Natural convection and thermal parameters affecting microsegregation during unsteady-state solidification of Al-Cu alloys

• Grant number: 12/16483-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: November 01, 2012
• End date: April 03, 2015
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: José Eduardo Spinelli
• Grantee: Pedro Deghaid Pereira
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil

Abstract

It is well known that melt flow affects the final as-cast structure. The flow continues even after pouring procedures, essentially moving in the interdendritic/intercellular channels or in the open liquid where transformation temperature is not reached. Interdendritic melt convection may be originated due to the thermal and solutal gradients immediately ahead the solidification front. This melt flow may interfere in the local solute distribution not only close to the liquid/solid interface but also between the dendritic arms. The melt interacts with the mush and its solutal and thermal diffusion layers, resulting in a situation where both temperature and solute concentration gradients play significant roles. For the case in which a single-phase solid is formed, the equilibrium concentration of solute in the solid at the interface between solid and liquid is different from the equilibrium concentration of solute in the liquid adjacent to it: this is termed as segregation. Based on the scale of the segregation event, it can be classified into two types, namely microsegregation and macrosegregation. Microsegregation refers to the segregation event that takes place at the microscopic level (i.e. grain boundary, interdendritic or intercellular regions), whereas macrosegregation occurs at the macroscopic level (i.e. the casting itself). Both at the macroscopic and the microscopic scale, segregation is one of the major factors limiting the final properties and performance of metallic alloys based products. For instance, in automotive applications, the quality of an engine block depends on the microstructures and the grains structure's homogeneity. The present purpose aims to perform upward and downward directional solidification experiments so that microsegregation behavior could be understood concerning growth either in favor or against gravity. Two Al-Cu chemistries have been chosen which are 6.0 and 10.0 wt%Cu. Such setups permit that the convective currents could be minimized or increased during transitory solidification. While the upward setup minimizes convection, the downward configuration is able to stimulate liquid flow immediately ahead solidification front.(AU)