EFFECT OF SILICON CARBIDE PARTICLE SIZE ON SLIDING WEAR BEHAVIOUR OF FRICTION STIR PROCESSED ALUMINIUM ALLOY 5083 SURFACE COMPOSITES

Abstract

Aluminum matrix composites are suitable materials for various engineering applications due to light weight and ease in fabrication. Surface composites are newer class of material having surface and bulk with different properties as reinforcement of ceramic particles is limited to surface only. Friction stir processing (FSP) is a promising solid state technique for fabricating surface composites of aluminum alloys. Grain refinement of the matrix is an additional advantage of surface composites fabricated by FSP route. FSP is a versatile technique with a comprehensive function for the fabrication, processing and synthesis of materials. Nano composites fabricated by FSP route also possess superior properties than those produced using conventional methods such as mechanical alloying, casting, rapid solidification, combustion synthesis, etc. In the present study, silicon carbide (SiC) partilces of 25-130 nni or 8 im size are reinforced in 5083 aluminium alloy and surface composites fabricated by FSP at 2000 rpm rotational speed and 40mm/min traverse speed. Microstructure and mechanical properties of base alloy, FSPed alloy, aluminium alloy surface composites are studied. The effect of reinforcing micro and nano size SiC particles on friction and wear behaviour of aluminium 5083 alloy are studied using ball-on-disc wear machine. Microstructures generally showed grain refinement with FSP. Surface composites prepared using micro size SiC particles exhibited uniform distribution of reinforcement without any defects, whereas that prepared using nano size SiC particles reveal clusters or bands of reinforcement. A maximum hardness of 191 1-IV, yield strength of 237 MP and moderate elongagtion of 12% are obtained for surface composites prepared using nano size SiC particles. When worn against steel ball in unlubricated sliding conditions at 5. 10 or 20 N load, the friction coefficient varied in a small window of 0.24 —0.30. However, wear volume decreased from base alloy to surface composties or with decrease in load. At least an order of magnitude decrease in wear volume from 1.32 mm3 at 20 N for base alloy to 0.30 mm3 at 5 N for surface composites prepared using nano size SiC particles.The formation and removal of a layer rich in aluminium an oxygen is generally atrribited for the wear. However, reinforcement of nano size SiC particles effectively bear the sliding load and reduced the extent of adhesive wear of the aluminium alloy.