Effect of cooling rate on structure and mechanical properties of monotectoid zinc aluminium alloys

The cooling curves of a number of monotectoid zinc-aluminium alloys have been obtained during casting at different pouring and mould temperatures using thermocouples and an analogue - digital converter in a computer. The average cooling rate for each ingot of the alloys was determined by taking the derivative of the cooling curves. The effect of cooling rate on the structure and properties of the alloys was investigated. It was observed that as the cooling rate increased the secondary dendrite arm spacing of the alloys decreased but their hardness, tensile strength and percentage elongation increased. Correlation of the experimental results showed that the cooling rate of the alloys could be related to their secondary dendrite arm spacing, hardness, tensile strength and percentage elongation using first and second degree mathematical equations. In addition, the Skenazi equation was found to be applicable to these alloys. As a result of this work, the optimum range of cooling rate for the alloys was found to be between 4.40-4.56 K s?1.