Effects of Grain Refinery Addition in the Microstructure and in the Mechanical Properties of Casted Aluminium Alloys

Abstract

Aluminium alloys are widely used in casting process because their low melting point, excellent flowability, and high heating transfer coefficient, which allow fast production cycles. However, this non-ferrous material can present coarse grains, like columnar grains, in its macrostructure after casting process. It´ s well known that mechanical properties of Aluminium alloys casted can be indicated by the grain size, as a result refined grains present a totally equiaxed microstructure, reducing problems with hot cracks and improving the machinability of casting material. With the purpose to induct a refined grain, inoculation treatment can be used in liquid metals, which increase the number of grains nucleus inside the liquid and, therefore, reduce the final medium grain size. Thus, the main goal of this work is refining the grain in aluminium alloy by adding Al-Ti-B alloy. This work is composed by the following steps: preparation of sand casting (60% of sand, 40% of clay, and 4% of water), moulding, melting, addition of inoculators of Al-Ti-B system, pouring, unmoulding of casted sample, and microstructural analysis. The fusion occurs at 750°C in a muffle furnace, using a crucible made of silicon carbide and graphite. The Al-Ti-B alloy (around 0.5% in weight), used as a grain refinery and donated by AMG Brazil, was added in this temperature, and held in furnace for 30 minutes. Micro and Macrostructures of casting samples with and without grain refinery were analysed. Keller solution was used in microstructural analysis.