Sajjad Amirkhanlou

Synthesis and characterization of 356-SiCp 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.

Manufacturing of High-Performance Al356/SiCp Composite by CAR Process

Al356/SiCp composites suffer from some important defects such as porosity, non-uniform distribution of the SiC particles, weak bonding between SiCp and matrix, and presence of coarse silicon fibers with non-uniform distribution, which collectively result in low mechanical properties. In order to overcome all the mentioned problems in this type of composite, this study used continual annealing and roll-bonding (CAR) process as a very effective method for manufacturing Al356/SiCp composite. The microstructure of the fabricated composite after twelve CAR cycles showed an excellent distribution of SiC and spherical silicon particles in the matrix with good bonding between SiC particles and matrix. The results also indicated that when the number of CAR cycles increases, the tensile strength of the produced composites improves, while their ductility decreases at first and then increases.

Microstructure and Mechanical Properties of Al356/SiCp Cast Composites Fabricated by a Novel Technique

In this study, SiCp containing composite powders were used as the reinforcement carrier media for manufacturing cast Al356/5 vol.% SiCp composites. Untreated SiCp, milled particulate Al-SiCp composite powder, and milled particulate Al-SiCp-Mg composite powder were injected into Al356 melt. The resultant composite slurries were then cast from either a fully liquid state (stir casting) or semisolid state (compocasting). The results revealed that by injection of composite powders, the uniformity of the SiCp in the Al356 matrix was greatly improved, the particle-free zones in the matrix were disappeared, the SiC particles became smaller, the porosity was decreased, and the matrix microstructure became finer. Compocasting changed the matrix dendritic microstructure to a finer non-dendritic one and also slightly improved the distribution of the SiCp. Simultaneous utilization of Al-SiCp-Mg composite powder and compocasting method increased the macro- and micro-hardness, impact energy, bending strength, and bending strain of Al356/SiCp composite by 35, 63, 20, 20, and 40%, respectively, as compared with those of the composite fabricated by injection of untreated SiCp and stir casting process.

Hydroxyapatite/alumina nanocrystalline composite powders synthesized by sol-gel process for biomedical applications

Hydroxyapatite/alumina nanocrystalline composite powders needed for various biomedical applications were successfully synthesized by sol-gel process. Structural and morphological investigations of the prepared composite powders were performed using X-ray diffractometer (XRD), scanning electron microscopy (SEM), X’Pert HighScore software, and Clemex Vision image analysis software. The results show that the crystallite size of the obtained composite powders is in the range of 25 to 90 nm. SEM evaluation shows that the obtained composite powders have a porous structure, which is very useful for biomedical applications. The spherical nanoparticles in the range of 60 to 800 nm are embedded in the agglomerated clusters of the prepared composite powders.

Effect of processing cycles on aluminum/tungsten carbide composites prepared by continual annealing and press bonding process

In the present work, a novel technique is introduced called CAPB (continual annealing and press bonding) for the manufacturing of a bulk aluminum matrix composite dispersed with 10 vol.% WC particles (Al/WCp). The microstructure of the fabricated composite after fourteen cycles of CAPB showed an excellent and homogenous distribution of the WC particles in the aluminum matrix and strong bonding between the various layers. The results indicated that the tensile strength of the composites increased with the number of CAPB cycles, and reached a maximum value of 140 MPa at the end of fourteenth cycle, which was 1.6 time higher than the obtained value for annealed aluminum (raw material, 88 MPa). Even though the elongation of the Al/WCp composite was reduced during the initial cycles of CAPB-ing, it increased significantly during the final cycles.

Manufacturing of nanostructured Al/WCp metal- matrix composites by accumulative press bonding

The accumulative press bonding (APB) process used as a novel technique in this study provides an effective alternative method for manufacturing Al/10 vol.% WCp metal matrix composites (MMCs). The results revealed that by increasing the number of APB cycles (a) the uniformity of WC particles in aluminum matrix improved, (b) the porosity of the composite eliminated, (c) the particle free zones decreased. The X-ray diffraction results also showed that nanostructured Al/WCp composite with the average crystallite size of 58.4 nm was successfully achieved by employing 14 cycles of APB technique. The tensile strength of the composites enhanced by increasing the number of APB cycles, and reached to a maximum value of 216 MPa at the end of 14th cycle, which is 2.45 and 1.2 times higher than obtained values for annealed (raw material, 88 MPa) and 14 cycles APB-ed monolithic aluminum (180 MPa), respectively