May 21 st – 23 rd 2014, Brno, Czech Republic, EU TRIBOLOGICAL CHARACTERISTICS OF HYPEREUTECTIC/CSF COMPOSITE FABRICATED BY INNOVATIVE THIXOMIXING METHOD Ebrahim AKBARZADEH, Antonio Forn ALONSO Light Alloys and Surfaces Treatment Design Centre (CDAL), Universitat Politècnica de Catalunya (UPC), Barcelona, Spain, EU, Ebrahim.akbarzadeh@estudiant.upc.edu Abstract Aluminum carbon fiber composite are being extensively used as light-weight materials in automobile and aeronautical sectors owing to their excellent strength. Furthermore, hypereutectic aluminum possess good tribological characteristics and low friction which coupled with short carbon fiber (Csf ) making them an ideal reinforcement to developing light weight material with good wear properties and high strength aluminum matrix composites. However, a few information is available regarding the tribological behavior of Csf reinforced metal matrix composites. This study focused on development of innovative method to make short carbon fiber composites by thixomixing route and assessing their tribological characteristics. The influences of the rotating speed, applied load and friction coefficient were discussed. The random oriented of short carbon fiber fabricated by specific mixer at semi-solid condition. Then, developed innovative composites were subjected to wear tests. A pin on disk is a common method was used with hardened steel as the counterpart. The full factorial method has been used to design the experiment with three parameters as: carbon fiber volume fraction, speed of sliding and load of wearing test. Worn surfaces before and after test and wear debris were characterized using scanning electron microscopy (SEM). The results indicated that Csf/Al composite had better tribological properties than Al alloy. Keywords: Wear test, Aluminum, carbon fiber, thixomixing, friction coefficient 1. INTRODUCTION Aluminum metal matrix composites (AMMCs) can be used as lightweight materials in aerospace or automobile industries such as piston or cylinder liners due to higher strength, good wear resistance, higher thermal conductivity and lower coefficient of friction [1]. Addition of carbon fibers improves the machinability and wear resistance similarly with Graphite particulates which provide the good tribological properties with excellent lubricity and lower coefficient of friction [2, 3]. The good mechanical strength and high wear resistance are not only essential for aluminum matrix composites while self-lubrication properties are also desirable [4]. Owing to these benefits, short carbon fiber (Csf) has been extensively utilized as reinforcement into Aluminum silicon coupled with high toughness and strength. In the metal-to metal contact of wearing, the carbon fiber which plays a role as lubricant based on its graphite microcrystalline composition. The surface of Csf/Al deformed plastically and carbon fibers ground onto the metal surface as small particles and reduced the frictional damages. Most of the previous methods such as powder metallurgy [5], stir casting [6] or squeeze casting infiltration [7] were not effective to disperse and distribute the carbon fibers into metal matrix. The thixotropic nature depends on viscosity of slurry, where the viscosity is related to fraction of solid, solid size, shear and temperature. Viscosity decreases rapidly during the initial period of shearing, is attributed to the dissociation of agglomerates of solid particles which are weakly bonded, trapping liquid alloy within the inter-aggregate spaces. In this paper, the process introduced as thixomixing and it is based on application of high shear stress (τ) on carbon fiber clusters and bundles. The semi -solid thixomixing prevent the reinforcement to either floating or sinking during the process. The key idea in this method is to apply sufficient high shear