Microstructures and Phases Analysis of the 60Al-40V Master Alloy Produced by the Aluminothermic Process

Abstract

Aluminothermic reaction process was used to produce the 60Al-40V master alloy from pure Al metal and vanadium pentoxide (V2O5). Material characterization techniques including light optical microscopy (LOM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were employed to analyse the microstructural, chemical composition and phases present in the alloy. Thermal analysis was carried out on the alloy using simultaneous differential scanning calorimetry and thermogravimetry (DSC-TG) analysis to determine the phase transformations. The microstructural analysis through both LOM and SEM indicated that the starting material consisted of the columnar dendritic structure. After the double heating cycle during the DSC-TG tests, the dendrite structure transformed to the globular structure. The globularization was attributed to the dendrite fragmentation obtained when heating the as-cast materials in the solidliquid region. This globular shape playing a positive role in enhancing the properties of the alloy. Through DSC-TG analysis, different peaks of transition temperatures were detected showing that the phase transformations occurred during the heating and cooling processes. The Al-rich phase (Al21V2) did not dissolve during homogenization. However, the intermetallic Al8V5 phase transformed to the Al3V phase during cooling. The chemical analysis of the produced master alloy was found to be 63 Al and 37 wt. % V. The phases in the alloy were principally identified to be Al3V and Al8V5 intermetallic phases. The analysis of the results shows that the most stable phase found at high temperature was the Al3V phase.