Preparation of aluminium 6063-graphite surface composites by an electrical resistance heat assisted pressing technique

Abstract

A simple electrical resistance heat assisted pressing technique is proposed and demonstrated for the surface graphitization of aluminium alloys. The aluminium substrate is first coated with a graphitic layer by solution casting. The aluminium-graphitic interface is then locally heated by electrical resistance heating followed by mechanical pressing. A graphite rich aluminium-graphite surface composite will be obtained. The important process parameters are the current and time used for electrical resistance heating and the pressure applied for mechanical impregnation. Microstructural characterization of the prepared samples revealed that the graphite flakes are uniformly distributed and embedded over the aluminium surface. Raman spectroscopic analysis of the graphitized surface shows a significant shift in major graphitic peaks with an increase in the intensity ratio (ID/IG). Formation of alumina (Al2O3) was detected in X-ray diffraction studies but no peaks corresponding to aluminium carbide (Al4C3) was observed. The surface mechanical properties were evaluated through microhardness testing. More than five times improvement in surface hardness as compared to bare aluminium was observed for graphitized aluminium. The surface hardness depends mainly on the processing parameters and subsequently the amount of graphite flakes impregnated on to the surface. The proposed method could be utilised as a solid state surface bonding process where surface composites are prepared by mechanical impregnation of particulate fillers at sub-melting substrate temperatures and at ambient working environment.