Investigation of the effects of liquid metal movement on microstructure and mechanical properties of a356 aluminum cast alloys

In this study, improvement of mould fiiling of A356 cast alloy in different gating systems was investigated. In addition, the effects of solidification requirements of A356 cast alloy on microstructure, mechanical properties and bifilm formations were studied in the form of suitable flow conditions. For this purpose, the square and circular shaped sprues having equall cross-sectional area were designed. Moreover, the runners having different output shape and cross-sectinoal area diffuser (square, circular and rectangular) and non-diffuser runners (square or circular) were designed. Designed gating systems, were first applied on simulation program and after, under the terms of the actual casting. A356 parts were characterized by tensile, hardness tests and density as well as micro and macro structures. Tensile samples were prepared soon after homogenization of A356. The samples were heat treated at 540 ° C for 8 hours followed by water quench. They were then naturally aged at room temperature for 24 hours and artificially aged at 170 C for 10 hours. The results obtained from the tensile tests were evaluated by the Weibull distribution statistical analysis. The highest Weibull modulus were found for the gating systems which are sprue of square cross-sectional runner of diffuser square cross-sectional and sprue of circular cross-sectional runner of non-diffuser circular cross-sectional. Solidification conditions of A356 at the gating systems having the highest Weibull module were controlled by the electrolytic copper, H13 hot work tool steel chills. Also, A356 was solidified in the isolated ceramic mould. Dendritic arm spacing which effects the mechanical properties and forms the microstructure of casting A356 was measured by image analysis program. Scanning electron microscope (SEM) was used for fracture surface examinations, to identify porosity and intermetallics. Also, optical microscopy was used to examine shapes, sizes and types of bifilms (folded layers of oxide films). As a result of the studies, the distance between the secondary dendrites was increased thank to increase in local solidification time and, the surfaces of folded oxide films were more smooth and expanded. With increasing the cooling rate, it has been noted that the second dendrite arms spacing are decreasing and mechanical properties are increased.