Affect of pressurized solidification on the secondary dendritic arm spacing in lead-tin alloy

Casting is an ancient manufacturing process. Solidification is a process in which liquid metal is let to freeze under various processing conditions to attain the properties, physical shape etc desired. When any liquid freezes into a solid there is a wave of a solid-liquid interface moving forward converting the liquid or molten metal into a solid. The microstructures formed tend to define the behavior and properties of the material in production and usage. Dendrites are the complex morphologies created when the solid-liquid interface advances into the melt during solidification. The morphologies and the side-arm spacing of these dendrites influence the mechanical properties of the cast products. Throughout time there has been lot of research to design new solidification routes and process flow to create materials with excellent properties to meet the ever increasing customer demands. One such effort is the inclusion of pressure as a variable during alloy solidification. It is the motive of this project to study the affect of pressure during solidification of Lead-Tin alloy on the secondary dendritic arm spacing, so as to achieve a complete understanding and control of the science of dendritic solidification. Loads ranging between -40 and -230 pounds were applied at a frequency of 0.5 Hz over a mold and piston system designed for the process of pressure application and simultaneous temperature gradients. The results obtained were compared with no pressure sample. It was observed that there is an increase in the secondary dendritic arm spacing due to the application of the pressure. After conducting the DAS measurements it was understood that coarsening took place in the case of pressure solidification, and could be the reason for increase in the secondary dendritic arm spacing, increase in the thickness of the secondary arms.