Influence of solidification variables on microstructure and microhardness of Al-Cu alloys using full factorial design

ABSTRACT

In this work a hypereutectic Al-40wt%Cu alloy was used to verify the influence of the input variables cooling rate (°C/min) and superheating (°C), on the output variable microhardness (HV). The samples were poured in ceramic and copper crucible and a thermocouple coupled to a data acquisition system measured the cooling rates that were 20°C/min and 24°C/min, respectively. The influence of these cooling rates and overheating of 100°C and 200°C above the melting temperature of the alloy on microhardness was evaluated. Vickers hardness measurements were performed on the sample cross section with an area of 0.8 cm². The samples were characterized microscopically to evaluate the microstructural formation. The potential of the variables involved in the study was evaluated by a 2² full factorial design. The results of the factorial design indicated that the samples solidified using overheating to 200°C above the melting temperature and cooled at a rate of 24°C/min obtained higher microhardness values. The alloys superheated to higher temperatures showed more refined microstructures with elongated grains, disordered growth directions and short dendritic spacing, causing a transition in columnar to equiaxial microstructure.

Keywords
Al-Cu alloys; Solidification; Factorial design; Microhardness