Evaluation of Simultaneous Effect of Melt Filtration and Cooling Rate on Tensile Properties of A356 Cast Alloy

BThe combined influence of both melt filtration and cooling rate on the microstructure and mechanical properties of A356 cast alloy was studied. A step casting model with five different thicknesses was used to obtain different cooling rates. The effect of melt filtration was studied by using 10 and 20 pores per inch (PPI) ceramic foam filters in the runner. Results showed that secondary dendrite arm spacing decreased from 80 mu m to 34 mu m with increasing cooling rate. Use of ceramic foam filters in the runner led to the reduction of melt velocity and surface turbulence, which prevented the incorporation of oxide films and air in the melt and consequently had an overall beneficial effect on the quality of the castings. A matrix index, which is the representative of both SDAS and microporosity content, was defined to consider the simultaneous effect of melt filtration and cooling rates on UTS variations. Also, the fracture surface study of test bars cast using 10 and 20 PPI ceramic foam filters showed features associated with ductile fracture.