EFFECTS OF COPPER ADDITION AND SECTION THICKNESS ON SOME MECHANICAL PROPERTIES AND THE MORPHOLOGY OF GRAPHITE FLAKES IN GREY CAST IRON

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Department of Engineering

ABSTRACT
This study determined the effects of copper addition and section thickness on some mechanical properties and the morphology of graphite flakes in grey cast iron. It also characterised the microstructure of grey cast iron evolved in the investigation. This was of the view of ensuring that automotive industry designers are able to make informed choice between competing materials and grey cast iron, thus reducing the overall cost of the automobile. Four classes of grey cast iron containing 0.02, 0.55, 0.7 and 1.15% amount of copper were investigated. The section thicknesses of the produced grey cast iron were 10 mm, 25 mm and 75 mm respectively. The chemical composition, mechanical properties, graphite flake measurements and microstructural characterisation of each section of the casting were carried out with the aid of optical emission spectrometer, mechanical testing equipment and scanning electron microscope. The 0.7% Cu alloyed grey cast iron with section thickness of 10 mm produced the highest tensile strength of 150.28 N/mm2, hardness value of 47.5 HRC and the least impact strength of 76.96 kJ/m2. It was also discovered from microstructural characterisation that 10 mm section thickness has the shortest graphite flake length of 64.32 μm. However, the 1.15% Cu alloyed grey iron with 75 mm section thickness had the least tensile strength of 58.36 N/mm2, hardness value of 40.1 HRC and the highest impact strength of 107.13 kJ/m2. This also supported the longest graphite flake length of 105.68 μm. This is attributed to the fact that addition of copper up to 0.7% in grey cast iron enhanced the pearlite phase and promotes the formation of ferrite when increased to 1.15% by weight. The results of microstructural examination revealed that the morphology of the graphite flakes changes from fine and small flakes to coarse and long viii flakes as the section thickness increases. The research showed that the developed type B (rosette graphite) flake having 85.95 μm length in the 1.15% Cu grey cast iron with 10 mm section thickness gave a good combination of mechanical properties having 2.85% elongation, 111.41 N/mm2 tensile strength, 44.4 HRC hardness and 89.65 kJ/m2 impact strength. It can be concluded that with the set of properties exhibited by the 0.7% Cu grey cast iron with 10 mm section thickness, automobile industry components and farm implements could be produced from this type of grey cast iron.