Precise fabrication of VAl master alloy with a designated composition by a novel Al reduction process

VAl master alloys are essential raw materials for producing high-quality titanium alloys, which are generally produced by aluminothermic reduction, metal-slag gravitational separation method. The conventional way faces the challenges of excessively high reaction temperatures, metallic inclusions in slag, and difficulties in fabricating higher-Al-content alloy in one step. To conquer these issues, this research has reported a new method to precisely fabricate VAl master alloy with a designated composition, which is an aluminum reduction coupled with an acid leaching process. The reduction byproduct of weak-acid-soluble calcium aluminate, the critical parameters for Al reduction, and the reaction routes are determined. This research has demonstrated that various VAl master alloys (expressed as AlV_x) are successfully prepared by heating the optimal mixture of V₂O₃ + (2 + 2x-)/xAl + 2.0CaO + 1.35CaCl₂ (in molar ratio) at 1000 °C for 5 h in Ar and pickling the reduction material using HCl acid with pH controlled at 1.2. Oxygen in 6Al4V, 4Al6V, and 2Al8V alloy powders are 400 ppm, 500–700 ppm, and 1800–2000 ppm, respectively. The 4Al6V powder produced by this reported method is compared with the commercial one, with comparable phase and chemical compositions but with finer sizes preferred in powder metallurgy sintering. The main reactions or phase changes that happen during heating include stepwise removal of surface and crystalline water from CaCl₂, melting of Al, reaction between V₂O₃ and CaO, melting of CaO-CaCl₂ binary compound, and Al reduction reaction. The method developed in this study can also be used to prepare other alloys, such as TiAl and TiFe alloy powders.