Investigation of reinforcement weight fraction and size on mechanical properties and machinability of aluminium based composites

Ill INVESTIGATION OF REINFORCEMENT WEIGHT FRACTION AND SIZE ON MECHANICAL PROPERTIES AND MACHINABILITY OF ALUMINIUM BASED COMPOSITES (PhD Thesis) Ibrahim ÇİFTÇİ GAZI UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY October 2003 ABSTRACT In this study; 2014-A1 based metal matrix composites (MMCs) containing three levels of SiC particles (8, 16 and 32 wt %) of different mean particle sizes (30, 45 and 110 ^m) were prepared using a melt stirring-squeeze casting route. Microstructural and mechanical properties of these composites were examined. These MMCs were subjected to machinability tests through single point continuous turning using uncoated cemented carbide, coated cemented carbide, cubic boron nitride (CBN) and diamond coated cemented carbide. The tests were performed dry and cutting tool wear and surface roughness criteria were investigated among the machinabilty criteria. In addition, cutting force measurements were also performed during machining using diamond coated cemented carbide tools. The tests were carried out at different cutting speeds while depth of cut and feed rate were kept constant. It is seen from the results that cutting tool wear increased with increasing SiC size and weight fraction for all the cutting tools used. Except for CBN cutting tools, tool wear also increased with increasing cutting speed. CBN cutting tools exhibited the highest wear resistance. Diamond coated cemented carbides showed better wear resistance than those of the other cemented carbides while uncoated carbide showed the worst wear resistance. When a comparison was made between the surfaces produced using uncoated and coated cemented carbide tools, it was seen thatIV uncoated cemented carbides produced better surface finishes in terms of Ra values, particularly at lower cutting speeds. This was explained by the presence of more stable built-up-edge (BUE), which causes poor surface finish, on the coated cemented carbides. In order to determine tool wear modes and mechanisms, worn cutting tools were investigated using optical and scanning electron microscopes (SEM). SEM investigation revealed that tool flank wear was the dominant wear mode for all the cutting tools. In addition to abrasive wear mechanism, chipping particularly at high cutting speeds was found to be effective for uncoated and coated cemented carbide tools. Both abrasive and adhesive wear mechanisms were found to be effective for CBN and diamond coated cemented carbide cutting tools. Additionally, chipping of CBN cutting tools was observed when machining the MMC material containing particles of 110 pjn in size. Science code : 708 Keywords : Metal matrix composite (MMC), melt stirring-squeeze casting method, machinability, cutting tool wear, surface roughness Page number : 129 Adviser : Prof. Dr. Mehmet TÜRKER