Abstract:
This research determines the effects of copper/antimony addition and wall section thickness on microstructure and mechanical properties of Ductile Cast Iron (DCI). The research was tailored towards developing a thin section DCI with better mechanical properties and lightweight thereby reducing the overall weight of automobile components. Four heats of DCI containing 0.0%, 0.4, 0.6 and 0.8% amounts of copper and 0.004% fixed antimony designated as Control, Alloy A, Alloy B and Alloy C respectively were investigated. The wall section thickness of the developed ductile cast iron was 11 mm, 13 mm and 15 mm respectively. The samples were configured to standard coupons. The chemical composition, mechanical properties, graphite nodule evaluation and microstructural characterisation of each thickness of the casting were carried out with the aid of Spectroscopic Analyzer, mechanical testing equipment, optical metallurgical microscope and Image Analysing Software (ImageJ) respectively. All the samples developed were of pearlitic-ferritic matrix structure. The chemistry of the produced alloy gives a hypereutectic alloy (CEV> 4.3%) and the addition of copper and antimony was found to increased the pearlitic phase to 75% volume fraction. Alloy C with wall section of 11 mm produced the highest tensile strength of 690.45 MPa, hardness value of 288.70 HBN, percentage nodularity of 98%, least impact energy of 35.03 J, % ductility of 4.92 and 128 nodule count/mm2. However, the Control sample with 11 mm wall section thickness had the least tensile strength of 330.27 MPa, hardness value of 134.90 HBN, impact energy of 50.90 J, ductility of 5.10%, 162 nodule count/mm2 and 80% nodularity. This is attributed to the addition of copper up to 0.8% and 0.004% antimony in ductile cast iron enhanced the pearlite phase and promotes the reduction of ferrite phase. The control sample and Alloy A for all wall sections had mechanical properties range as; tensile strength 330-490MPa, yield strength 207-355MPa, impact energy 41-55J, hardness value 134-223 HBN, ductility 4.96-5.10%, 135-209 nodule count/mm2 and nodularity of 80-93%. Alloy B and C have the best mechanical properties with tensile strength ranging from 560-690 MPa, yield strength 360-440MPa, impact energy 35-43J, Hardness value within 230-288 HBN, ductility 4.89-4.94%, 98-189/mm2 nodule count, 80-98% nodularity and 60-75% volume fraction of pearlite. Alloy B can be used for wheel hub while Alloy C can be used for crankshaft
