EFFECTS OF ALUMINIUM ADDITION AND AUSTEMPERING TEMPERATURES ON AL-ALLOYED DUCTILE IRON MICROSTRUCTURE AND MECHANICAL PROPERTIES

The research investigates the effect of varying amounts of aluminium (1.05, 1.575, 2.29, 3.02 and 3.74 wt.%) addition and heat treatment (austempering at 300, 350, 400^oC) on the microstructure and mechanical properties of ductile cast iron alloys. The graphitizing effects of the Al alloy and varied austempering temperatures on the hardness, tensile strength, and impact toughness of the ductile cast iron (DCI) were evaluated. The results of the influences of Al addition and heat treatment on the properties of the DCI determined were graphically presented while the characterization was done using a scanning electron microscope (SEM). The microstructures revealed that the addition of Al into the matrix brings about the precipitation of ferrite around the graphite nodules. The combined effects of the increase in Al content and austempering temperatures produced greater hardness values on the Al-alloyed DCI samples than the as-cast sample. The hardness values for the entire samples ranged from 27.25 to 57.03 BHN. Tensile strength increased with an increase in Al content and lower austempering temperatures, whereas, the impact toughness increased with increase in Al content and higher austempering temperature. The results of the research revealed that the addition of Al to ductile iron and austempering treatment led to an improvement in the hardness, tensile strength, and impact toughness of the alloys.