Optimization of Al Matrix Reinforced with B 4 C Particles MOHSEN OSTAD SHABANI 1,2 and ALI MAZAHERY 1 1.—Karaj Branch, Islamic Azad University, Karaj, Iran. 2.—e-mail: vahid_ostadshabany@ yahoo.com In the current study, abrasive wear resistance and mechanical properties of A356 composite reinforced with B 4 C particulates were investigated. A center particle swarm optimization algorithm (CenterPSO) is proposed to predict the optimal process conditions in fabrication of aluminum matrix composites. Unlike other ordinary particles, the center particle has no explicit velocity and is set to the center of the swarm at every iteration. Other aspects of the center particle are the same as that of the ordinary particle, such as fitness evalua- tion and competition for the best particle of the swarm. Because the center of the swarm is a promising position, the center particle generally gets good fitness value. More importantly, due to frequent appearance as the best par- ticle of swarm, it often attracts other particles and guides the search direction of the whole swarm. INTRODUCTION There has been a marked effect on the judicious selection of materials in the last decades because of the increasing demand for weight reduction and low fuel consumption in the structural applications, particularly aerospace and automotive industries. Low density, high thermal conductivity, and high specific strength of aluminum alloys has caused a great upsurge in using these alloys. 1–3 However, their low hardness and poor wear resistance are the main obstacles for their high-performance mechan- ical and tribological applications. To overcome this problem, hard reinforcement phases such as par- ticulates, fibers, and whiskers are introduced into Al-based matrix in order to improve their high specific strength, stiffness, wear resistance, fatigue resistance, and elevated temperature applica- tions. 4–10 Particulate aluminum matrix composites (AMCs) are isotropic in their properties and are easier to process via powder metallurgy or cast ranging route compared to AMCs reinforced with ceramic whis- kers and fibers. There are several manufacturing techniques for particle reinforced AMCs such as liquid metal infiltration, spray decomposition, squeeze casting, compocasting, powder metallurgy, and mechanical alloying. Stir casting of MMCs is an attractive processing method for these advanced materials since it is relatively inexpensive and offers a wide variety of material and processing condition options. Generally, these composites con- sist of a metal matrix, which is melted during casting, and ceramic reinforcement, which is added to the molten matrix material by a mechanical stirrer. 11–14 The enhancement in tribological properties of AMCs has been effectively attainable by introducing the ceramic particles. It has been generally observed that increasing the SiC or Al 2 O 3 particle content enhances the wear resistance of the base alloy. The wear resistance of the composite was found to be considerably higher than that of the matrix alloy and increased with increasing particle content. The hard particles resist against destruc- tion action of abrasive and protect the surface, so with increasing its content, the wear resistance enhances. This result is consistent with the rule that in general, materials with higher hardness have better wear and abrasive resistance. 15–17 Numerous research works have been reported on mechanical properties and dry sliding wear behav- ior of AMCs reinforced with various particulates such as SiC, boron, TiC, Si 3 N 4 , silica sand, MgO, B 4 N, and Al 2 O 3 . Reinforcement of aluminum alloys with Al 2 O 3 or SiC has generally been observed to improve the ultimate tensile and the yield strengths of the metal. However, the ductility of the AMCs deteriorates significantly with high ceramic particle concentration. 18–22 JOM, Vol. 65, No. 2, 2013 DOI: 10.1007/s11837-012-0502-2 Ó 2012 TMS 272 (Published online November 14, 2012)