This paper reports the effects of annealing and age hardening heat treatments on the microstructural morphology and mechanical properties of 7075 Al alloy. The material was cast in the form of round cylindrical rods inside green sand mould from where some samples were rapidly cooled by early knockout and others gradually cooled to room temperature. From the samples that were gradually cooled some were annealed while others were age hardened. Both the as-cast in each category and heat treated samples were subjected to some mechanical tests and the morphology of the resulting microstructures were characterised by optical microscopy. From the results obtained there is formation of microsegregations of MgZn 2 during gradual solidification which was not present during rapid cooling. It was also found out that age hardening and annealing heat treatment operation eliminated these microsegregations and improve mechanical properties of 7075 Al alloy. It is concluded that microsegregation can be eliminated by rapid solidification and appropriate heat treatment process.
Grey cast iron is characterized by presence of a large portion of its carbon in the form of graphite flakes which are observable in their microstructures. Their properties are significantly dependent on the micro-constituents of the, cast iron components. A way of controlling the microstructure of cast iron is through the controlled cooling rates during solidification. To control cooling rate, the heat storage capacity of the mould is important. This paper presents the characteristic effects of graphite flake sizes on some mechanical properties of grey cast iron. Six mould materials with heat storage capacities ranging from 1.52 kJ.m-2 .K-1 .s-1/2 to 2.16 kJ.m-2 .K-1 .s-1/2 were prepared and used to cast some grey cast iron samples whose microstructures were observed by optical microscopy. Mechanical properties of the grey iron were evaluated. The results show that the properties increased with the heat storage capacity of the mould. Also, the microstructures show a dependence on heat storage capacity of the mould.
A low component count, microcontroller-based potentiostat circuit was developed through the use of operational amplifiers arranged in different feedback configurations. This was developed to alleviate the cost burden of equipment procurement in low-cost and budget applications. Simplicity was achieved in the design by the use of the microcontroller's native functionalities and a low-cost R/2R resistor ladder digital-to-analogue converter. The potentiostat was used to investigate the Ni 2+ /Ni(s) redox couple in a 3-electrode cell with a silver/silver chloride reference electrode and graphite counter and working electrodes. Linear sweep voltammograms were obtained at scan rates of 10, 20, 30 and 40 mV/s. The analysis of the peak current versus (scan rate) 1/2 plot indicated that the Ni 2+ /Ni(s) reduction, though conforming to the Randles-Sevcik equation, was a nonreversible redox reaction.
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