (Al2O3, SiO2) and nitrides and carbides (B4C and SiC) were used as sintering reinforcements to improve the hardness, strength, and relative density of the metal matrix composites. Using different synthesis routes, such as powder metallurgy and spark plasma sintering, each technique has its own specific parameters and method to apply. Other manufacturing method variables that affect the final product and the AMMC composite properties include the matrix alloys, the heat and temperature treatment condition, the particle size, and volume fraction. Satisfying all the mentioned properties would result in increasing the strength of the matrix with good interfacial strength of the bonded particulates, resulting in enhanced properties [
In this study, SiC nanoparticles (0.3, 0.6, and 0.9 vol.%) reinforced Al matrix composites were synthesized using powder metallurgy process followed by microwave sintering technique. The physical, microstructure, conductivity behaviour, and mechanical properties of the composites, including their compression strength and yield strength, were investigated.
The commercially available elemental aluminum (APS 10
Al was used as matrix material; SiC with amount of 0.3, 0.6, and 0.9 vol.%, respectively, was used as the reinforcement in the composites. The powders were blended for 30 min using high-energy ball mill with the rotation speed of 200 rotations per minute (rpm). At this stage no balls were used to prevent particles size reduction. After blending, the mixed powders were then compacted into cylindrical pellets in hydraulic press unit by applying uniaxial compression pressure of 20 MPa and the load was maintained for two minutes under ambient conditions. The maximum pressure was optimized to get better densification and to avoid porosity in the pellets. The green compacted pellets were then subjected to sintering process. Sintering is the most important step in the synthesis of composites, as the sintering temperature and soaking time play an important role in the mechanical and physical properties of the final product. The microwave sintering process was carried out in a microwave furnace which has a silicon carbide ceramic crucible with alumina insulation as inside lining of the furnace (VB Ceramic Consultants, Chennai, India). The samples were placed in the central cavity and sintered in a microwave furnace (multimode cavity) at 2.45 GHz. SiC was selected as a microwave susceptor to aid the heating during the sintering process of the composites. The sintering process temperature was set at 550°C ± 5°C with a 30 min holding time and a heating rate of approximately 25°C/min. The sintered samples were left to slowly cool down to room temperature. The schematic diagram of the microwave sintering set-up and as-developed samples are shown in Figure
(a) Schematic diagram and (b) as-prepared samples of Al-SiC nanocomposites.
The percentage of dimensional shrinkage was calculated by measuring the diameters of the composites before and after the sintering process. X-ray diffraction diagram of the sintered composites samples was carried out using an automated Shimadzu diffractometer. The samples were exposed to Cu
The Al-SiC starts to contract, when a specific temperature is reached. As the temperature increases the thermal redundancy of the composites continues. The thermal redundancy stops at the sintering temperature during the dwell time, but the contracting continues as a sintering effect.
As shown in Figure
Variation of shrinkage with SiC percent.
The X-ray diffraction patterns of Al-SiC nanocomposites with different volume fractions of the reinforcement are presented in Figure
XRD patterns of Al-SiC nanocomposites.
The XRD results reveal that main elements present are Al (largest peak) and SiC (shorter peak).
The microstructure of the Al-SiC nanocomposites was investigated by SEM and the corresponding micrographs are shown in Figure
(a–c) SEM micrographs of Al-SiC nanocomposites and (d) EDX spectrum of Al-0.9 vol.% SiC nanocomposite.
The tendency of agglomeration at higher volume fractions of reinforcement arises, because of the large difference in the sizes of Al powder and SiC particles. The nanosized powders tend to fill in the interstitial spaces between the aluminum powders during mixing and compaction. Previous studies had reported that agglomeration of SiC particles in Al matrix resulted in the degradation of mechanical properties, as reinforcement clustering along with voids in the particles acted as preexisting cracks, limiting the stress transfer from the soft matrix to the hard reinforcements during deformation [
The atomic force microscopic (AFM) analysis is ideal for quantitatively measuring the nanometric dimensional surface roughness and for visualizing the surface texture of the nanocomposites. Two dimensional (2D) and X-ray profile AFM images of pure Al and 0.3, 0.6, and 0.9 vol.% SiC nanoparticles reinforced Al nanocomposites are shown in Figures
(a–d) Surface morphology of Al-SiC nanocomposites under profilometer.
The composites hardness is a property related to the material ability to resist plastic deformation. Factors that can change or influence the disruption movement can affect Al-SiC nanocomposites hardness. The composite hardness value depends on different factors, such as the volume fraction and density of the reinforcement phase (SiC). It is evident from Figure
Microhardness of Al-SiC nanocomposites as a function of SiC content.
Figure
Engineering stress-strain curves for A-SiC nanocomposites under compression loading.
According to Orowan mechanism, the strengthening depends on the uniform dispersion and distribution of the reinforcing particles. Generally, nanosized particles are preferred over the micron-sized particles due to their smaller size and their effective ability in blocking the dislocation motions. Moreover, they are less prone to cracks or damage during the synthesis process of the composite [
The compressive fractography results are shown in Figures
(a–d) Representative compressive fracture surface morphology of Al-SiC nanocomposites.
In this study, the electric resistance of the Al-SiC nanocomposites was analyzed and changed into the electrical conductivity according to the ASTM standard B193-72. Figure
Electrical conductivity of Al-SiC nanocomposites as a function of SiC content.
The electrical properties of the Al-SiC nanocomposite are vital parameters, due to their wide application in electrical circuits and supportive structures in optical devices. SiC particles hold very low electrical conductivity and because of that, their incorporation in Al alloys leads to a drastic decrease in the alloy electrical conductivity [
Al-SiC nanocomposites were successfully synthesized using ball milling and microwave sintering technique. The effects of SiC nanoparticles on the physical, microstructural, mechanical, and electrical properties of Al-SiC nanocomposites were investigated. The X-ray diffraction examinations did not confirm the formation of new phases; both Al and SiC peaks are shown. The microstructural examination using SEM confirms the uniform distribution of SiC nanoparticles in the matrix. With the addition of 0.9 vol.% SiC in Al matrix, an increase of 75% in hardness, 56% in yield strength, and 15% in UCS was observed compared with pure Al. Electrical conductivity values of Al-SiC composites decrease, since SiC is nonconductive material. As a result, the microwave sintered Al-SiC nanocomposites are suitable for manufacture and industrial applications.
Statements made herein are solely the responsibility of the authors.
The authors declare that there are no conflicts of interest regarding the publication of this article.
This publication was made possible by NPRP Grant 7–159-2-076 from Qatar National Research Fund (a member of the Qatar Foundation).